rtiow: add support to send rendering output to https://github.com/Tom94/tev

rtiow: move image writer to an instance instead of wrappers around global.
rtiow: set default binary to run tracer.
2023-10-29 10:44:59 -07:00 · 2023-10-29 09:17:32 -07:00 · 2023-10-29 09:17:10 -07:00 · 2023-09-21 10:25:23 -07:00 · 2023-09-21 10:24:50 -07:00 · 2023-02-15 21:32:08 -08:00
147 changed files with 14873 additions and 2498 deletions
--- a/.drone.yml
+++ b/.drone.yml
@@ -10,27 +10,29 @@ steps:
  - env | sort
  - find $PWD

+- name: rtchallenge
+  image: registry.z.xinu.tv/drone/omnibus
+  commands:
+  - (cd rtchallenge && cargo build --examples)
+  - (cd rtchallenge && cargo test)
+  - (cd rtchallenge && cargo build --examples --no-default-features)
+  - (cd rtchallenge && cargo test --no-default-features)
+
 - name: rtiow
  image: registry.z.xinu.tv/drone/omnibus
  commands:
-  - sccache -s
  - apt-get update && apt-get install -y libgoogle-perftools-dev
  - (cd rtiow && ./build_all_features.sh)
  - (cd rtiow && cargo test --verbose --all)
-  - sccache -s

 - name: aobench
  image: registry.z.xinu.tv/drone/omnibus
  commands:
-  - sccache -s
  - (cd aobench && cargo build --verbose --all)
  - (cd aobench && cargo test --verbose --all)
-  - sccache -s

 - name: bheisler
  image: registry.z.xinu.tv/drone/omnibus
  commands:
-  - sccache -s
  - (cd bheisler && cargo build --verbose --all)
  - (cd bheisler && cargo test --verbose --all)
-  - sccache -s
--- a/.gitignore
+++ b/.gitignore
@@ -1,2 +1,4 @@
 **/target
 **/*.rs.bk
+**/zig-out
+**/zig-cache
--- a/README.md
+++ b/README.md
@@ -5,3 +5,5 @@ Raytracers

 Random collection of ray tracing experiments.

+# TODO
+Implement http://www.kevinbeason.com/smallpt/
--- a/aobench/Cargo.lock
+++ b/aobench/Cargo.lock
@@ -1,63 +1,72 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
 [[package]]
 name = "ansi_term"
 version = "0.11.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
- "winapi 0.3.5 (registry+https://github.com/rust-lang/crates.io-index)",
+ "winapi 0.3.9 (registry+https://github.com/rust-lang/crates.io-index)",
 ]

 [[package]]
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 version = "0.1.0"
 dependencies = [
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- "rand 0.5.4 (registry+https://github.com/rust-lang/crates.io-index)",
- "stderrlog 0.4.1 (registry+https://github.com/rust-lang/crates.io-index)",
- "structopt 0.2.10 (registry+https://github.com/rust-lang/crates.io-index)",
+ "log 0.4.14 (registry+https://github.com/rust-lang/crates.io-index)",
+ "rand 0.5.6 (registry+https://github.com/rust-lang/crates.io-index)",
+ "stderrlog 0.4.3 (registry+https://github.com/rust-lang/crates.io-index)",
+ "structopt 0.2.18 (registry+https://github.com/rust-lang/crates.io-index)",
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 [[package]]
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 dependencies = [
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- "termion 1.5.1 (registry+https://github.com/rust-lang/crates.io-index)",
- "winapi 0.3.5 (registry+https://github.com/rust-lang/crates.io-index)",
+ "libc 0.2.97 (registry+https://github.com/rust-lang/crates.io-index)",
+ "termion 1.5.6 (registry+https://github.com/rust-lang/crates.io-index)",
+ "winapi 0.3.9 (registry+https://github.com/rust-lang/crates.io-index)",
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+[[package]]
+name = "autocfg"
+version = "1.0.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
 [[package]]
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+version = "1.2.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"

 [[package]]
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+version = "1.0.0"
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 [[package]]
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+version = "0.4.19"
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- "num-traits 0.2.5 (registry+https://github.com/rust-lang/crates.io-index)",
- "time 0.1.40 (registry+https://github.com/rust-lang/crates.io-index)",
+ "libc 0.2.97 (registry+https://github.com/rust-lang/crates.io-index)",
+ "num-integer 0.1.44 (registry+https://github.com/rust-lang/crates.io-index)",
+ "num-traits 0.2.14 (registry+https://github.com/rust-lang/crates.io-index)",
+ "time 0.1.44 (registry+https://github.com/rust-lang/crates.io-index)",
+ "winapi 0.3.9 (registry+https://github.com/rust-lang/crates.io-index)",
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 [[package]]
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-version = "2.32.0"
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 source = "registry+https://github.com/rust-lang/crates.io-index"
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- "bitflags 1.0.3 (registry+https://github.com/rust-lang/crates.io-index)",
- "strsim 0.7.0 (registry+https://github.com/rust-lang/crates.io-index)",
- "textwrap 0.10.0 (registry+https://github.com/rust-lang/crates.io-index)",
- "unicode-width 0.1.5 (registry+https://github.com/rust-lang/crates.io-index)",
- "vec_map 0.8.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "atty 0.2.11 (registry+https://github.com/rust-lang/crates.io-index)",
+ "bitflags 1.2.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "strsim 0.8.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "textwrap 0.11.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "unicode-width 0.1.8 (registry+https://github.com/rust-lang/crates.io-index)",
+ "vec_map 0.8.2 (registry+https://github.com/rust-lang/crates.io-index)",
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 [[package]]
@@ -65,57 +74,65 @@ name = "cloudabi"
 version = "0.0.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
- "bitflags 1.0.3 (registry+https://github.com/rust-lang/crates.io-index)",
+ "bitflags 1.2.1 (registry+https://github.com/rust-lang/crates.io-index)",
 ]

 [[package]]
-name = "fuchsia-zircon"
+name = "fuchsia-cprng"
+version = "0.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
+[[package]]
+name = "heck"
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 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
- "bitflags 1.0.3 (registry+https://github.com/rust-lang/crates.io-index)",
- "fuchsia-zircon-sys 0.3.3 (registry+https://github.com/rust-lang/crates.io-index)",
+ "unicode-segmentation 1.7.1 (registry+https://github.com/rust-lang/crates.io-index)",
 ]

-[[package]]
-name = "fuchsia-zircon-sys"
-version = "0.3.3"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-
 [[package]]
 name = "lazy_static"
-version = "1.0.2"
+version = "0.2.11"
 source = "registry+https://github.com/rust-lang/crates.io-index"

 [[package]]
 name = "libc"
-version = "0.2.42"
+version = "0.2.97"
 source = "registry+https://github.com/rust-lang/crates.io-index"

 [[package]]
 name = "log"
-version = "0.4.3"
+version = "0.4.14"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
- "cfg-if 0.1.4 (registry+https://github.com/rust-lang/crates.io-index)",
+ "cfg-if 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)",
 ]

 [[package]]
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-version = "0.1.39"
+version = "0.1.44"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
- "num-traits 0.2.5 (registry+https://github.com/rust-lang/crates.io-index)",
+ "autocfg 1.0.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "num-traits 0.2.14 (registry+https://github.com/rust-lang/crates.io-index)",
 ]

 [[package]]
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-version = "0.2.5"
+version = "0.2.14"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "autocfg 1.0.1 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "numtoa"
+version = "0.1.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"

 [[package]]
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-version = "0.4.9"
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 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
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@@ -123,135 +140,154 @@ dependencies = [

 [[package]]
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-version = "0.6.3"
+version = "0.6.13"
 source = "registry+https://github.com/rust-lang/crates.io-index"
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+ "proc-macro2 0.4.30 (registry+https://github.com/rust-lang/crates.io-index)",
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 [[package]]
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- "rand_core 0.2.1 (registry+https://github.com/rust-lang/crates.io-index)",
- "winapi 0.3.5 (registry+https://github.com/rust-lang/crates.io-index)",
+ "fuchsia-cprng 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "libc 0.2.97 (registry+https://github.com/rust-lang/crates.io-index)",
+ "rand_core 0.3.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "winapi 0.3.9 (registry+https://github.com/rust-lang/crates.io-index)",
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-version = "0.2.1"
+version = "0.3.1"
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+dependencies = [
+ "rand_core 0.4.2 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "rand_core"
+version = "0.4.2"
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 [[package]]
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-version = "0.1.40"
+version = "0.2.8"
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+dependencies = [
+ "bitflags 1.2.1 (registry+https://github.com/rust-lang/crates.io-index)",
+]

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- "winapi 0.3.5 (registry+https://github.com/rust-lang/crates.io-index)",
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+[[package]]
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 [[package]]
@@ -269,7 +305,7 @@ dependencies = [

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 [[package]]
@@ -277,9 +313,14 @@ name = "void"
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 source = "registry+https://github.com/rust-lang/crates.io-index"

+[[package]]
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+version = "0.10.0+wasi-snapshot-preview1"
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+
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@@ -291,56 +332,61 @@ name = "winapi-i686-pc-windows-gnu"
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+[[package]]
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+
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--- a/aobench/Cargo.toml
+++ b/aobench/Cargo.toml
@@ -2,9 +2,10 @@
 name = "aobench"
 version = "0.1.0"
 authors = ["Bill Thiede <rust@xinu.tv>"]
+edition = "2018"

 [dependencies]
 log = "0.4"
+rand = "0.5"
 stderrlog = "0.4.1"
 structopt = "0.2.10"
-rand = "0.5"
--- a/aobench/src/main.rs
+++ b/aobench/src/main.rs
@@ -1,11 +1,3 @@
-#[macro_use]
-extern crate log;
-extern crate rand;
-extern crate stderrlog;
-#[macro_use]
-extern crate structopt;
-
-use rand::Rng;
 use std::clone::Clone;
 use std::f64;
 use std::fmt;
@@ -14,6 +6,9 @@ use std::io::Write;
 use std::ops::Add;
 use std::ops::Mul;
 use std::ops::Sub;
+
+use log::info;
+use rand::Rng;
 use structopt::StructOpt;

 fn vdot(v0: &Vector, v1: &Vector) -> f64 {
--- a/bheisler/Cargo.lock
+++ b/bheisler/Cargo.lock
@@ -1,3 +1,5 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
 [[package]]
 name = "adler32"
 version = "1.0.3"
--- a/git-hooks/README.md
+++ b/git-hooks/README.md
@@ -0,0 +1,8 @@
+# Installing
+Symlink the files in this directory into your `.git/hooks/` directory to
+enable policies for this project. Example:
+
+```bash
+$ cd .git/hooks
+$ ln -s ../../git-hooks/pre-commit .
+```
--- a/git-hooks/pre-commit
+++ b/git-hooks/pre-commit
@@ -0,0 +1,33 @@
+#!/usr/bin/env bash
+set -e
+SCRIPT_DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" &> /dev/null && pwd )"
+
+pushd () {
+    command pushd "$@" > /dev/null
+}
+
+popd () {
+    command popd "$@" > /dev/null
+}
+
+for workspace in rtchallenge rtiow; do
+  pushd ${workspace:?}
+  cargo fmt -- --check || (echo "To fix, run: cd ${workspace:?} && cargo fmt" && false)
+  popd
+done
+
+RT=rtchallenge
+AFFECTED="$(git diff-index --cached --name-only HEAD)"
+#echo "AFFECTED $AFFECTED"
+RT_AFFECTED=$(echo "${AFFECTED:?}" | grep ${RT:?} || true)
+NO_FEATURES_TARGET_DIR="${SCRIPT_DIR:?}/../../rtchallenge/target/no-default-features"
+if [ ! -z "$RT_AFFECTED" ]; then
+  echo "Files for the rt challenge were touched, running tests"
+  cd ${RT:?} && \
+    cargo build --examples && \
+    cargo test && \
+    cargo build --target-dir=${NO_FEATURES_TARGET_DIR:?} --no-default-features --examples && \
+    cargo test --target-dir=${NO_FEATURES_TARGET_DIR:?} --no-default-features 
+fi
+# Uncomment to debug presubmit.
+#exit 1
--- a/rtchallenge/Cargo.lock
+++ b/rtchallenge/Cargo.lock
--- a/rtchallenge/Cargo.toml
+++ b/rtchallenge/Cargo.toml
@@ -0,0 +1,34 @@
+[package]
+name = "rtchallenge"
+version = "0.1.0"
+authors = ["Bill Thiede <git@xinu.tv>"]
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[features]
+default = [ "float-as-double" ]
+float-as-double = []
+
+[dependencies]
+anyhow = "1.0.41"
+core_affinity = "0.5.10"
+criterion = "0.3.4"
+derive_builder = "0.10.2"
+enum-utils = "0.1.2"
+num_cpus = "1.13.0"
+png = "0.16.8"
+rand = "0.8.4"
+rayon = "1.5.1"
+serde = { version = "1.0", features = ["derive"] }
+serde_json = "1.0.64"
+structopt = "0.3.22"
+thiserror = "1.0.25"
+
+
+[[bench]]
+name = "matrices"
+harness = false
+
+[profile.release]
+debug = true
--- a/rtchallenge/README.md
+++ b/rtchallenge/README.md
@@ -0,0 +1,4 @@
+# The Ray Tracer Challenge: A Test-Driven Guide to Your First 3D Renderer
+This is a rust implementation of https://pragprog.com/titles/jbtracer/the-ray-tracer-challenge/
+
+It attempts to be a test-driven developed ray tracer.
--- a/rtchallenge/benches/matrices.rs
+++ b/rtchallenge/benches/matrices.rs
@@ -0,0 +1,13 @@
+use criterion::{black_box, criterion_group, criterion_main, Criterion};
+
+use rtchallenge::matrices::Matrix4x4;
+
+fn criterion_benchmark(c: &mut Criterion) {
+    let mut i = Matrix4x4::identity();
+    c.bench_function("inverse_new", |b| b.iter(|| i = i.inverse()));
+    let mut i = Matrix4x4::identity();
+    c.bench_function("inverse_old", |b| b.iter(|| i = i.inverse_old()));
+}
+
+criterion_group!(benches, criterion_benchmark);
+criterion_main!(benches);
--- a/rtchallenge/examples/balls.rs
+++ b/rtchallenge/examples/balls.rs
@@ -0,0 +1,119 @@
+use std::time::Instant;
+
+use anyhow::Result;
+use structopt::StructOpt;
+
+use rtchallenge::{
+    camera::{Camera, RenderStrategy},
+    float::consts::PI,
+    lights::PointLightBuilder,
+    materials::MaterialBuilder,
+    matrices::Matrix4x4,
+    shapes::{Geometry, ShapeBuilder},
+    transformations::view_transform,
+    tuples::Tuple,
+    world::WorldBuilder,
+    Float, WHITE,
+};
+
+/// Experimenting with balls.
+#[derive(StructOpt, Debug)]
+#[structopt(name = "balls")]
+struct Opt {
+    #[structopt(long, default_value = "rayon")]
+    render_strategy: RenderStrategy,
+    /// Number of samples per pixel.  0 renders from the center of the pixel, 1 or more samples N
+    /// times randomly across the pixel.
+    #[structopt(short, long, default_value = "0")]
+    samples: usize,
+}
+
+fn main() -> Result<()> {
+    let start = Instant::now();
+    let opt = Opt::from_args();
+    let width = 2560;
+    let height = 1440;
+
+    let light1 = PointLightBuilder::default()
+        .position(Tuple::point(-5., 5., -5.))
+        .intensity(WHITE)
+        .build()?;
+    let light2 = PointLightBuilder::default()
+        .position(Tuple::point(5., 5., -5.))
+        .intensity([0.2, 0.2, 0.6])
+        .build()?;
+    let light3 = PointLightBuilder::default()
+        .position(Tuple::point(0., 2., -5.))
+        .intensity([0.2, 0.2, 0.1])
+        .build()?;
+
+    let ball_size = 0.5;
+    let num_per_axis = 3;
+    let center_to_center = 4. * ball_size;
+    let from = Tuple::point(
+        -5. * center_to_center,
+        5. * center_to_center,
+        -4. * center_to_center,
+    );
+    let to = Tuple::point(
+        num_per_axis as Float * center_to_center / 2.,
+        0., //num_per_axis as Float * center_to_center / 2.,
+        num_per_axis as Float * center_to_center / 2.,
+    );
+    let up = Tuple::point(0., 1., 0.);
+    let mut camera = Camera::new(width, height, PI / 6.);
+    camera.set_transform(view_transform(from, to, up));
+    camera.render_strategy = opt.render_strategy;
+    camera.samples_per_pixel = opt.samples;
+
+    let floor = ShapeBuilder::default()
+        .geometry(Geometry::Plane)
+        .transform(Matrix4x4::translation(0., -ball_size, 0.))
+        .material(
+            MaterialBuilder::default()
+                .color([0.2, 0.2, 0.2])
+                .specular(0.)
+                .build()?,
+        )
+        .build()?;
+    let mut objects = vec![floor];
+
+    for z in 0..num_per_axis {
+        for y in 0..num_per_axis {
+            for x in 0..num_per_axis {
+                objects.push(
+                    ShapeBuilder::default()
+                        .transform(
+                            Matrix4x4::translation(
+                                x as Float * center_to_center,
+                                y as Float * center_to_center,
+                                z as Float * center_to_center,
+                            ) * Matrix4x4::scaling(ball_size, ball_size, ball_size),
+                        )
+                        .material(
+                            MaterialBuilder::default()
+                                .color([0.1, 1., 0.5])
+                                .ambient(y as Float / 4.)
+                                .diffuse(x as Float / 4.)
+                                .specular(z as Float / 4.)
+                                .build()?,
+                        )
+                        .build()?,
+                );
+            }
+        }
+    }
+
+    let world = WorldBuilder::default()
+        .lights(vec![light1, light2, light3])
+        .objects(objects)
+        .build()?;
+
+    let image = camera.render(&world);
+
+    let path = "/tmp/balls.png";
+    println!("saving output to {}", path);
+    image.write_to_file(path)?;
+    println!("Render time {:.3} seconds", start.elapsed().as_secs_f32());
+    Ok(())
+}
--- a/rtchallenge/examples/eoc1.rs
+++ b/rtchallenge/examples/eoc1.rs
@@ -0,0 +1,39 @@
+use rtchallenge::tuples::Tuple;
+
+#[derive(Debug)]
+struct Environment {
+    gravity: Tuple,
+    wind: Tuple,
+}
+#[derive(Debug)]
+struct Projectile {
+    position: Tuple,
+    velocity: Tuple,
+}
+
+fn tick(env: &Environment, proj: &Projectile) -> Projectile {
+    let position = proj.position + proj.velocity;
+    let velocity = proj.velocity + env.gravity + env.wind;
+    Projectile { position, velocity }
+}
+fn main() {
+    let mut p = Projectile {
+        position: Tuple::point(0., 1., 0.),
+        velocity: 4. * Tuple::vector(1., 1., 0.).normalize(),
+    };
+    let e = Environment {
+        gravity: Tuple::vector(0., -0.1, 0.).normalize(),
+        wind: Tuple::vector(-0.01, 0., 0.),
+    };
+
+    let mut i = 0;
+    while p.position.y > 0. {
+        p = tick(&e, &p);
+        println!("tick {}: position {:?}", i, p.position);
+        i += 1;
+        if i > 100 {
+            eprintln!("too many iterations");
+            return;
+        }
+    }
+}
--- a/rtchallenge/examples/eoc10.rs
+++ b/rtchallenge/examples/eoc10.rs
@@ -0,0 +1,171 @@
+use std::time::Instant;
+
+use anyhow::Result;
+use structopt::StructOpt;
+
+use rtchallenge::prelude::*;
+
+use rtchallenge::{
+    camera::RenderStrategy,
+    float::consts::PI,
+    patterns::{test_pattern, BLACK_PAT, WHITE_PAT},
+    WHITE,
+};
+
+/// End of chapter 10 challenge.
+#[derive(StructOpt, Debug)]
+#[structopt(name = "eoc10")]
+struct Opt {
+    /// Strategy for casting rays into image.
+    #[structopt(long, default_value = "rayon")]
+    render_strategy: RenderStrategy,
+    /// Number of samples per pixel.  0 renders from the center of the pixel, 1 or more samples N
+    /// times randomly across the pixel.
+    #[structopt(short, long, default_value = "0")]
+    samples: usize,
+    /// Rendered image width in pixels.
+    #[structopt(short, long, default_value = "2560")]
+    width: usize,
+    /// Rendered image height in pixels.
+    #[structopt(short, long, default_value = "1440")]
+    height: usize,
+}
+
+fn main() -> Result<()> {
+    let start = Instant::now();
+    let opt = Opt::from_args();
+
+    let light1 = PointLightBuilder::default()
+        .position(point(-5., 5., -5.))
+        .intensity(WHITE)
+        .build()?;
+    let light2 = PointLightBuilder::default()
+        .position(point(5., 5., -5.))
+        .intensity([0.2, 0.2, 0.6])
+        .build()?;
+    let light3 = PointLightBuilder::default()
+        .position(point(0., 2., -5.))
+        .intensity([0.2, 0.2, 0.1])
+        .build()?;
+
+    let from = point(2., 2., -10.);
+    let to = point(2., 1., 0.);
+    let up = point(0., 1., 0.);
+    let camera = CameraBuilder::default()
+        .hsize(opt.width)
+        .vsize(opt.height)
+        .field_of_view(PI / 4.)
+        .transform(view_transform(from, to, up))
+        .render_strategy(opt.render_strategy)
+        .samples_per_pixel(opt.samples)
+        .build()?;
+
+    let floor = plane()
+        .material(
+            MaterialBuilder::default()
+                .color(
+                    checkers_pattern(WHITE_PAT, BLACK_PAT)
+                        .transform(translation(1., 0., 0.) * scaling(2., 2., 2.))
+                        .build()?,
+                )
+                .specular(0.)
+                .build()?,
+        )
+        .build()?;
+    let sphere_size = scaling(0.5, 0.5, 0.5);
+
+    let x1y1 = sphere()
+        .transform(translation(1., 1., 0.) * sphere_size)
+        .material(
+            MaterialBuilder::default()
+                .color(
+                    gradient_pattern([0., 0., 1.].into(), [1., 1., 0.].into())
+                        .transform(scaling(2., 1., 1.) * translation(-0.5, 0., 0.))
+                        .build()?,
+                )
+                .diffuse(0.7)
+                .specular(0.3)
+                .build()?,
+        )
+        .build()?;
+
+    let x2y1 = sphere()
+        .transform(translation(2., 1., 0.) * sphere_size)
+        .material(
+            MaterialBuilder::default()
+                .color(stripe_pattern(WHITE_PAT, BLACK_PAT).build()?)
+                .diffuse(0.7)
+                .specular(0.3)
+                .build()?,
+        )
+        .build()?;
+
+    let x3y1 = sphere()
+        .transform(translation(3., 1., 0.) * sphere_size)
+        .material(
+            MaterialBuilder::default()
+                .color(
+                    stripe_pattern(WHITE_PAT, BLACK_PAT)
+                        .transform(scaling(0.2, 1., 1.))
+                        .build()?,
+                )
+                .diffuse(0.7)
+                .specular(0.0)
+                .build()?,
+        )
+        .build()?;
+
+    let x1y2 = sphere()
+        .transform(translation(1., 2., 0.) * sphere_size)
+        .material(
+            MaterialBuilder::default()
+                .color(test_pattern().build()?)
+                .diffuse(0.7)
+                .specular(0.3)
+                .build()?,
+        )
+        .build()?;
+
+    let x2y2 = sphere()
+        .transform(translation(2., 2., 0.) * sphere_size)
+        .material(
+            MaterialBuilder::default()
+                .color(
+                    ring_pattern(WHITE_PAT, BLACK_PAT)
+                        .transform(scaling(0.2, 0.2, 0.2))
+                        .build()?,
+                )
+                .diffuse(0.7)
+                .specular(0.3)
+                .build()?,
+        )
+        .build()?;
+
+    let x3y2 = sphere()
+        .transform(translation(3., 2., 0.) * sphere_size)
+        .material(
+            MaterialBuilder::default()
+                .color(
+                    checkers_pattern(WHITE_PAT, BLACK_PAT)
+                        .transform(scaling(0.5, 0.5, 0.5))
+                        .build()?,
+                )
+                .diffuse(0.7)
+                .specular(0.3)
+                .build()?,
+        )
+        .build()?;
+
+    let world = WorldBuilder::default()
+        .lights(vec![light1, light2, light3])
+        .objects(vec![floor, x1y1, x2y1, x3y1, x1y2, x2y2, x3y2])
+        .build()?;
+
+    let image = camera.render(&world);
+
+    let path = "/tmp/eoc10.png";
+    println!("saving output to {}", path);
+    image.write_to_file(path)?;
+    println!("Render time {:.3} seconds", start.elapsed().as_secs_f32());
+    Ok(())
+}
--- a/rtchallenge/examples/eoc11.rs
+++ b/rtchallenge/examples/eoc11.rs
@@ -0,0 +1,218 @@
+use std::time::Instant;
+
+use anyhow::Result;
+use structopt::StructOpt;
+
+use rtchallenge::prelude::*;
+
+use rtchallenge::{
+    camera::RenderStrategy,
+    float::consts::PI,
+    patterns::{test_pattern, BLACK_PAT, WHITE_PAT},
+    WHITE,
+};
+
+/// End of chapter 11 challenge.
+#[derive(StructOpt, Debug)]
+#[structopt(name = "eoc11")]
+struct Opt {
+    /// Strategy for casting rays into image.
+    #[structopt(long, default_value = "rayon")]
+    render_strategy: RenderStrategy,
+    /// Number of samples per pixel.  0 renders from the center of the pixel, 1 or more samples N
+    /// times randomly across the pixel.
+    #[structopt(short, long, default_value = "0")]
+    samples: usize,
+    /// Rendered image width in pixels.
+    #[structopt(short, long, default_value = "2560")]
+    width: usize,
+    /// Rendered image height in pixels.
+    #[structopt(short, long, default_value = "1440")]
+    height: usize,
+}
+
+fn main() -> Result<()> {
+    let start = Instant::now();
+    let opt = Opt::from_args();
+
+    let light1 = PointLightBuilder::default()
+        .position(point(-5., 5., -5.))
+        .intensity(WHITE)
+        .build()?;
+    let light2 = PointLightBuilder::default()
+        .position(point(5., 5., -5.))
+        .intensity([0.2, 0.2, 0.6])
+        .build()?;
+    let light3 = PointLightBuilder::default()
+        .position(point(0., 2., -5.))
+        .intensity([0.2, 0.2, 0.1])
+        .build()?;
+
+    let from = point(2., 8., -10.);
+    let to = point(2., 1., -1.);
+    let up = point(0., 1., 0.);
+    let camera = CameraBuilder::default()
+        .hsize(opt.width)
+        .vsize(opt.height)
+        .field_of_view(PI / 6.)
+        .transform(view_transform(from, to, up))
+        .render_strategy(opt.render_strategy)
+        .samples_per_pixel(opt.samples)
+        .build()?;
+
+    let floor = plane()
+        .material(
+            MaterialBuilder::default()
+                .color(
+                    checkers_pattern(
+                        ring_pattern([0.8, 0.8, 0.2].into(), [0.8, 0.2, 0.8].into())
+                            .transform(scaling(1. / 8., 1. / 8., 1. / 8.))
+                            .build()?,
+                        ring_pattern([0.2, 0.8, 0.2].into(), [0.8, 0.2, 0.2].into())
+                            .transform(scaling(1. / 4., 1. / 4., 1. / 4.))
+                            .build()?,
+                    )
+                    .transform(translation(0., 1., 0.) * scaling(2., 2., 2.))
+                    .build()?,
+                )
+                .specular(0.)
+                .reflective(0.5)
+                .build()?,
+        )
+        .build()?;
+    let sphere_size = scaling(0.5, 0.5, 0.5);
+
+    let x1y1 = sphere()
+        .transform(translation(1., 1., 0.) * sphere_size)
+        .material(
+            MaterialBuilder::default()
+                .color(
+                    gradient_pattern([0., 0., 1.].into(), [1., 1., 0.].into())
+                        .transform(scaling(2., 1., 1.) * translation(-0.5, 0., 0.))
+                        .build()?,
+                )
+                .diffuse(0.7)
+                .specular(0.3)
+                .reflective(0.5)
+                .build()?,
+        )
+        .build()?;
+
+    let x2y1 = sphere()
+        .transform(translation(2., 1., 0.) * sphere_size)
+        .material(
+            MaterialBuilder::default()
+                .color(stripe_pattern(WHITE_PAT, BLACK_PAT).build()?)
+                .diffuse(0.7)
+                .specular(0.3)
+                .build()?,
+        )
+        .build()?;
+
+    let x3y1 = sphere()
+        .transform(translation(3., 1., 0.) * sphere_size)
+        .material(
+            MaterialBuilder::default()
+                .color(
+                    stripe_pattern(WHITE_PAT, BLACK_PAT)
+                        .transform(scaling(0.2, 1., 1.))
+                        .build()?,
+                )
+                .diffuse(0.7)
+                .specular(0.0)
+                .build()?,
+        )
+        .build()?;
+
+    let x1y2 = sphere()
+        .transform(translation(1., 2., 0.) * sphere_size)
+        .material(
+            MaterialBuilder::default()
+                .color(test_pattern().build()?)
+                .diffuse(0.7)
+                .specular(0.3)
+                .build()?,
+        )
+        .build()?;
+
+    let x2y2 = sphere()
+        .transform(translation(2., 2., 0.) * sphere_size)
+        .material(
+            MaterialBuilder::default()
+                .color(
+                    ring_pattern(WHITE_PAT, BLACK_PAT)
+                        .transform(scaling(0.2, 0.2, 0.2))
+                        .build()?,
+                )
+                .diffuse(0.7)
+                .specular(0.3)
+                .build()?,
+        )
+        .build()?;
+
+    let x3y2 = sphere()
+        .transform(translation(3., 2., 0.) * sphere_size)
+        .material(
+            MaterialBuilder::default()
+                .color(
+                    checkers_pattern(WHITE_PAT, BLACK_PAT)
+                        .transform(scaling(0.5, 0.5, 0.5))
+                        .build()?,
+                )
+                .diffuse(0.7)
+                .specular(0.3)
+                .build()?,
+        )
+        .build()?;
+
+    let x1y2z1 = sphere()
+        .transform(translation(1., 2., -1.) * sphere_size)
+        .material(
+            MaterialBuilder::default()
+                .color([0.8, 0.2, 0.2])
+                .diffuse(0.7)
+                .specular(0.3)
+                .transparency(0.5)
+                .build()?,
+        )
+        .build()?;
+
+    let x2y2z1 = sphere()
+        .transform(translation(2., 2., -1.) * sphere_size)
+        .material(
+            MaterialBuilder::default()
+                .color([0.8, 0.2, 0.2])
+                .diffuse(0.7)
+                .specular(0.3)
+                .transparency(0.9)
+                .refractive_index(1.5)
+                .build()?,
+        )
+        .build()?;
+
+    let x2y4z1 = sphere()
+        .transform(translation(2., 4., 0.) * sphere_size)
+        .material(
+            MaterialBuilder::default()
+                .color([0.2, 0.2, 0.8])
+                .diffuse(0.7)
+                .specular(0.3)
+                .build()?,
+        )
+        .build()?;
+
+    let world = WorldBuilder::default()
+        .lights(vec![light1, light2, light3])
+        .objects(vec![
+            floor, x1y1, x2y1, x3y1, x1y2, x2y2, x3y2, x1y2z1, x2y2z1, x2y4z1,
+        ])
+        .build()?;
+
+    let image = camera.render(&world);
+
+    let path = "/tmp/eoc11.png";
+    println!("saving output to {}", path);
+    image.write_to_file(path)?;
+    println!("Render time {:.3} seconds", start.elapsed().as_secs_f32());
+    Ok(())
+}
--- a/rtchallenge/examples/eoc12.rs
+++ b/rtchallenge/examples/eoc12.rs
@@ -0,0 +1,232 @@
+use std::time::Instant;
+
+use anyhow::Result;
+use structopt::StructOpt;
+
+use rtchallenge::prelude::*;
+
+use rtchallenge::{
+    camera::RenderStrategy,
+    float::consts::PI,
+    patterns::{test_pattern, BLACK_PAT, WHITE_PAT},
+    WHITE,
+};
+
+/// End of chapter 12 challenge.
+#[derive(StructOpt, Debug)]
+#[structopt(name = "eoc12")]
+struct Opt {
+    /// Strategy for casting rays into image.
+    #[structopt(long, default_value = "rayon")]
+    render_strategy: RenderStrategy,
+    /// Number of samples per pixel.  0 renders from the center of the pixel, 1 or more samples N
+    /// times randomly across the pixel.
+    #[structopt(short, long, default_value = "0")]
+    samples: usize,
+    /// Rendered image width in pixels.
+    #[structopt(short, long, default_value = "2560")]
+    width: usize,
+    /// Rendered image height in pixels.
+    #[structopt(short, long, default_value = "1440")]
+    height: usize,
+}
+
+fn main() -> Result<()> {
+    let start = Instant::now();
+    let opt = Opt::from_args();
+
+    let light1 = PointLightBuilder::default()
+        .position(point(-5., 5., -5.))
+        .intensity(WHITE)
+        .build()?;
+    let light2 = PointLightBuilder::default()
+        .position(point(5., 5., -5.))
+        .intensity([0.2, 0.2, 0.6])
+        .build()?;
+    let light3 = PointLightBuilder::default()
+        .position(point(0., 2., -5.))
+        .intensity([0.2, 0.2, 0.1])
+        .build()?;
+
+    let from = point(2., 8., -10.);
+    let to = point(2., 1., -1.);
+    let up = point(0., 1., 0.);
+    let camera = CameraBuilder::default()
+        .hsize(opt.width)
+        .vsize(opt.height)
+        .field_of_view(PI / 6.)
+        .transform(view_transform(from, to, up))
+        .render_strategy(opt.render_strategy)
+        .samples_per_pixel(opt.samples)
+        .build()?;
+
+    let floor = plane()
+        .material(
+            MaterialBuilder::default()
+                .color(
+                    checkers_pattern(
+                        ring_pattern([0.8, 0.8, 0.2].into(), [0.8, 0.2, 0.8].into())
+                            .transform(scaling(1. / 8., 1. / 8., 1. / 8.))
+                            .build()?,
+                        ring_pattern([0.2, 0.8, 0.2].into(), [0.8, 0.2, 0.2].into())
+                            .transform(scaling(1. / 4., 1. / 4., 1. / 4.))
+                            .build()?,
+                    )
+                    .transform(translation(0., 1., 0.) * scaling(2., 2., 2.))
+                    .build()?,
+                )
+                .specular(0.)
+                .reflective(0.5)
+                .build()?,
+        )
+        .build()?;
+    let sphere_size = scaling(0.5, 0.5, 0.5);
+
+    let x1y1 = sphere()
+        .transform(translation(1., 1., 0.) * sphere_size)
+        .material(
+            MaterialBuilder::default()
+                .color(
+                    gradient_pattern([0., 0., 1.].into(), [1., 1., 0.].into())
+                        .transform(scaling(2., 1., 1.) * translation(-0.5, 0., 0.))
+                        .build()?,
+                )
+                .diffuse(0.7)
+                .specular(0.3)
+                .reflective(0.5)
+                .build()?,
+        )
+        .build()?;
+
+    let x2y1 = sphere()
+        .transform(translation(2., 1., 0.) * sphere_size)
+        .material(
+            MaterialBuilder::default()
+                .color(stripe_pattern(WHITE_PAT, BLACK_PAT).build()?)
+                .diffuse(0.7)
+                .specular(0.3)
+                .build()?,
+        )
+        .build()?;
+
+    let x3y1 = sphere()
+        .transform(translation(3., 1., 0.) * sphere_size)
+        .material(
+            MaterialBuilder::default()
+                .color(
+                    stripe_pattern(WHITE_PAT, BLACK_PAT)
+                        .transform(scaling(0.2, 1., 1.))
+                        .build()?,
+                )
+                .diffuse(0.7)
+                .specular(0.0)
+                .build()?,
+        )
+        .build()?;
+
+    let x1y2 = sphere()
+        .transform(translation(1., 2., 0.) * sphere_size)
+        .material(
+            MaterialBuilder::default()
+                .color(test_pattern().build()?)
+                .diffuse(0.7)
+                .specular(0.3)
+                .build()?,
+        )
+        .build()?;
+
+    let x2y2 = sphere()
+        .transform(translation(2., 2., 0.) * sphere_size)
+        .material(
+            MaterialBuilder::default()
+                .color(
+                    ring_pattern(WHITE_PAT, BLACK_PAT)
+                        .transform(scaling(0.2, 0.2, 0.2))
+                        .build()?,
+                )
+                .diffuse(0.7)
+                .specular(0.3)
+                .build()?,
+        )
+        .build()?;
+
+    let x3y2 = sphere()
+        .transform(translation(3., 2., 0.) * sphere_size)
+        .material(
+            MaterialBuilder::default()
+                .color(
+                    checkers_pattern(WHITE_PAT, BLACK_PAT)
+                        .transform(scaling(0.5, 0.5, 0.5))
+                        .build()?,
+                )
+                .diffuse(0.7)
+                .specular(0.3)
+                .build()?,
+        )
+        .build()?;
+
+    let x1y2z1 = sphere()
+        .transform(translation(1., 2., -1.) * sphere_size)
+        .material(
+            MaterialBuilder::default()
+                .color([0.8, 0.2, 0.2])
+                .diffuse(0.7)
+                .specular(0.3)
+                .transparency(0.5)
+                .build()?,
+        )
+        .build()?;
+
+    let x2y2z1 = sphere()
+        .transform(translation(2., 2., -1.) * sphere_size)
+        .material(
+            MaterialBuilder::default()
+                .color([0.8, 0.2, 0.2])
+                .diffuse(0.7)
+                .specular(0.3)
+                .transparency(0.9)
+                .refractive_index(1.5)
+                .build()?,
+        )
+        .build()?;
+
+    let x3y2z1 = cube()
+        .transform(
+            translation(3., 2., -1.) * (sphere_size * scaling(0.5, 0.5, 0.5)) * rotation_y(PI / 4.),
+        )
+        .material(
+            MaterialBuilder::default()
+                .color([0.8, 0.8, 0.2])
+                .diffuse(0.7)
+                .specular(0.3)
+                .reflective(0.5)
+                .build()?,
+        )
+        .build()?;
+
+    let x2y4z1 = sphere()
+        .transform(translation(2., 4., 0.) * sphere_size)
+        .material(
+            MaterialBuilder::default()
+                .color([0.2, 0.2, 0.8])
+                .diffuse(0.7)
+                .specular(0.3)
+                .build()?,
+        )
+        .build()?;
+
+    let world = WorldBuilder::default()
+        .lights(vec![light1, light2, light3])
+        .objects(vec![
+            floor, x1y1, x2y1, x3y1, x1y2, x2y2, x3y2, x1y2z1, x2y2z1, x2y4z1, x3y2z1,
+        ])
+        .build()?;
+
+    let image = camera.render(&world);
+
+    let path = "/tmp/eoc12.png";
+    println!("saving output to {}", path);
+    image.write_to_file(path)?;
+    println!("Render time {:.3} seconds", start.elapsed().as_secs_f32());
+    Ok(())
+}
--- a/rtchallenge/examples/eoc14.rs
+++ b/rtchallenge/examples/eoc14.rs
@@ -0,0 +1,232 @@
+use std::time::Instant;
+
+use anyhow::Result;
+use structopt::StructOpt;
+
+use rtchallenge::prelude::*;
+
+use rtchallenge::{
+    camera::RenderStrategy,
+    float::consts::PI,
+    patterns::{test_pattern, BLACK_PAT, WHITE_PAT},
+    WHITE,
+};
+
+/// End of chapter 14 challenge.
+#[derive(StructOpt, Debug)]
+#[structopt(name = "eoc14")]
+struct Opt {
+    /// Strategy for casting rays into image.
+    #[structopt(long, default_value = "rayon")]
+    render_strategy: RenderStrategy,
+    /// Number of samples per pixel.  0 renders from the center of the pixel, 1 or more samples N
+    /// times randomly across the pixel.
+    #[structopt(short, long, default_value = "0")]
+    samples: usize,
+    /// Rendered image width in pixels.
+    #[structopt(short, long, default_value = "2560")]
+    width: usize,
+    /// Rendered image height in pixels.
+    #[structopt(short, long, default_value = "1440")]
+    height: usize,
+}
+
+fn main() -> Result<()> {
+    let start = Instant::now();
+    let opt = Opt::from_args();
+
+    let light1 = PointLightBuilder::default()
+        .position(point(-5., 5., -5.))
+        .intensity(WHITE)
+        .build()?;
+    let light2 = PointLightBuilder::default()
+        .position(point(5., 5., -5.))
+        .intensity([0.2, 0.2, 0.6])
+        .build()?;
+    let light3 = PointLightBuilder::default()
+        .position(point(0., 2., -5.))
+        .intensity([0.2, 0.2, 0.1])
+        .build()?;
+
+    let from = point(2., 8., -10.);
+    let to = point(2., 2., -1.);
+    let up = point(0., 1., 0.);
+    let camera = CameraBuilder::default()
+        .hsize(opt.width)
+        .vsize(opt.height)
+        .field_of_view(PI / 12.)
+        .transform(view_transform(from, to, up))
+        .render_strategy(opt.render_strategy)
+        .samples_per_pixel(opt.samples)
+        .build()?;
+
+    let floor = plane()
+        .material(
+            MaterialBuilder::default()
+                .color(
+                    checkers_pattern(
+                        ring_pattern([0.8, 0.8, 0.2].into(), [0.8, 0.2, 0.8].into())
+                            .transform(scaling(1. / 8., 1. / 8., 1. / 8.))
+                            .build()?,
+                        ring_pattern([0.2, 0.8, 0.2].into(), [0.8, 0.2, 0.2].into())
+                            .transform(scaling(1. / 4., 1. / 4., 1. / 4.))
+                            .build()?,
+                    )
+                    .transform(translation(0., 1., 0.) * scaling(2., 2., 2.))
+                    .build()?,
+                )
+                .specular(0.)
+                .reflective(0.5)
+                .build()?,
+        )
+        .build()?;
+    let sphere_size = scaling(0.5, 0.5, 0.5);
+
+    let x1y1 = sphere()
+        .transform(translation(1., 1., 0.) * sphere_size)
+        .material(
+            MaterialBuilder::default()
+                .color(
+                    gradient_pattern([0., 0., 1.].into(), [1., 1., 0.].into())
+                        .transform(scaling(2., 1., 1.) * translation(-0.5, 0., 0.))
+                        .build()?,
+                )
+                .diffuse(0.7)
+                .specular(0.3)
+                .reflective(0.5)
+                .build()?,
+        )
+        .build()?;
+
+    let x2y1 = sphere()
+        .transform(translation(2., 1., 0.) * sphere_size)
+        .material(
+            MaterialBuilder::default()
+                .color(stripe_pattern(WHITE_PAT, BLACK_PAT).build()?)
+                .diffuse(0.7)
+                .specular(0.3)
+                .build()?,
+        )
+        .build()?;
+
+    let x3y1 = sphere()
+        .transform(translation(3., 1., 0.) * sphere_size)
+        .material(
+            MaterialBuilder::default()
+                .color(
+                    stripe_pattern(WHITE_PAT, BLACK_PAT)
+                        .transform(scaling(0.2, 1., 1.))
+                        .build()?,
+                )
+                .diffuse(0.7)
+                .specular(0.0)
+                .build()?,
+        )
+        .build()?;
+
+    let x1y2 = sphere()
+        .transform(translation(1., 2., 0.) * sphere_size)
+        .material(
+            MaterialBuilder::default()
+                .color(test_pattern().build()?)
+                .diffuse(0.7)
+                .specular(0.3)
+                .build()?,
+        )
+        .build()?;
+
+    let x2y2 = sphere()
+        .transform(translation(2., 2., 0.) * sphere_size)
+        .material(
+            MaterialBuilder::default()
+                .color(
+                    ring_pattern(WHITE_PAT, BLACK_PAT)
+                        .transform(scaling(0.2, 0.2, 0.2))
+                        .build()?,
+                )
+                .diffuse(0.7)
+                .specular(0.3)
+                .build()?,
+        )
+        .build()?;
+
+    let x3y2 = sphere()
+        .transform(translation(3., 2., 0.) * sphere_size)
+        .material(
+            MaterialBuilder::default()
+                .color(
+                    checkers_pattern(WHITE_PAT, BLACK_PAT)
+                        .transform(scaling(0.5, 0.5, 0.5))
+                        .build()?,
+                )
+                .diffuse(0.7)
+                .specular(0.3)
+                .build()?,
+        )
+        .build()?;
+
+    let x1y2z1 = sphere()
+        .transform(translation(1., 2., -1.) * sphere_size)
+        .material(
+            MaterialBuilder::default()
+                .color([0.8, 0.2, 0.2])
+                .diffuse(0.7)
+                .specular(0.3)
+                .transparency(0.5)
+                .build()?,
+        )
+        .build()?;
+
+    let x2y2z1 = sphere()
+        .transform(translation(2., 2., -1.) * sphere_size)
+        .material(
+            MaterialBuilder::default()
+                .color([0.8, 0.2, 0.2])
+                .diffuse(0.7)
+                .specular(0.3)
+                .transparency(0.9)
+                .refractive_index(1.5)
+                .build()?,
+        )
+        .build()?;
+
+    let x3y2z1 = cube()
+        .transform(
+            translation(3., 2., -1.) * (sphere_size * scaling(0.5, 0.5, 0.5)) * rotation_y(PI / 4.),
+        )
+        .material(
+            MaterialBuilder::default()
+                .color([0.8, 0.8, 0.2])
+                .diffuse(0.7)
+                .specular(0.3)
+                .reflective(0.5)
+                .build()?,
+        )
+        .build()?;
+
+    let x2y4z1 = sphere()
+        .transform(translation(2., 4., 0.) * sphere_size)
+        .material(
+            MaterialBuilder::default()
+                .color([0.2, 0.2, 0.8])
+                .diffuse(0.7)
+                .specular(0.3)
+                .build()?,
+        )
+        .build()?;
+
+    let world = WorldBuilder::default()
+        .lights(vec![light1, light2, light3])
+        .objects(vec![
+            floor, x1y1, x2y1, x3y1, x1y2, x2y2, x3y2, x1y2z1, x2y2z1, x2y4z1, x3y2z1,
+        ])
+        .build()?;
+
+    let image = camera.render(&world);
+
+    let path = "/tmp/eoc14.png";
+    println!("saving output to {}", path);
+    image.write_to_file(path)?;
+    println!("Render time {:.3} seconds", start.elapsed().as_secs_f32());
+    Ok(())
+}
--- a/rtchallenge/examples/eoc2.rs
+++ b/rtchallenge/examples/eoc2.rs
@@ -0,0 +1,73 @@
+use anyhow::{bail, Result};
+
+use rtchallenge::{
+    canvas::Canvas,
+    tuples::{Color, Tuple},
+    Float,
+};
+
+#[derive(Debug)]
+struct Environment {
+    gravity: Tuple,
+    wind: Tuple,
+}
+#[derive(Debug)]
+struct Projectile {
+    position: Tuple,
+    velocity: Tuple,
+}
+
+fn tick(env: &Environment, proj: &Projectile) -> Projectile {
+    let position = proj.position + proj.velocity;
+    let velocity = proj.velocity + env.gravity + env.wind;
+    Projectile { position, velocity }
+}
+
+fn draw_dot(c: &mut Canvas, x: usize, y: usize) {
+    let red = Color::new(1., 0., 0.);
+    c.set(x.saturating_sub(1), y.saturating_sub(1), red);
+    c.set(x, y.saturating_sub(1), red);
+    c.set(x + 1, y.saturating_sub(1), red);
+    c.set(x.saturating_sub(1), y, red);
+    c.set(x, y, red);
+    c.set(x + 1, y, red);
+    c.set(x.saturating_sub(1), y + 1, red);
+    c.set(x, y + 1, red);
+    c.set(x + 1, y + 1, red);
+}
+fn main() -> Result<()> {
+    let position = Tuple::point(0., 1., 0.);
+    let velocity = Tuple::vector(1., 1.8, 0.).normalize() * 11.25;
+    let mut p = Projectile { position, velocity };
+    let gravity = Tuple::vector(0., -0.1, 0.);
+    let wind = Tuple::vector(-0.01, 0., 0.);
+    let e = Environment { gravity, wind };
+
+    let w = 800;
+    let h = 600;
+    let bg = Color::new(0.2, 0.2, 0.2);
+    let mut c = Canvas::new(w, h, bg);
+    let mut i = 0;
+    let w = w as Float;
+    let h = h as Float;
+    while p.position.y > 0. {
+        p = tick(&e, &p);
+        println!("tick {}: proj {:?}", i, p);
+        let x = p.position.x;
+        let y = p.position.y;
+        if x > 0. && x < w && y > 0. && y < h {
+            let x = x as usize;
+            let y = (h - y) as usize;
+            draw_dot(&mut c, x, y)
+        }
+        i += 1;
+        if i > 1000 {
+            bail!("too many iterations");
+        }
+    }
+
+    let path = "/tmp/output.png";
+    println!("saving output to {}", path);
+    c.write_to_file(path)?;
+    Ok(())
+}
--- a/rtchallenge/examples/eoc4.rs
+++ b/rtchallenge/examples/eoc4.rs
@@ -0,0 +1,50 @@
+use anyhow::Result;
+
+use rtchallenge::{
+    canvas::Canvas,
+    float::consts::PI,
+    matrices::Matrix4x4,
+    tuples::{Color, Tuple},
+    Float,
+};
+
+fn draw_dot(c: &mut Canvas, x: usize, y: usize) {
+    let red = Color::new(1., 0., 0.);
+    c.set(x.saturating_sub(1), y.saturating_sub(1), red);
+    c.set(x, y.saturating_sub(1), red);
+    c.set(x + 1, y.saturating_sub(1), red);
+    c.set(x.saturating_sub(1), y, red);
+    c.set(x, y, red);
+    c.set(x + 1, y, red);
+    c.set(x.saturating_sub(1), y + 1, red);
+    c.set(x, y + 1, red);
+    c.set(x + 1, y + 1, red);
+}
+fn main() -> Result<()> {
+    let w = 200;
+    let h = w;
+    let bg = Color::new(0.2, 0.2, 0.2);
+    let mut c = Canvas::new(w, h, bg);
+    let t = Matrix4x4::translation(0., 0.4, 0.);
+    let p = Tuple::point(0., 0., 0.);
+    let rot_hour = Matrix4x4::rotation_z(-PI / 6.);
+
+    let mut p = t * p;
+    let w = w as Float;
+    let h = h as Float;
+    // The 'world' exists between -0.5 - 0.5 in X-Y plane.
+    // To convert to screen space, we translate by 0.5, scale to canvas size,
+    // and invert the Y-axis.
+    let world_to_screen =
+        Matrix4x4::scaling(w as Float, -h as Float, 1.0) * Matrix4x4::translation(0.5, -0.5, 0.);
+    for _ in 0..12 {
+        let canvas_pixel = world_to_screen * p;
+        draw_dot(&mut c, canvas_pixel.x as usize, canvas_pixel.y as usize);
+        p = rot_hour * p;
+    }
+
+    let path = "/tmp/eoc4.png";
+    println!("saving output to {}", path);
+    c.write_to_file(path)?;
+    Ok(())
+}
--- a/rtchallenge/examples/eoc5.rs
+++ b/rtchallenge/examples/eoc5.rs
@@ -0,0 +1,45 @@
+use anyhow::Result;
+
+use rtchallenge::{
+    canvas::Canvas,
+    matrices::Matrix4x4,
+    rays::Ray,
+    shapes::{intersect, Shape},
+    tuples::{Color, Tuple},
+    Float,
+};
+
+fn main() -> Result<()> {
+    let w = 200;
+    let h = w;
+    let bg = Color::new(0.2, 0.2, 0.2);
+    let mut c = Canvas::new(w, h, bg);
+    let ray_origin = Tuple::point(0., 0., -5.);
+    let wall_z = 10.;
+    let wall_size = 7.;
+    let pixel_size = wall_size / w as Float;
+    let half = wall_size / 2.;
+    let color = Color::new(1., 0., 0.);
+    let mut shape = Shape::sphere();
+    shape.set_transform(
+        Matrix4x4::shearing(1., 0., 0., 0., 0., 0.) * Matrix4x4::scaling(0.5, 1., 1.0),
+    );
+
+    for y in 0..h {
+        let world_y = half - pixel_size * y as Float;
+        for x in 0..w {
+            let world_x = -half + pixel_size * x as Float;
+            let position = Tuple::point(world_x, world_y, wall_z);
+            let r = Ray::new(ray_origin, (position - ray_origin).normalize());
+            let xs = intersect(&shape, &r);
+            if xs.hit().is_some() {
+                c.set(x, y, color);
+            }
+        }
+    }
+
+    let path = "/tmp/eoc5.png";
+    println!("saving output to {}", path);
+    c.write_to_file(path)?;
+    Ok(())
+}
--- a/rtchallenge/examples/eoc6.rs
+++ b/rtchallenge/examples/eoc6.rs
@@ -0,0 +1,65 @@
+use anyhow::Result;
+
+use rtchallenge::{
+    canvas::Canvas,
+    lights::PointLight,
+    materials::{lighting, Material},
+    rays::Ray,
+    shapes::{intersect, Shape},
+    tuples::{Color, Tuple},
+    Float, WHITE,
+};
+
+fn main() -> Result<()> {
+    let w = 640;
+    let h = w;
+    let bg = Color::new(0.2, 0.2, 0.2);
+    let mut c = Canvas::new(w, h, bg);
+    let ray_origin = Tuple::point(0., 0., -5.);
+    let wall_z = 10.;
+    let wall_size = 7.;
+    let pixel_size = wall_size / w as Float;
+    let half = wall_size / 2.;
+    let mut shape = Shape::sphere();
+    shape.material = Material {
+        color: Color::new(1., 0.2, 1.).into(),
+        specular: 0.5,
+        diffuse: 0.7,
+        shininess: 30.,
+        ..Material::default()
+    };
+    let light_position = Tuple::point(-10., 10., -10.);
+    let light_color = WHITE;
+    let light = PointLight::new(light_position, light_color);
+    let in_shadow = false;
+    for y in 0..h {
+        let world_y = half - pixel_size * y as Float;
+        for x in 0..w {
+            let world_x = -half + pixel_size * x as Float;
+            let position = Tuple::point(world_x, world_y, wall_z);
+            let direction = (position - ray_origin).normalize();
+            let r = Ray::new(ray_origin, direction);
+            let xs = intersect(&shape, &r);
+            if let Some(hit) = xs.hit() {
+                let point = r.position(hit.t);
+                let normal = hit.object.normal_at(point);
+                let eye = -r.direction;
+                let color = lighting(
+                    &hit.object.material,
+                    &hit.object,
+                    &light,
+                    point,
+                    eye,
+                    normal,
+                    in_shadow,
+                );
+                c.set(x, y, color);
+            }
+        }
+    }
+
+    let path = "/tmp/eoc6.png";
+    println!("saving output to {}", path);
+    c.write_to_file(path)?;
+    Ok(())
+}
--- a/rtchallenge/examples/eoc7.rs
+++ b/rtchallenge/examples/eoc7.rs
@@ -0,0 +1,108 @@
+use std::time::Instant;
+
+use anyhow::Result;
+use structopt::StructOpt;
+
+use rtchallenge::{
+    camera::{Camera, RenderStrategy},
+    float::consts::PI,
+    lights::PointLight,
+    materials::Material,
+    matrices::Matrix4x4,
+    shapes::Shape,
+    transformations::view_transform,
+    tuples::{Color, Tuple},
+    world::World,
+    WHITE,
+};
+
+/// End of chapter 7 challenge.
+#[derive(StructOpt, Debug)]
+#[structopt(name = "eoc7")]
+struct Opt {
+    #[structopt(long, default_value = "rayon")]
+    render_strategy: RenderStrategy,
+}
+
+fn main() -> Result<()> {
+    let start = Instant::now();
+    let opt = Opt::from_args();
+    let width = 1024;
+    let height = 1024;
+    let light_position = Tuple::point(-10., 10., -10.);
+    let light_color = WHITE;
+    let light = PointLight::new(light_position, light_color);
+    let mut camera = Camera::new(width, height, PI / 3.);
+    let from = Tuple::point(0., 1.5, -5.);
+    let to = Tuple::point(0., 1., 0.);
+    let up = Tuple::point(0., 1., 0.);
+    camera.set_transform(view_transform(from, to, up));
+    camera.render_strategy = opt.render_strategy;
+
+    let mut floor = Shape::sphere();
+    floor.set_transform(Matrix4x4::scaling(10., 0.01, 10.));
+    floor.material = Material {
+        color: Color::new(1., 0.9, 0.9).into(),
+        specular: 0.,
+        ..Material::default()
+    };
+
+    let mut left_wall = Shape::sphere();
+    left_wall.set_transform(
+        Matrix4x4::translation(0., 0., 5.)
+            * Matrix4x4::rotation_y(-PI / 4.)
+            * Matrix4x4::rotation_x(PI / 2.)
+            * Matrix4x4::scaling(10., 0.01, 10.),
+    );
+    left_wall.material = floor.material.clone();
+
+    let mut right_wall = Shape::sphere();
+    right_wall.set_transform(
+        Matrix4x4::translation(0., 0., 5.)
+            * Matrix4x4::rotation_y(PI / 4.)
+            * Matrix4x4::rotation_x(PI / 2.)
+            * Matrix4x4::scaling(10., 0.01, 10.),
+    );
+    right_wall.material = floor.material.clone();
+
+    let mut middle = Shape::sphere();
+    middle.set_transform(Matrix4x4::translation(-0.5, 1., 0.5));
+    middle.material = Material {
+        color: Color::new(0.1, 1., 0.5).into(),
+        diffuse: 0.7,
+        specular: 0.3,
+        ..Material::default()
+    };
+
+    let mut right = Shape::sphere();
+    right.set_transform(Matrix4x4::translation(1.5, 0.5, -0.5) * Matrix4x4::scaling(0.5, 0.5, 0.5));
+    right.material = Material {
+        color: Color::new(0.5, 1., 0.1).into(),
+        diffuse: 0.7,
+        specular: 0.3,
+        ..Material::default()
+    };
+
+    let mut left = Shape::sphere();
+    left.set_transform(
+        Matrix4x4::translation(-1.5, 0.33, -0.75) * Matrix4x4::scaling(0.33, 0.33, 0.33),
+    );
+    left.material = Material {
+        color: Color::new(1., 0.8, 0.1).into(),
+        diffuse: 0.7,
+        specular: 0.3,
+        ..Material::default()
+    };
+
+    let mut world = World::default();
+    world.lights = vec![light];
+    world.objects = vec![floor, left_wall, right_wall, middle, right, left];
+
+    let image = camera.render(&world);
+
+    let path = "/tmp/eoc7.png";
+    println!("saving output to {}", path);
+    image.write_to_file(path)?;
+    println!("Render time {:.3} seconds", start.elapsed().as_secs_f32());
+    Ok(())
+}
--- a/rtchallenge/examples/eoc8.rs
+++ b/rtchallenge/examples/eoc8.rs
@@ -0,0 +1,120 @@
+use std::time::Instant;
+
+use anyhow::Result;
+use structopt::StructOpt;
+
+use rtchallenge::{
+    camera::{Camera, RenderStrategy},
+    float::consts::PI,
+    lights::PointLight,
+    materials::Material,
+    matrices::Matrix4x4,
+    shapes::Shape,
+    transformations::view_transform,
+    tuples::{Color, Tuple},
+    world::World,
+    WHITE,
+};
+
+/// End of chapter 8 challenge.
+#[derive(StructOpt, Debug)]
+#[structopt(name = "eoc8")]
+struct Opt {
+    #[structopt(long, default_value = "rayon")]
+    render_strategy: RenderStrategy,
+    /// Number of samples per pixel.  0 renders from the center of the pixel, 1 or more samples N
+    /// times randomly across the pixel.
+    #[structopt(short, long, default_value = "0")]
+    samples: usize,
+}
+
+fn main() -> Result<()> {
+    let start = Instant::now();
+    let opt = Opt::from_args();
+    let width = 2560;
+    let height = 1440;
+
+    let light_position = Tuple::point(-10., 10., -10.);
+    let light_color = WHITE;
+    let light1 = PointLight::new(light_position, light_color);
+    let light_position = Tuple::point(10., 10., -10.);
+    let light_color = Color::new(0.2, 0.2, 0.2);
+    let light2 = PointLight::new(light_position, light_color);
+    let light_position = Tuple::point(0., 10., -10.);
+    let light3 = PointLight::new(light_position, light_color);
+
+    let mut camera = Camera::new(width, height, PI / 4.);
+    let from = Tuple::point(0., 1.5, -5.);
+    let to = Tuple::point(0., 1., 0.);
+    let up = Tuple::point(0., 1., 0.);
+    camera.set_transform(view_transform(from, to, up));
+    camera.render_strategy = opt.render_strategy;
+    camera.samples_per_pixel = opt.samples;
+
+    let mut floor = Shape::sphere();
+    floor.set_transform(Matrix4x4::scaling(10., 0.01, 10.));
+    floor.material = Material {
+        color: Color::new(1., 0.9, 0.9).into(),
+        specular: 0.,
+        ..Material::default()
+    };
+
+    let mut left_wall = Shape::sphere();
+    left_wall.set_transform(
+        Matrix4x4::translation(0., 0., 5.)
+            * Matrix4x4::rotation_y(-PI / 4.)
+            * Matrix4x4::rotation_x(PI / 2.)
+            * Matrix4x4::scaling(10., 0.01, 10.),
+    );
+    left_wall.material = floor.material.clone();
+
+    let mut right_wall = Shape::sphere();
+    right_wall.set_transform(
+        Matrix4x4::translation(0., 0., 5.)
+            * Matrix4x4::rotation_y(PI / 4.)
+            * Matrix4x4::rotation_x(PI / 2.)
+            * Matrix4x4::scaling(10., 0.00001, 10.),
+    );
+    right_wall.material = floor.material.clone();
+
+    let mut middle = Shape::sphere();
+    middle.set_transform(Matrix4x4::translation(-0.5, 1., 0.5));
+    middle.material = Material {
+        color: Color::new(0.1, 1., 0.5).into(),
+        diffuse: 0.7,
+        specular: 0.3,
+        ..Material::default()
+    };
+
+    let mut right = Shape::sphere();
+    right.set_transform(Matrix4x4::translation(1.5, 0.5, -0.5) * Matrix4x4::scaling(0.5, 0.5, 0.5));
+    right.material = Material {
+        color: Color::new(1., 1., 1.).into(),
+        diffuse: 0.7,
+        specular: 0.0,
+        ..Material::default()
+    };
+
+    let mut left = Shape::sphere();
+    left.set_transform(
+        Matrix4x4::translation(-1.5, 0.33, -0.75) * Matrix4x4::scaling(0.33, 0.33, 0.33),
+    );
+    left.material = Material {
+        color: Color::new(1., 0.8, 0.1).into(),
+        diffuse: 0.7,
+        specular: 0.3,
+        ..Material::default()
+    };
+
+    let mut world = World::default();
+    world.lights = vec![light1, light2, light3];
+    world.objects = vec![floor, left_wall, right_wall, middle, right, left];
+
+    let image = camera.render(&world);
+
+    let path = "/tmp/eoc8.png";
+    println!("saving output to {}", path);
+    image.write_to_file(path)?;
+    println!("Render time {:.3} seconds", start.elapsed().as_secs_f32());
+    Ok(())
+}
--- a/rtchallenge/examples/eoc9-prelude.rs
+++ b/rtchallenge/examples/eoc9-prelude.rs
@@ -0,0 +1,122 @@
+use std::time::Instant;
+
+use anyhow::Result;
+use structopt::StructOpt;
+
+use rtchallenge::prelude::*;
+
+use rtchallenge::{camera::RenderStrategy, float::consts::PI, WHITE};
+
+/// End of chapter 9 challenge.
+#[derive(StructOpt, Debug)]
+#[structopt(name = "eoc9")]
+struct Opt {
+    /// Strategy for casting rays into image.
+    #[structopt(long, default_value = "rayon")]
+    render_strategy: RenderStrategy,
+    /// Number of samples per pixel.  0 renders from the center of the pixel, 1 or more samples N
+    /// times randomly across the pixel.
+    #[structopt(short, long, default_value = "0")]
+    samples: usize,
+    /// Rendered image width in pixels.
+    #[structopt(short, long, default_value = "2560")]
+    width: usize,
+    /// Rendered image height in pixels.
+    #[structopt(short, long, default_value = "1440")]
+    height: usize,
+}
+
+fn main() -> Result<()> {
+    let start = Instant::now();
+    let opt = Opt::from_args();
+
+    let light1 = PointLightBuilder::default()
+        .position(point(-5., 5., -5.))
+        .intensity(WHITE)
+        .build()?;
+    let light2 = PointLightBuilder::default()
+        .position(point(5., 5., -5.))
+        .intensity([0.2, 0.2, 0.6])
+        .build()?;
+    let light3 = PointLightBuilder::default()
+        .position(point(0., 2., -5.))
+        .intensity([0.2, 0.2, 0.1])
+        .build()?;
+
+    let from = point(0., 1.5, -5.);
+    let to = point(0., 1., 0.);
+    let up = point(0., 1., 0.);
+    let camera = CameraBuilder::default()
+        .hsize(opt.width)
+        .vsize(opt.height)
+        .field_of_view(PI / 4.)
+        .transform(view_transform(from, to, up))
+        .render_strategy(opt.render_strategy)
+        .samples_per_pixel(opt.samples)
+        .build()?;
+
+    let floor = plane()
+        .material(
+            MaterialBuilder::default()
+                .color([1., 0.2, 0.2])
+                .specular(0.)
+                .build()?,
+        )
+        .build()?;
+
+    let ceiling = plane()
+        .transform(translation(0., 6., 0.) * rotation_x(PI))
+        .material(
+            MaterialBuilder::default()
+                .color([0.6, 0.6, 0.8])
+                .specular(0.2)
+                .build()?,
+        )
+        .build()?;
+
+    let middle = sphere()
+        .transform(translation(-0.5, 0.5, 0.5))
+        .material(
+            MaterialBuilder::default()
+                .color([0.1, 1., 0.5])
+                .diffuse(0.7)
+                .specular(0.3)
+                .build()?,
+        )
+        .build()?;
+
+    let right = sphere()
+        .transform(translation(1.5, 0.5, -0.5) * scaling(0.5, 0.5, 0.5))
+        .material(
+            MaterialBuilder::default()
+                .color([1., 1., 1.])
+                .diffuse(0.7)
+                .specular(0.0)
+                .build()?,
+        )
+        .build()?;
+
+    let left = sphere()
+        .transform(translation(-1.5, 0.33, -0.75) * scaling(0.33, 0.33, 0.33))
+        .material(
+            MaterialBuilder::default()
+                .color([1., 0.8, 0.1])
+                .diffuse(0.7)
+                .specular(0.3)
+                .build()?,
+        )
+        .build()?;
+
+    let world = WorldBuilder::default()
+        .lights(vec![light1, light2, light3])
+        .objects(vec![floor, ceiling, middle, right, left])
+        .build()?;
+
+    let image = camera.render(&world);
+
+    let path = "/tmp/eoc9.png";
+    println!("saving output to {}", path);
+    image.write_to_file(path)?;
+    println!("Render time {:.3} seconds", start.elapsed().as_secs_f32());
+    Ok(())
+}
--- a/rtchallenge/examples/eoc9.rs
+++ b/rtchallenge/examples/eoc9.rs
@@ -0,0 +1,114 @@
+use std::time::Instant;
+
+use anyhow::Result;
+use structopt::StructOpt;
+
+use rtchallenge::{
+    camera::{Camera, RenderStrategy},
+    float::consts::PI,
+    lights::PointLight,
+    materials::Material,
+    matrices::Matrix4x4,
+    shapes::Shape,
+    transformations::view_transform,
+    tuples::{Color, Tuple},
+    world::World,
+    WHITE,
+};
+
+/// End of chapter 9 challenge.
+#[derive(StructOpt, Debug)]
+#[structopt(name = "eoc9")]
+struct Opt {
+    /// Strategy for casting rays into image.
+    #[structopt(long, default_value = "rayon")]
+    render_strategy: RenderStrategy,
+    /// Number of samples per pixel.  0 renders from the center of the pixel, 1 or more samples N
+    /// times randomly across the pixel.
+    #[structopt(short, long, default_value = "0")]
+    samples: usize,
+    /// Rendered image width in pixels.
+    #[structopt(short, long, default_value = "2560")]
+    width: usize,
+    /// Rendered image height in pixels.
+    #[structopt(short, long, default_value = "1440")]
+    height: usize,
+}
+
+fn main() -> Result<()> {
+    let start = Instant::now();
+    let opt = Opt::from_args();
+
+    let light_position = Tuple::point(-5., 5., -5.);
+    let light_color = WHITE;
+    let light1 = PointLight::new(light_position, light_color);
+    let light_position = Tuple::point(5., 5., -5.);
+    let light_color = Color::new(0.2, 0.2, 0.6);
+    let light2 = PointLight::new(light_position, light_color);
+    let light_position = Tuple::point(0., 2., -5.);
+    let light_color = Color::new(0.2, 0.2, 0.1);
+    let light3 = PointLight::new(light_position, light_color);
+
+    let mut camera = Camera::new(opt.width, opt.height, PI / 4.);
+    let from = Tuple::point(0., 1.5, -5.);
+    let to = Tuple::point(0., 1., 0.);
+    let up = Tuple::point(0., 1., 0.);
+    camera.set_transform(view_transform(from, to, up));
+    camera.render_strategy = opt.render_strategy;
+    camera.samples_per_pixel = opt.samples;
+
+    let mut floor = Shape::plane();
+    floor.material = Material {
+        color: Color::new(1., 0.2, 0.2).into(),
+        specular: 0.,
+        ..Material::default()
+    };
+    let mut ceiling = Shape::plane();
+    ceiling.set_transform(Matrix4x4::translation(0., 6., 0.) * Matrix4x4::rotation_x(PI));
+    ceiling.material = Material {
+        color: Color::new(0.6, 0.6, 0.8).into(),
+        specular: 0.2,
+        ..Material::default()
+    };
+
+    let mut middle = Shape::sphere();
+    middle.set_transform(Matrix4x4::translation(-0.5, 0.5, 0.5));
+    middle.material = Material {
+        color: Color::new(0.1, 1., 0.5).into(),
+        diffuse: 0.7,
+        specular: 0.3,
+        ..Material::default()
+    };
+
+    let mut right = Shape::sphere();
+    right.set_transform(Matrix4x4::translation(1.5, 0.5, -0.5) * Matrix4x4::scaling(0.5, 0.5, 0.5));
+    right.material = Material {
+        color: Color::new(1., 1., 1.).into(),
+        diffuse: 0.7,
+        specular: 0.0,
+        ..Material::default()
+    };
+
+    let mut left = Shape::sphere();
+    left.set_transform(
+        Matrix4x4::translation(-1.5, 0.33, -0.75) * Matrix4x4::scaling(0.33, 0.33, 0.33),
+    );
+    left.material = Material {
+        color: Color::new(1., 0.8, 0.1).into(),
+        diffuse: 0.7,
+        specular: 0.3,
+        ..Material::default()
+    };
+
+    let mut world = World::default();
+    world.lights = vec![light1, light2, light3];
+    world.objects = vec![floor, ceiling, middle, right, left];
+
+    let image = camera.render(&world);
+
+    let path = "/tmp/eoc9.png";
+    println!("saving output to {}", path);
+    image.write_to_file(path)?;
+    println!("Render time {:.3} seconds", start.elapsed().as_secs_f32());
+    Ok(())
+}
--- a/rtchallenge/examples/glass.rs
+++ b/rtchallenge/examples/glass.rs
@@ -0,0 +1,115 @@
+use std::time::Instant;
+
+use anyhow::Result;
+use structopt::StructOpt;
+
+use rtchallenge::prelude::*;
+
+use rtchallenge::{
+    camera::RenderStrategy,
+    float::consts::PI,
+    patterns::{BLACK_PAT, WHITE_PAT},
+    WHITE,
+};
+
+/// Experiment with transparency.
+#[derive(StructOpt, Debug)]
+#[structopt(name = "glass")]
+struct Opt {
+    /// Strategy for casting rays into image.
+    #[structopt(long, default_value = "rayon")]
+    render_strategy: RenderStrategy,
+    /// Number of samples per pixel.  0 renders from the center of the pixel, 1 or more samples N
+    /// times randomly across the pixel.
+    #[structopt(short, long, default_value = "0")]
+    samples: usize,
+    /// Rendered image width in pixels.
+    #[structopt(short, long, default_value = "2560")]
+    width: usize,
+    /// Rendered image height in pixels.
+    #[structopt(short, long, default_value = "1440")]
+    height: usize,
+}
+
+fn main() -> Result<()> {
+    let start = Instant::now();
+    let opt = Opt::from_args();
+
+    let light1 = PointLightBuilder::default()
+        .position(point(-5., 5., -5.))
+        .intensity(WHITE)
+        .build()?;
+    let light2 = PointLightBuilder::default()
+        .position(point(5., 5., -5.))
+        .intensity([0.2, 0.2, 0.6])
+        .build()?;
+    let light3 = PointLightBuilder::default()
+        .position(point(0., 2., -5.))
+        .intensity([0.2, 0.2, 0.1])
+        .build()?;
+
+    let from = point(0., 0., -10.);
+    let to = point(0., 0., 0.);
+    let up = point(0., 1., 0.);
+    let camera = CameraBuilder::default()
+        .hsize(opt.width)
+        .vsize(opt.height)
+        .field_of_view(PI / 4.)
+        .transform(view_transform(from, to, up))
+        .render_strategy(opt.render_strategy)
+        .samples_per_pixel(opt.samples)
+        .build()?;
+
+    let floor = plane()
+        .transform(rotation_x(PI / 2.))
+        .material(
+            MaterialBuilder::default()
+                .color(checkers_pattern(BLACK_PAT, WHITE_PAT).build()?)
+                .reflective(0.5)
+                .build()?,
+        )
+        .build()?;
+    let ceiling = plane()
+        .transform(translation(0., 0., -20.) * rotation_x(PI / 2.))
+        .material(MaterialBuilder::default().color([0.2, 0.2, 0.8]).build()?)
+        .build()?;
+
+    let mut objects = Vec::new();
+    for x in 0..5 {
+        for y in 0..5 {
+            let trans = y as Float / 5.;
+            let index = 1. + x as Float / 5.;
+            dbg!(x, y, trans, index);
+            objects.push(
+                sphere()
+                    .transform(
+                        translation(x as Float - 2., y as Float - 2., -2.) * scaling(0.5, 0.5, 0.5),
+                    )
+                    .material(
+                        MaterialBuilder::default()
+                            .color([0.5, 0.5, 0.5])
+                            .transparency(trans)
+                            .refractive_index(index)
+                            .build()?,
+                    )
+                    .build()?,
+            );
+        }
+    }
+
+    objects.push(floor);
+    objects.push(ceiling);
+
+    let world = WorldBuilder::default()
+        .lights(vec![light1, light2, light3])
+        .objects(objects)
+        .build()?;
+
+    let image = camera.render(&world);
+
+    let path = "/tmp/glass.png";
+    println!("saving output to {}", path);
+    image.write_to_file(path)?;
+    println!("Render time {:.3} seconds", start.elapsed().as_secs_f32());
+    Ok(())
+}
--- a/rtchallenge/rustfmt.toml
+++ b/rtchallenge/rustfmt.toml
@@ -0,0 +1,2 @@
+imports_granularity = "Crate"
+format_code_in_doc_comments = true
--- a/rtchallenge/src/camera.rs
+++ b/rtchallenge/src/camera.rs
@@ -0,0 +1,436 @@
+use std::{
+    str::FromStr,
+    sync::{
+        mpsc::{sync_channel, Receiver, SyncSender},
+        Arc, Mutex,
+    },
+    thread,
+};
+
+use derive_builder::Builder;
+use rand::Rng;
+use rayon::iter::{IntoParallelIterator, ParallelIterator};
+use serde::Deserialize;
+use structopt::StructOpt;
+
+use crate::{
+    canvas::Canvas,
+    matrices::Matrix4x4,
+    rays::Ray,
+    tuples::{Color, Tuple},
+    world::World,
+    Float, BLACK,
+};
+
+const MAX_DEPTH_RECURSION: usize = 10;
+
+#[derive(Copy, Clone, StructOpt, Debug, Deserialize)]
+#[serde(rename_all = "kebab-case")]
+pub enum RenderStrategy {
+    Serial,
+    Rayon,
+    WorkerPool,
+}
+
+impl Default for RenderStrategy {
+    fn default() -> RenderStrategy {
+        RenderStrategy::Rayon
+    }
+}
+
+impl FromStr for RenderStrategy {
+    type Err = serde_json::error::Error;
+    fn from_str(s: &str) -> Result<RenderStrategy, serde_json::error::Error> {
+        serde_json::from_str(&format!("\"{}\"", s))
+    }
+}
+
+#[derive(Builder, Clone, Debug, Default)]
+#[builder(setter(skip), build_fn(skip))]
+pub struct Camera {
+    #[builder(setter(skip = "false"))]
+    hsize: usize,
+    #[builder(setter(skip = "false"))]
+    vsize: usize,
+    #[builder(setter(skip = "false"))]
+    field_of_view: Float,
+    #[builder(setter(skip = "false"))]
+    transform: Matrix4x4,
+    inverse_transform: Matrix4x4,
+    pixel_size: Float,
+    half_width: Float,
+    half_height: Float,
+    #[builder(setter(skip = "false"))]
+    pub render_strategy: RenderStrategy,
+    /// 0 renders from the center of the pixel, 1 or higher is random sampling of the pixel.
+    #[builder(setter(skip = "false"))]
+    pub samples_per_pixel: usize,
+}
+
+impl CameraBuilder {
+    pub fn build(&self) -> Result<Camera, CameraBuilderError> {
+        let hsize = match self.hsize {
+            Some(ref value) => Clone::clone(value),
+            None => {
+                return Err(Into::into(::derive_builder::UninitializedFieldError::from(
+                    "hsize",
+                )))
+            }
+        };
+        let vsize = match self.vsize {
+            Some(ref value) => Clone::clone(value),
+            None => {
+                return Err(Into::into(::derive_builder::UninitializedFieldError::from(
+                    "vsize",
+                )))
+            }
+        };
+        let field_of_view = match self.field_of_view {
+            Some(ref value) => Clone::clone(value),
+            None => {
+                return Err(Into::into(::derive_builder::UninitializedFieldError::from(
+                    "field_of_view",
+                )))
+            }
+        };
+        let mut c = Camera::new(hsize, vsize, field_of_view);
+        if let Some(transform) = self.transform {
+            c.set_transform(transform);
+        }
+        if let Some(render_strategy) = self.render_strategy {
+            c.render_strategy = render_strategy;
+        }
+        if let Some(samples_per_pixel) = self.samples_per_pixel {
+            c.samples_per_pixel = samples_per_pixel;
+        }
+        Ok(c)
+    }
+}
+
+enum Request {
+    Line { width: usize, y: usize },
+}
+
+enum Response {
+    Line { y: usize, pixels: Canvas },
+}
+
+impl Camera {
+    /// Create a camera with a canvas of pixel hsize (height) and vsize (width)
+    /// with the given field of view (in radians).
+    pub fn new(hsize: usize, vsize: usize, field_of_view: Float) -> Camera {
+        let half_view = (field_of_view / 2.).tan();
+        let aspect = hsize as Float / vsize as Float;
+        let (half_width, half_height) = if aspect >= 1. {
+            (half_view, half_view / aspect)
+        } else {
+            (half_view * aspect, half_view)
+        };
+        let pixel_size = 2. * half_width / hsize as Float;
+        Camera {
+            hsize,
+            vsize,
+            field_of_view,
+            transform: Matrix4x4::identity(),
+            inverse_transform: Matrix4x4::identity(),
+            pixel_size,
+            half_height,
+            half_width,
+            render_strategy: RenderStrategy::Rayon,
+            samples_per_pixel: 0,
+        }
+    }
+    pub fn hsize(&self) -> usize {
+        self.hsize
+    }
+    pub fn vsize(&self) -> usize {
+        self.vsize
+    }
+    pub fn field_of_view(&self) -> Float {
+        self.field_of_view
+    }
+    pub fn transform(&self) -> Matrix4x4 {
+        self.transform
+    }
+    pub fn set_transform(&mut self, t: Matrix4x4) {
+        self.transform = t;
+        self.inverse_transform = t.inverse();
+    }
+    pub fn pixel_size(&self) -> Float {
+        self.pixel_size
+    }
+    pub fn supersample_rays_for_pixel(&self, px: usize, py: usize, samples: usize) -> Vec<Ray> {
+        let mut rng = rand::thread_rng();
+
+        (0..samples)
+            .map(|_| {
+                // The offset from the edge of the canvas to the pixel's corner.
+                let xoffset = (px as Float + rng.gen::<Float>()) * self.pixel_size;
+                let yoffset = (py as Float + rng.gen::<Float>()) * self.pixel_size;
+
+                // The untransformed coordinates of the pixle in world space.
+                // (Remember that the camera looks toward -z, so +x is to the left.)
+                let world_x = self.half_width - xoffset;
+                let world_y = self.half_height - yoffset;
+
+                // Using the camera matrix, transofmrm the canvas point and the origin,
+                // and then compute the ray's direction vector.
+                // (Remember that the canvas is at z>=-1).
+                let pixel = self.inverse_transform * Tuple::point(world_x, world_y, -1.);
+                let origin = self.inverse_transform * Tuple::point(0., 0., 0.);
+                let direction = (pixel - origin).normalize();
+
+                Ray::new(origin, direction)
+            })
+            .collect()
+    }
+
+    /// Calculate ray that starts at the camera and passes through the (x,y)
+    /// pixel on the canvas.
+    pub fn ray_for_pixel(&self, px: usize, py: usize) -> Ray {
+        // The offset from the edge of the canvas to the pixel's corner.
+        let xoffset = (px as Float + 0.5) * self.pixel_size;
+        let yoffset = (py as Float + 0.5) * self.pixel_size;
+
+        // The untransformed coordinates of the pixel in world space.
+        // (Remember that the camera looks toward -z, so +x is to the left.)
+        let world_x = self.half_width - xoffset;
+        let world_y = self.half_height - yoffset;
+
+        // Using the camera matrix, transform the canvas point and the origin,
+        // and then compute the ray's direction vector.
+        // (Remember that the canvas is at z>=-1).
+        let pixel = self.inverse_transform * Tuple::point(world_x, world_y, -1.);
+        let origin = self.inverse_transform * Tuple::point(0., 0., 0.);
+        let direction = (pixel - origin).normalize();
+
+        Ray::new(origin, direction)
+    }
+
+    /// Use camera to render an image of the given world.
+    pub fn render(&self, w: &World) -> Canvas {
+        use RenderStrategy::*;
+
+        match self.render_strategy {
+            Serial => self.render_serial(w),
+            Rayon => self.render_parallel_rayon(w),
+            WorkerPool => self.render_parallel_one_tread_per_core(w),
+        }
+    }
+
+    /// This render function spins up one thread per core, and pins the thread
+    /// to the core.  It then sends work requests to the worker threads,
+    /// requesting a full line of the image by rendered.  The main thread
+    /// collects results and stores them in the canvas returned to the user.
+    fn render_parallel_one_tread_per_core(&self, world: &World) -> Canvas {
+        let mut image = Canvas::new(self.hsize, self.vsize, BLACK);
+        let num_threads = num_cpus::get();
+        let (pixel_req_tx, pixel_req_rx) = sync_channel(2 * num_threads);
+        let (pixel_resp_tx, pixel_resp_rx) = sync_channel(2 * num_threads);
+        let pixel_req_rx = Arc::new(Mutex::new(pixel_req_rx));
+
+        // Create copy of world and camera we can share with all workers.
+        // It's probably okay to clone camera, but world could get large (think
+        // textures and high poly count models).
+        // TODO(wathiede): prevent second copy of world when they start getting
+        // large.
+        let world = Arc::new(world.clone());
+        let camera = Arc::new(self.clone());
+
+        let core_ids = core_affinity::get_core_ids().unwrap();
+        println!("Creating {} render threads", core_ids.len());
+        // Create a worker thread for each CPU core and pin the thread to the core.
+        let mut handles = core_ids
+            .into_iter()
+            .map(|id| {
+                let w = Arc::clone(&world);
+                let c = Arc::clone(&camera);
+                let pixel_req_rx = pixel_req_rx.clone();
+                let pixel_resp_tx = pixel_resp_tx.clone();
+                thread::spawn(move || {
+                    core_affinity::set_for_current(id);
+                    render_worker_task(&c, &w, pixel_req_rx, &pixel_resp_tx);
+                })
+            })
+            .collect::<Vec<_>>();
+        drop(pixel_req_rx);
+        drop(pixel_resp_tx);
+
+        // Send render requests over channels to worker threads.
+        let (w, h) = (camera.hsize, camera.vsize);
+        handles.push(thread::spawn(move || {
+            for y in 0..h {
+                pixel_req_tx
+                    .send(Request::Line { width: w, y })
+                    .expect("failed to send line request");
+            }
+            drop(pixel_req_tx);
+        }));
+
+        // Read responses from channel and blit image data.
+        for resp in pixel_resp_rx {
+            match resp {
+                Response::Line { y, pixels } => {
+                    for x in 0..camera.hsize {
+                        image.set(x, y, pixels.get(x, 0));
+                    }
+                }
+            }
+        }
+
+        // Wait for all the threads to exit.
+        for thr in handles {
+            thr.join().expect("thread join");
+        }
+        image
+    }
+
+    /// This renderer use rayon to split each row into a seperate thread.  It
+    /// seems to have more consistent performance than worker pool, equally fast
+    /// as WP at WP's fastest. The downside is the flame graph looks a mess.  A
+    /// strength over `render_parallel_one_tread_per_core` is that it doesn't
+    /// require `Camera` and `World` to be cloneable.
+    fn render_parallel_rayon(&self, w: &World) -> Canvas {
+        let image_mu = Mutex::new(Canvas::new(self.hsize, self.vsize, BLACK));
+
+        (0..self.vsize).into_par_iter().for_each(|y| {
+            let mut row_image = Canvas::new(self.hsize, 1, BLACK);
+            for x in 0..self.hsize {
+                let color = self.sample(w, x, y);
+                row_image.set(x, 0, color);
+            }
+            // TODO(wathiede): create a row based setter for memcpying the row as a whole.
+            let mut image = image_mu.lock().expect("failed to lock image mutex");
+            for x in 0..self.hsize {
+                image.set(x, y, row_image.get(x, 0));
+            }
+        });
+        image_mu
+            .into_inner()
+            .expect("failed to get image out of mutex")
+    }
+
+    /// Reference render implementation from the book.  Single threaded, nothing fancy.
+    fn render_serial(&self, w: &World) -> Canvas {
+        let mut image = Canvas::new(self.hsize, self.vsize, BLACK);
+        for y in 0..self.vsize {
+            for x in 0..self.hsize {
+                let color = self.sample(w, x, y);
+                image.set(x, y, color);
+            }
+        }
+        image
+    }
+
+    fn sample(&self, w: &World, x: usize, y: usize) -> Color {
+        if self.samples_per_pixel > 0 {
+            let color = self
+                .supersample_rays_for_pixel(x, y, self.samples_per_pixel)
+                .iter()
+                .map(|ray| w.color_at(ray, MAX_DEPTH_RECURSION))
+                .fold(BLACK, |acc, c| acc + c);
+            color / self.samples_per_pixel as Float
+        } else {
+            let ray = self.ray_for_pixel(x, y);
+            w.color_at(&ray, MAX_DEPTH_RECURSION)
+        }
+    }
+}
+fn render_worker_task(
+    c: &Camera,
+    w: &World,
+    input_chan: Arc<Mutex<Receiver<Request>>>,
+    output_chan: &SyncSender<Response>,
+) {
+    loop {
+        let job = { input_chan.lock().unwrap().recv() };
+        match job {
+            Err(_) => {
+                // From the docs:
+                // "The recv operation can only fail if the sending half of a
+                // channel (or sync_channel) is disconnected, implying that no
+                // further messages will ever be received."
+                return;
+            }
+            Ok(req) => match req {
+                Request::Line { width, y } => {
+                    let mut pixels = Canvas::new(width, 1, BLACK);
+                    for x in 0..width {
+                        let color = c.sample(w, x, y);
+                        pixels.set(x, 0, color);
+                    }
+                    output_chan
+                        .send(Response::Line { y, pixels })
+                        .expect("failed to send pixel response");
+                }
+            },
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::{
+        camera::Camera,
+        float::consts::PI,
+        matrices::Matrix4x4,
+        transformations::view_transform,
+        tuples::{point, vector},
+        world::World,
+        Float, EPSILON,
+    };
+    #[test]
+    fn new() {
+        let hsize = 160;
+        let vsize = 120;
+        let field_of_view = PI / 2.;
+        let c = Camera::new(hsize, vsize, field_of_view);
+        assert_eq!(c.hsize(), 160);
+        assert_eq!(c.vsize(), 120);
+        assert_eq!(c.transform(), Matrix4x4::identity());
+
+        // Pixel size for a horizontal canvas.
+        let c = Camera::new(200, 150, PI / 2.);
+        assert!((c.pixel_size() - 0.010).abs() < EPSILON);
+
+        // Pixel size for a horizontal canvas.
+        let c = Camera::new(150, 200, PI / 2.);
+        assert!((c.pixel_size() - 0.010).abs() < EPSILON);
+    }
+    #[test]
+    fn ray_for_pixel() {
+        // Constructing a ray through the center of the canvas.
+        let c = Camera::new(201, 101, PI / 2.);
+        let r = c.ray_for_pixel(100, 50);
+        assert_eq!(r.origin, point(0., 0., 0.));
+        assert_eq!(r.direction, vector(0., 0., -1.));
+
+        // Constructing a ray through the corner of the canvas.
+        let c = Camera::new(201, 101, PI / 2.);
+        let r = c.ray_for_pixel(0, 0);
+        assert_eq!(r.origin, point(0., 0., 0.));
+        assert_eq!(r.direction, vector(0.66519, 0.33259, -0.66851));
+
+        // Constructing a ray when the camera is transformed.
+        let mut c = Camera::new(201, 101, PI / 2.);
+        c.set_transform(Matrix4x4::rotation_y(PI / 4.) * Matrix4x4::translation(0., -2., 5.));
+        let r = c.ray_for_pixel(100, 50);
+        assert_eq!(r.origin, point(0., 2., -5.));
+        assert_eq!(
+            r.direction,
+            vector((2. as Float).sqrt() / 2., 0., -(2. as Float).sqrt() / 2.)
+        );
+    }
+    #[test]
+    fn render() {
+        // Rendering a world with a camera.
+        let w = World::test_world();
+        let mut c = Camera::new(11, 11, PI / 2.);
+        let from = point(0., 0., -5.);
+        let to = point(0., 0., 0.);
+        let up = vector(0., 1., 0.);
+        c.set_transform(view_transform(from, to, up));
+        let image = c.render(&w);
+        assert_eq!(image.get(5, 5), [0.38066, 0.47583, 0.2855].into());
+    }
+}
--- a/rtchallenge/src/canvas.rs
+++ b/rtchallenge/src/canvas.rs
@@ -0,0 +1,96 @@
+use std::{fs::File, io::BufWriter, path::Path};
+
+use png;
+use thiserror::Error;
+
+use crate::tuples::Color;
+
+#[derive(Error, Debug)]
+pub enum CanvasError {
+    #[error("faile to write canvas")]
+    IOError(#[from] std::io::Error),
+    #[error("faile to encode canvas to png")]
+    EncodingError(#[from] png::EncodingError),
+}
+pub struct Canvas {
+    pub height: usize,
+    pub width: usize,
+    pub pixels: Vec<Color>,
+}
+
+impl Canvas {
+    pub fn new(width: usize, height: usize, background: Color) -> Canvas {
+        let pixels = vec![background; width * height];
+        Canvas {
+            width,
+            height,
+            pixels,
+        }
+    }
+
+    pub fn set(&mut self, x: usize, y: usize, c: Color) {
+        if x > self.width {
+            return;
+        }
+        if y > self.height {
+            return;
+        }
+        self.pixels[x + y * self.width] = c;
+    }
+    pub fn get(&self, x: usize, y: usize) -> Color {
+        self.pixels[x + y * self.width]
+    }
+    pub fn write_to_file<P>(&self, path: P) -> Result<(), CanvasError>
+    where
+        P: AsRef<Path>,
+    {
+        let path = Path::new(path.as_ref());
+        let file = File::create(path)?;
+        let w = &mut BufWriter::new(file);
+
+        let mut encoder = png::Encoder::new(w, self.width as u32, self.height as u32);
+        encoder.set_color(png::ColorType::RGB);
+        encoder.set_depth(png::BitDepth::Eight);
+        let mut writer = encoder.write_header()?;
+
+        let data: Vec<u8> = self
+            .pixels
+            .iter()
+            .flat_map(|p| {
+                vec![
+                    (p.red.clamp(0., 1.) * 255.) as u8,
+                    (p.green.clamp(0., 1.) * 255.) as u8,
+                    (p.blue.clamp(0., 1.) * 255.) as u8,
+                ]
+            })
+            .collect();
+        writer.write_image_data(&data)?;
+        Ok(())
+    }
+}
+#[cfg(test)]
+mod tests {
+    use super::Canvas;
+
+    use crate::{tuples::Color, BLACK};
+
+    #[test]
+    fn create_canvas() {
+        let bg = BLACK;
+        let c = Canvas::new(10, 20, bg);
+        assert_eq!(c.width, 10);
+        assert_eq!(c.height, 20);
+        for (i, p) in c.pixels.iter().enumerate() {
+            assert_eq!(p, &BLACK, "pixel {} not {:?}: {:?}", i, &BLACK, p);
+        }
+    }
+
+    #[test]
+    fn write_to_canvas() {
+        let bg = Color::new(0.2, 0.2, 0.2);
+        let mut c = Canvas::new(10, 20, bg);
+        let red = Color::new(1., 0., 0.);
+        c.set(2, 3, red);
+        assert_eq!(c.get(2, 3), red);
+    }
+}
--- a/rtchallenge/src/intersections.rs
+++ b/rtchallenge/src/intersections.rs
@@ -0,0 +1,433 @@
+use std::ops::Index;
+
+use crate::{
+    rays::Ray,
+    shapes::Shape,
+    tuples::{dot, reflect, Tuple},
+    Float, EPSILON,
+};
+
+#[derive(Debug, Clone)]
+pub struct Intersection<'i> {
+    pub t: Float,
+    pub object: &'i Shape,
+}
+impl<'i> PartialEq for Intersection<'i> {
+    fn eq(&self, rhs: &Intersection) -> bool {
+        ((self.t - rhs.t).abs() < EPSILON) && (self.object == rhs.object)
+    }
+}
+
+impl<'i> Intersection<'i> {
+    /// Create new `Intersection` at the given `t` that hits the given `object`.
+    pub fn new(t: Float, object: &Shape) -> Intersection {
+        Intersection { t, object }
+    }
+}
+
+/// Aggregates `Intersection`s.
+#[derive(Debug, Default, PartialEq)]
+pub struct Intersections<'i>(Vec<Intersection<'i>>);
+
+/// Create an [Intersections] from a single [Intersection] to aid in tests.
+impl<'i> From<Intersection<'i>> for Intersections<'i> {
+    fn from(i: Intersection<'i>) -> Intersections<'i> {
+        Intersections::new(vec![i])
+    }
+}
+
+impl<'i> Intersections<'i> {
+    pub fn new(xs: Vec<Intersection<'i>>) -> Intersections {
+        Intersections(xs)
+    }
+    pub fn is_empty(&self) -> bool {
+        self.0.is_empty()
+    }
+    pub fn len(&self) -> usize {
+        self.0.len()
+    }
+    /// Finds nearest hit for this collection of intersections.
+    pub fn hit(&self) -> Option<&Intersection> {
+        self.0.iter().filter(|i| i.t > 0.).min_by(|i1, i2| {
+            i1.t.partial_cmp(&i2.t)
+                .expect("an intersection has a t value that is NaN")
+        })
+    }
+}
+
+impl<'i> IntoIterator for Intersections<'i> {
+    type Item = Intersection<'i>;
+    type IntoIter = std::vec::IntoIter<Self::Item>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        self.0.into_iter()
+    }
+}
+
+impl<'i> Index<usize> for Intersections<'i> {
+    type Output = Intersection<'i>;
+    fn index(&self, idx: usize) -> &Self::Output {
+        &self.0[idx]
+    }
+}
+
+#[derive(Debug)]
+pub struct PrecomputedData<'i> {
+    pub t: Float,
+    pub object: &'i Shape,
+    pub point: Tuple,
+    pub under_point: Tuple,
+    pub over_point: Tuple,
+    pub eyev: Tuple,
+    pub normalv: Tuple,
+    pub reflectv: Tuple,
+    pub inside: bool,
+    pub n1: Float,
+    pub n2: Float,
+}
+
+/// Precomputes data common to all intersections.
+pub fn prepare_computations<'i>(
+    hit: &'i Intersection,
+    r: &Ray,
+    xs: &Intersections,
+) -> PrecomputedData<'i> {
+    let point = r.position(hit.t);
+    let normalv = hit.object.normal_at(point);
+    let eyev = -r.direction;
+    let (inside, normalv) = if dot(normalv, eyev) < 0. {
+        (true, -normalv)
+    } else {
+        (false, normalv)
+    };
+    let reflectv = reflect(r.direction, normalv);
+
+    let mut n1 = -1.;
+    let mut n2 = -1.;
+    let mut containers: Vec<&Shape> = Vec::new();
+    for i in xs.0.iter() {
+        if hit == i {
+            if containers.is_empty() {
+                n1 = 1.;
+            } else {
+                n1 = containers.last().unwrap().material.refractive_index;
+            }
+        }
+
+        match containers.iter().position(|o| o == &i.object) {
+            Some(idx) => {
+                containers.remove(idx);
+            }
+            None => containers.push(i.object),
+        }
+
+        if hit == i {
+            if containers.is_empty() {
+                n2 = 1.;
+            } else {
+                n2 = containers.last().unwrap().material.refractive_index;
+            }
+            break;
+        }
+    }
+
+    let over_point = point + normalv * EPSILON;
+    let under_point = point - normalv * EPSILON;
+    PrecomputedData {
+        t: hit.t,
+        object: hit.object,
+        point,
+        over_point,
+        under_point,
+        normalv,
+        reflectv,
+        inside,
+        eyev,
+        n1,
+        n2,
+    }
+}
+
+/// Compute Schlick approximation to Fresnel's equations.
+pub fn schlick(comps: &PrecomputedData) -> Float {
+    // Find the cosine of the angle between the eye and normal vectors.
+    let mut cos = dot(comps.eyev, comps.normalv);
+    // Total internal reflection can only occur if n1 > n2.
+    if comps.n1 > comps.n2 {
+        let n = comps.n1 / comps.n2;
+        let sin2_t = n * n * (1. - cos * cos);
+        if sin2_t > 1. {
+            return 1.;
+        }
+        // Compute cosine of theta_t using trig identity.
+        let cos_t = (1. - sin2_t).sqrt();
+        // When n1 > n2 use cos(theta_t) instead.
+        cos = cos_t;
+    }
+
+    let r0 = (comps.n1 - comps.n2) / (comps.n1 + comps.n2);
+    let r0 = r0 * r0;
+    r0 + (1. - r0) * (1. - cos) * (1. - cos) * (1. - cos) * (1. - cos) * (1. - cos)
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::{
+        intersections::{prepare_computations, schlick, Intersection, Intersections},
+        materials::MaterialBuilder,
+        matrices::{scaling, translation},
+        rays::Ray,
+        shapes::{glass_sphere, intersect, Shape},
+        tuples::{point, vector},
+        Float, EPSILON,
+    };
+
+    #[test]
+    fn intersection() {
+        // An intersection ecapsulates t and object.
+        let s = Shape::sphere();
+        let i = Intersection::new(3.5, &s);
+        assert_eq!(i.t, 3.5);
+        assert_eq!(i.object, &s);
+    }
+    #[test]
+    fn intersections() {
+        let s = Shape::sphere();
+        let i1 = Intersection::new(1., &s);
+        let i2 = Intersection::new(2., &s);
+        let xs = Intersections::new(vec![i1, i2]);
+        assert_eq!(xs.len(), 2);
+        assert_eq!(xs[0].t, 1.);
+        assert_eq!(xs[1].t, 2.);
+
+        let r = Ray::new(point(0., 0., -5.), vector(0., 0., 1.));
+        let xs = intersect(&s, &r);
+        assert_eq!(xs.len(), 2);
+        assert_eq!(xs[0].object, &s);
+        assert_eq!(xs[1].object, &s);
+    }
+
+    mod hit {
+        use super::*;
+
+        #[test]
+        fn when_all_intersections_have_positive_t() {
+            let s = Shape::sphere();
+            let i1 = Intersection::new(1., &s);
+            let i2 = Intersection::new(2., &s);
+            let xs = Intersections::new(vec![i2, i1.clone()]);
+            let i = xs.hit();
+            assert_eq!(i, Some(&i1));
+        }
+        #[test]
+        fn when_some_intersections_have_negative_t() {
+            let s = Shape::sphere();
+            let i1 = Intersection::new(-1., &s);
+            let i2 = Intersection::new(1., &s);
+            let xs = Intersections::new(vec![i2.clone(), i1]);
+            let i = xs.hit();
+            assert_eq!(i, Some(&i2));
+        }
+        #[test]
+        fn when_all_intersections_have_negative_t() {
+            let s = Shape::sphere();
+            let i1 = Intersection::new(-2., &s);
+            let i2 = Intersection::new(-1., &s);
+            let xs = Intersections::new(vec![i2, i1]);
+            let i = xs.hit();
+            assert_eq!(i, None);
+        }
+        #[test]
+        fn always_the_lowest_nonnegative_intersection() {
+            let s = Shape::sphere();
+            let i1 = Intersection::new(5., &s);
+            let i2 = Intersection::new(7., &s);
+            let i3 = Intersection::new(-3., &s);
+            let i4 = Intersection::new(2., &s);
+            let xs = Intersections::new(vec![i1, i2, i3, i4.clone()]);
+            let i = xs.hit();
+            assert_eq!(i, Some(&i4));
+        }
+    }
+
+    mod prepare_computations {
+        use super::*;
+
+        #[test]
+        fn precomputing_the_state_of_intersection() -> Result<(), Box<dyn std::error::Error>> {
+            let r = Ray::new(point(0., 0., -5.), vector(0., 0., 1.));
+            let shape = Shape::sphere();
+            let xs = Intersections::from(Intersection::new(4., &shape));
+            let comps = prepare_computations(&xs[0], &r, &xs);
+            assert_eq!(comps.t, xs[0].t);
+            assert_eq!(comps.object, xs[0].object);
+            assert_eq!(comps.point, point(0., 0., -1.));
+            assert_eq!(comps.eyev, vector(0., 0., -1.));
+            assert_eq!(comps.normalv, vector(0., 0., -1.));
+            Ok(())
+        }
+
+        #[test]
+        fn hit_when_intersection_occurs_outside() -> Result<(), Box<dyn std::error::Error>> {
+            // The hit, when an intersection occurs on the outside.
+            let r = Ray::new(point(0., 0., -5.), vector(0., 0., 1.));
+            let shape = Shape::sphere();
+            let xs = Intersections::from(Intersection::new(4., &shape));
+            let comps = prepare_computations(&xs[0], &r, &xs);
+            assert_eq!(comps.inside, false);
+            Ok(())
+        }
+
+        #[test]
+        fn hit_when_intersection_occurs_inside() -> Result<(), Box<dyn std::error::Error>> {
+            // The hit, when an intersection occurs on the inside.
+            let r = Ray::new(point(0., 0., 0.), vector(0., 0., 1.));
+            let shape = Shape::sphere();
+            let xs = Intersections::from(Intersection::new(1., &shape));
+            let comps = prepare_computations(&xs[0], &r, &xs);
+            assert_eq!(comps.point, point(0., 0., 1.));
+            assert_eq!(comps.eyev, vector(0., 0., -1.));
+            assert_eq!(comps.inside, true);
+            // Normal would have been (0, 0, 1), but is inverted when inside.
+            assert_eq!(comps.normalv, vector(0., 0., -1.));
+            Ok(())
+        }
+
+        #[test]
+        fn hit_should_offset_the_point() -> Result<(), Box<dyn std::error::Error>> {
+            // The hit should offset the point.
+            let r = Ray::new(point(0., 0., -5.), vector(0., 0., 1.));
+            let mut shape = Shape::sphere();
+            shape.set_transform(translation(0., 0., 1.));
+            let xs = Intersections::from(Intersection::new(5., &shape));
+            let comps = prepare_computations(&xs[0], &r, &xs);
+            assert!(comps.over_point.z < -EPSILON / 2.);
+            assert!(comps.point.z > comps.over_point.z);
+            Ok(())
+        }
+
+        #[test]
+        fn precomputing_the_reflection_vector() -> Result<(), Box<dyn std::error::Error>> {
+            // Precomputing the reflection vector.
+            let shape = Shape::plane();
+            let r = Ray::new(
+                point(0., 1., -1.),
+                vector(0., -(2 as Float).sqrt() / 2., (2 as Float).sqrt() / 2.),
+            );
+            let xs = Intersections::from(Intersection::new((2 as Float).sqrt(), &shape));
+            let comps = prepare_computations(&xs[0], &r, &xs);
+            assert_eq!(
+                comps.reflectv,
+                vector(0., (2 as Float).sqrt() / 2., (2 as Float).sqrt() / 2.)
+            );
+            Ok(())
+        }
+
+        #[test]
+        fn finding_n1_and_n2() -> Result<(), Box<dyn std::error::Error>> {
+            // Finding n1 and n2 at various intersections.
+            let a = glass_sphere()
+                .transform(scaling(2., 2., 2.))
+                .material(
+                    MaterialBuilder::default()
+                        .transparency(1.)
+                        .refractive_index(1.5)
+                        .build()?,
+                )
+                .build()?;
+            let b = glass_sphere()
+                .transform(translation(0., 0., -0.25))
+                .material(
+                    MaterialBuilder::default()
+                        .transparency(1.)
+                        .refractive_index(2.)
+                        .build()?,
+                )
+                .build()?;
+            let c = glass_sphere()
+                .transform(translation(0., 0., 0.25))
+                .material(
+                    MaterialBuilder::default()
+                        .transparency(1.)
+                        .refractive_index(2.5)
+                        .build()?,
+                )
+                .build()?;
+            let r = Ray::new(point(0., 0., -4.), vector(0., 0., 1.));
+            let xs = Intersections::new(vec![
+                Intersection::new(2., &a),
+                Intersection::new(2.75, &b),
+                Intersection::new(3.25, &c),
+                Intersection::new(4.75, &b),
+                Intersection::new(5.25, &c),
+                Intersection::new(6., &a),
+            ]);
+            for (index, n1, n2) in &[
+                (0, 1.0, 1.5),
+                (1, 1.5, 2.0),
+                (2, 2.0, 2.5),
+                (3, 2.5, 2.5),
+                (4, 2.5, 1.5),
+                (5, 1.5, 1.0),
+            ] {
+                let comps = prepare_computations(&xs[*index], &r, &xs);
+                assert_eq!(comps.n1, *n1);
+                assert_eq!(comps.n2, *n2);
+            }
+            Ok(())
+        }
+
+        #[test]
+        fn under_point_offset_below_surface() -> Result<(), Box<dyn std::error::Error>> {
+            // The under point is offset below the surface.
+            let r = Ray::new(point(0., 0., -5.), vector(0., 0., 1.));
+            let shape = glass_sphere().transform(translation(0., 0., 1.)).build()?;
+            let xs = Intersections::from(Intersection::new(5., &shape));
+            let comps = prepare_computations(&xs[0], &r, &xs);
+            assert!(comps.under_point.z > EPSILON / 2.);
+            assert!(comps.point.z < comps.under_point.z);
+
+            Ok(())
+        }
+    }
+    mod schlick {
+        use super::*;
+
+        #[test]
+        fn under_total_reflection() -> Result<(), Box<dyn std::error::Error>> {
+            let shape = glass_sphere().build()?;
+            let r = Ray::new(point(0., 0., (2 as Float).sqrt() / 2.), vector(0., 1., 0.));
+            let xs = Intersections::new(vec![
+                Intersection::new(-(2 as Float).sqrt() / 2., &shape),
+                Intersection::new((2 as Float).sqrt() / 2., &shape),
+            ]);
+            let comps = prepare_computations(&xs[1], &r, &xs);
+            let reflectance = schlick(&comps);
+            assert_eq!(reflectance, 1.);
+            Ok(())
+        }
+        #[test]
+        fn perpendicular_viewing_angle() -> Result<(), Box<dyn std::error::Error>> {
+            let shape = glass_sphere().build()?;
+            let r = Ray::new(point(0., 0., 0.), vector(0., 1., 0.));
+            let xs = Intersections::new(vec![
+                Intersection::new(-1., &shape),
+                Intersection::new(1., &shape),
+            ]);
+            let comps = prepare_computations(&xs[1], &r, &xs);
+            let reflectance = schlick(&comps);
+            assert!((reflectance - 0.04).abs() < EPSILON);
+            Ok(())
+        }
+        #[test]
+        fn small_angle_n2_greater_n1() -> Result<(), Box<dyn std::error::Error>> {
+            let shape = glass_sphere().build()?;
+            let r = Ray::new(point(0., 0.99, -2.), vector(0., 0., 1.));
+            let xs = Intersections::new(vec![Intersection::new(1.8589, &shape)]);
+            let comps = prepare_computations(&xs[0], &r, &xs);
+            let reflectance = schlick(&comps);
+            assert!((reflectance - 0.48873).abs() < EPSILON);
+            Ok(())
+        }
+    }
+}
--- a/rtchallenge/src/lib.rs
+++ b/rtchallenge/src/lib.rs
@@ -0,0 +1,55 @@
+pub mod camera;
+pub mod canvas;
+pub mod intersections;
+pub mod lights;
+pub mod materials;
+pub mod matrices;
+pub mod patterns;
+pub mod rays;
+pub mod shapes;
+pub mod transformations;
+pub mod tuples;
+pub mod world;
+
+/// Value considered close enough for PartialEq implementations.
+pub const EPSILON: Float = 0.00001;
+
+pub const BLACK: tuples::Color = tuples::Color::new(0., 0., 0.);
+pub const WHITE: tuples::Color = tuples::Color::new(1., 1., 1.);
+
+#[cfg(feature = "float-as-double")]
+/// submodule to defined types, constants and methods when `Float` is defined as a `f64` using the
+/// "float-as-double" cargo feature.
+pub mod float {
+    pub use std::f64::*;
+    /// Alias of the `f64` type, to be used through out the codebase anywhere a default sized
+    /// `Float` is necessary.
+    pub type Float = f64;
+}
+
+#[cfg(not(feature = "float-as-double"))]
+/// submodule to defined types, constants and methods when `Float` is defined as a `f32` when not using the
+/// "float-as-double" cargo feature.
+pub mod float {
+    pub use std::f32::*;
+    /// Alias of the `f32` type, to be used through out the codebase anywhere a default sized
+    /// `Float` is necessary.
+    pub type Float = f32;
+}
+
+pub use float::Float;
+
+pub mod prelude {
+    pub use crate::{
+        camera::{Camera, CameraBuilder},
+        lights::{PointLight, PointLightBuilder},
+        materials::{Material, MaterialBuilder},
+        matrices::{identity, rotation_x, rotation_y, rotation_z, scaling, shearing, translation},
+        patterns::{checkers_pattern, gradient_pattern, ring_pattern, stripe_pattern},
+        shapes::{cube, plane, sphere, test_shape},
+        transformations::view_transform,
+        tuples::{point, vector, Color},
+        world::{World, WorldBuilder},
+        Float,
+    };
+}
--- a/rtchallenge/src/lights.rs
+++ b/rtchallenge/src/lights.rs
@@ -0,0 +1,39 @@
+use derive_builder::Builder;
+
+use crate::tuples::{Color, Tuple};
+
+#[derive(Builder, Clone, Debug, Default, PartialEq)]
+#[builder(default)]
+pub struct PointLight {
+    pub position: Tuple,
+    #[builder(setter(into))]
+    pub intensity: Color,
+}
+
+impl PointLight {
+    /// Creates a new `PositionLight` at the given `position` and with the given
+    /// `intensity`.
+    pub fn new<C>(position: Tuple, intensity: C) -> PointLight
+    where
+        C: Into<Color>,
+    {
+        PointLight {
+            position,
+            intensity: intensity.into(),
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::{lights::PointLight, tuples::point, WHITE};
+
+    #[test]
+    fn new() {
+        let intensity = WHITE;
+        let position = point(0., 0., 0.);
+        let light = PointLight::new(position, intensity);
+        assert_eq!(light.position, position);
+        assert_eq!(light.intensity, intensity);
+    }
+}
--- a/rtchallenge/src/main.rs
+++ b/rtchallenge/src/main.rs
@@ -0,0 +1,3 @@
+fn main() {
+    println!("Hello, world!");
+}
--- a/rtchallenge/src/materials.rs
+++ b/rtchallenge/src/materials.rs
@@ -0,0 +1,236 @@
+use derive_builder::Builder;
+
+use crate::{
+    lights::PointLight,
+    patterns::Pattern,
+    shapes::Shape,
+    tuples::{dot, reflect, Color, Tuple},
+    Float, BLACK, WHITE,
+};
+
+#[derive(Builder, Debug, PartialEq, Clone)]
+#[builder(default)]
+pub struct Material {
+    #[builder(setter(into))]
+    pub color: Pattern,
+    pub ambient: Float,
+    pub diffuse: Float,
+    pub specular: Float,
+    pub shininess: Float,
+    pub reflective: Float,
+    pub transparency: Float,
+    pub refractive_index: Float,
+}
+
+impl Default for Material {
+    /// Creates the default material.
+    fn default() -> Material {
+        Material {
+            color: WHITE.into(),
+            ambient: 0.1,
+            diffuse: 0.9,
+            specular: 0.9,
+            shininess: 200.,
+            reflective: 0.0,
+            transparency: 0.0,
+            refractive_index: 1.0,
+        }
+    }
+}
+
+/// Compute lighting contributions using the Phong reflection model.
+pub fn lighting(
+    material: &Material,
+    object: &Shape,
+    light: &PointLight,
+    point: Tuple,
+    eyev: Tuple,
+    normalv: Tuple,
+    in_shadow: bool,
+) -> Color {
+    // Combine the surface color with the light's color.
+    let color = material.color.pattern_at_object(object, point);
+    let effective_color = color * light.intensity;
+    // Find the direciton of the light source.
+    let lightv = (light.position - point).normalize();
+    // Compute the ambient distribution.
+    let ambient = effective_color * material.ambient;
+    // This is the cosine of the angle between the light vector an the normal
+    // vector.  A negative number means the light is on the other side of the
+    // surface.
+    let light_dot_normal = dot(lightv, normalv);
+    let (diffuse, specular) = if light_dot_normal < 0. {
+        (BLACK, BLACK)
+    } else {
+        // Compute the diffuse contribution.
+        let diffuse = effective_color * material.diffuse * light_dot_normal;
+        // This represents the cosine of the angle between the relfection vector
+        // and the eye vector.  A negative number means the light reflects away
+        // from the eye.
+        let reflectv = reflect(-lightv, normalv);
+        let reflect_dot_eye = dot(reflectv, eyev);
+        let specular = if reflect_dot_eye <= 0. {
+            BLACK
+        } else {
+            // Compute the specular contribution.
+            let factor = reflect_dot_eye.powf(material.shininess);
+            light.intensity * material.specular * factor
+        };
+        (diffuse, specular)
+    };
+    if in_shadow {
+        ambient
+    } else {
+        ambient + diffuse + specular
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::{materials::Material, WHITE};
+
+    #[test]
+    fn default() {
+        let m = Material::default();
+        assert_eq!(
+            m,
+            Material {
+                color: WHITE.into(),
+                ambient: 0.1,
+                diffuse: 0.9,
+                specular: 0.9,
+                shininess: 200.,
+                reflective: 0.0,
+                transparency: 0.0,
+                refractive_index: 1.0,
+            }
+        );
+    }
+
+    mod lighting {
+        use crate::{
+            lights::PointLight,
+            materials::{lighting, Material},
+            patterns::{Pattern, BLACK_PAT, WHITE_PAT},
+            shapes::Shape,
+            tuples::{point, vector, Color},
+            Float, BLACK, WHITE,
+        };
+
+        #[test]
+        fn eye_between_light_and_surface() {
+            let in_shadow = false;
+            let m = Material::default();
+            let position = point(0., 0., 0.);
+            let object = Shape::sphere();
+
+            // Lighting with the eye between the light and the surface.
+            let eyev = vector(0., 0., -1.);
+            let normalv = vector(0., 0., -1.);
+            let light = PointLight::new(point(0., 0., -10.), WHITE);
+            let result = lighting(&m, &object, &light, position, eyev, normalv, in_shadow);
+            assert_eq!(result, Color::new(1.9, 1.9, 1.9));
+        }
+
+        #[test]
+        fn eye_between_light_and_surface_offset_45() {
+            // Lighting with the eye between the light and the surface, eye offset 45°.
+            let in_shadow = false;
+            let m = Material::default();
+            let position = point(0., 0., 0.);
+            let object = Shape::sphere();
+            let eyev = vector(0., (2. as Float).sqrt() / 2., -(2. as Float).sqrt() / 2.);
+            let normalv = vector(0., 0., -1.);
+            let light = PointLight::new(point(0., 0., -10.), WHITE);
+            let result = lighting(&m, &object, &light, position, eyev, normalv, in_shadow);
+            assert_eq!(result, WHITE);
+        }
+        #[test]
+        fn eye_opposite_surface_light_offset_45() {
+            // Lighting with the eye opposite surface, light offset 45°.
+            let in_shadow = false;
+            let m = Material::default();
+            let position = point(0., 0., 0.);
+            let object = Shape::sphere();
+            let eyev = vector(0., 0., -1.);
+            let normalv = vector(0., 0., -1.);
+            let light = PointLight::new(point(0., 10., -10.), WHITE);
+            let result = lighting(&m, &object, &light, position, eyev, normalv, in_shadow);
+            assert_eq!(result, Color::new(0.7364, 0.7364, 0.7364));
+        }
+        #[test]
+        fn eye_in_path_of_reflection_vector() {
+            // Lighting with the eye in the path of the reflection vector.
+            let in_shadow = false;
+            let m = Material::default();
+            let position = point(0., 0., 0.);
+            let object = Shape::sphere();
+            let eyev = vector(0., -(2.0 as Float).sqrt() / 2., -(2.0 as Float).sqrt() / 2.);
+            let normalv = vector(0., 0., -1.);
+            let light = PointLight::new(point(0., 10., -10.), WHITE);
+            let result = lighting(&m, &object, &light, position, eyev, normalv, in_shadow);
+            assert_eq!(result, Color::new(1.63639, 1.63639, 1.63639));
+        }
+        #[test]
+        fn light_behind_surface() {
+            // Lighting with the light behind the surface.
+            let in_shadow = false;
+            let m = Material::default();
+            let position = point(0., 0., 0.);
+            let object = Shape::sphere();
+            let eyev = vector(0., 0., -1.);
+            let normalv = vector(0., 0., -1.);
+            let light = PointLight::new(point(0., 0., 10.), WHITE);
+            let result = lighting(&m, &object, &light, position, eyev, normalv, in_shadow);
+            assert_eq!(result, Color::new(0.1, 0.1, 0.1));
+        }
+        #[test]
+        fn surface_in_shadow() {
+            // Lighting with the surface in shadow.
+            let m = Material::default();
+            let position = point(0., 0., 0.);
+            let object = Shape::sphere();
+            let in_shadow = true;
+            let eyev = vector(0., 0., -1.);
+            let normalv = vector(0., 0., -1.);
+            let light = PointLight::new(point(0., 0., -10.), WHITE);
+            let result = lighting(&m, &object, &light, position, eyev, normalv, in_shadow);
+            assert_eq!(result, Color::new(0.1, 0.1, 0.1));
+        }
+        #[test]
+        fn pattern_applied() {
+            // Lighting with a pattern applied.
+            let object = Shape::sphere();
+            let m = Material {
+                color: Pattern::stripe(WHITE_PAT, BLACK_PAT),
+                ambient: 1.,
+                diffuse: 0.,
+                specular: 0.,
+                ..Material::default()
+            };
+            let eyev = vector(0., 0., -1.);
+            let normalv = vector(0., 0., -1.);
+            let light = PointLight::new(point(0., 0., -10.), WHITE);
+            let c1 = lighting(
+                &m,
+                &object,
+                &light,
+                point(0.9, 0., 0.),
+                eyev,
+                normalv,
+                false,
+            );
+            let c2 = lighting(
+                &m,
+                &object,
+                &light,
+                point(1.1, 0., 0.),
+                eyev,
+                normalv,
+                false,
+            );
+            assert_eq!(c1, WHITE);
+            assert_eq!(c2, BLACK);
+        }
+    }
+}
--- a/rtchallenge/src/matrices.rs
+++ b/rtchallenge/src/matrices.rs
@@ -0,0 +1,922 @@
+use std::{
+    fmt,
+    ops::{Index, IndexMut, Mul, Sub},
+};
+
+use crate::{tuples::Tuple, Float, EPSILON};
+
+/// Short hand for creating a Matrix4x4 set to the identity matrix.
+pub fn identity() -> Matrix4x4 {
+    Matrix4x4::identity()
+}
+/// Short hand for creating a Matrix4x4 for rotating around the X-axis.
+pub fn rotation_x(radians: Float) -> Matrix4x4 {
+    Matrix4x4::rotation_x(radians)
+}
+/// Short hand for creating a Matrix4x4 for rotating around the Y-axis.
+pub fn rotation_y(radians: Float) -> Matrix4x4 {
+    Matrix4x4::rotation_y(radians)
+}
+/// Short hand for creating a Matrix4x4 for rotating around the Z-axis.
+pub fn rotation_z(radians: Float) -> Matrix4x4 {
+    Matrix4x4::rotation_z(radians)
+}
+/// Short hand for creating a Matrix4x4 that scales in the given x,y,z axis.
+pub fn scaling(x: Float, y: Float, z: Float) -> Matrix4x4 {
+    Matrix4x4::scaling(x, y, z)
+}
+/// Short hand for creating a Matrix4x4 that shears across the given axis pairs.
+pub fn shearing(xy: Float, xz: Float, yx: Float, yz: Float, zx: Float, zy: Float) -> Matrix4x4 {
+    Matrix4x4::shearing(xy, xz, yx, yz, zx, zy)
+}
+/// Short hand for creating a Matrix4x4 that translations along the given x,y,z axis.
+pub fn translation(x: Float, y: Float, z: Float) -> Matrix4x4 {
+    Matrix4x4::translation(x, y, z)
+}
+
+#[derive(Debug)]
+pub struct Matrix2x2 {
+    m: [[Float; 2]; 2],
+}
+impl Matrix2x2 {
+    /// Create a `Matrix2x2` with each of the given rows.
+    pub fn new(r0: [Float; 2], r1: [Float; 2]) -> Matrix2x2 {
+        Matrix2x2 { m: [r0, r1] }
+    }
+
+    /// Calculate the determinant of a 2x2.
+    pub fn determinant(&self) -> Float {
+        let m = self;
+        m[(0, 0)] * m[(1, 1)] - m[(0, 1)] * m[(1, 0)]
+    }
+}
+impl Index<(usize, usize)> for Matrix2x2 {
+    type Output = Float;
+    fn index(&self, (row, col): (usize, usize)) -> &Self::Output {
+        &self.m[row][col]
+    }
+}
+impl PartialEq for Matrix2x2 {
+    fn eq(&self, rhs: &Matrix2x2) -> bool {
+        let l = self.m;
+        let r = rhs.m;
+        for i in 0..2 {
+            for j in 0..2 {
+                let d = (l[i][j] - r[i][j]).abs();
+                if d > EPSILON {
+                    return false;
+                }
+            }
+        }
+        true
+    }
+}
+
+#[derive(Debug)]
+pub struct Matrix3x3 {
+    m: [[Float; 3]; 3],
+}
+impl Matrix3x3 {
+    /// Create a `Matrix3x2` with each of the given rows.
+    pub fn new(r0: [Float; 3], r1: [Float; 3], r2: [Float; 3]) -> Matrix3x3 {
+        Matrix3x3 { m: [r0, r1, r2] }
+    }
+    /// submatrix extracts a 2x2 matrix ignoring the 0-based `row` and `col` given.
+    pub fn submatrix(&self, row: usize, col: usize) -> Matrix2x2 {
+        assert!(row < 3);
+        assert!(col < 3);
+        let mut rows = vec![];
+        for r in 0..3 {
+            if r != row {
+                let mut v = vec![];
+                for c in 0..3 {
+                    if c != col {
+                        v.push(self[(r, c)]);
+                    }
+                }
+                rows.push(v);
+            }
+        }
+        let m = [[rows[0][0], rows[0][1]], [rows[1][0], rows[1][1]]];
+        Matrix2x2 { m }
+    }
+
+    /// Compute minor of a 3x3 matrix.
+    pub fn minor(&self, row: usize, col: usize) -> Float {
+        self.submatrix(row, col).determinant()
+    }
+
+    /// Compute cofactor of a 3x3 matrix.
+    pub fn cofactor(&self, row: usize, col: usize) -> Float {
+        let negate = if (row + col) % 2 == 0 { 1. } else { -1. };
+        self.submatrix(row, col).determinant() * negate
+    }
+
+    /// Compute determinant of a 3x3 matrix.
+    pub fn determinant(&self) -> Float {
+        (0..3).map(|i| self.cofactor(0, i) * self[(0, i)]).sum()
+    }
+}
+impl Index<(usize, usize)> for Matrix3x3 {
+    type Output = Float;
+    fn index(&self, (row, col): (usize, usize)) -> &Self::Output {
+        &self.m[row][col]
+    }
+}
+
+impl PartialEq for Matrix3x3 {
+    fn eq(&self, rhs: &Matrix3x3) -> bool {
+        let l = self.m;
+        let r = rhs.m;
+        for i in 0..3 {
+            for j in 0..3 {
+                let d = (l[i][j] - r[i][j]).abs();
+                if d > EPSILON {
+                    return false;
+                }
+            }
+        }
+        true
+    }
+}
+
+/// Matrix4x4 represents a 4x4 matrix in row-major form. So, element `m[i][j]` corresponds to m<sub>i,j</sub>
+/// where `i` is the row number and `j` is the column number.
+#[derive(Copy, Clone, Default)]
+pub struct Matrix4x4 {
+    m: [[Float; 4]; 4],
+}
+
+impl From<[Float; 16]> for Matrix4x4 {
+    fn from(t: [Float; 16]) -> Self {
+        Matrix4x4 {
+            m: [
+                [t[0], t[1], t[2], t[3]],
+                [t[4], t[5], t[6], t[7]],
+                [t[8], t[9], t[10], t[11]],
+                [t[12], t[13], t[14], t[15]],
+            ],
+        }
+    }
+}
+
+impl Matrix4x4 {
+    /// Create a `Matrix4x4` containing the identity, all zeros with ones along the diagonal.
+    pub const fn identity() -> Matrix4x4 {
+        Matrix4x4::new(
+            [1., 0., 0., 0.],
+            [0., 1., 0., 0.],
+            [0., 0., 1., 0.],
+            [0., 0., 0., 1.],
+        )
+    }
+
+    /// Create a `Matrix4x4` with each of the given rows.
+    pub const fn new(r0: [Float; 4], r1: [Float; 4], r2: [Float; 4], r3: [Float; 4]) -> Matrix4x4 {
+        Matrix4x4 {
+            m: [r0, r1, r2, r3],
+        }
+    }
+
+    /// Creates a 4x4 matrix representing a translation of x,y,z.
+    pub fn translation(x: Float, y: Float, z: Float) -> Matrix4x4 {
+        Matrix4x4::new(
+            [1., 0., 0., x],
+            [0., 1., 0., y],
+            [0., 0., 1., z],
+            [0., 0., 0., 1.],
+        )
+    }
+
+    /// Creates a 4x4 matrix representing a scaling of x,y,z.
+    pub fn scaling(x: Float, y: Float, z: Float) -> Matrix4x4 {
+        Matrix4x4::new(
+            [x, 0., 0., 0.],
+            [0., y, 0., 0.],
+            [0., 0., z, 0.],
+            [0., 0., 0., 1.],
+        )
+    }
+
+    /// Creates a 4x4 matrix representing a rotation around the x-axis.
+    pub fn rotation_x(radians: Float) -> Matrix4x4 {
+        let r = radians;
+        Matrix4x4::new(
+            [1., 0., 0., 0.],
+            [0., r.cos(), -r.sin(), 0.],
+            [0., r.sin(), r.cos(), 0.],
+            [0., 0., 0., 1.],
+        )
+    }
+
+    /// Creates a 4x4 matrix representing a rotation around the y-axis.
+    pub fn rotation_y(radians: Float) -> Matrix4x4 {
+        let r = radians;
+        Matrix4x4::new(
+            [r.cos(), 0., r.sin(), 0.],
+            [0., 1., 0., 0.],
+            [-r.sin(), 0., r.cos(), 0.],
+            [0., 0., 0., 1.],
+        )
+    }
+
+    /// Creates a 4x4 matrix representing a rotation around the z-axis.
+    pub fn rotation_z(radians: Float) -> Matrix4x4 {
+        let r = radians;
+        Matrix4x4::new(
+            [r.cos(), -r.sin(), 0., 0.],
+            [r.sin(), r.cos(), 0., 0.],
+            [0., 0., 1., 0.],
+            [0., 0., 0., 1.],
+        )
+    }
+
+    /// Transpose self, returning a new matrix that has been reflected across the diagonal.
+    pub fn transpose(&self) -> Matrix4x4 {
+        let m = self.m;
+        Matrix4x4 {
+            m: [
+                [m[0][0], m[1][0], m[2][0], m[3][0]],
+                [m[0][1], m[1][1], m[2][1], m[3][1]],
+                [m[0][2], m[1][2], m[2][2], m[3][2]],
+                [m[0][3], m[1][3], m[2][3], m[3][3]],
+            ],
+        }
+    }
+    /// Create a transform matrix that will shear (skew) points.
+    /// # Examples
+    pub fn shearing(xy: Float, xz: Float, yx: Float, yz: Float, zx: Float, zy: Float) -> Matrix4x4 {
+        Matrix4x4::new(
+            [1., xy, xz, 0.],
+            [yx, 1., yz, 0.],
+            [zx, zy, 1., 0.],
+            [0., 0., 0., 1.],
+        )
+    }
+
+    /// Returns a new matrix that is the inverse of self. If self is A, inverse returns A<sup>-1</sup>, where
+    /// AA<sup>-1</sup> = I.
+    /// This implementation uses a numerically stable Gauss–Jordan elimination routine to compute the inverse.
+    pub fn inverse_rtiow(&self) -> Matrix4x4 {
+        // TODO(wathiede): how come the C++ version doesn't need to deal with non-invertable
+        // matrix.
+        let mut indxc: [usize; 4] = Default::default();
+        let mut indxr: [usize; 4] = Default::default();
+        let mut ipiv: [usize; 4] = Default::default();
+        let mut minv = self.m;
+
+        for i in 0..4 {
+            let mut irow: usize = 0;
+            let mut icol: usize = 0;
+            let mut big: Float = 0.;
+            // Choose pivot
+            for j in 0..4 {
+                if ipiv[j] != 1 {
+                    for (k, ipivk) in ipiv.iter().enumerate() {
+                        if *ipivk == 0 {
+                            if minv[j][k].abs() >= big {
+                                big = minv[j][k].abs();
+                                irow = j;
+                                icol = k;
+                            }
+                        } else if *ipivk > 1 {
+                            eprintln!("Singular matrix in MatrixInvert");
+                        }
+                    }
+                }
+            }
+            ipiv[icol] += 1;
+            // Swap rows _irow_ and _icol_ for pivot
+            if irow != icol {
+                // Can't figure out how to make swap work here.
+                #[allow(clippy::manual_swap)]
+                for k in 0..4 {
+                    let tmp = minv[irow][k];
+                    minv[irow][k] = minv[icol][k];
+                    minv[icol][k] = tmp;
+                }
+            }
+            indxr[i] = irow;
+            indxc[i] = icol;
+            if minv[icol][icol] == 0. {
+                eprintln!("Singular matrix in MatrixInvert");
+            }
+
+            // Set $m[icol][icol]$ to one by scaling row _icol_ appropriately
+            let pivinv: Float = minv[icol][icol].recip();
+            minv[icol][icol] = 1.;
+            for j in 0..4 {
+                minv[icol][j] *= pivinv;
+            }
+
+            // Subtract this row from others to zero out their columns
+            for j in 0..4 {
+                if j != icol {
+                    let save = minv[j][icol];
+                    minv[j][icol] = 0.;
+                    for k in 0..4 {
+                        minv[j][k] -= minv[icol][k] * save;
+                    }
+                }
+            }
+        }
+        // Swap columns to reflect permutation
+        for j in (0..4).rev() {
+            if indxr[j] != indxc[j] {
+                for mi in &mut minv {
+                    mi.swap(indxr[j], indxc[j])
+                }
+            }
+        }
+        Matrix4x4 { m: minv }
+    }
+    /// submatrix extracts a 3x3 matrix ignoring the 0-based `row` and `col` given.
+    pub fn submatrix(&self, row: usize, col: usize) -> Matrix3x3 {
+        assert!(row < 4);
+        assert!(col < 4);
+        let mut rows = vec![];
+        for r in 0..4 {
+            if r != row {
+                let mut v = vec![];
+                for c in 0..4 {
+                    if c != col {
+                        v.push(self[(r, c)]);
+                    }
+                }
+                rows.push(v);
+            }
+        }
+        let m = [
+            [rows[0][0], rows[0][1], rows[0][2]],
+            [rows[1][0], rows[1][1], rows[1][2]],
+            [rows[2][0], rows[2][1], rows[2][2]],
+        ];
+        Matrix3x3 { m }
+    }
+
+    /// Compute minor of a 4x4 matrix.
+    pub fn minor(&self, row: usize, col: usize) -> Float {
+        self.submatrix(row, col).determinant()
+    }
+    /// Compute cofactor of a 4x4 matrix.
+    pub fn cofactor(&self, row: usize, col: usize) -> Float {
+        let negate = if (row + col) % 2 == 0 { 1. } else { -1. };
+        self.submatrix(row, col).determinant() * negate
+    }
+    /// Compute determinant of a 4x4 matrix.
+    pub fn determinant(&self) -> Float {
+        (0..4).map(|i| self.cofactor(0, i) * self[(0, i)]).sum()
+    }
+
+    /// Compute invertibility of matrix (i.e. non-zero determinant.
+    pub fn invertable(&self) -> bool {
+        self.determinant() != 0.
+    }
+
+    /// Compute the inverse of a 4x4 matrix.
+    pub fn inverse(&self) -> Matrix4x4 {
+        self.inverse_rtc()
+    }
+    pub fn inverse_rtc(&self) -> Matrix4x4 {
+        let m = self;
+        if !m.invertable() {
+            panic!("Matrix4x4::inverse called on matrix with determinant() == 0");
+        }
+        let mut m2 = Matrix4x4::identity();
+        let det = m.determinant();
+        for row in 0..4 {
+            for col in 0..4 {
+                let c = m.cofactor(row, col);
+                m2[(col, row)] = c / det;
+            }
+        }
+        m2
+    }
+}
+
+impl fmt::Debug for Matrix4x4 {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        if f.alternate() {
+            write!(
+                f,
+                "\n  {:8.5?}\n  {:8.5?}\n  {:8.5?}\n  {:8.5?}",
+                self.m[0], self.m[1], self.m[2], self.m[3]
+            )
+        } else {
+            write!(
+                f,
+                "[{:?} {:?} {:?} {:?}]",
+                self.m[0], self.m[1], self.m[2], self.m[3]
+            )
+        }
+    }
+}
+
+impl Mul<Matrix4x4> for Matrix4x4 {
+    type Output = Matrix4x4;
+
+    /// Implement matrix multiplication for `Matrix4x4`.
+    fn mul(self, m2: Matrix4x4) -> Matrix4x4 {
+        let m1 = self;
+        let mut r: Matrix4x4 = Default::default();
+        for i in 0..4 {
+            for j in 0..4 {
+                r.m[i][j] = m1.m[i][0] * m2.m[0][j]
+                    + m1.m[i][1] * m2.m[1][j]
+                    + m1.m[i][2] * m2.m[2][j]
+                    + m1.m[i][3] * m2.m[3][j];
+            }
+        }
+        r
+    }
+}
+
+impl Mul<Tuple> for Matrix4x4 {
+    type Output = Tuple;
+
+    /// Implement matrix multiplication for `Matrix4x4` * `Tuple`.
+    fn mul(self, t: Tuple) -> Tuple {
+        let m = self;
+        Tuple {
+            x: m.m[0][0] * t.x + m.m[0][1] * t.y + m.m[0][2] * t.z + m.m[0][3] * t.w,
+            y: m.m[1][0] * t.x + m.m[1][1] * t.y + m.m[1][2] * t.z + m.m[1][3] * t.w,
+            z: m.m[2][0] * t.x + m.m[2][1] * t.y + m.m[2][2] * t.z + m.m[2][3] * t.w,
+            w: m.m[3][0] * t.x + m.m[3][1] * t.y + m.m[3][2] * t.z + m.m[3][3] * t.w,
+        }
+    }
+}
+
+impl Sub for Matrix4x4 {
+    type Output = Matrix4x4;
+
+    fn sub(self, m2: Matrix4x4) -> Matrix4x4 {
+        let m1 = self;
+        let mut r: Matrix4x4 = Default::default();
+        for i in 0..4 {
+            for j in 0..4 {
+                r.m[i][j] = m1.m[i][j] - m2.m[i][j];
+            }
+        }
+        r
+    }
+}
+
+impl PartialEq for Matrix4x4 {
+    fn eq(&self, rhs: &Matrix4x4) -> bool {
+        let l = self.m;
+        let r = rhs.m;
+        for i in 0..4 {
+            for j in 0..4 {
+                let d = (l[i][j] - r[i][j]).abs();
+                if d > EPSILON {
+                    return false;
+                }
+            }
+        }
+        true
+    }
+}
+
+impl Index<(usize, usize)> for Matrix4x4 {
+    type Output = Float;
+    fn index(&self, (row, col): (usize, usize)) -> &Self::Output {
+        &self.m[row][col]
+    }
+}
+
+impl IndexMut<(usize, usize)> for Matrix4x4 {
+    fn index_mut(&mut self, (row, col): (usize, usize)) -> &mut Self::Output {
+        &mut self.m[row][col]
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    use crate::{
+        float::consts::PI,
+        tuples::{point, vector},
+    };
+
+    #[test]
+    fn example4x4() {
+        // Individual transformations are applied in sequence.
+        let p = point(1., 0., 1.);
+        let a = Matrix4x4::rotation_x(PI / 2.);
+        let b = Matrix4x4::scaling(5., 5., 5.);
+        let c = Matrix4x4::translation(10., 5., 7.);
+        // Apply rotation first.
+        let p2 = a * p;
+        assert_eq!(p2, point(1., -1., 0.));
+        // Then apply scaling.
+        let p3 = b * p2;
+        assert_eq!(p3, point(5., -5., 0.));
+        // Then apply translation.
+        let p4 = c * p3;
+        assert_eq!(p4, point(15., 0., 7.));
+
+        // Chained transformations must be applied in reverse order.
+        let p = point(1., 0., 1.);
+        let a = Matrix4x4::rotation_x(PI / 2.);
+        let b = Matrix4x4::scaling(5., 5., 5.);
+        let c = Matrix4x4::translation(10., 5., 7.);
+        let t = c * b * a;
+        assert_eq!(t * p, point(15., 0., 7.));
+    }
+
+    #[test]
+    fn translation() {
+        let transform = Matrix4x4::translation(5., -3., 2.);
+        let p = point(-3., 4., 5.);
+        assert_eq!(transform * p, point(2., 1., 7.));
+
+        let inv = transform.inverse();
+        assert_eq!(inv * p, point(-8., 7., 3.));
+
+        let v = vector(-3., 4., 5.);
+        assert_eq!(transform * v, v);
+    }
+    #[test]
+    fn scaling() {
+        // A scaling matrix applied to a point.
+        let transform = Matrix4x4::scaling(2., 3., 4.);
+        let p = point(-4., 6., 8.);
+        assert_eq!(transform * p, point(-8., 18., 32.));
+
+        // A scaling matrix applied to a vector.
+        let v = vector(-4., 6., 8.);
+        assert_eq!(transform * v, vector(-8., 18., 32.));
+
+        // Multiplying by the inverse of a scaling matrix.
+        let inv = transform.inverse();
+        assert_eq!(inv * v, vector(-2., 2., 2.));
+
+        // Reflection is scaling by a negative value.
+        let transform = Matrix4x4::scaling(-1., 1., 1.);
+        let p = point(2., 3., 4.);
+        assert_eq!(transform * p, point(-2., 3., 4.));
+    }
+    #[test]
+    fn rotation_x() {
+        // A scaling matrix applied to a point.
+        let p = point(0., 1., 0.);
+        let half_quarter = Matrix4x4::rotation_x(PI / 4.);
+        let full_quarter = Matrix4x4::rotation_x(PI / 2.);
+
+        assert_eq!(
+            half_quarter * p,
+            point(0., (2.0 as Float).sqrt() / 2., (2.0 as Float).sqrt() / 2.)
+        );
+        assert_eq!(full_quarter * p, point(0., 0., 1.),);
+    }
+    #[test]
+    fn rotation_y() {
+        // A scaling matrix applied to a point.
+        let p = point(0., 0., 1.);
+        let half_quarter = Matrix4x4::rotation_y(PI / 4.);
+        let full_quarter = Matrix4x4::rotation_y(PI / 2.);
+
+        assert_eq!(
+            half_quarter * p,
+            point((2.0 as Float).sqrt() / 2., 0., (2.0 as Float).sqrt() / 2.)
+        );
+        assert_eq!(full_quarter * p, point(1., 0., 0.,),);
+    }
+    #[test]
+    fn rotation_z() {
+        // A scaling matrix applied to a point.
+        let p = point(0., 1., 0.);
+        let half_quarter = Matrix4x4::rotation_z(PI / 4.);
+        let full_quarter = Matrix4x4::rotation_z(PI / 2.);
+
+        assert_eq!(
+            half_quarter * p,
+            point(-(2.0 as Float).sqrt() / 2., (2.0 as Float).sqrt() / 2., 0.)
+        );
+        assert_eq!(full_quarter * p, point(-1., 0., 0.,),);
+    }
+    #[test]
+    fn transpose() {
+        let m = Matrix4x4::new(
+            [2., 0., 0., 0.],
+            [3., 1., 0., 0.],
+            [4., 0., 1., 0.],
+            [5., 6., 7., 1.],
+        );
+        let m_t = Matrix4x4::new(
+            [2., 3., 4., 5.],
+            [0., 1., 0., 6.],
+            [0., 0., 1., 7.],
+            [0., 0., 0., 1.],
+        );
+        assert_eq!(m.transpose(), m_t);
+
+        assert_eq!(Matrix4x4::identity(), Matrix4x4::identity().transpose());
+    }
+    #[test]
+    fn shearing() {
+        // A shearing transform moves x in proportion to y.
+        let transform = Matrix4x4::shearing(1., 0., 0., 0., 0., 0.);
+        let p = point(2., 3., 4.);
+        assert_eq!(transform * p, point(5., 3., 4.));
+
+        // A shearing transform moves x in proportion to z.
+        let transform = Matrix4x4::shearing(0., 1., 0., 0., 0., 0.);
+        let p = point(2., 3., 4.);
+        assert_eq!(transform * p, point(6., 3., 4.));
+
+        // A shearing transform moves y in proportion to x.
+        let transform = Matrix4x4::shearing(0., 0., 1., 0., 0., 0.);
+        let p = point(2., 3., 4.);
+        assert_eq!(transform * p, point(2., 5., 4.));
+
+        // A shearing transform moves y in proportion to z.
+        let transform = Matrix4x4::shearing(0., 0., 0., 1., 0., 0.);
+        let p = point(2., 3., 4.);
+        assert_eq!(transform * p, point(2., 7., 4.));
+
+        // A shearing transform moves z in proportion to x.
+        let transform = Matrix4x4::shearing(0., 0., 0., 0., 1., 0.);
+        let p = point(2., 3., 4.);
+        assert_eq!(transform * p, point(2., 3., 6.));
+
+        // A shearing transform moves z in proportion to y.
+        let transform = Matrix4x4::shearing(0., 0., 0., 0., 0., 1.);
+        let p = point(2., 3., 4.);
+        assert_eq!(transform * p, point(2., 3., 7.));
+    }
+    #[test]
+    fn inverse_rtiow() {
+        let i = Matrix4x4::identity();
+        assert_eq!(i.inverse_rtiow() * i, i);
+
+        let m = Matrix4x4::new(
+            [2., 0., 0., 0.],
+            [0., 3., 0., 0.],
+            [0., 0., 4., 0.],
+            [0., 0., 0., 1.],
+        );
+        assert_eq!(m.inverse_rtiow() * m, i);
+        assert_eq!(m * m.inverse_rtiow(), i);
+    }
+    #[test]
+    fn determinant_2x2() {
+        let a = Matrix2x2::new([1., 5.], [-3., 2.]);
+
+        assert_eq!(a.determinant(), 17.);
+    }
+    #[test]
+    fn determinant_3x3() {
+        let a = Matrix3x3::new([1., 2., 6.], [-5., 8., -4.], [2., 6., 4.]);
+        assert_eq!(a.cofactor(0, 0), 56.);
+        assert_eq!(a.cofactor(0, 1), 12.);
+        assert_eq!(a.cofactor(0, 2), -46.);
+        assert_eq!(a.determinant(), -196.);
+    }
+    #[test]
+    fn determinant_4x4() {
+        let a = Matrix4x4::new(
+            [-2., -8., 3., 5.],
+            [-3., 1., 7., 3.],
+            [1., 2., -9., 6.],
+            [-6., 7., 7., -9.],
+        );
+        assert_eq!(a.cofactor(0, 0), 690.);
+        assert_eq!(a.cofactor(0, 1), 447.);
+        assert_eq!(a.cofactor(0, 2), 210.);
+        assert_eq!(a.cofactor(0, 3), 51.);
+        assert_eq!(a.determinant(), -4071.);
+    }
+    #[test]
+    fn submatrix_3x3() {
+        assert_eq!(
+            Matrix3x3::new([1., 5., 0.], [-3., 2., 7.], [0., 6., -3.],).submatrix(0, 2),
+            Matrix2x2::new([-3., 2.], [0., 6.])
+        );
+    }
+    #[test]
+    fn submatrix_4x4() {
+        assert_eq!(
+            Matrix4x4::new(
+                [-6., 1., 1., 6.],
+                [-8., 5., 8., 6.],
+                [-1., 0., 8., 2.],
+                [-7., 1., -1., 1.],
+            )
+            .submatrix(2, 1),
+            Matrix3x3::new([-6., 1., 6.], [-8., 8., 6.], [-7., -1., 1.],)
+        );
+    }
+    #[test]
+    fn minor_3x3() {
+        let a = Matrix3x3::new([3., 5., 0.], [2., -1., -7.], [6., -1., 5.]);
+        let b = a.submatrix(1, 0);
+        assert_eq!(b.determinant(), 25.0);
+        assert_eq!(b.determinant(), a.minor(1, 0));
+    }
+    #[test]
+    fn cofactor_3x3() {
+        let a = Matrix3x3::new([3., 5., 0.], [2., -1., -7.], [6., -1., 5.]);
+        assert_eq!(a.minor(0, 0), -12.);
+        assert_eq!(a.cofactor(0, 0), -12.);
+        assert_eq!(a.minor(1, 0), 25.);
+        assert_eq!(a.cofactor(1, 0), -25.);
+    }
+    #[test]
+    fn construct2x2() {
+        let m = Matrix2x2::new([-3., 5.], [1., -2.]);
+
+        assert_eq!(m[(0, 0)], -3.);
+        assert_eq!(m[(0, 1)], 5.);
+        assert_eq!(m[(1, 0)], 1.);
+        assert_eq!(m[(1, 1)], -2.);
+    }
+    #[test]
+    fn construct3x3() {
+        let m = Matrix3x3::new([-3., 5., 0.], [1., -2., -7.], [0., 1., 1.]);
+
+        assert_eq!(m[(0, 0)], -3.);
+        assert_eq!(m[(1, 1)], -2.);
+        assert_eq!(m[(2, 2)], 1.);
+    }
+    #[test]
+    fn invertable() {
+        let a = Matrix4x4::new(
+            [6., 4., 4., 4.],
+            [5., 5., 7., 6.],
+            [4., -9., 3., -7.],
+            [9., 1., 7., -6.],
+        );
+        assert_eq!(a.determinant(), -2120.);
+        assert_eq!(a.invertable(), true);
+
+        let a = Matrix4x4::new(
+            [-4., 2., -2., -3.],
+            [9., 6., 2., 6.],
+            [0., -5., 1., -5.],
+            [0., 0., 0., 0.],
+        );
+        assert_eq!(a.determinant(), 0.);
+        assert_eq!(a.invertable(), false);
+    }
+    #[test]
+    fn inverse() {
+        let a = Matrix4x4::new(
+            [-5., 2., 6., -8.],
+            [1., -5., 1., 8.],
+            [7., 7., -6., -7.],
+            [1., -3., 7., 4.],
+        );
+        let b = a.inverse();
+
+        assert_eq!(a.determinant(), 532.);
+        assert_eq!(a.cofactor(2, 3), -160.);
+        assert_eq!(b[(3, 2)], -160. / 532.);
+        assert_eq!(a.cofactor(3, 2), 105.);
+        assert_eq!(b[(2, 3)], 105. / 532.);
+        assert_eq!(
+            b,
+            Matrix4x4::new(
+                [0.21804512, 0.45112783, 0.24060151, -0.04511278],
+                [-0.8082707, -1.456767, -0.44360903, 0.5206767],
+                [-0.078947365, -0.2236842, -0.05263158, 0.19736843],
+                [-0.52255636, -0.81390977, -0.30075186, 0.30639097]
+            )
+        );
+
+        // Second test case
+        assert_eq!(
+            Matrix4x4::new(
+                [8., -5., 9., 2.],
+                [7., 5., 6., 1.],
+                [-6., 0., 9., 6.],
+                [-3., 0., -9., -4.],
+            )
+            .inverse(),
+            Matrix4x4::new(
+                [-0.15384616, -0.15384616, -0.2820513, -0.53846157],
+                [-0.07692308, 0.12307692, 0.025641026, 0.03076923],
+                [0.35897437, 0.35897437, 0.43589744, 0.9230769],
+                [-0.6923077, -0.6923077, -0.7692308, -1.9230769]
+            ),
+        );
+
+        // Third test case
+        assert_eq!(
+            Matrix4x4::new(
+                [9., 3., 0., 9.],
+                [-5., -2., -6., -3.],
+                [-4., 9., 6., 4.],
+                [-7., 6., 6., 2.],
+            )
+            .inverse(),
+            Matrix4x4::new(
+                [-0.04074074, -0.07777778, 0.14444445, -0.22222222],
+                [-0.07777778, 0.033333335, 0.36666667, -0.33333334],
+                [-0.029012345, -0.14629629, -0.10925926, 0.12962963],
+                [0.17777778, 0.06666667, -0.26666668, 0.33333334]
+            ),
+        );
+
+        let a = Matrix4x4::new(
+            [3., -9., 7., 3.],
+            [3., -8., 2., -9.],
+            [-4., 4., 4., 1.],
+            [-6., 5., -1., 1.],
+        );
+        let b = Matrix4x4::new(
+            [8., 2., 2., 2.],
+            [3., -1., 7., 0.],
+            [7., 0., 5., 4.],
+            [6., -2., 0., 5.],
+        );
+        let c = a * b;
+        assert_eq!(c * b.inverse(), a);
+    }
+    #[test]
+    fn construct4x4() {
+        let m = Matrix4x4::new(
+            [1., 2., 3., 4.],
+            [5.5, 6.5, 7.5, 8.5],
+            [9., 10., 11., 12.],
+            [13.5, 14.5, 15.5, 16.5],
+        );
+
+        assert_eq!(m[(0, 0)], 1.);
+        assert_eq!(m[(0, 3)], 4.);
+        assert_eq!(m[(1, 0)], 5.5);
+        assert_eq!(m[(1, 2)], 7.5);
+        assert_eq!(m[(2, 2)], 11.);
+        assert_eq!(m[(3, 0)], 13.5);
+        assert_eq!(m[(3, 2)], 15.5);
+    }
+    #[test]
+    fn equality4x4() {
+        let a = Matrix4x4::new(
+            [1., 2., 3., 4.],
+            [5., 6., 7., 8.],
+            [9., 8., 7., 6.],
+            [5., 4., 3., 2.],
+        );
+        let b = Matrix4x4::new(
+            [1., 2., 3., 4.],
+            [5., 6., 7., 8.],
+            [9., 8., 7., 6.],
+            [5., 4., 3., 2.],
+        );
+        assert_eq!(a, b);
+    }
+    #[test]
+    fn inequality4x4() {
+        let a = Matrix4x4::new(
+            [1., 2., 3., 4.],
+            [5., 6., 7., 8.],
+            [9., 8., 7., 6.],
+            [5., 4., 3., 2.],
+        );
+        let b = Matrix4x4::new(
+            [2., 3., 4., 5.],
+            [6., 7., 8., 9.],
+            [8., 7., 6., 5.],
+            [4., 3., 2., 1.],
+        );
+        assert_ne!(a, b);
+    }
+    #[test]
+    fn mul4x4() {
+        let a = Matrix4x4::new(
+            [1., 2., 3., 4.],
+            [5., 6., 7., 8.],
+            [9., 8., 7., 6.],
+            [5., 4., 3., 2.],
+        );
+        let b = Matrix4x4::new(
+            [-2., 1., 2., 3.],
+            [3., 2., 1., -1.],
+            [4., 3., 6., 5.],
+            [1., 2., 7., 8.],
+        );
+        assert_eq!(
+            a * b,
+            Matrix4x4::new(
+                [20., 22., 50., 48.],
+                [44., 54., 114., 108.],
+                [40., 58., 110., 102.],
+                [16., 26., 46., 42.],
+            )
+        );
+    }
+    #[test]
+    fn mul4x4_tuple() {
+        let a = Matrix4x4::new(
+            [1., 2., 3., 4.],
+            [2., 4., 4., 2.],
+            [8., 6., 4., 1.],
+            [0., 0., 0., 1.],
+        );
+        let b = Tuple::new(1., 2., 3., 1.);
+
+        assert_eq!(a * b, Tuple::new(18., 24., 33., 1.));
+    }
+}
--- a/rtchallenge/src/patterns.rs
+++ b/rtchallenge/src/patterns.rs
@@ -0,0 +1,444 @@
+use derive_builder::Builder;
+
+use crate::{
+    matrices::Matrix4x4,
+    shapes::Shape,
+    tuples::{Color, Tuple},
+    BLACK, WHITE,
+};
+
+pub const BLACK_PAT: Pattern = Pattern {
+    color: ColorMapper::Constant(BLACK),
+    transform: Matrix4x4::identity(),
+    inverse_transform: Matrix4x4::identity(),
+};
+pub const WHITE_PAT: Pattern = Pattern {
+    color: ColorMapper::Constant(WHITE),
+    transform: Matrix4x4::identity(),
+    inverse_transform: Matrix4x4::identity(),
+};
+
+#[derive(Debug, PartialEq, Clone)]
+pub enum ColorMapper {
+    /// TestPattern the color returned is the pattern space point after going through world->object and object->pattern space translation.
+    TestPattern,
+    /// Solid color, the same sampled every where.
+    Constant(Color),
+    /// Pattern that alternates between the given patterns along each unit of the X-axis.  The
+    /// strip extends infinitely in the positive and negative Y and Z axes.
+    Stripe { a: Box<Pattern>, b: Box<Pattern> },
+    /// Linear blend between `a` and `b` along the X-axis.
+    Gradient { a: Box<Pattern>, b: Box<Pattern> },
+    /// Bullseye pattern in the XZ plane.
+    Ring { a: Box<Pattern>, b: Box<Pattern> },
+    /// Traditional ray tracer tile floor pattern.
+    Checkers { a: Box<Pattern>, b: Box<Pattern> },
+}
+
+impl From<Color> for ColorMapper {
+    fn from(c: Color) -> ColorMapper {
+        ColorMapper::Constant(c)
+    }
+}
+
+impl From<Color> for Box<Pattern> {
+    fn from(c: Color) -> Box<Pattern> {
+        Box::new(Pattern {
+            color: ColorMapper::Constant(c),
+            ..Pattern::default()
+        })
+    }
+}
+
+#[derive(Builder, Debug, PartialEq, Clone)]
+#[builder(default, pattern = "immutable")]
+pub struct Pattern {
+    pub color: ColorMapper,
+    transform: Matrix4x4,
+    #[builder(private, default = "self.default_inverse_transform()?")]
+    inverse_transform: Matrix4x4,
+}
+
+impl PatternBuilder {
+    fn default_inverse_transform(&self) -> Result<Matrix4x4, String> {
+        Ok(self.transform.unwrap_or(Matrix4x4::identity()).inverse())
+    }
+}
+
+impl Default for Pattern {
+    fn default() -> Pattern {
+        Pattern {
+            color: ColorMapper::Constant(WHITE),
+            transform: Matrix4x4::identity(),
+            inverse_transform: Matrix4x4::identity(),
+        }
+    }
+}
+
+/// Creates a [Pattern] with a color type of [ColorMapper::Constant] from the given [Color]
+impl<C> From<C> for Pattern
+where
+    C: Into<Color>,
+{
+    fn from(c: C) -> Self {
+        Pattern {
+            color: ColorMapper::Constant(c.into()),
+            ..Pattern::default()
+        }
+    }
+}
+
+/// Builder for creating a material pattern used for testing.  The color returned is the pattern space point
+/// after going through world->object and object->pattern space translation.
+pub fn test_pattern() -> PatternBuilder {
+    PatternBuilder::default().color(ColorMapper::TestPattern)
+}
+
+/// Builder for creating a material pattern that alternates between the given colors along each unit of the
+/// X-axis.  The strip extends infinitely in the positive and negative Y and Z axes.
+pub fn stripe_pattern(a: Pattern, b: Pattern) -> PatternBuilder {
+    PatternBuilder::default().color(ColorMapper::Stripe {
+        a: a.into(),
+        b: b.into(),
+    })
+}
+
+/// Builder for creating a material pattern that gradually blends between the given colors along
+/// the X-axis.
+pub fn gradient_pattern(a: Pattern, b: Pattern) -> PatternBuilder {
+    PatternBuilder::default().color(ColorMapper::Gradient {
+        a: a.into(),
+        b: b.into(),
+    })
+}
+
+/// Builder for creating a material pattern that alternates between the given colors in a ring
+/// shape in the XZ plane.
+pub fn ring_pattern(a: Pattern, b: Pattern) -> PatternBuilder {
+    PatternBuilder::default().color(ColorMapper::Ring {
+        a: a.into(),
+        b: b.into(),
+    })
+}
+
+/// Builder for creating a material pattern that alternates between the given colors along the X, Y
+/// and Z pattern.  Creates traditional ray tracer tile floor pattern.
+pub fn checkers_pattern(a: Pattern, b: Pattern) -> PatternBuilder {
+    PatternBuilder::default().color(ColorMapper::Checkers {
+        a: a.into(),
+        b: b.into(),
+    })
+}
+
+/// Generic implementation for mapping points to colors according to the given [ColorMapper].
+impl Pattern {
+    /// Create a pattern used for testing.  The color returned is the pattern space point
+    /// after going through world->object and object->pattern space translation.
+    pub fn test() -> Pattern {
+        Pattern {
+            color: ColorMapper::TestPattern,
+            ..Pattern::default()
+        }
+    }
+
+    /// Create a pattern that alternates between the given Patterns along each unit of the
+    /// X-axis.  The strip extends infinitely in the positive and negative Y and Z axes.
+    pub fn stripe(a: Pattern, b: Pattern) -> Pattern {
+        Pattern {
+            color: ColorMapper::Stripe {
+                a: a.into(),
+                b: b.into(),
+            },
+            ..Pattern::default()
+        }
+    }
+
+    /// Create a pattern that gradually blends between the given Patterns along the X-axis.
+    pub fn gradient(a: Pattern, b: Pattern) -> Pattern {
+        Pattern {
+            color: ColorMapper::Gradient {
+                a: a.into(),
+                b: b.into(),
+            },
+            ..Pattern::default()
+        }
+    }
+
+    /// Create a pattern that alternates between the given Patterns in a ring in the XZ plane.
+    pub fn ring(a: Pattern, b: Pattern) -> Pattern {
+        Pattern {
+            color: ColorMapper::Ring {
+                a: a.into(),
+                b: b.into(),
+            },
+            ..Pattern::default()
+        }
+    }
+
+    /// Create a pattern that alternates between the given Patterns along the X, Y and Z axis.
+    pub fn checkers(a: Pattern, b: Pattern) -> Pattern {
+        Pattern {
+            color: ColorMapper::Checkers {
+                a: a.into(),
+                b: b.into(),
+            },
+            ..Pattern::default()
+        }
+    }
+
+    /// Sample the color at the given point in untranslated object space.
+    pub fn pattern_at(&self, object_point: Tuple) -> Color {
+        let point = self.inverse_transform * object_point;
+        match &self.color {
+            ColorMapper::TestPattern => [point.x, point.y, point.z].into(),
+            ColorMapper::Constant(c) => *c,
+            ColorMapper::Stripe { a, b } => {
+                let x = point.x.floor();
+                if x % 2. == 0. {
+                    a.pattern_at(point)
+                } else {
+                    b.pattern_at(point)
+                }
+            }
+            ColorMapper::Gradient { a, b } => {
+                let a = a.pattern_at(point);
+                let b = b.pattern_at(point);
+                let distance = b - a;
+                let fraction = point.x - point.x.floor();
+                a + distance * fraction
+            }
+            ColorMapper::Ring { a, b } => {
+                let a = a.pattern_at(point);
+                let b = b.pattern_at(point);
+                let px = point.x;
+                let pz = point.z;
+                if (px * px + pz * pz).sqrt().floor() % 2. == 0. {
+                    a
+                } else {
+                    b
+                }
+            }
+            ColorMapper::Checkers { a, b } => {
+                let a = a.pattern_at(point);
+                let b = b.pattern_at(point);
+                let d = point.x.floor() + point.y.floor() + point.z.floor();
+                if d % 2. == 0. {
+                    a
+                } else {
+                    b
+                }
+            }
+        }
+    }
+    /// Sample the color at the given world point on the given object.
+    /// This function respects the object and the pattern's transform matrix.
+    pub fn pattern_at_object(&self, object: &Shape, world_point: Tuple) -> Color {
+        let object_point = object.inverse_transform() * world_point;
+        self.pattern_at(object_point)
+    }
+    pub fn transform(&self) -> Matrix4x4 {
+        self.transform
+    }
+
+    pub fn inverse_transform(&self) -> Matrix4x4 {
+        self.inverse_transform
+    }
+
+    pub fn set_transform(&mut self, t: Matrix4x4) {
+        self.transform = t;
+        self.inverse_transform = t.inverse();
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::{
+        matrices::identity,
+        patterns::{ColorMapper, Pattern, BLACK_PAT, WHITE_PAT},
+        BLACK, WHITE,
+    };
+
+    #[test]
+    fn test_create() {
+        let pattern = Pattern::test();
+        assert_eq!(pattern.transform(), identity());
+    }
+
+    #[test]
+    fn stripe_create() {
+        let pattern = Pattern::stripe(BLACK_PAT, WHITE_PAT);
+        assert_eq!(
+            pattern.color,
+            ColorMapper::Stripe {
+                a: BLACK.into(),
+                b: WHITE.into(),
+            }
+        );
+    }
+    #[test]
+    fn gradient_create() {
+        println!("SHOE ME SOMETHING");
+        println!("* * * 1");
+        let pattern = Pattern::gradient(BLACK_PAT, WHITE_PAT);
+        println!("* * * 2");
+        assert_eq!(
+            pattern.color,
+            ColorMapper::Gradient {
+                a: BLACK.into(),
+                b: WHITE.into(),
+            }
+        );
+    }
+    #[test]
+    fn ring_create() {
+        let pattern = Pattern::ring(BLACK_PAT, WHITE_PAT);
+        assert_eq!(
+            pattern.color,
+            ColorMapper::Ring {
+                a: BLACK.into(),
+                b: WHITE.into()
+            }
+        );
+    }
+    #[test]
+    fn checkers_create() {
+        let pattern = Pattern::checkers(BLACK_PAT, WHITE_PAT);
+        assert_eq!(
+            pattern.color,
+            ColorMapper::Checkers {
+                a: BLACK.into(),
+                b: WHITE.into()
+            }
+        );
+    }
+
+    mod pattern_at {
+        use super::*;
+        use crate::tuples::point;
+
+        #[test]
+        fn test_returns_coordinates() {
+            // A test returns the pattern space coordinates of the point.
+            let pattern = Pattern::test();
+            let p = point(1., 2., 3.);
+            assert_eq!(pattern.pattern_at(p), [p.x, p.y, p.z].into());
+        }
+
+        #[test]
+        fn stripe_alternates_between_two_colors() {
+            // A stripe alternates between two colors.
+            let pattern = Pattern::stripe(WHITE_PAT, BLACK_PAT);
+            for (p, want) in &[
+                // A stripe pattern is constant in y.
+                (point(0., 0., 0.), WHITE),
+                (point(0., 1., 0.), WHITE),
+                (point(0., 2., 0.), WHITE),
+                // A stripe pattern is constant in z.
+                (point(0., 0., 0.), WHITE),
+                (point(0., 0., 1.), WHITE),
+                (point(0., 0., 2.), WHITE),
+                // A stripe pattern alternates in z.
+                (point(0., 0., 0.), WHITE),
+                (point(0.9, 0., 0.), WHITE),
+                (point(1., 0., 0.), BLACK),
+                (point(-0.1, 0., 0.), BLACK),
+                (point(-1., 0., 0.), BLACK),
+                (point(-1.1, 0., 0.), WHITE),
+            ] {
+                assert_eq!(pattern.pattern_at(*p), *want, "{:?}", p);
+            }
+        }
+
+        #[test]
+        fn gradient_linearly_interpolates_between_colors() {
+            // A gradient linearly interpolates between two colors.
+            let pattern = Pattern::gradient(WHITE_PAT, BLACK_PAT);
+            assert_eq!(pattern.pattern_at(point(0., 0., 0.)), WHITE);
+            assert_eq!(
+                pattern.pattern_at(point(0.25, 0., 0.)),
+                [0.75, 0.75, 0.75].into()
+            );
+            assert_eq!(
+                pattern.pattern_at(point(0.5, 0., 0.)),
+                [0.5, 0.5, 0.5].into()
+            );
+            assert_eq!(
+                pattern.pattern_at(point(0.75, 0., 0.)),
+                [0.25, 0.25, 0.25].into()
+            );
+        }
+
+        #[test]
+        fn ring_extend_in_x_and_z() {
+            // A ring should extend both in x and z.
+            let pattern = Pattern::ring(WHITE_PAT, BLACK_PAT);
+            assert_eq!(pattern.pattern_at(point(0., 0., 0.)), WHITE);
+            assert_eq!(pattern.pattern_at(point(1., 0., 0.)), BLACK);
+            assert_eq!(pattern.pattern_at(point(0., 0., 1.)), BLACK);
+            // 0.708 is slight more than 2.sqrt()/2.
+            assert_eq!(pattern.pattern_at(point(0.708, 0., 0.708)), BLACK);
+        }
+
+        #[test]
+        fn checkers_repeat_along_x_axis() {
+            // Checkers should repeat along X-axis.
+            let pattern = Pattern::checkers(WHITE_PAT, BLACK_PAT);
+            assert_eq!(pattern.pattern_at(point(0., 0., 0.)), WHITE);
+            assert_eq!(pattern.pattern_at(point(0.99, 0., 0.)), WHITE);
+            assert_eq!(pattern.pattern_at(point(1.01, 0., 0.)), BLACK);
+        }
+
+        #[test]
+        fn checkers_repeat_along_y_axis() {
+            // Checkers should repeat along Y-axis.
+            let pattern = Pattern::checkers(WHITE_PAT, BLACK_PAT);
+            assert_eq!(pattern.pattern_at(point(0., 0., 0.)), WHITE);
+            assert_eq!(pattern.pattern_at(point(0., 0.99, 0.)), WHITE);
+            assert_eq!(pattern.pattern_at(point(0., 1.01, 0.)), BLACK);
+        }
+
+        #[test]
+        fn checkers_repeat_along_z_axis() {
+            // Checkers should repeat along Z-axis.
+            let pattern = Pattern::checkers(WHITE_PAT, BLACK_PAT);
+            assert_eq!(pattern.pattern_at(point(0., 0., 0.)), WHITE);
+            assert_eq!(pattern.pattern_at(point(0., 0., 0.99)), WHITE);
+            assert_eq!(pattern.pattern_at(point(0., 0., 1.01)), BLACK);
+        }
+    }
+
+    mod pattern_at_object {
+        use std::error::Error;
+
+        use crate::{
+            matrices::scaling,
+            patterns::{stripe_pattern, BLACK_PAT, WHITE_PAT},
+            shapes::{Shape, ShapeBuilder},
+            tuples::point,
+            WHITE,
+        };
+
+        #[test]
+        fn stripes_with_an_object_transformation() -> Result<(), Box<dyn Error>> {
+            // Stripes with an object transformation.
+            let object = ShapeBuilder::sphere()
+                .transform(scaling(2., 2., 2.))
+                .build()?;
+            let pattern = stripe_pattern(WHITE_PAT, BLACK_PAT).build()?;
+            let c = pattern.pattern_at_object(&object, point(1.5, 0., 0.));
+            assert_eq!(c, WHITE);
+            Ok(())
+        }
+
+        #[test]
+        fn stripes_with_a_pattern_transformation() -> Result<(), Box<dyn Error>> {
+            // Stripes with a pattern transformation.
+            let object = Shape::sphere();
+            let mut pattern = stripe_pattern(WHITE_PAT, BLACK_PAT).build()?;
+            pattern.set_transform(scaling(2., 2., 2.));
+            let c = pattern.pattern_at_object(&object, point(1.5, 0., 0.));
+            assert_eq!(c, WHITE);
+            Ok(())
+        }
+    }
+}
--- a/rtchallenge/src/rays.rs
+++ b/rtchallenge/src/rays.rs
@@ -0,0 +1,74 @@
+use crate::{matrices::Matrix4x4, tuples::Tuple, Float};
+
+/// Rays have an origin and a direction. This datatype is the 'ray' in 'raytracer'.
+#[derive(Debug, Default, Clone, PartialEq)]
+pub struct Ray {
+    pub origin: Tuple,
+    pub direction: Tuple,
+}
+
+impl Ray {
+    /// Create a ray with the given origin point and direction vector.
+    /// Will panic if origin not a point or direction not a vector.
+    pub fn new(origin: Tuple, direction: Tuple) -> Ray {
+        assert!(origin.is_point(), "Ray origin must be a point");
+        assert!(direction.is_vector(), "Ray direction must be a vector");
+        Ray { origin, direction }
+    }
+
+    /// Compute a point from the given distance along the `Ray`.
+    pub fn position(&self, t: Float) -> Tuple {
+        self.origin + self.direction * t
+    }
+
+    /// Apply Matrix4x4 transforms to Ray.
+    pub fn transform(&self, m: Matrix4x4) -> Ray {
+        Ray {
+            origin: m * self.origin,
+            direction: m * self.direction,
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::{
+        matrices::Matrix4x4,
+        rays::Ray,
+        tuples::{point, vector},
+    };
+    #[test]
+    fn create() {
+        let origin = point(1., 2., 3.);
+        let direction = vector(4., 5., 6.);
+        let r = Ray::new(origin, direction);
+        assert_eq!(r.origin, origin);
+        assert_eq!(r.direction, direction);
+    }
+    #[test]
+    fn position() {
+        let r = Ray::new(point(2., 3., 4.), vector(1., 0., 0.));
+        assert_eq!(r.position(0.), point(2., 3., 4.));
+        assert_eq!(r.position(1.), point(3., 3., 4.));
+        assert_eq!(r.position(-1.), point(1., 3., 4.));
+        assert_eq!(r.position(2.5), point(4.5, 3., 4.));
+    }
+    #[test]
+    fn transform_translating_ray() {
+        // Translating a ray
+        let r = Ray::new(point(1., 2., 3.), vector(0., 1., 0.));
+        let m = Matrix4x4::translation(3., 4., 5.);
+        let r2 = r.transform(m);
+        assert_eq!(r2.origin, point(4., 6., 8.));
+        assert_eq!(r2.direction, vector(0., 1., 0.));
+    }
+    #[test]
+    fn transform_scaling_ray() {
+        // Scaling a ray
+        let r = Ray::new(point(1., 2., 3.), vector(0., 1., 0.));
+        let m = Matrix4x4::scaling(2., 3., 4.);
+        let r2 = r.transform(m);
+        assert_eq!(r2.origin, point(2., 6., 12.));
+        assert_eq!(r2.direction, vector(0., 3., 0.));
+    }
+}
--- a/rtchallenge/src/shapes.rs
+++ b/rtchallenge/src/shapes.rs
@@ -0,0 +1,825 @@
+use std::sync::{Arc, Mutex};
+
+use derive_builder::Builder;
+
+use crate::{
+    intersections::Intersections,
+    materials::{Material, MaterialBuilder},
+    matrices::Matrix4x4,
+    rays::Ray,
+    tuples::Tuple,
+};
+
+#[derive(Default, PartialEq, Debug, Clone)]
+pub struct TestData {
+    pub saved_ray: Option<Ray>,
+}
+
+#[derive(Debug, Clone)]
+pub enum Geometry {
+    /// Shape with predictable normals useful for debugging.
+    TestShape(Arc<Mutex<TestData>>),
+    /// Sphere represents the unit-sphere (radius of unit 1.) at the origin 0., 0., 0.
+    Sphere,
+    /// Flat surface that extends infinitely in the XZ axes.
+    Plane,
+    /// AABB cube at origin from -1,1 in each direction.
+    Cube,
+    /// Takes shape from children held within.
+    Group(Vec<Shape>),
+}
+
+impl Default for Geometry {
+    fn default() -> Geometry {
+        Geometry::Sphere
+    }
+}
+
+impl PartialEq for Geometry {
+    fn eq(&self, rhs: &Geometry) -> bool {
+        use Geometry::*;
+        match (self, rhs) {
+            (TestShape(l), TestShape(r)) => *l.lock().unwrap() == *r.lock().unwrap(),
+            (Sphere, Sphere) => true,
+            (Plane, Plane) => true,
+            (Cube, Cube) => true,
+            (Group(v1), Group(v2)) => v1 == v2,
+            _ => false,
+        }
+    }
+}
+
+/// Shape represents visible objects.  A signal instance of Shape can generically represent one of
+/// many different shapes based on the value of it's geometry field.  Users chose the shape by
+/// calling the appropriate constructor, i.e. [Shape::sphere].
+#[derive(Builder, Debug, Clone, PartialEq)]
+#[builder(default, pattern = "owned", build_fn(skip))]
+pub struct Shape {
+    transform: Matrix4x4,
+    inverse_transform: Matrix4x4,
+    pub material: Material,
+    geometry: Geometry,
+}
+
+/// Short hand for creating a ShapeBuilder with a plane geometry.
+pub fn plane() -> ShapeBuilder {
+    ShapeBuilder::plane()
+}
+/// Short hand for creating a ShapeBuilder with a sphere geometry.
+pub fn sphere() -> ShapeBuilder {
+    ShapeBuilder::sphere()
+}
+
+/// Short hand for creating a ShapeBuilder with a test shape geometry.
+pub fn test_shape() -> ShapeBuilder {
+    ShapeBuilder::test_shape()
+}
+
+/// Short hand for creating a ShapeBuilder with a cube geometry.
+pub fn cube() -> ShapeBuilder {
+    ShapeBuilder::cube()
+}
+
+/// Short hand for creating a ShapeBuilder with a group geometry.
+pub fn group() -> ShapeBuilder {
+    ShapeBuilder::group()
+}
+
+/// Helper for producing a sphere with a glassy material.
+pub fn glass_sphere() -> ShapeBuilder {
+    ShapeBuilder::sphere().material(
+        MaterialBuilder::default()
+            .transparency(1.)
+            .refractive_index(1.5)
+            .build()
+            .unwrap(),
+    )
+}
+impl ShapeBuilder {
+    /// Short hand for creating a ShapeBuilder with a plane geometry.
+    pub fn plane() -> ShapeBuilder {
+        ShapeBuilder::default().geometry(Geometry::Plane)
+    }
+    /// Short hand for creating a ShapeBuilder with a sphere geometry.
+    pub fn sphere() -> ShapeBuilder {
+        ShapeBuilder::default().geometry(Geometry::Sphere)
+    }
+    /// Short hand for creating a ShapeBuilder with a test shape geometry.
+    pub fn test_shape() -> ShapeBuilder {
+        ShapeBuilder::default().geometry(Geometry::TestShape(Arc::new(Mutex::new(
+            TestData::default(),
+        ))))
+    }
+    /// Short hand for creating a ShapeBuilder with a cube geometry.
+    pub fn cube() -> ShapeBuilder {
+        ShapeBuilder::default().geometry(Geometry::Cube)
+    }
+    /// Short hand for creating a ShapeBuilder with a group geometry.
+    pub fn group() -> ShapeBuilder {
+        ShapeBuilder::default().geometry(Geometry::Group(Vec::new()))
+    }
+
+    /// Add child shapes, only valid for Group::Geometry.
+    pub fn add_child(mut self, child: Shape) -> ShapeBuilder {
+        if let Some(Geometry::Group(ref mut children)) = &mut self.geometry {
+            children.push(child);
+        }
+        self
+    }
+
+    pub fn build(&self) -> Result<Shape, ShapeBuilderError> {
+        let mut s = Shape::default();
+
+        if let Some(transform) = &self.transform {
+            s.set_transform(*transform);
+        }
+        if let Some(material) = &self.material {
+            s.material = material.clone();
+        };
+        if let Some(geometry) = &self.geometry {
+            s.geometry = geometry.clone();
+        };
+        let transform = s.transform();
+        if let Geometry::Group(ref mut children) = s.geometry {
+            children
+                .iter_mut()
+                .for_each(|c| c.set_transform(transform * c.transform()));
+        }
+        Ok(s)
+    }
+}
+
+impl Default for Shape {
+    fn default() -> Shape {
+        Shape {
+            transform: Matrix4x4::identity(),
+            inverse_transform: Matrix4x4::identity(),
+            material: Material::default(),
+            geometry: Geometry::default(),
+        }
+    }
+}
+
+impl Shape {
+    /// Create a test shape useful for debugging.
+    pub fn test_shape() -> Shape {
+        Shape {
+            transform: Matrix4x4::identity(),
+            inverse_transform: Matrix4x4::identity(),
+            material: Material::default(),
+            geometry: Geometry::TestShape(Arc::new(Mutex::new(TestData::default()))),
+        }
+    }
+    pub fn sphere() -> Shape {
+        Shape {
+            transform: Matrix4x4::identity(),
+            inverse_transform: Matrix4x4::identity(),
+            material: Material::default(),
+            geometry: Geometry::Sphere,
+        }
+    }
+    pub fn plane() -> Shape {
+        Shape {
+            transform: Matrix4x4::identity(),
+            inverse_transform: Matrix4x4::identity(),
+            material: Material::default(),
+            geometry: Geometry::Plane,
+        }
+    }
+    pub fn cube() -> Shape {
+        Shape {
+            transform: Matrix4x4::identity(),
+            inverse_transform: Matrix4x4::identity(),
+            material: Material::default(),
+            geometry: Geometry::Cube,
+        }
+    }
+    pub fn group() -> Shape {
+        Shape {
+            transform: Matrix4x4::identity(),
+            inverse_transform: Matrix4x4::identity(),
+            material: Material::default(),
+            geometry: Geometry::Group(Vec::new()),
+        }
+    }
+    /// Find the normal at the point on the sphere.
+    pub fn normal_at(&self, world_point: Tuple) -> Tuple {
+        let object_point = self.inverse_transform * world_point;
+        let object_normal = match self.geometry {
+            Geometry::Sphere => object_point - Tuple::point(0., 0., 0.),
+            Geometry::Plane => Tuple::vector(0., 1., 0.),
+            Geometry::TestShape(_) => object_point,
+            Geometry::Cube => cube::local_normal_at(object_point),
+            Geometry::Group(_) => todo!("normal_at"),
+        };
+        let mut world_normal = self.inverse_transform.transpose() * object_normal;
+        world_normal.w = 0.;
+        world_normal.normalize()
+    }
+
+    pub fn transform(&self) -> Matrix4x4 {
+        self.transform
+    }
+
+    pub fn inverse_transform(&self) -> Matrix4x4 {
+        self.inverse_transform
+    }
+
+    pub fn set_transform(&mut self, t: Matrix4x4) {
+        self.transform = t;
+        self.inverse_transform = t.inverse();
+    }
+    pub fn geometry(&self) -> &Geometry {
+        &self.geometry
+    }
+}
+
+/// Intersect a ray with a shapes.
+pub fn intersect<'s>(shape: &'s Shape, ray: &Ray) -> Intersections<'s> {
+    let local_ray = ray.transform(shape.inverse_transform);
+    match shape.geometry {
+        Geometry::Sphere => sphere::intersect(shape, &local_ray),
+        Geometry::Plane => plane::intersect(shape, &local_ray),
+        Geometry::TestShape(_) => test_shape::intersect(shape, &local_ray),
+        Geometry::Cube => cube::intersect(shape, &local_ray),
+        Geometry::Group(_) => group::intersect(shape, ray),
+    }
+}
+
+mod test_shape {
+    use crate::{
+        intersections::Intersections,
+        rays::Ray,
+        shapes::{Geometry, Shape},
+    };
+    pub fn intersect<'s>(shape: &'s Shape, ray: &Ray) -> Intersections<'s> {
+        if let Geometry::TestShape(s) = &shape.geometry {
+            s.lock()
+                .expect("couldn't grab mutex for TestData")
+                .saved_ray = Some(ray.clone());
+        }
+        Intersections::default()
+    }
+}
+
+mod sphere {
+    use crate::{
+        intersections::{Intersection, Intersections},
+        rays::Ray,
+        shapes::Shape,
+        tuples::{dot, Tuple},
+    };
+    pub fn intersect<'s>(shape: &'s Shape, ray: &Ray) -> Intersections<'s> {
+        let sphere_to_ray = ray.origin - Tuple::point(0., 0., 0.);
+        let a = dot(ray.direction, ray.direction);
+        let b = 2. * dot(ray.direction, sphere_to_ray);
+        let c = dot(sphere_to_ray, sphere_to_ray) - 1.;
+        let discriminant = b * b - 4. * a * c;
+        if discriminant < 0. {
+            return Intersections::default();
+        }
+        Intersections::new(vec![
+            Intersection::new((-b - discriminant.sqrt()) / (2. * a), shape),
+            Intersection::new((-b + discriminant.sqrt()) / (2. * a), shape),
+        ])
+    }
+}
+
+mod plane {
+    use crate::{
+        intersections::{Intersection, Intersections},
+        rays::Ray,
+        shapes::Shape,
+        EPSILON,
+    };
+    pub fn intersect<'s>(shape: &'s Shape, ray: &Ray) -> Intersections<'s> {
+        if (ray.direction.y).abs() < EPSILON {
+            return Intersections::default();
+        }
+        Intersections::new(vec![Intersection::new(
+            -ray.origin.y / ray.direction.y,
+            shape,
+        )])
+    }
+}
+
+mod cube {
+    use crate::{
+        intersections::{Intersection, Intersections},
+        rays::Ray,
+        shapes::Shape,
+        tuples::{vector, Tuple},
+        Float, EPSILON,
+    };
+
+    fn check_axis(origin: Float, direction: Float) -> (Float, Float) {
+        let tmin_numerator = -1. - origin;
+        let tmax_numerator = 1. - origin;
+
+        let (tmin, tmax) = if direction.abs() >= EPSILON {
+            (tmin_numerator / direction, tmax_numerator / direction)
+        } else {
+            (
+                tmin_numerator * Float::INFINITY,
+                tmax_numerator * Float::INFINITY,
+            )
+        };
+
+        if tmin > tmax {
+            return (tmax, tmin);
+        }
+        (tmin, tmax)
+    }
+
+    pub fn intersect<'s>(shape: &'s Shape, ray: &Ray) -> Intersections<'s> {
+        let (xtmin, xtmax) = check_axis(ray.origin.x, ray.direction.x);
+        let (ytmin, ytmax) = check_axis(ray.origin.y, ray.direction.y);
+        let (ztmin, ztmax) = check_axis(ray.origin.z, ray.direction.z);
+
+        let tmin = xtmin.max(ytmin).max(ztmin);
+        let tmax = xtmax.min(ytmax).min(ztmax);
+
+        if tmin > tmax {
+            return Intersections::default();
+        }
+        Intersections::new(vec![
+            Intersection::new(tmin, shape),
+            Intersection::new(tmax, shape),
+        ])
+    }
+    pub fn local_normal_at(point: Tuple) -> Tuple {
+        let x = point.x.abs();
+        let y = point.y.abs();
+        let z = point.z.abs();
+        let maxc = x.max(y).max(z);
+        if maxc == x {
+            return vector(point.x, 0., 0.);
+        }
+        if maxc == y {
+            return vector(0., point.y, 0.);
+        }
+        vector(0., 0., point.z)
+    }
+    #[cfg(test)]
+    mod tests {
+        use crate::{
+            rays::Ray,
+            shapes::Shape,
+            tuples::{point, vector},
+            EPSILON,
+        };
+
+        use super::{intersect, local_normal_at};
+
+        #[test]
+        fn ray_intersects_cube() {
+            let c = Shape::cube();
+            for (name, o, d, t1, t2) in [
+                ("+x", point(5., 0.5, 0.), vector(-1., 0., 0.), 4., 6.),
+                ("-x", point(-5., 0.5, 0.), vector(1., 0., 0.), 4., 6.),
+                ("+y", point(0.5, 5., 0.), vector(0., -1., 0.), 4., 6.),
+                ("-y", point(0.5, -5., 0.), vector(0., 1., 0.), 4., 6.),
+                ("+z", point(0.5, 0., 5.), vector(0., 0., -1.), 4., 6.),
+                ("-z", point(0.5, 0., -5.), vector(0., 0., 1.), 4., 6.),
+                ("inside", point(0., 0.5, 0.), vector(0., 0., 1.), -1., 1.),
+            ] {
+                let r = Ray::new(o, d);
+                let xs = intersect(&c, &r);
+                assert_eq!(xs.len(), 2, "{}", name);
+                assert!((xs[0].t - t1).abs() < EPSILON, "{} t1 {}", name, xs[0].t);
+                assert!((xs[1].t - t2).abs() < EPSILON, "{} t2 {}", name, xs[1].t);
+            }
+        }
+
+        #[test]
+        fn ray_misses_cube() {
+            let c = Shape::cube();
+            for (o, d) in [
+                (point(-2., 0., 0.), vector(0.2673, 0.5345, 0.8018)),
+                (point(0., -2., 0.), vector(0.8018, 0.2673, 0.5345)),
+                (point(0., 0., -2.), vector(0.5345, 0.8018, 0.2673)),
+                (point(2., 0., 2.), vector(0., 0., -1.)),
+                (point(0., 2., 2.), vector(0., -1., 0.)),
+                (point(2., 2., -5.), vector(-1., 0., 0.)),
+            ] {
+                let r = Ray::new(o, d);
+                let xs = intersect(&c, &r);
+                assert_eq!(xs.len(), 0, "({:?}, {:?})", o, d);
+            }
+        }
+        #[test]
+        fn normal_cube_surface() {
+            for (p, n) in [
+                (point(1., 0.8, -0.8), vector(1., 0., 0.)),
+                (point(-1., -0.2, 0.9), vector(-1., 0., 0.)),
+                (point(-0.4, 1., -0.1), vector(0., 1., 0.)),
+                (point(0.3, -1., -0.7), vector(0., -1., 0.)),
+                (point(-0.6, 0.3, 1.), vector(0., 0., 1.)),
+                (point(0.4, 0.4, -1.), vector(0., 0., -1.)),
+                (point(1., 1., 1.), vector(1., 0., 0.)),
+                (point(-1., -1., -1.), vector(-1., 0., 0.)),
+            ] {
+                let normal = local_normal_at(p);
+                assert_eq!(n, normal);
+            }
+        }
+    }
+}
+
+mod group {
+    use crate::{intersections::Intersections, rays::Ray, shapes::Shape};
+
+    use super::Geometry;
+
+    pub fn intersect<'s>(shape: &'s Shape, ray: &Ray) -> Intersections<'s> {
+        if let Geometry::Group(children) = &shape.geometry {
+            let mut intersections: Vec<_> = children
+                .iter()
+                .flat_map(|c| super::intersect(c, ray))
+                .collect();
+            intersections.sort_by(|a, b| {
+                a.t.partial_cmp(&b.t)
+                    .expect("an intersection has a t value that is NaN")
+            });
+            return Intersections::new(intersections);
+        }
+        unreachable!();
+    }
+    #[cfg(test)]
+    mod tests {
+        use crate::{
+            matrices::{scaling, translation},
+            rays::Ray,
+            shapes::{intersect, Shape, ShapeBuilder},
+            tuples::{point, vector},
+        };
+
+        #[test]
+        fn intersecting_empty_group() {
+            let g = Shape::group();
+            let r = Ray::new(point(0., 0., 0.), vector(0., 0., 1.));
+            let xs = intersect(&g, &r);
+            assert_eq!(xs.len(), 0);
+        }
+
+        #[test]
+        fn intersecting_nonempty_group() -> Result<(), Box<dyn std::error::Error>> {
+            let s1 = Shape::sphere();
+            let s2 = ShapeBuilder::sphere()
+                .transform(translation(0., 0., -3.))
+                .build()?;
+            let s3 = ShapeBuilder::sphere()
+                .transform(translation(5., 0., 0.))
+                .build()?;
+            let g = ShapeBuilder::group()
+                .add_child(s1.clone())
+                .add_child(s2.clone())
+                .add_child(s3.clone())
+                .build()?;
+            let r = Ray::new(point(0., 0., -5.), vector(0., 0., 1.));
+            let xs = intersect(&g, &r);
+            assert_eq!(xs.len(), 4);
+            assert_eq!(xs[0].object, &s2);
+            assert_eq!(xs[1].object, &s2);
+            assert_eq!(xs[2].object, &s1);
+            assert_eq!(xs[3].object, &s1);
+            Ok(())
+        }
+        #[test]
+        fn intersecting_transformed_group() -> Result<(), Box<dyn std::error::Error>> {
+            let g = ShapeBuilder::group()
+                .transform(scaling(2., 2., 2.))
+                .add_child(
+                    ShapeBuilder::sphere()
+                        .transform(translation(5., 0., 0.))
+                        .build()?,
+                )
+                .build()?;
+            let r = Ray::new(point(10., 0., -10.), vector(0., 0., 1.));
+            let xs = intersect(&g, &r);
+            assert_eq!(xs.len(), 2);
+            Ok(())
+        }
+    }
+}
+#[cfg(test)]
+mod tests {
+    mod shape_builder {
+        use std::error::Error;
+
+        use crate::shapes::{plane, sphere, test_shape, Shape};
+
+        #[test]
+        fn plane_builder() -> Result<(), Box<dyn Error>> {
+            assert_eq!(plane().build()?, Shape::plane());
+            Ok(())
+        }
+        #[test]
+        fn sphere_builder() -> Result<(), Box<dyn Error>> {
+            assert_eq!(sphere().build()?, Shape::sphere());
+            Ok(())
+        }
+        #[test]
+        fn test_shape_builder() -> Result<(), Box<dyn Error>> {
+            assert_eq!(test_shape().build()?, Shape::test_shape());
+            Ok(())
+        }
+    }
+    mod shape {
+        use crate::{
+            materials::Material,
+            matrices::{identity, translation},
+            shapes::Shape,
+        };
+
+        #[test]
+        fn test_shape() {
+            let mut s = Shape::test_shape();
+            // The default transform.
+            assert_eq!(s.transform(), identity());
+            // The default material.
+            assert_eq!(s.material, Material::default());
+            // Assigning a material.
+            let m = Material {
+                ambient: 1.,
+                ..Material::default()
+            };
+            s.material = m.clone();
+            assert_eq!(s.material, m);
+        }
+        #[test]
+        fn sphere() {
+            // A sphere's default transform is the identity matrix.
+            let s = Shape::sphere();
+            assert_eq!(s.transform(), identity());
+
+            // It can be changed by directly setting the transform member.
+            let mut s = Shape::sphere();
+            let t = translation(2., 3., 4.);
+            s.set_transform(t.clone());
+            assert_eq!(s.transform(), t);
+
+            // Default Sphere has the default material.
+            assert_eq!(s.material, Material::default());
+            // It can be overridden.
+            let mut s = Shape::sphere();
+            let mut m = Material::default();
+            m.ambient = 1.;
+            s.material = m.clone();
+            assert_eq!(s.material, m);
+        }
+    }
+    mod normal_at {
+        use crate::{float::consts::PI, matrices::Matrix4x4, shapes::Shape, tuples::Tuple, Float};
+        #[test]
+        fn compute_normal_on_translated_shape() {
+            // Computing the normal on a translated shape.
+            let mut s = Shape::test_shape();
+            s.set_transform(Matrix4x4::translation(0., 1., 0.));
+            let n = s.normal_at(Tuple::point(0., 1.70711, -0.70711));
+            assert_eq!(n, Tuple::vector(0., 0.70711, -0.70711));
+        }
+        #[test]
+        fn compute_normal_on_scaled_shape() {
+            // Computing the normal on a scaled shape.
+            let mut s = Shape::test_shape();
+            s.set_transform(Matrix4x4::scaling(1., 0.5, 1.) * Matrix4x4::rotation_z(PI / 5.));
+            let n = s.normal_at(Tuple::point(
+                0.,
+                (2. as Float).sqrt() / 2.,
+                -(2. as Float).sqrt() / 2.,
+            ));
+            assert_eq!(n, Tuple::vector(0., 0.97014, -0.24254));
+        }
+        #[test]
+        fn sphere_normal_on_x_axis() {
+            // Normal on X-axis
+            let s = Shape::sphere();
+            let n = s.normal_at(Tuple::point(1., 0., 0.));
+            assert_eq!(n, Tuple::vector(1., 0., 0.));
+        }
+        #[test]
+        fn sphere_normal_on_y_axis() {
+            // Normal on Y-axis
+            let s = Shape::sphere();
+            let n = s.normal_at(Tuple::point(0., 1., 0.));
+            assert_eq!(n, Tuple::vector(0., 1., 0.));
+        }
+        #[test]
+        fn sphere_normal_on_z_axis() {
+            // Normal on Z-axis
+            let s = Shape::sphere();
+            let n = s.normal_at(Tuple::point(0., 0., 1.));
+            assert_eq!(n, Tuple::vector(0., 0., 1.));
+        }
+        #[test]
+        fn sphere_normal_non_axial() {
+            // Normal on a sphere at a nonaxial point.
+            let s = Shape::sphere();
+            let n = s.normal_at(Tuple::point(
+                (3. as Float).sqrt() / 3.,
+                (3. as Float).sqrt() / 3.,
+                (3. as Float).sqrt() / 3.,
+            ));
+            assert_eq!(
+                n,
+                Tuple::vector(
+                    (3. as Float).sqrt() / 3.,
+                    (3. as Float).sqrt() / 3.,
+                    (3. as Float).sqrt() / 3.,
+                )
+            );
+        }
+        #[test]
+        fn normals_are_normalized() {
+            // Normals returned are normalized.
+            let s = Shape::sphere();
+            let n = s.normal_at(Tuple::point(
+                (3. as Float).sqrt() / 3.,
+                (3. as Float).sqrt() / 3.,
+                (3. as Float).sqrt() / 3.,
+            ));
+            assert_eq!(n, n.normalize());
+        }
+        #[test]
+        fn compute_normal_on_translated_sphere() {
+            // Compute the normal on a translated sphere.
+            let mut s = Shape::sphere();
+            s.set_transform(Matrix4x4::translation(0., 1., 0.));
+            let n = s.normal_at(Tuple::point(0., 1.70711, -0.70711));
+            assert_eq!(n, Tuple::vector(0., 0.70711, -0.70711));
+        }
+        #[test]
+        fn compute_normal_on_scaled_sphere() {
+            // Compute the normal on a transformed sphere.
+            let mut s = Shape::sphere();
+            s.set_transform(Matrix4x4::scaling(1., 0.5, 1.) * Matrix4x4::rotation_z(PI / 5.));
+            let n = s.normal_at(Tuple::point(
+                0.,
+                (2. as Float).sqrt() / 2.,
+                -(2. as Float).sqrt() / 2.,
+            ));
+            assert_eq!(n, Tuple::vector(0., 0.97014, -0.24254));
+        }
+        #[test]
+        fn nomal_of_plane_constant() {
+            // Normal of a plane is constant everywhere.
+            let p = Shape::plane();
+            assert_eq!(
+                p.normal_at(Tuple::point(0., 0., 0.)),
+                Tuple::vector(0., 1., 0.)
+            );
+            assert_eq!(
+                p.normal_at(Tuple::point(10., 0., -10.)),
+                Tuple::vector(0., 1., 0.)
+            );
+            assert_eq!(
+                p.normal_at(Tuple::point(-5., 0., 150.)),
+                Tuple::vector(0., 1., 0.)
+            );
+        }
+    }
+    mod intersect {
+        use crate::{
+            intersections::{Intersection, Intersections},
+            matrices::Matrix4x4,
+            rays::Ray,
+            shapes::{intersect, Geometry, Shape},
+            tuples::Tuple,
+        };
+
+        #[test]
+        fn scaled_shape_with_ray() {
+            // Intersecting a scaled shape with a ray.
+            let r = Ray::new(Tuple::point(0., 0., -5.), Tuple::vector(0., 0., 1.));
+            let mut s = Shape::test_shape();
+            s.set_transform(Matrix4x4::scaling(2., 2., 2.));
+            let _xs = intersect(&s, &r);
+            if let Geometry::TestShape(data) = s.geometry() {
+                if let Some(ray) = &data.lock().unwrap().saved_ray {
+                    assert_eq!(ray.origin, Tuple::point(0., 0., -2.5));
+                    assert_eq!(ray.direction, Tuple::vector(0., 0., 0.5));
+                } else {
+                    panic!("ray wasn't set");
+                };
+            } else {
+                panic!("test_shape returned a non-TestShape geometry")
+            };
+        }
+        #[test]
+        fn translated_shape_with_ray() {
+            // Intersecting a translated shape with a ray.
+            let r = Ray::new(Tuple::point(0., 0., -5.), Tuple::vector(0., 0., 1.));
+            let mut s = Shape::test_shape();
+            s.set_transform(Matrix4x4::translation(5., 0., 0.));
+            let _xs = intersect(&s, &r);
+            if let Geometry::TestShape(data) = s.geometry() {
+                if let Some(ray) = &data.lock().unwrap().saved_ray {
+                    assert_eq!(ray.origin, Tuple::point(-5., 0., -5.));
+                    assert_eq!(ray.direction, Tuple::vector(0., 0., 1.));
+                } else {
+                    panic!("ray wasn't set");
+                };
+            } else {
+                panic!("test_shape returned a non-TestShape geometry")
+            };
+        }
+        #[test]
+        fn ray_intersects_sphere_two_points() {
+            // A ray intersects a sphere in two points.
+            let r = Ray::new(Tuple::point(0., 0., -5.), Tuple::vector(0., 0., 1.));
+            let s = Shape::sphere();
+            let xs = intersect(&s, &r);
+            assert_eq!(
+                xs,
+                Intersections::new(vec![Intersection::new(4., &s), Intersection::new(6., &s)])
+            );
+        }
+        #[test]
+        fn ray_intersects_at_tangent() {
+            // A ray intersects a sphere at a tangent.
+            let r = Ray::new(Tuple::point(0., 2., -5.), Tuple::vector(0., 0., 1.));
+            let s = Shape::sphere();
+            let xs = intersect(&s, &r);
+            assert_eq!(xs, Intersections::default());
+        }
+        #[test]
+        fn ray_originates_inside_sphere() {
+            // A ray originates inside a sphere.
+            let r = Ray::new(Tuple::point(0., 0., 0.), Tuple::vector(0., 0., 1.));
+            let s = Shape::sphere();
+            let xs = intersect(&s, &r);
+            assert_eq!(
+                xs,
+                Intersections::new(vec![Intersection::new(-1., &s), Intersection::new(1., &s)])
+            );
+        }
+        #[test]
+        fn sphere_behind_ray() {
+            // A sphere is behind a ray.
+            let r = Ray::new(Tuple::point(0., 0., 5.), Tuple::vector(0., 0., 1.));
+            let s = Shape::sphere();
+            let xs = intersect(&s, &r);
+            assert_eq!(
+                xs,
+                Intersections::new(vec![Intersection::new(-6., &s), Intersection::new(-4., &s)])
+            );
+        }
+        #[test]
+        fn ray_intersects_scaled_sphere() {
+            // Intersect a scaled sphere with a ray.
+            let r = Ray::new(Tuple::point(0., 0., -5.), Tuple::vector(0., 0., 1.));
+            let mut s = Shape::sphere();
+            s.set_transform(Matrix4x4::scaling(2., 2., 2.));
+            let xs = intersect(&s, &r);
+            assert_eq!(xs.len(), 2, "xs {:?}", xs);
+            assert_eq!(xs[0].t, 3., "xs {:?}", xs);
+            assert_eq!(xs[1].t, 7., "xs {:?}", xs);
+        }
+        #[test]
+        fn ray_intersects_translated_sphere() {
+            // Intersect a translated sphere with a ray.
+            let r = Ray::new(Tuple::point(0., 0., -5.), Tuple::vector(0., 0., 1.));
+            let mut s = Shape::sphere();
+            s.set_transform(Matrix4x4::translation(5., 0., 0.));
+            let xs = intersect(&s, &r);
+            assert_eq!(xs.len(), 0);
+        }
+        #[test]
+        fn ray_parallel_to_plane() {
+            // Intersect with a ray parallel to the plane.
+            let p = Shape::plane();
+            let r = Ray::new(Tuple::point(0., 10., 0.), Tuple::vector(0., 0., 1.));
+            let xs = intersect(&p, &r);
+            assert_eq!(xs.len(), 0);
+        }
+        #[test]
+        fn ray_coplanar_to_plane() {
+            // Intersect with a coplanar.
+            let p = Shape::plane();
+            let r = Ray::new(Tuple::point(0., 0., 0.), Tuple::vector(0., 0., 1.));
+            let xs = intersect(&p, &r);
+            assert_eq!(xs.len(), 0);
+        }
+        #[test]
+        fn ray_intersects_plane_from_above() {
+            // A ray intersecting a plane from above.
+            let p = Shape::plane();
+            let r = Ray::new(Tuple::point(0., 1., 0.), Tuple::vector(0., -1., 0.));
+            let xs = intersect(&p, &r);
+            assert_eq!(xs.len(), 1);
+            assert_eq!(xs[0].t, 1.);
+            assert_eq!(xs[0].object, &p);
+        }
+        #[test]
+        fn ray_intersects_plane_from_below() {
+            // A ray intersecting a plane from below.
+            let p = Shape::plane();
+            let r = Ray::new(Tuple::point(0., -1., 0.), Tuple::vector(0., 1., 0.));
+            let xs = intersect(&p, &r);
+            assert_eq!(xs.len(), 1);
+            assert_eq!(xs[0].t, 1.);
+            assert_eq!(xs[0].object, &p);
+        }
+    }
+}
--- a/rtchallenge/src/transformations.rs
+++ b/rtchallenge/src/transformations.rs
@@ -0,0 +1,71 @@
+use crate::{
+    matrices::Matrix4x4,
+    tuples::{cross, Tuple},
+};
+
+/// Create a matrix representing a eye at `from` looking at `to`, with an `up`
+/// as the up vector.
+pub fn view_transform(from: Tuple, to: Tuple, up: Tuple) -> Matrix4x4 {
+    let forward = (to - from).normalize();
+    let left = cross(forward, up.normalize());
+    let true_up = cross(left, forward);
+    Matrix4x4::new(
+        [left.x, left.y, left.z, 0.],
+        [true_up.x, true_up.y, true_up.z, 0.],
+        [-forward.x, -forward.y, -forward.z, 0.],
+        [0., 0., 0., 1.],
+    ) * Matrix4x4::translation(-from.x, -from.y, -from.z)
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::{
+        matrices::{identity, scaling, translation, Matrix4x4},
+        transformations::view_transform,
+        tuples::{point, vector},
+    };
+    #[test]
+    fn default_orientation() {
+        // The transformation matrix for the default orientation.
+        let from = point(0., 0., 0.);
+        let to = point(0., 0., -1.);
+        let up = vector(0., 1., 0.);
+        let t = view_transform(from, to, up);
+        assert_eq!(t, identity());
+    }
+    #[test]
+    fn looking_positive_z() {
+        // A view transformation matrix looking in positive z direction.
+        let from = point(0., 0., 0.);
+        let to = point(0., 0., 1.);
+        let up = vector(0., 1., 0.);
+        let t = view_transform(from, to, up);
+        assert_eq!(t, scaling(-1., 1., -1.));
+    }
+    #[test]
+    fn transformation_moves_world() {
+        // The view transformation moves the world.
+        let from = point(0., 0., 8.);
+        let to = point(0., 0., 0.);
+        let up = vector(0., 1., 0.);
+        let t = view_transform(from, to, up);
+        assert_eq!(t, translation(0., 0., -8.));
+    }
+    #[test]
+    fn arbitrary_view() {
+        // An arbitrary view transformation.
+        let from = point(1., 3., 2.);
+        let to = point(4., -2., 8.);
+        let up = vector(1., 1., 0.);
+        let t = view_transform(from, to, up);
+        assert_eq!(
+            t,
+            Matrix4x4::new(
+                [-0.50709, 0.50709, 0.67612, -2.36643],
+                [0.76772, 0.60609, 0.12122, -2.82843],
+                [-0.35857, 0.59761, -0.71714, 0.],
+                [0., 0., 0., 1.],
+            )
+        );
+    }
+}
--- a/rtchallenge/src/tuples.rs
+++ b/rtchallenge/src/tuples.rs
@@ -0,0 +1,439 @@
+use std::ops::{Add, Div, Mul, Neg, Sub};
+
+use crate::{Float, EPSILON};
+
+/// Short hand for creating a Tuple that represents a point, w=1.
+pub fn point(x: Float, y: Float, z: Float) -> Tuple {
+    Tuple::point(x, y, z)
+}
+
+/// Short hand for creating a Tuple that represents a vector, w=0.
+pub fn vector(x: Float, y: Float, z: Float) -> Tuple {
+    Tuple::vector(x, y, z)
+}
+
+#[derive(Debug, Default, Copy, Clone)]
+pub struct Tuple {
+    pub x: Float,
+    pub y: Float,
+    pub z: Float,
+    pub w: Float,
+}
+
+impl Tuple {
+    pub fn point(x: Float, y: Float, z: Float) -> Tuple {
+        Tuple::new(x, y, z, 1.0)
+    }
+
+    pub fn vector(x: Float, y: Float, z: Float) -> Tuple {
+        Tuple::new(x, y, z, 0.0)
+    }
+
+    pub fn new(x: Float, y: Float, z: Float, w: Float) -> Tuple {
+        Tuple { x, y, z, w }
+    }
+
+    pub fn is_point(&self) -> bool {
+        self.w == 1.0
+    }
+
+    pub fn is_vector(&self) -> bool {
+        self.w == 0.0
+    }
+
+    pub fn magnitude(&self) -> Float {
+        (self.x * self.x + self.y * self.y + self.z * self.z + self.w * self.w).sqrt()
+    }
+
+    pub fn normalize(&self) -> Tuple {
+        let m = self.magnitude();
+        Tuple {
+            x: self.x / m,
+            y: self.y / m,
+            z: self.z / m,
+            w: self.w / m,
+        }
+    }
+}
+
+/// Reflects vector v across normal n.
+pub fn reflect(v: Tuple, n: Tuple) -> Tuple {
+    v - n * 2. * dot(v, n)
+}
+
+impl Add for Tuple {
+    type Output = Self;
+    fn add(self, other: Self) -> Self {
+        Self {
+            x: self.x + other.x,
+            y: self.y + other.y,
+            z: self.z + other.z,
+            w: self.w + other.w,
+        }
+    }
+}
+
+impl Div<Float> for Tuple {
+    type Output = Self;
+    fn div(self, rhs: Float) -> Self::Output {
+        Self::Output {
+            x: self.x / rhs,
+            y: self.y / rhs,
+            z: self.z / rhs,
+            w: self.w / rhs,
+        }
+    }
+}
+
+impl Mul<Float> for Tuple {
+    type Output = Self;
+    fn mul(self, rhs: Float) -> Self::Output {
+        Self::Output {
+            x: self.x * rhs,
+            y: self.y * rhs,
+            z: self.z * rhs,
+            w: self.w * rhs,
+        }
+    }
+}
+
+impl Mul<Tuple> for Float {
+    type Output = Tuple;
+    fn mul(self, rhs: Tuple) -> Self::Output {
+        Self::Output {
+            x: self * rhs.x,
+            y: self * rhs.y,
+            z: self * rhs.z,
+            w: self * rhs.w,
+        }
+    }
+}
+
+impl Neg for Tuple {
+    type Output = Self;
+    fn neg(self) -> Self::Output {
+        Self {
+            x: -self.x,
+            y: -self.y,
+            z: -self.z,
+            w: -self.w,
+        }
+    }
+}
+impl Sub for Tuple {
+    type Output = Self;
+    fn sub(self, other: Self) -> Self {
+        Self {
+            x: self.x - other.x,
+            y: self.y - other.y,
+            z: self.z - other.z,
+            w: self.w - other.w,
+        }
+    }
+}
+
+impl PartialEq for Tuple {
+    fn eq(&self, rhs: &Tuple) -> bool {
+        ((self.x - rhs.x).abs() < EPSILON)
+            && ((self.y - rhs.y).abs() < EPSILON)
+            && ((self.z - rhs.z).abs() < EPSILON)
+            && ((self.w - rhs.w).abs() < EPSILON)
+    }
+}
+pub fn dot(a: Tuple, b: Tuple) -> Float {
+    a.x * b.x + a.y * b.y + a.z * b.z + a.w * b.w
+}
+pub fn cross(a: Tuple, b: Tuple) -> Tuple {
+    Tuple::vector(
+        a.y * b.z - a.z * b.y,
+        a.z * b.x - a.x * b.z,
+        a.x * b.y - a.y * b.x,
+    )
+}
+
+#[derive(Copy, Clone, Debug, Default)]
+pub struct Color {
+    pub red: Float,
+    pub green: Float,
+    pub blue: Float,
+}
+
+impl Color {
+    pub const fn new(red: Float, green: Float, blue: Float) -> Color {
+        Color { red, green, blue }
+    }
+}
+
+impl From<[Float; 3]> for Color {
+    fn from(rgb: [Float; 3]) -> Self {
+        Color {
+            red: rgb[0],
+            green: rgb[1],
+            blue: rgb[2],
+        }
+    }
+}
+
+impl PartialEq for Color {
+    fn eq(&self, rhs: &Color) -> bool {
+        ((self.red - rhs.red).abs() < EPSILON)
+            && ((self.green - rhs.green).abs() < EPSILON)
+            && ((self.blue - rhs.blue).abs() < EPSILON)
+    }
+}
+
+impl Add for Color {
+    type Output = Self;
+    fn add(self, other: Self) -> Self {
+        Self {
+            red: self.red + other.red,
+            green: self.green + other.green,
+            blue: self.blue + other.blue,
+        }
+    }
+}
+
+impl Div<Float> for Color {
+    type Output = Self;
+    fn div(self, rhs: Float) -> Self::Output {
+        Self::Output {
+            red: self.red / rhs,
+            green: self.green / rhs,
+            blue: self.blue / rhs,
+        }
+    }
+}
+
+impl Mul<Float> for Color {
+    type Output = Self;
+    fn mul(self, rhs: Float) -> Self::Output {
+        Self::Output {
+            red: self.red * rhs,
+            green: self.green * rhs,
+            blue: self.blue * rhs,
+        }
+    }
+}
+
+impl Mul<Color> for Float {
+    type Output = Color;
+    fn mul(self, rhs: Color) -> Self::Output {
+        Self::Output {
+            red: self * rhs.red,
+            green: self * rhs.green,
+            blue: self * rhs.blue,
+        }
+    }
+}
+
+impl Mul<Color> for Color {
+    type Output = Color;
+    fn mul(self, rhs: Color) -> Self::Output {
+        Self::Output {
+            red: self.red * rhs.red,
+            green: self.green * rhs.green,
+            blue: self.blue * rhs.blue,
+        }
+    }
+}
+
+impl Neg for Color {
+    type Output = Self;
+    fn neg(self) -> Self::Output {
+        Self {
+            red: -self.red,
+            green: -self.green,
+            blue: -self.blue,
+        }
+    }
+}
+
+impl Sub for Color {
+    type Output = Self;
+    fn sub(self, other: Self) -> Self {
+        Self {
+            red: self.red - other.red,
+            green: self.green - other.green,
+            blue: self.blue - other.blue,
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::{cross, dot, reflect, Color, Float, Tuple, EPSILON};
+    #[test]
+    fn is_point() {
+        // A tuple with w = 1 is a point
+        let a = Tuple::new(4.3, -4.2, 3.1, 1.0);
+        assert_eq!(a.x, 4.3);
+        assert_eq!(a.y, -4.2);
+        assert_eq!(a.z, 3.1);
+        assert_eq!(a.w, 1.0);
+        assert!(a.is_point());
+        assert!(!a.is_vector());
+    }
+    #[test]
+    fn is_vector() {
+        // A tuple with w = 0 is a point
+        let a = Tuple::new(4.3, -4.2, 3.1, 0.0);
+        assert_eq!(a.x, 4.3);
+        assert_eq!(a.y, -4.2);
+        assert_eq!(a.z, 3.1);
+        assert_eq!(a.w, 0.0);
+        assert!(!a.is_point());
+        assert!(a.is_vector());
+    }
+    #[test]
+    fn point_tuple() {
+        assert_eq!(Tuple::point(4., -4., 3.), Tuple::new(4., -4., 3., 1.))
+    }
+    #[test]
+    fn vector_tuple() {
+        assert_eq!(Tuple::vector(4., -4., 3.), Tuple::new(4., -4., 3., 0.))
+    }
+    #[test]
+    fn add_two_tuples() {
+        let a1 = Tuple::new(3., -2., 5., 1.);
+        let a2 = Tuple::new(-2., 3., 1., 0.);
+        assert_eq!(a1 + a2, Tuple::new(1., 1., 6., 1.));
+    }
+    #[test]
+    fn sub_two_points() {
+        let p1 = Tuple::point(3., 2., 1.);
+        let p2 = Tuple::point(5., 6., 7.);
+        assert_eq!(p1 - p2, Tuple::vector(-2., -4., -6.));
+    }
+    #[test]
+    fn sub_vector_point() {
+        let p = Tuple::point(3., 2., 1.);
+        let v = Tuple::vector(5., 6., 7.);
+        assert_eq!(p - v, Tuple::point(-2., -4., -6.));
+    }
+    #[test]
+    fn sub_two_vectors() {
+        let v1 = Tuple::vector(3., 2., 1.);
+        let v2 = Tuple::vector(5., 6., 7.);
+        assert_eq!(v1 - v2, Tuple::vector(-2., -4., -6.));
+    }
+    #[test]
+    fn sub_zero_vector() {
+        let zero = Tuple::vector(0., 0., 0.);
+        let v = Tuple::vector(1., -2., 3.);
+        assert_eq!(zero - v, Tuple::vector(-1., 2., -3.));
+    }
+    #[test]
+    fn negate_tuple() {
+        let a = Tuple::new(1., -2., 3., -4.);
+        assert_eq!(-a, Tuple::new(-1., 2., -3., 4.));
+    }
+    #[test]
+    fn mul_tuple_scalar() {
+        let a = Tuple::new(1., -2., 3., -4.);
+        assert_eq!(a * 3.5, Tuple::new(3.5, -7., 10.5, -14.));
+        assert_eq!(3.5 * a, Tuple::new(3.5, -7., 10.5, -14.));
+    }
+    #[test]
+    fn mul_tuple_fraction() {
+        let a = Tuple::new(1., -2., 3., -4.);
+        assert_eq!(a * 0.5, Tuple::new(0.5, -1., 1.5, -2.));
+        assert_eq!(0.5 * a, Tuple::new(0.5, -1., 1.5, -2.));
+    }
+    #[test]
+    fn div_tuple_scalar() {
+        let a = Tuple::new(1., -2., 3., -4.);
+        assert_eq!(a / 2., Tuple::new(0.5, -1., 1.5, -2.));
+    }
+    #[test]
+    fn vector_magnitude() {
+        assert_eq!(1., Tuple::vector(1., 0., 0.).magnitude());
+        assert_eq!(1., Tuple::vector(0., 1., 0.).magnitude());
+        assert_eq!(1., Tuple::vector(0., 0., 1.).magnitude());
+        assert_eq!((14. as Float).sqrt(), Tuple::vector(1., 2., 3.).magnitude());
+        assert_eq!(
+            (14. as Float).sqrt(),
+            Tuple::vector(-1., -2., -3.).magnitude()
+        );
+    }
+    #[test]
+    fn vector_normalize() {
+        assert_eq!(
+            Tuple::vector(1., 0., 0.),
+            Tuple::vector(4., 0., 0.).normalize()
+        );
+        assert_eq!(
+            Tuple::vector(
+                1. / (14. as Float).sqrt(),
+                2. / (14. as Float).sqrt(),
+                3. / (14. as Float).sqrt()
+            ),
+            Tuple::vector(1., 2., 3.).normalize()
+        );
+    }
+    #[test]
+    fn vector_normalize_magnitude() {
+        let len = Tuple::vector(1., 2., 3.).normalize().magnitude();
+        assert!((1. - len).abs() < EPSILON);
+    }
+    #[test]
+    fn dot_two_tuples() {
+        let a = Tuple::vector(1., 2., 3.);
+        let b = Tuple::vector(2., 3., 4.);
+        assert_eq!(20., dot(a, b));
+    }
+    #[test]
+    fn cross_two_tuples() {
+        let a = Tuple::vector(1., 2., 3.);
+        let b = Tuple::vector(2., 3., 4.);
+        assert_eq!(Tuple::vector(-1., 2., -1.), cross(a, b));
+        assert_eq!(Tuple::vector(1., -2., 1.), cross(b, a));
+    }
+
+    #[test]
+    fn color_rgb() {
+        let c = Color::new(-0.5, 0.4, 1.7);
+        assert_eq!(c.red, -0.5);
+        assert_eq!(c.green, 0.4);
+        assert_eq!(c.blue, 1.7);
+    }
+    #[test]
+    fn add_color() {
+        let c1 = Color::new(0.9, 0.6, 0.75);
+        let c2 = Color::new(0.7, 0.1, 0.25);
+        assert_eq!(c1 + c2, Color::new(0.9 + 0.7, 0.6 + 0.1, 0.75 + 0.25));
+    }
+    #[test]
+    fn sub_color() {
+        let c1 = Color::new(0.9, 0.6, 0.75);
+        let c2 = Color::new(0.7, 0.1, 0.25);
+        assert_eq!(c1 - c2, Color::new(0.9 - 0.7, 0.6 - 0.1, 0.75 - 0.25));
+    }
+    #[test]
+    fn mul_color_scalar() {
+        let c = Color::new(0.2, 0.3, 0.4);
+        assert_eq!(c * 2., Color::new(0.2 * 2., 0.3 * 2., 0.4 * 2.));
+        assert_eq!(2. * c, Color::new(0.2 * 2., 0.3 * 2., 0.4 * 2.));
+    }
+    #[test]
+    fn mul_colors() {
+        let c1 = Color::new(1., 0.2, 0.4);
+        let c2 = Color::new(0.9, 1., 0.1);
+        assert_eq!(c1 * c2, Color::new(1.0 * 0.9, 0.2 * 1., 0.4 * 0.1));
+    }
+    #[test]
+    fn reflect_approaching_at_45() {
+        // Reflecting a vector approaching at 45°
+        let v = Tuple::vector(1., -1., 0.);
+        let n = Tuple::vector(0., 1., 0.);
+        let r = reflect(v, n);
+        assert_eq!(r, Tuple::vector(1., 1., 0.));
+    }
+    #[test]
+    fn reflect_slanted_surface() {
+        // Reflecting off a slanted surface.
+        let v = Tuple::vector(0., -1., 0.);
+        let n = Tuple::vector((2. as Float).sqrt() / 2., (2. as Float).sqrt() / 2., 0.);
+        let r = reflect(v, n);
+        assert_eq!(r, Tuple::vector(1., 0., 0.));
+    }
+}
--- a/rtchallenge/src/world.rs
+++ b/rtchallenge/src/world.rs
@@ -0,0 +1,555 @@
+use derive_builder::Builder;
+
+use crate::{
+    intersections::{prepare_computations, schlick, Intersections, PrecomputedData},
+    lights::PointLight,
+    materials::{lighting, Material},
+    matrices::Matrix4x4,
+    rays::Ray,
+    shapes::{intersect, Shape},
+    tuples::{dot, Color, Tuple},
+    BLACK, WHITE,
+};
+
+/// World holds all drawable objects and the light(s) that illuminate them.
+#[derive(Builder, Clone, Debug, Default)]
+#[builder(default)]
+pub struct World {
+    pub lights: Vec<PointLight>,
+    pub objects: Vec<Shape>,
+}
+
+impl World {
+    /// Creates a world suitable for use across multiple tests in from the book.
+    pub fn test_world() -> World {
+        let light = PointLight::new(Tuple::point(-10., 10., -10.), WHITE);
+        let mut s1 = Shape::sphere();
+        s1.material = Material {
+            color: [0.8, 1., 0.6].into(),
+            diffuse: 0.7,
+            specular: 0.2,
+            ..Material::default()
+        };
+        let mut s2 = Shape::sphere();
+        s2.set_transform(Matrix4x4::scaling(0.5, 0.5, 0.5));
+        World {
+            lights: vec![light],
+            objects: vec![s1, s2],
+        }
+    }
+
+    /// Intersects the ray with this world.
+    pub fn intersect(&self, r: &Ray) -> Intersections {
+        let mut xs: Vec<_> = self.objects.iter().flat_map(|o| intersect(o, r)).collect();
+        xs.sort_by(|i1, i2| {
+            i1.t.partial_cmp(&i2.t)
+                .expect("an intersection has a t value that is NaN")
+        });
+        Intersections::new(xs)
+    }
+
+    /// Compute shaded value for given precomputation.
+    pub fn shade_hit(&self, comps: &PrecomputedData, remaining: usize) -> Color {
+        let surface = self
+            .lights
+            .iter()
+            .fold(Color::new(0., 0., 0.), |acc, light| {
+                let shadowed = self.is_shadowed(comps.over_point, light);
+                let surface = lighting(
+                    &comps.object.material,
+                    comps.object,
+                    light,
+                    comps.over_point,
+                    comps.eyev,
+                    comps.normalv,
+                    shadowed,
+                );
+                acc + surface
+            });
+        let reflected = self.reflected_color(comps, remaining);
+        let refracted = self.refracted_color(comps, remaining);
+        let material = &comps.object.material;
+        if material.reflective > 0. && material.transparency > 0. {
+            let reflectance = schlick(comps);
+            surface + reflected * reflectance + refracted * (1. - reflectance)
+        } else {
+            surface + reflected + refracted
+        }
+    }
+    /// Compute color for given ray fired at the world.
+    pub fn color_at(&self, r: &Ray, remaining: usize) -> Color {
+        let xs = self.intersect(r);
+        match xs.hit() {
+            Some(hit) => {
+                let comps = prepare_computations(hit, r, &xs);
+                self.shade_hit(&comps, remaining)
+            }
+            None => BLACK,
+        }
+    }
+
+    /// Determine if point in world is in a shadow.
+    pub fn is_shadowed(&self, point: Tuple, light: &PointLight) -> bool {
+        let v = light.position - point;
+        let distance = v.magnitude();
+        let direction = v.normalize();
+
+        let r = Ray::new(point, direction);
+        let intersections = self.intersect(&r);
+        if let Some(h) = intersections.hit() {
+            return h.t < distance;
+        }
+        false
+    }
+
+    /// Compute reflected color for the given precomputation.
+    pub fn reflected_color(&self, comps: &PrecomputedData, remaining: usize) -> Color {
+        if remaining == 0 {
+            return BLACK;
+        }
+        if comps.object.material.reflective == 0. {
+            return BLACK;
+        }
+        // Fire reflected ray to figure out color.
+        let reflect_ray = Ray::new(comps.over_point, comps.reflectv);
+        let color = self.color_at(&reflect_ray, remaining - 1);
+        color * comps.object.material.reflective
+    }
+
+    /// Compute refracted color for the given precomputation.
+    pub fn refracted_color(&self, comps: &PrecomputedData, remaining: usize) -> Color {
+        if remaining == 0 {
+            return BLACK;
+        }
+        if comps.object.material.transparency == 0. {
+            return BLACK;
+        }
+        // Find the ratio of the first index of refraction to the secon
+        // (This is inverted from the definition of Snell's Law.)
+        let n_ratio = comps.n1 / comps.n2;
+
+        // cos(theta_i) is the same as the dot product of the two vectors
+        // TODO(wathiede): is cosine faster than doc productings?
+        let cos_i = dot(comps.eyev, comps.normalv);
+
+        // Find the sin(theta_t)^2 via trigonometric identity.
+        let sin2_t = n_ratio * n_ratio * (1. - cos_i * cos_i);
+
+        if sin2_t > 1. {
+            // Total internal reflection.
+            return BLACK;
+        }
+        // Find cos(theta_t) via trigonometric identity.
+        let cos_t = (1. - sin2_t).sqrt();
+        // Compute the direction of the refracted ray.
+        let direction = comps.normalv * (n_ratio * cos_i - cos_t) - comps.eyev * n_ratio;
+        // Create the refracted ray.
+        let refract_ray = Ray::new(comps.under_point, direction);
+        // Find he color of the refracted ray, making sure to multiply by the transparency value to
+        // account for any opacity.
+        self.color_at(&refract_ray, remaining - 1) * comps.object.material.transparency
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::{
+        float::consts::SQRT_2,
+        intersections::{prepare_computations, Intersection, Intersections},
+        lights::PointLight,
+        materials::MaterialBuilder,
+        matrices::translation,
+        patterns::test_pattern,
+        rays::Ray,
+        shapes::{plane, sphere, Shape, ShapeBuilder},
+        tuples::{point, vector},
+        world::{World, WorldBuilder},
+        Float, BLACK, WHITE,
+    };
+
+    mod intersect {
+        use super::*;
+
+        #[test]
+        fn intersection_with_test_world() {
+            let w = World::test_world();
+            let r = Ray::new(point(0., 0., -5.), vector(0., 0., 1.));
+            let xs = w.intersect(&r);
+            assert_eq!(xs.len(), 4);
+            assert_eq!(xs[0].t, 4.);
+            assert_eq!(xs[1].t, 4.5);
+            assert_eq!(xs[2].t, 5.5);
+            assert_eq!(xs[3].t, 6.);
+        }
+    }
+    mod world {
+        use super::*;
+
+        #[test]
+        fn default_world() {
+            let w = World::default();
+            assert!(w.objects.is_empty());
+            assert_eq!(w.lights.len(), 0);
+        }
+        #[test]
+        fn test_world() {
+            let w = World::test_world();
+            assert_eq!(w.objects.len(), 2);
+            assert!(!w.lights.is_empty());
+        }
+    }
+    mod shade_hit {
+        use super::*;
+
+        #[test]
+        fn shading_an_intersection() {
+            // Shading an intersection.
+            let w = World::test_world();
+            let r = Ray::new(point(0., 0., -5.), vector(0., 0., 1.));
+            let s = &w.objects[0];
+            let xs = Intersections::from(Intersection::new(4., &s));
+            let comps = prepare_computations(&xs[0], &r, &xs);
+            let c = w.shade_hit(&comps, 1);
+            assert_eq!(c, [0.38066, 0.47583, 0.2855].into());
+        }
+        #[test]
+        fn shading_an_intersection_from_inside() {
+            // Shading an intersection from the inside.
+            let mut w = World::test_world();
+            w.lights = vec![PointLight::new(point(0., 0.25, 0.), WHITE)];
+            let r = Ray::new(point(0., 0., 0.), vector(0., 0., 1.));
+            let s = &w.objects[1];
+            let xs = Intersections::from(Intersection::new(0.5, &s));
+            let comps = prepare_computations(&xs[0], &r, &xs);
+            let c = w.shade_hit(&comps, 1);
+            assert_eq!(c, [0.90498, 0.90498, 0.90498].into());
+        }
+        #[test]
+        fn shading_an_intersection_in_shadow() {
+            // Shading with an intersection in shadow.
+            let mut w = World::default();
+            w.lights = vec![PointLight::new(point(0., 0., -10.), WHITE)];
+            let s1 = Shape::sphere();
+            let mut s2 = Shape::sphere();
+            s2.set_transform(translation(0., 0., 10.));
+            w.objects = vec![s1, s2.clone()];
+            let r = Ray::new(point(0., 0., 5.), vector(0., 0., 1.));
+            let xs = Intersections::from(Intersection::new(4., &s2));
+            let comps = prepare_computations(&xs[0], &r, &xs);
+            let c = w.shade_hit(&comps, 1);
+            assert_eq!(c, [0.1, 0.1, 0.1].into());
+        }
+        #[test]
+        fn shading_with_a_reflective_material() -> Result<(), Box<dyn std::error::Error>> {
+            // Shading with a reflective material.
+            let mut w = World::test_world();
+            let shape = ShapeBuilder::plane()
+                .material(MaterialBuilder::default().reflective(0.5).build()?)
+                .transform(translation(0., -1., 0.))
+                .build()?;
+            w.objects.push(shape.clone());
+            let r = Ray::new(
+                point(0., 0., -3.),
+                vector(0., -(2 as Float).sqrt() / 2., (2 as Float).sqrt() / 2.),
+            );
+            let xs = Intersections::from(Intersection::new((2 as Float).sqrt(), &shape));
+            let comps = prepare_computations(&xs[0], &r, &xs);
+            let c = w.shade_hit(&comps, 1);
+            assert_eq!(c, [0.87676, 0.92434, 0.82917].into());
+            Ok(())
+        }
+        #[test]
+        fn shading_with_a_transparent_material() -> Result<(), Box<dyn std::error::Error>> {
+            // shade_hit() with a transparent material.
+            let mut w = World::test_world();
+            let floor = plane()
+                .transform(translation(0., -1., 0.))
+                .material(
+                    MaterialBuilder::default()
+                        .transparency(0.5)
+                        .refractive_index(1.5)
+                        .build()?,
+                )
+                .build()?;
+            w.objects.push(floor.clone());
+            let ball = sphere()
+                .material(
+                    MaterialBuilder::default()
+                        .color([1., 0., 0.])
+                        .ambient(0.5)
+                        .build()?,
+                )
+                .transform(translation(0., -3.5, -0.5))
+                .build()?;
+            w.objects.push(ball);
+            let r = Ray::new(
+                point(0., 0., -3.),
+                vector(0., -(2 as Float).sqrt() / 2., (2 as Float).sqrt() / 2.),
+            );
+            let xs = Intersections::new(vec![Intersection::new((2 as Float).sqrt(), &floor)]);
+            let comps = prepare_computations(&xs[0], &r, &xs);
+            let c = w.shade_hit(&comps, 5);
+            assert_eq!(c, [0.93642, 0.68642, 0.68643].into());
+            Ok(())
+        }
+        #[test]
+        fn reflective_transparent_material() -> Result<(), Box<dyn std::error::Error>> {
+            let mut w = World::test_world();
+            let floor = plane()
+                .transform(translation(0., -1., 0.))
+                .material(
+                    MaterialBuilder::default()
+                        .reflective(0.5)
+                        .transparency(0.5)
+                        .refractive_index(1.5)
+                        .build()?,
+                )
+                .build()?;
+            w.objects.push(floor.clone());
+            let ball = sphere()
+                .transform(translation(0., -3.5, -0.5))
+                .material(
+                    MaterialBuilder::default()
+                        .color([1., 0., 0.])
+                        .ambient(0.5)
+                        .build()?,
+                )
+                .build()?;
+            w.objects.push(ball);
+            let r = Ray::new(point(0., 0., -3.), vector(0., -SQRT_2 / 2., SQRT_2 / 2.));
+            let xs = Intersections::new(vec![Intersection::new(SQRT_2, &floor)]);
+            let comps = prepare_computations(&xs[0], &r, &xs);
+            let color = w.shade_hit(&comps, 5);
+            assert_eq!(color, [0.93391, 0.69643, 0.69243].into());
+            Ok(())
+        }
+    }
+    mod color_at {
+        use super::*;
+
+        #[test]
+        fn color_when_ray_misses() {
+            // The color when a ray misses.
+            let w = World::test_world();
+            let r = Ray::new(point(0., 0., -5.), vector(0., 1., 0.));
+            let c = w.color_at(&r, 1);
+            assert_eq!(c, BLACK);
+        }
+        #[test]
+        fn color_when_ray_hits() {
+            // The color when a ray hits.
+            let w = World::test_world();
+            let r = Ray::new(point(0., 0., -5.), vector(0., 0., 1.));
+            let c = w.color_at(&r, 1);
+            assert_eq!(c, [0.38066, 0.47583, 0.2855].into());
+        }
+        #[test]
+        fn color_with_an_intersection_behind_ray() {
+            // The color with an intersection behind the ray.
+            let w = {
+                let mut w = World::test_world();
+                let mut outer = &mut w.objects[0];
+                outer.material.ambient = 1.;
+                let inner = &mut w.objects[1];
+                inner.material.ambient = 1.;
+                w
+            };
+            let r = Ray::new(point(0., 0., 0.75), vector(0., 0., -1.));
+            let c = w.color_at(&r, 1);
+            // inner.material.color is WHITE
+            assert_eq!(c, WHITE);
+        }
+        #[test]
+        fn ensure_mutually_reflective_surfaces_terminate() -> Result<(), Box<dyn std::error::Error>>
+        {
+            // Ensure mutually reflective surfaces don't infinitely recurse.
+            let lower = ShapeBuilder::plane()
+                .material(MaterialBuilder::default().reflective(1.).build()?)
+                .transform(translation(0., -1., 0.))
+                .build()?;
+            let upper = ShapeBuilder::plane()
+                .material(MaterialBuilder::default().reflective(1.).build()?)
+                .transform(translation(0., 1., 0.))
+                .build()?;
+            let w = WorldBuilder::default()
+                .lights(vec![PointLight::new(point(0., 0., 0.), WHITE)])
+                .objects(vec![lower, upper])
+                .build()?;
+            let r = Ray::new(point(0., 0., 0.), vector(0., 1., 0.));
+            // This should complete without stack overflow.
+            w.color_at(&r, 1);
+            Ok(())
+        }
+    }
+    mod is_shadowed {
+        use super::*;
+
+        #[test]
+        fn no_shadow_when_nothing_collinear_with_point_and_light() {
+            // There is no shadow when nothing is collinear with point and light.
+            let w = World::test_world();
+            let light = &w.lights[0];
+
+            let p = point(0., 10., 0.);
+            assert_eq!(w.is_shadowed(p, light), false);
+        }
+        #[test]
+        fn shadow_when_object_between_point_and_light() {
+            // The shadow when an object is between the point and the light.
+            let w = World::test_world();
+            let light = &w.lights[0];
+
+            let p = point(10., -10., 10.);
+            assert_eq!(w.is_shadowed(p, light), true);
+        }
+
+        #[test]
+        fn no_shadow_when_object_behind_light() {
+            // There is no shadow when an object is behind the light.
+            let w = World::test_world();
+            let light = &w.lights[0];
+
+            let p = point(-20., 20., -20.);
+            assert_eq!(w.is_shadowed(p, light), false);
+        }
+        #[test]
+        fn no_shadow_when_object_behind_point() {
+            // There is no shadow when an object is behind the point.
+            let w = World::test_world();
+            let light = &w.lights[0];
+
+            let p = point(-2., 2., -2.);
+            assert_eq!(w.is_shadowed(p, light), false);
+        }
+    }
+
+    mod reflected_color {
+        use super::*;
+
+        #[test]
+        fn reflected_color_for_nonreflective_material() {
+            // The reflected color for a nonreflective material.
+            let r = Ray::new(point(0., 0., 0.), vector(0., 0., 1.));
+            let mut w = World::test_world();
+            w.objects[1].material.ambient = 1.;
+            let xs = Intersections::from(Intersection::new(1., &w.objects[1]));
+            let comps = prepare_computations(&xs[0], &r, &xs);
+            let c = w.reflected_color(&comps, 1);
+            assert_eq!(c, BLACK);
+        }
+        #[test]
+        fn reflected_color_for_reflective_material() -> Result<(), Box<dyn std::error::Error>> {
+            // The reflected color for a reflective material.
+            let mut w = World::test_world();
+            let shape = ShapeBuilder::plane()
+                .material(MaterialBuilder::default().reflective(0.5).build()?)
+                .transform(translation(0., -1., 0.))
+                .build()?;
+            w.objects.push(shape.clone());
+            let r = Ray::new(
+                point(0., 0., -3.),
+                vector(0., -(2 as Float).sqrt() / 2., (2 as Float).sqrt() / 2.),
+            );
+            let xs = Intersections::from(Intersection::new((2 as Float).sqrt(), &shape));
+            let comps = prepare_computations(&xs[0], &r, &xs);
+            let c = w.reflected_color(&comps, 1);
+            assert_eq!(c, [0.19033, 0.23791, 0.14274].into());
+            Ok(())
+        }
+        #[test]
+        fn reflected_color_at_maximum_recursion_depth() -> Result<(), Box<dyn std::error::Error>> {
+            // The reflected color at the maximum recursion depth.
+            let mut w = World::test_world();
+            let shape = ShapeBuilder::plane()
+                .material(MaterialBuilder::default().reflective(0.5).build()?)
+                .transform(translation(0., -1., 0.))
+                .build()?;
+            w.objects.push(shape.clone());
+            let r = Ray::new(
+                point(0., 0., -3.),
+                vector(0., -(2 as Float).sqrt() / 2., (2 as Float).sqrt() / 2.),
+            );
+            let xs = Intersections::from(Intersection::new((2 as Float).sqrt(), &shape));
+            let comps = prepare_computations(&xs[0], &r, &xs);
+            let _ = w.reflected_color(&comps, 0);
+            // Just needs to get here without infinite recursion.
+
+            Ok(())
+        }
+    }
+    mod refracted_color {
+        use super::*;
+
+        #[test]
+        fn refracted_color_with_opaque_surface() {
+            // The refracted color with an opaque surface.
+            let w = World::test_world();
+            let shape = &w.objects[0];
+            let r = Ray::new(point(0., 0., -5.), vector(0., 0., 1.));
+            let xs = Intersections::new(vec![
+                Intersection::new(4., &shape),
+                Intersection::new(6., &shape),
+            ]);
+            let comps = prepare_computations(&xs[0], &r, &xs);
+            let c = w.refracted_color(&comps, 5);
+            assert_eq!(c, BLACK);
+        }
+        #[test]
+        fn refracted_color_at_maximum_recursion_depth() {
+            // The refracted color at the maximum recursive depth.
+            let mut w = World::test_world();
+            w.objects[0].material.transparency = 1.0;
+            w.objects[0].material.refractive_index = 1.5;
+            let shape = &w.objects[0];
+            let r = Ray::new(point(0., 0., -5.), vector(0., 0., 1.));
+            let xs = Intersections::new(vec![
+                Intersection::new(4., &shape),
+                Intersection::new(6., &shape),
+            ]);
+            let comps = prepare_computations(&xs[0], &r, &xs);
+            let c = w.refracted_color(&comps, 0);
+            assert_eq!(c, BLACK);
+        }
+        #[test]
+        fn refracted_color_under_total_internal_reflection() {
+            // The refracted color under total internal reflection.
+            let mut w = World::test_world();
+            w.objects[0].material.transparency = 1.0;
+            w.objects[0].material.refractive_index = 1.5;
+            let shape = &w.objects[0];
+            let r = Ray::new(point(0., 0., (2 as Float).sqrt() / 2.), vector(0., 1., 0.));
+            let xs = Intersections::new(vec![
+                Intersection::new(-(2 as Float).sqrt() / 2., &shape),
+                Intersection::new((2 as Float).sqrt() / 2., &shape),
+            ]);
+            let comps = prepare_computations(&xs[1], &r, &xs);
+            let c = w.refracted_color(&comps, 5);
+            assert_eq!(c, BLACK);
+        }
+        #[test]
+        fn refracted_color_with_a_refracted_ray() -> Result<(), Box<dyn std::error::Error>> {
+            // The refracted color with a refracted ray.
+            let mut w = World::test_world();
+            w.objects[0].material.ambient = 1.;
+            w.objects[0].material.color = test_pattern().build()?;
+
+            w.objects[1].material.transparency = 1.;
+            w.objects[1].material.refractive_index = 1.5;
+
+            let r = Ray::new(point(0., 0., 0.1), vector(0., 1., 0.));
+            let a = &w.objects[0];
+            let b = &w.objects[1];
+            let xs = Intersections::new(vec![
+                Intersection::new(-0.9899, &a),
+                Intersection::new(-0.4899, &b),
+                Intersection::new(0.4899, &b),
+                Intersection::new(0.9899, &a),
+            ]);
+            let comps = prepare_computations(&xs[2], &r, &xs);
+            let c = w.refracted_color(&comps, 5);
+            assert_eq!(c, [0., 0.99887, 0.04721].into());
+
+            Ok(())
+        }
+    }
+}
--- a/rtiow/Cargo.lock
+++ b/rtiow/Cargo.lock
--- a/rtiow/Cargo.toml
+++ b/rtiow/Cargo.toml
@@ -1,36 +1,15 @@
-[package]
-authors = ["Bill Thiede <rust@xinu.tv>"]
-edition = "2018"
-name = "rtiow"
-version = "0.1.0"
+[workspace]
+resolver = "2"

-[[bench]]
-harness = false
-name = "spheres"
-
-[dependencies]
-actix-web = "0.7.8"
-askama = "0.7.1"
-chrono = "*"
-core_affinity = "0.5"
-cpuprofiler = { version = "0.0.3", optional = true }
-image = "0.19.0"
-lazy_static = "1.1.0"
-log = "0.4.5"
-num_cpus = "1.8.0"
-rand = "0.5.5"
-serde = "1.0.79"
-serde_derive = "1.0.79"
-serde_json = "1.0.41"
-stderrlog = "0.4.1"
-structopt = "0.2.10"
-
-[dev-dependencies]
-criterion = "0.2"
-
-[profile]
+members = [
+  "noise_explorer",
+  "noise_explorer_warp",
+  "renderer",
+  "tracer",
+  "vec3",
+]
 [profile.release]
 debug = true

-[features]
-profile = ["cpuprofiler"]
+[profile.dev]
+opt-level = 3 
--- a/rtiow/benches/spheres.rs
+++ b/rtiow/benches/spheres.rs
@@ -1,37 +0,0 @@
-#[macro_use]
-extern crate criterion;
-
-use criterion::Criterion;
-use criterion::ParameterizedBenchmark;
-
-use rtiow::hitable::Hit;
-use rtiow::material::Lambertian;
-use rtiow::ray::Ray;
-use rtiow::sphere::Sphere;
-use rtiow::texture::ConstantTexture;
-use rtiow::vec3::Vec3;
-
-fn criterion_benchmark(c: &mut Criterion) {
-    let sphere = Sphere::new(
-        Vec3::new(0., 0., 0.),
-        1.,
-        Lambertian::new(ConstantTexture::new([1., 0., 0.])),
-    );
-    let rays = vec![
-        // Hit
-        Ray::new([0., 0., -2.], [0., 0., 1.], 0.),
-        // Miss
-        Ray::new([0., 0., -2.], [0., 0., -1.], 0.),
-    ];
-    c.bench(
-        "sphere",
-        ParameterizedBenchmark::new(
-            "Sphere",
-            move |b, r| b.iter(|| sphere.hit(*r, 0., 1.)),
-            rays,
-        ),
-    );
-}
-
-criterion_group!(benches, criterion_benchmark);
-criterion_main!(benches);
--- a/rtiow/build_all_features.sh
+++ b/rtiow/build_all_features.sh
@@ -1,4 +1,4 @@
 set -e
 export RUSTFLAGS="-D warnings"
-cargo build
-cargo build --features=profile
+cargo build --all
+cargo build --all --features=profile
--- a/rtiow/noise_explorer/Cargo.toml
+++ b/rtiow/noise_explorer/Cargo.toml
@@ -0,0 +1,20 @@
+[package]
+name = "noise_explorer"
+version = "0.1.0"
+authors = ["Bill Thiede <git@xinu.tv>"]
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+actix-web = "0.7.19"
+askama = "0.7.2"
+image = "0.22.5"
+log = "0.4.17"
+rand = "0.8.5"
+rand_xorshift = "0.3.0"
+renderer = { path = "../renderer" }
+serde = "1.0.152"
+serde_derive = "1.0.152"
+stderrlog = "0.4.3"
+structopt = "0.2.18"
--- a/rtiow/noise_explorer/rustfmt.toml
+++ b/rtiow/noise_explorer/rustfmt.toml
@@ -0,0 +1,2 @@
+imports_granularity = "Crate"
+format_code_in_doc_comments = true
--- a/rtiow/noise_explorer/src/Dockerfile
+++ b/rtiow/noise_explorer/src/Dockerfile
--- a/rtiow/noise_explorer/src/config.dbuild
+++ b/rtiow/noise_explorer/src/config.dbuild
--- a/rtiow/noise_explorer/src/main.rs
+++ b/rtiow/noise_explorer/src/main.rs
@@ -1,56 +1,26 @@
-extern crate actix_web;
-extern crate askama;
-#[macro_use]
-extern crate log;
-extern crate image;
-extern crate rand;
-#[macro_use]
-extern crate serde_derive;
-extern crate serde;
-extern crate stderrlog;
+use std::{fmt, time::SystemTime};

-extern crate structopt;
-
-extern crate rtiow;
-
-use std::fmt;
-use std::time::SystemTime;
-
-use actix_web::http;
-use actix_web::middleware;
-use actix_web::server;
-use actix_web::App;
-use actix_web::HttpRequest;
-use actix_web::HttpResponse;
-use actix_web::Path;
-use actix_web::Query;
-use actix_web::Result;
+use actix_web::{http, middleware, server, App, HttpRequest, HttpResponse, Path, Query, Result};
 use askama::Template;
+use log::info;
 use rand::SeedableRng;
-use rand::XorShiftRng;
+use rand_xorshift::XorShiftRng;
+use serde_derive::Deserialize;
 use structopt::StructOpt;

-use rtiow::noise;
-use rtiow::noise::lode::Lode;
-use rtiow::noise::perlin::Perlin;
-use rtiow::noise::NoiseType;
-use rtiow::texture::NoiseTexture;
-use rtiow::texture::Texture;
-use rtiow::vec3::Vec3;
+use renderer::{
+    noise,
+    noise::{lode::Lode, perlin::Perlin, NoiseType},
+    texture::{NoiseTexture, Texture},
+    vec3::Vec3,
+};

-#[derive(Debug, StructOpt)]
+#[derive(StructOpt)]
 #[structopt(name = "noise_explorer", about = "CLI for exploring Perlin noise")]
 struct Opt {
    /// HTTP listen address
    #[structopt(long = "addr", default_value = "0.0.0.0:8889")]
    pub addr: String,
-
-    /// Width of noise images
-    #[structopt(short = "w", long = "width", default_value = "128")]
-    pub width: u32,
-    /// Height of noise images
-    #[structopt(short = "h", long = "height", default_value = "128")]
-    pub height: u32,
 }

 #[derive(Copy, Clone, Debug, Deserialize, PartialEq)]
@@ -75,11 +45,6 @@ struct OptionalParams {
    pixel_scale: f32,
 }

-#[derive(Debug, Deserialize)]
-struct NoiseSourceParam {
-    noise_source: NoiseSource,
-}
-
 #[derive(Debug, Deserialize)]
 struct NoiseParams {
    width: u32,
@@ -151,13 +116,15 @@ fn render_noise(noise_params: NoiseParams) -> image::GrayImage {
        .optional
        .unwrap_or(OptionalParams { pixel_scale: 1.0 });
    const SEED: [u8; 16] = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15];
-    let rng: &mut XorShiftRng = &mut SeedableRng::from_seed(SEED);
+    let mut rng: XorShiftRng = SeedableRng::from_seed(SEED);
    let mut img = image::GrayImage::new(noise_params.width, noise_params.height);
    let tex: NoiseTexture<Box<dyn noise::NoiseSource>> = match noise_params.noise_source {
        NoiseSource::Perlin => {
-            NoiseTexture::new(Box::new(Perlin::new(rng)), noise_params.noise_type)
+            NoiseTexture::new(Box::new(Perlin::new(&mut rng)), noise_params.noise_type)
+        }
+        NoiseSource::Lode => {
+            NoiseTexture::new(Box::new(Lode::new(&mut rng)), noise_params.noise_type)
        }
-        NoiseSource::Lode => NoiseTexture::new(Box::new(Lode::new(rng)), noise_params.noise_type),
    };
    info!("{:?}", noise_params);

@@ -364,7 +331,7 @@ fn build_specimens(
 }

 fn style(_req: &HttpRequest) -> Result<HttpResponse> {
-    let bytes = include_bytes!("../../templates/style.css");
+    let bytes = include_bytes!("../templates/style.css");
    Ok(HttpResponse::Ok().content_type("text/css").body(&bytes[..]))
 }

@@ -428,7 +395,6 @@ fn noise_marble(
    np: Path<NoiseParamsMarble>,
    optional: Option<Query<OptionalParams>>,
 ) -> Result<HttpResponse> {
-    info!("optional {:?}", optional);
    noise(NoiseParams {
        width: np.width,
        height: np.height,
@@ -477,16 +443,9 @@ fn main() -> Result<(), std::io::Error> {
 mod tests {
    use std::str;

-    use actix_web::http::Method;
-    use actix_web::test::TestServer;
-    use actix_web::HttpMessage;
-    use actix_web::Path;
-    use actix_web::Query;
+    use actix_web::{http::Method, test::TestServer, HttpMessage, Path, Query};

-    use super::NoiseParamsMarble;
-    use super::NoiseParamsScale;
-    use super::NoiseParamsTurbulence;
-    use super::OptionalParams;
+    use super::{NoiseParamsMarble, NoiseParamsScale, NoiseParamsTurbulence, OptionalParams};

    #[test]
    fn noise_param_from_req() {
--- a/rtiow/noise_explorer/templates/index.html
+++ b/rtiow/noise_explorer/templates/index.html
--- a/rtiow/noise_explorer/templates/style.css
+++ b/rtiow/noise_explorer/templates/style.css
--- a/rtiow/noise_explorer_warp/Cargo.toml
+++ b/rtiow/noise_explorer_warp/Cargo.toml
@@ -0,0 +1,19 @@
+[package]
+name = "noise_explorer_warp"
+version = "0.1.0"
+authors = ["Bill Thiede <git@xinu.tv>"]
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+askama = "0.7.2"
+image = "0.22.5"
+log = "0.4.17"
+rand = "0.5.6"
+renderer = { path = "../renderer" }
+serde = "1.0.152"
+serde_derive = "1.0.152"
+stderrlog = "0.4.3"
+structopt = "0.2.18"
+warp = "0.1.23"
--- a/rtiow/noise_explorer_warp/rustfmt.toml
+++ b/rtiow/noise_explorer_warp/rustfmt.toml
@@ -0,0 +1,2 @@
+imports_granularity = "Crate"
+format_code_in_doc_comments = true
--- a/rtiow/noise_explorer_warp/src/main.rs
+++ b/rtiow/noise_explorer_warp/src/main.rs
@@ -0,0 +1,3 @@
+fn main() {
+    println!("Hello, world!");
+}
--- a/rtiow/renderer/Cargo.toml
+++ b/rtiow/renderer/Cargo.toml
@@ -0,0 +1,42 @@
+[package]
+name = "renderer"
+version = "0.1.0"
+authors = ["Bill Thiede <git@xinu.tv>"]
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+[[bench]]
+harness = false
+name = "spheres"
+[[bench]]
+harness = false
+name = "aabb"
+
+[dependencies]
+chrono = "*"
+core_affinity = "0.5"
+cpuprofiler = { version = "0.0.3", optional = true }
+image = "0.22.5"
+lazy_static = "1.4.0"
+log = "0.4.17"
+num_cpus = "1.15.0"
+rand = "0.8.5"
+serde = "1.0.152"
+serde_derive = "1.0.152"
+serde_json = "1.0.93"
+structopt = "0.2.18"
+vec3 = {path = "../vec3"}
+stl = {path = "../../../stl"}
+strum = { version = "0.24.1", features = ["derive"] }
+strum_macros = "0.24.3"
+thiserror = "1.0.38"
+tev_client = "0.5.2"
+#stl = {git = "https://git-private.z.xinu.tv/wathiede/stl"}
+
+[dev-dependencies]
+criterion = "0.4"
+pretty_assertions = "1.3.0"
+proptest = "1.1.0"
+
+[features]
+profile = ["cpuprofiler"]
--- a/rtiow/renderer/benches/aabb.rs
+++ b/rtiow/renderer/benches/aabb.rs
@@ -0,0 +1,47 @@
+use criterion::*;
+use renderer::{aabb::AABB, ray::Ray};
+
+fn bench(c: &mut Criterion) {
+    let bb = AABB::new([1., -1., -1.], [3., 1., 1.]);
+    let r_hit = Ray::new([0., 0., 0.], [1., 0., 0.], 0.);
+    let r_miss = Ray::new([0., 0., 0.], [-1., 0., 0.], 0.);
+    let t_min = 0.001;
+    let t_max = f32::MAX;
+
+    let mut group = c.benchmark_group("aabb");
+    group.throughput(Throughput::Elements(1));
+    group.bench_with_input(BenchmarkId::new("hit_naive", "r_hit"), &r_hit, |b, r| {
+        b.iter(|| bb.hit_naive(*r, t_min, t_max))
+    });
+    group.bench_with_input(BenchmarkId::new("hit2", "r_hit"), &r_hit, |b, r| {
+        b.iter(|| bb.hit2(*r, t_min, t_max))
+    });
+    //group.bench_with_input(BenchmarkId::new("hit_precompute", "r_hit"), &r_hit, |b, r| { b.iter(|| bb.hit_precompute(*r, t_min, t_max)) });
+    group.bench_with_input(BenchmarkId::new("hit_fast", "r_hit"), &r_hit, |b, r| {
+        b.iter(|| bb.hit_fast(*r, t_min, t_max))
+    });
+    #[cfg(target_arch = "x86_64")]
+    group.bench_with_input(BenchmarkId::new("hit_simd", "r_hit"), &r_hit, |b, r| {
+        b.iter(|| bb.hit_simd(*r, t_min, t_max))
+    });
+
+    group.bench_with_input(BenchmarkId::new("hit_naive", "r_miss"), &r_miss, |b, r| {
+        b.iter(|| bb.hit_naive(*r, t_min, t_max))
+    });
+    group.bench_with_input(BenchmarkId::new("hit2", "r_miss"), &r_miss, |b, r| {
+        b.iter(|| bb.hit2(*r, t_min, t_max))
+    });
+    //group.bench_with_input(BenchmarkId::new("hit_precompute", "r_miss"), &r_miss, |b, r| { b.iter(|| bb.hit_precompute(*r, t_min, t_max)) });
+    group.bench_with_input(BenchmarkId::new("hit_fast", "r_miss"), &r_miss, |b, r| {
+        b.iter(|| bb.hit_fast(*r, t_min, t_max))
+    });
+    #[cfg(target_arch = "x86_64")]
+    group.bench_with_input(BenchmarkId::new("hit_simd", "r_miss"), &r_miss, |b, r| {
+        b.iter(|| bb.hit_simd(*r, t_min, t_max))
+    });
+
+    group.finish();
+}
+
+criterion_group!(benches, bench);
+criterion_main!(benches);
--- a/rtiow/renderer/benches/spheres.rs
+++ b/rtiow/renderer/benches/spheres.rs
@@ -0,0 +1,32 @@
+use criterion::*;
+
+use renderer::{
+    hitable::Hit, material::Lambertian, ray::Ray, sphere::Sphere, texture::ConstantTexture,
+    vec3::Vec3,
+};
+
+fn criterion_benchmark(c: &mut Criterion) {
+    let sphere = Sphere::new(
+        Vec3::new(0., 0., 0.),
+        1.,
+        Lambertian::new(ConstantTexture::new([1., 0., 0.])),
+    );
+    let rays = vec![
+        // Hit
+        Ray::new([0., 0., -2.], [0., 0., 1.], 0.),
+        // Miss
+        Ray::new([0., 0., -2.], [0., 0., -1.], 0.),
+    ];
+    let mut group = c.benchmark_group("sphere");
+    group.throughput(Throughput::Elements(1));
+    group.bench_with_input(BenchmarkId::new("Sphere", "hit"), &rays[0], |b, r| {
+        b.iter(|| sphere.hit(*r, 0., 1.))
+    });
+    group.bench_with_input(BenchmarkId::new("Sphere", "miss"), &rays[1], |b, r| {
+        b.iter(|| sphere.hit(*r, 0., 1.))
+    });
+    group.finish()
+}
+
+criterion_group!(benches, criterion_benchmark);
+criterion_main!(benches);
--- a/rtiow/renderer/images/envmap.jpg
+++ b/rtiow/renderer/images/envmap.jpg
--- a/rtiow/renderer/images/world.jpg
+++ b/rtiow/renderer/images/world.jpg
--- a/rtiow/renderer/rustfmt.toml
+++ b/rtiow/renderer/rustfmt.toml
@@ -0,0 +1,2 @@
+imports_granularity = "Crate"
+format_code_in_doc_comments = true
--- a/rtiow/renderer/src/aabb.rs
+++ b/rtiow/renderer/src/aabb.rs
@@ -0,0 +1,377 @@
+use std::fmt;
+
+use crate::{ray::Ray, vec3::Vec3};
+
+#[derive(Default, Copy, Clone, PartialEq)]
+pub struct AABB {
+    bounds: [Vec3; 2],
+}
+
+impl fmt::Display for AABB {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "({})-({})", self.bounds[0], self.bounds[1])
+    }
+}
+
+fn min(x: f32, y: f32) -> f32 {
+    if x < y {
+        x
+    } else {
+        y
+    }
+}
+
+fn max(x: f32, y: f32) -> f32 {
+    if x > y {
+        x
+    } else {
+        y
+    }
+}
+
+impl fmt::Debug for AABB {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(
+            f,
+            "AABB: <{} - {}> Vol: {} Area: {}",
+            self.bounds[0],
+            self.bounds[1],
+            self.volume(),
+            self.area()
+        )
+    }
+}
+
+impl AABB {
+    // Create AABB with min = f32::MAX and max = -f32::MAX. It is expected the caller will use grow to create
+    // a vaild AABB.
+    pub fn infinite() -> AABB {
+        AABB {
+            bounds: [Vec3::from(f32::MAX), Vec3::from(f32::MIN)],
+        }
+    }
+    pub fn new<V: Into<Vec3>>(min: V, max: V) -> AABB {
+        let min: Vec3 = min.into();
+        let max: Vec3 = max.into();
+        assert!(min.x <= max.x);
+        assert!(min.y <= max.y);
+        assert!(min.z <= max.z);
+        AABB { bounds: [min, max] }
+    }
+
+    pub fn area(&self) -> f32 {
+        if self.max().x == f32::MIN || self.min().x == f32::MAX {
+            return 0.;
+        }
+        let e = self.max() - self.min();
+        let v = e.x * e.y + e.y * e.z + e.z * e.x;
+        if v.is_finite() {
+            v
+        } else {
+            0.
+        }
+    }
+    pub fn volume(&self) -> f32 {
+        if self.max().x == f32::MIN || self.min().x == f32::MAX {
+            return 0.;
+        }
+        let v = (self.min().x - self.max().x).abs()
+            * (self.min().y - self.max().y).abs()
+            * (self.min().z - self.max().z).abs();
+        if v.is_finite() {
+            v
+        } else {
+            0.
+        }
+    }
+
+    pub fn grow(&mut self, v: Vec3) {
+        self.bounds[0] = vec3::min(self.bounds[0], v);
+        self.bounds[1] = vec3::max(self.bounds[1], v);
+    }
+
+    pub fn longest_axis(&self) -> usize {
+        let xd = (self.min().x - self.max().x).abs();
+        let yd = (self.min().y - self.max().y).abs();
+        let zd = (self.min().z - self.max().z).abs();
+
+        if xd >= yd && xd >= zd {
+            return 0;
+        }
+        if yd >= xd && yd >= zd {
+            return 1;
+        }
+        2
+    }
+
+    pub fn mid_point(&self) -> Vec3 {
+        self.bounds[0] + (self.bounds[1] - self.bounds[0]) / 2.
+    }
+
+    pub fn min(&self) -> Vec3 {
+        self.bounds[0]
+    }
+
+    pub fn max(&self) -> Vec3 {
+        self.bounds[1]
+    }
+
+    // TODO(wathiede): implement branchless https://tavianator.com/cgit/dimension.git/tree/libdimension/bvh/bvh.c#n194
+
+    pub fn hit(&self, r: Ray, t_min: f32, t_max: f32) -> bool {
+        self.hit_simd(r, t_min, t_max).is_some()
+    }
+
+    pub fn hit_distance(&self, r: Ray, t_min: f32, t_max: f32) -> Option<f32> {
+        self.hit_simd(r, t_min, t_max)
+    }
+
+    pub fn hit_naive(&self, r: Ray, t_min: f32, t_max: f32) -> Option<f32> {
+        let mut t_min = t_min;
+        let mut t_max = t_max;
+        for axis in 0..3 {
+            let t0 = ((self.min()[axis] - r.origin[axis]) * r.inv_direction[axis])
+                .min((self.max()[axis] - r.origin[axis]) * r.inv_direction[axis]);
+            let t1 = ((self.min()[axis] - r.origin[axis]) * r.inv_direction[axis])
+                .max((self.max()[axis] - r.origin[axis]) * r.inv_direction[axis]);
+            t_min = t0.max(t_min);
+            t_max = t1.min(t_max);
+            if t_max <= t_min {
+                return None;
+            }
+        }
+        Some(t_min)
+    }
+
+    pub fn hit2(&self, r: Ray, t_min: f32, t_max: f32) -> Option<f32> {
+        let mut t_min = t_min;
+        let mut t_max = t_max;
+        for axis in 0..3 {
+            let d_inv = 1.0 / r.direction[axis];
+            let t0 = min(
+                (self.min()[axis] - r.origin[axis]) * d_inv,
+                (self.max()[axis] - r.origin[axis]) * d_inv,
+            );
+            let t1 = max(
+                (self.min()[axis] - r.origin[axis]) * d_inv,
+                (self.max()[axis] - r.origin[axis]) * d_inv,
+            );
+            t_min = max(t0, t_min);
+            t_max = min(t1, t_max);
+            if t_max <= t_min {
+                return None;
+            }
+        }
+        Some(t_min)
+    }
+
+    pub fn hit_precompute(&self, r: Ray, t0: f32, t1: f32) -> Option<f32> {
+        // TODO(wathiede): this has bugs.
+        let mut t_min = (self.bounds[r.sign[0]].x - r.origin.x) * r.inv_direction.x;
+        let mut t_max = (self.bounds[1 - r.sign[0]].x - r.origin.x) * r.inv_direction.x;
+        let t_y_min = (self.bounds[r.sign[0]].y - r.origin.y) * r.inv_direction.y;
+        let t_y_max = (self.bounds[1 - r.sign[0]].y - r.origin.y) * r.inv_direction.y;
+
+        if t_min > t_y_max || t_y_min > t_max {
+            return None;
+        }
+
+        if t_y_min > t_min {
+            t_min = t_y_min;
+        }
+        if t_y_max < t_max {
+            t_max = t_y_max;
+        }
+
+        let t_z_min = (self.bounds[r.sign[2]].z - r.origin.z) * r.inv_direction.z;
+        let t_z_max = (self.bounds[1 - r.sign[2]].z - r.origin.z) * r.inv_direction.z;
+        if t_min > t_z_max || t_z_min > t_max {
+            return None;
+        }
+        if t_z_min > t_min {
+            t_min = t_z_min;
+        }
+        if t_z_max < t_max {
+            t_max = t_z_max;
+        }
+        if t_min < t1 && t_max > t0 {
+            Some(t_min)
+        } else {
+            None
+        }
+    }
+
+    pub fn hit_simd(&self, r: Ray, t_min: f32, t_max: f32) -> Option<f32> {
+        #[cfg(target_arch = "x86_64")]
+        unsafe {
+            use std::arch::x86_64::*;
+            let o4 = _mm_set_ps(0., r.origin.z, r.origin.y, r.origin.x);
+            let d4 = _mm_set_ps(0., r.inv_direction.z, r.inv_direction.y, r.inv_direction.x);
+            let bmin4 = _mm_set_ps(0., self.min().z, self.min().y, self.min().x);
+            let bmax4 = _mm_set_ps(0., self.max().z, self.max().y, self.max().x);
+            let mask4 = _mm_cmpeq_ps(_mm_setzero_ps(), _mm_set_ps(1., 0., 0., 0.));
+            let t1 = _mm_mul_ps(_mm_sub_ps(_mm_and_ps(bmin4, mask4), o4), d4);
+            let t2 = _mm_mul_ps(_mm_sub_ps(_mm_and_ps(bmax4, mask4), o4), d4);
+            let vmax4 = _mm_max_ps(t1, t2);
+            let vmin4 = _mm_min_ps(t1, t2);
+            let vmax4: (f32, f32, f32, f32) = std::mem::transmute(vmax4);
+            let vmin4: (f32, f32, f32, f32) = std::mem::transmute(vmin4);
+            let tmax = min(min(vmax4.0, min(vmax4.1, vmax4.2)), t_max);
+            let tmin = max(max(vmin4.0, max(vmin4.1, vmin4.2)), t_min);
+            if tmin <= tmax {
+                Some(tmin)
+            } else {
+                None
+            }
+        }
+        #[cfg(target_arch = "aarch64")]
+        // TODO(wathiede): add NEON implementation.
+        self.hit2(r, t_min, t_max)
+    }
+
+    pub fn hit_fast(&self, r: Ray, _t_min: f32, _t_max: f32) -> Option<f32> {
+        let b = self;
+        let mut t1 = (b.min()[0] - r.origin[0]) * 1. / r.direction[0];
+        let mut t2 = (b.max()[0] - r.origin[0]) * 1. / r.direction[0];
+
+        let mut tmin = t1.min(t2);
+        let mut tmax = t1.max(t2);
+
+        for i in 1..3 {
+            t1 = (b.min()[i] - r.origin[i]) * 1. / r.direction[i];
+            t2 = (b.max()[i] - r.origin[i]) * 1. / r.direction[i];
+
+            tmin = tmin.max(t1.min(t2));
+            tmax = tmax.min(t1.max(t2));
+        }
+
+        if tmax > tmin.max(0.0) {
+            Some(tmin)
+        } else {
+            None
+        }
+    }
+}
+
+pub fn surrounding_box(box0: &AABB, box1: &AABB) -> AABB {
+    let min = Vec3::new(
+        box0.min().x.min(box1.min().x),
+        box0.min().y.min(box1.min().y),
+        box0.min().z.min(box1.min().z),
+    );
+    let max = Vec3::new(
+        box0.max().x.max(box1.max().x),
+        box0.max().y.max(box1.max().y),
+        box0.max().z.max(box1.max().z),
+    );
+    AABB::new(min, max)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn infinite() {
+        let bb = AABB::infinite();
+        assert_eq!(bb.area(), 0.);
+        assert_eq!(bb.volume(), 0.);
+    }
+
+    macro_rules! hit_test {
+        ($($name:ident,)*) => {
+            $(
+                mod $name {
+                    use super::*;
+                    const T_MIN: f32 = 0.001;
+                    const T_MAX: f32 = f32::MAX;
+
+                    fn test_bb() -> AABB {
+                        AABB::new([-1., -1., -1.], [1., 1., 1.])
+                    }
+
+                    #[test]
+                    fn hit_front() {
+                        let bb = test_bb();
+                        let r = Ray::new([-2., 0., 0.], [1., 0., 0.], 0.5);
+                        assert!(bb.$name(r, T_MIN, T_MAX).is_some());
+                    }
+                    #[test]
+                    fn hit_back() {
+                        let bb = test_bb();
+                        let r = Ray::new([2., 0., 0.], [-1., 0., 0.], 0.5);
+                        assert!(bb.$name(r, T_MIN, T_MAX).is_some());
+                    }
+                    #[test]
+                    fn hit_top() {
+                        let bb = test_bb();
+                        let r = Ray::new([0., 2., 0.], [0., -1., 0.], 0.5);
+                        assert!(bb.$name(r, T_MIN, T_MAX).is_some());
+                    }
+                    #[test]
+                    fn hit_bottom() {
+                        let bb = test_bb();
+                        let r = Ray::new([0., -2., 0.], [0., 1., 0.], 0.5);
+                        assert!(bb.$name(r, T_MIN, T_MAX).is_some());
+                    }
+                    #[test]
+                    fn hit_left() {
+                        let bb = test_bb();
+                        let r = Ray::new([0., 0., -2.], [0., 0., 1.], 0.5);
+                        assert!(bb.$name(r, T_MIN, T_MAX).is_some());
+                    }
+                    #[test]
+                    fn hit_right() {
+                        let bb = test_bb();
+                        let r = Ray::new([0., 0., 2.], [0., 0., -1.], 0.5);
+                        assert!(bb.$name(r, T_MIN, T_MAX).is_some());
+                    }
+
+                    #[test]
+                    fn miss_front() {
+                        let bb = test_bb();
+                        let r = Ray::new([0., 1.1, -1.1], [0., -1., 0.], 0.5);
+                        assert_eq!(bb.$name(r, T_MIN, T_MAX), None);
+                    }
+                    #[test]
+                    fn miss_back() {
+                        let bb = test_bb();
+                        let r = Ray::new([0., 1.1, 1.1], [0., -1., 0.], 0.5);
+                        assert_eq!(bb.$name(r, T_MIN, T_MAX), None);
+                    }
+                    #[test]
+                    fn miss_top() {
+                        let bb = test_bb();
+                        let r = Ray::new([0., 1.1, -1.1], [0., 0., 1.], 0.5);
+                        assert_eq!(bb.$name(r, T_MIN, T_MAX), None);
+                    }
+                    #[test]
+                    fn miss_bottom() {
+                        let bb = test_bb();
+                        let r = Ray::new([0., -1.1, -1.1], [0., 0., 1.], 0.5);
+                        assert_eq!(bb.$name(r, T_MIN, T_MAX), None);
+                    }
+                    #[test]
+                    fn miss_left() {
+                        let bb = test_bb();
+                        let r = Ray::new([-1.1, 0., -1.1], [0., 0., 1.], 0.5);
+                        assert_eq!(bb.$name(r, T_MIN, T_MAX), None);
+                    }
+                    #[test]
+                    fn miss_right() {
+                        let bb = test_bb();
+                        let r = Ray::new([1.1, 0., -1.1], [0., 0., 1.], 0.5);
+                        assert_eq!(bb.$name(r, T_MIN, T_MAX), None);
+                    }
+                }
+            )*
+        }
+    }
+
+    hit_test! {
+        hit_naive,
+        hit_simd,
+        hit_fast,
+        hit2,
+    }
+}
--- a/rtiow/renderer/src/build.rs
+++ b/rtiow/renderer/src/build.rs
--- a/rtiow/renderer/src/bvh.rs
+++ b/rtiow/renderer/src/bvh.rs
@@ -1,16 +1,15 @@
-use std;
-use std::fmt;
-use std::time::Instant;
+use std::{self, fmt, time::Instant};

-use rand;
-use rand::Rng;
+use log::info;
+use rand::{self, Rng};

-use crate::aabb::surrounding_box;
-use crate::aabb::AABB;
-use crate::hitable::Hit;
-use crate::hitable::HitRecord;
-use crate::ray::Ray;
+use crate::{
+    aabb::{surrounding_box, AABB},
+    hitable::{Hit, HitRecord},
+    ray::Ray,
+};

+#[derive(Debug)]
 enum BVHNode {
    Leaf(Box<dyn Hit>),
    Branch {
@@ -77,10 +76,10 @@ fn box_z_compare(ah: &Box<dyn Hit>, bh: &Box<dyn Hit>) -> std::cmp::Ordering {
 // returns a reference.)
 fn vec_first_into<T>(v: Vec<T>) -> T {
    if v.len() != 1 {
-        panic!(format!(
+        panic!(
            "vec_first_into called for vector length != 1, length {}",
            v.len()
-        ));
+        );
    }
    v.into_iter().next().unwrap()
 }
@@ -105,7 +104,7 @@ impl BVHNode {
        } else {
            let mut l: Vec<Box<dyn Hit>> = l.into_iter().collect();
            let mut rng = rand::thread_rng();
-            match rng.gen_range::<u16>(0, 3) {
+            match rng.gen_range(0..3) {
                0 => l.sort_by(box_x_compare),
                1 => l.sort_by(box_y_compare),
                2 => l.sort_by(box_z_compare),
@@ -180,6 +179,7 @@ impl Hit for BVHNode {
    }
 }

+#[derive(Debug)]
 pub struct BVH {
    root: BVHNode,
 }
@@ -231,12 +231,13 @@ impl Hit for BVH {

 #[cfg(test)]
 mod tests {
-    use crate::aabb::AABB;
-    use crate::material::Lambertian;
-    use crate::material::Metal;
-    use crate::sphere::Sphere;
-    use crate::texture::ConstantTexture;
-    use crate::vec3::Vec3;
+    use crate::{
+        aabb::AABB,
+        material::{Lambertian, Metal},
+        sphere::Sphere,
+        texture::ConstantTexture,
+        vec3::Vec3,
+    };

    use super::*;

--- a/rtiow/renderer/src/bvh_triangles.rs
+++ b/rtiow/renderer/src/bvh_triangles.rs
@@ -0,0 +1,711 @@
+/// Implementation based on blog post @
+/// https://jacco.ompf2.com/2022/04/13/how-to-build-a-bvh-part-1-basics/
+use std::f32::EPSILON;
+use std::fmt;
+
+use log::info;
+use stl::STL;
+
+use crate::{
+    aabb::AABB,
+    hitable::{Hit, HitRecord},
+    material::Material,
+    ray::Ray,
+    vec3::{cross, dot, Vec3},
+};
+
+#[derive(Debug, PartialEq)]
+struct BVHNode {
+    aabb: AABB,
+    // When tri_count==0, left_first holds the left child's index in bvh_nodes. When >0 left_first
+    // holds the index for the first triangle in triangles.
+    left_first: u32,
+    tri_count: u32,
+}
+
+impl BVHNode {
+    fn is_leaf(&self) -> bool {
+        self.tri_count > 0
+    }
+
+    fn cost(&self) -> f32 {
+        let area = self.aabb.area();
+        self.tri_count as f32 * area
+    }
+}
+
+#[derive(Clone, PartialEq)]
+pub struct Triangle {
+    centroid: Vec3,
+    verts: [Vec3; 3],
+}
+impl fmt::Debug for Triangle {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(
+            f,
+            "Tri: <{}, {}, {}> @ {}",
+            self.verts[0], self.verts[1], self.verts[2], self.centroid
+        )
+    }
+}
+
+pub struct BVHTriangles<M>
+where
+    M: Material,
+{
+    pub triangles: Vec<Triangle>,
+    triangle_index: Vec<usize>,
+    material: M,
+    bvh_nodes: Vec<BVHNode>,
+}
+
+#[derive(Debug, Default)]
+struct Bin {
+    bounds: AABB,
+    tri_count: usize,
+}
+
+impl<M> fmt::Debug for BVHTriangles<M>
+where
+    M: Material,
+{
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "{} triangles", self.triangles.len())?;
+        if f.alternate() {
+            writeln!(f)?;
+        }
+        for (i, t) in self.triangles.iter().enumerate() {
+            if f.alternate() {
+                write!(f, "\t")?;
+            }
+            write!(f, "{i:>3} {:?} ", t)?;
+            if f.alternate() {
+                writeln!(f)?;
+            }
+        }
+        if f.alternate() {
+            writeln!(f)?;
+        }
+        for (i, n) in self.bvh_nodes.iter().enumerate() {
+            write!(f, "N[{i}] {n:?}")?;
+            if f.alternate() {
+                writeln!(f)?;
+            }
+            let n = &self.bvh_nodes[i];
+            if n.is_leaf() {
+                for t_idx in n.left_first..(n.left_first + n.tri_count) {
+                    if f.alternate() {
+                        write!(f, "\t")?;
+                    }
+                    write!(f, "{:?} ", self.triangles[t_idx as usize])?;
+                    if f.alternate() {
+                        writeln!(f)?;
+                    }
+                }
+            }
+        }
+        Ok(())
+    }
+}
+
+#[derive(Debug)]
+struct SplitCost {
+    pos: f32,
+    axis: usize,
+    cost: f32,
+}
+
+const ROOT_NODE_IDX: usize = 0;
+impl<M> BVHTriangles<M>
+where
+    M: Material,
+{
+    pub fn new(stl: &STL, material: M, scale_factor: f32) -> BVHTriangles<M> {
+        let now = std::time::Instant::now();
+
+        assert_eq!(std::mem::size_of::<BVHNode>(), 32);
+        let div3 = 1. / 3.;
+        let triangles: Vec<_> = stl
+            .triangles
+            .iter()
+            .map(|t| {
+                let v0 = t.verts[0] * scale_factor;
+                let v1 = t.verts[1] * scale_factor;
+                let v2 = t.verts[2] * scale_factor;
+                let centroid = (v0 + v1 + v2) * div3;
+                Triangle {
+                    centroid,
+                    verts: [v0, v1, v2],
+                }
+            })
+            .collect();
+        let triangle_index = (0..triangles.len()).collect();
+
+        let n = 2 * triangles.len() - 2;
+        let bvh_nodes = Vec::with_capacity(n);
+        let mut bvh = BVHTriangles {
+            triangles,
+            triangle_index,
+            bvh_nodes,
+            material,
+        };
+        bvh.build_bvh();
+        info!(
+            "BVHTriangles build time {:0.3}s",
+            now.elapsed().as_secs_f32()
+        );
+        struct Stats {
+            nodes: usize,
+            leafs: usize,
+            min_tris: u32,
+            max_tris: u32,
+        }
+        impl Default for Stats {
+            fn default() -> Self {
+                Stats {
+                    nodes: 0,
+                    leafs: 0,
+                    min_tris: u32::MAX,
+                    max_tris: u32::MIN,
+                }
+            }
+        }
+        let stats = bvh.bvh_nodes.iter().fold(Stats::default(), |mut stats, n| {
+            stats.nodes += 1;
+            if n.is_leaf() {
+                stats.leafs += 1;
+                stats.min_tris = n.tri_count.min(stats.min_tris);
+                stats.max_tris = n.tri_count.max(stats.max_tris);
+            }
+            stats
+        });
+        info!("BVHTriangles build stats:");
+        info!("  Nodes:   {}", stats.nodes);
+        info!("  Leaves:  {}", stats.leafs);
+        info!("  Tris:    {}", bvh.triangles.len());
+        info!("  Min Tri: {}", stats.min_tris);
+        info!("  Max Tri: {}", stats.max_tris);
+        info!("  Avg Tri: {}", bvh.triangles.len() / stats.leafs);
+        info!("  Predict: {}", bvh.bvh_nodes.capacity());
+        info!("  Actual:  {}", bvh.bvh_nodes.len());
+        info!(
+            "  Savings:  {} bytes",
+            (bvh.bvh_nodes.capacity() - bvh.bvh_nodes.len()) * std::mem::size_of::<BVHNode>()
+        );
+        bvh.bvh_nodes.shrink_to_fit();
+        //dbg!(&bvh);
+        bvh
+    }
+
+    fn build_bvh(&mut self) {
+        // assign all triangles to root node
+        let root = BVHNode {
+            aabb: AABB::default(),
+            left_first: 0,
+            tri_count: self.triangles.len() as u32,
+        };
+        self.bvh_nodes.push(root);
+        self.update_node_bounds(ROOT_NODE_IDX);
+        // subdivide recursively
+        self.subdivide(ROOT_NODE_IDX);
+    }
+    fn update_node_bounds(&mut self, node_idx: usize) {
+        let node = &mut self.bvh_nodes[node_idx];
+        let mut aabb_min: Vec3 = f32::MAX.into();
+        let mut aabb_max: Vec3 = f32::MIN.into();
+        for i in node.left_first..(node.left_first + node.tri_count) {
+            let leaf_tri_idx = self.triangle_index[i as usize];
+            let leaf_tri = &self.triangles[leaf_tri_idx];
+            aabb_min = vec3::min(aabb_min, leaf_tri.verts[0]);
+            aabb_min = vec3::min(aabb_min, leaf_tri.verts[1]);
+            aabb_min = vec3::min(aabb_min, leaf_tri.verts[2]);
+            aabb_max = vec3::max(aabb_max, leaf_tri.verts[0]);
+            aabb_max = vec3::max(aabb_max, leaf_tri.verts[1]);
+            aabb_max = vec3::max(aabb_max, leaf_tri.verts[2]);
+        }
+        node.aabb = AABB::new(aabb_min, aabb_max);
+    }
+
+    fn find_best_split_plane(&self, node: &BVHNode) -> SplitCost {
+        let mut best = SplitCost {
+            pos: 0.,
+            cost: f32::MAX,
+            axis: usize::MAX,
+        };
+
+        for axis in 0..3 {
+            let mut bounds_min = f32::MAX;
+            let mut bounds_max = f32::MIN;
+
+            for i in 0..node.tri_count {
+                let triangle = &self.triangles[self.triangle_index[(node.left_first + i) as usize]];
+                bounds_min = bounds_min.min(triangle.centroid[axis]);
+                bounds_max = bounds_max.max(triangle.centroid[axis]);
+            }
+
+            if bounds_min == bounds_max {
+                continue;
+            }
+
+            const NUM_BINS: usize = 8;
+            let mut bins: Vec<_> = (0..NUM_BINS)
+                .map(|_| Bin {
+                    bounds: AABB::infinite(),
+                    tri_count: 0,
+                })
+                .collect();
+            let scale = bins.len() as f32 / (bounds_max - bounds_min);
+            // populate the bins
+            for i in 0..node.tri_count {
+                let triangle = &self.triangles[self.triangle_index[(node.left_first + i) as usize]];
+                let bin_idx = (triangle.centroid[axis] - bounds_min) * scale;
+                let bin_idx = (bins.len() - 1).min(bin_idx as usize);
+
+                bins[bin_idx].tri_count += 1;
+                bins[bin_idx].bounds.grow(triangle.verts[0]);
+                bins[bin_idx].bounds.grow(triangle.verts[1]);
+                bins[bin_idx].bounds.grow(triangle.verts[2]);
+            }
+
+            // gather data for the 7 planes between the 8 bins
+            let mut left_area: Vec<_> = (0..bins.len() - 1).map(|_| 0.).collect();
+            let mut right_area: Vec<_> = (0..bins.len() - 1).map(|_| 0.).collect();
+            let mut left_count: Vec<_> = (0..bins.len() - 1).map(|_| 0).collect();
+            let mut right_count: Vec<_> = (0..bins.len() - 1).map(|_| 0).collect();
+            let mut left_box = AABB::infinite();
+            let mut right_box = AABB::infinite();
+            let mut left_sum = 0;
+            let mut right_sum = 0;
+            for i in 0..(bins.len() - 1) {
+                left_sum += bins[i].tri_count;
+                left_count[i] = left_sum;
+                left_box.grow(bins[i].bounds.min());
+                left_box.grow(bins[i].bounds.max());
+                left_area[i] = left_box.area();
+
+                right_sum += bins[bins.len() - 1 - i].tri_count;
+                right_count[bins.len() - 2 - i] = right_sum;
+                right_box.grow(bins[bins.len() - 1 - i].bounds.min());
+                right_box.grow(bins[bins.len() - 1 - i].bounds.max());
+                right_area[bins.len() - 2 - i] = right_box.area();
+            }
+
+            let scale = (bounds_max - bounds_min) / bins.len() as f32;
+            // calculate SAH cost for the 7 planes
+            for i in 0..(bins.len() - 1) {
+                let plane_cost =
+                    left_count[i] as f32 * left_area[i] + right_count[i] as f32 * right_area[i];
+                if plane_cost < best.cost {
+                    best.axis = axis;
+                    best.pos = bounds_min + scale * (i as f32 + 1.);
+                    best.cost = plane_cost;
+                }
+            }
+        }
+        best
+    }
+
+    fn subdivide(&mut self, idx: usize) {
+        let (left_first, tri_count, left_count, i) = {
+            let node = &self.bvh_nodes[idx];
+            let split = self.find_best_split_plane(&node);
+            let no_split_cost = node.cost();
+            // Stop subdividing if it isn't getting any better.
+            if split.cost >= no_split_cost {
+                return;
+            }
+
+            // Split the group in two halves.
+            let mut i = node.left_first as isize;
+            let mut j = i + node.tri_count as isize - 1;
+            while i <= j {
+                if self.triangles[self.triangle_index[i as usize]].centroid[split.axis] < split.pos
+                {
+                    i += 1;
+                } else {
+                    self.triangles.swap(
+                        self.triangle_index[i as usize],
+                        self.triangle_index[j as usize],
+                    );
+                    j -= 1;
+                }
+            }
+
+            // Create child nodes for each half.
+            let left_count = i as u32 - node.left_first;
+            if left_count == 0 || left_count == node.tri_count {
+                return;
+            }
+            (node.left_first, node.tri_count, left_count, i)
+        };
+
+        // create child nodes
+        let left_child_idx = self.bvh_nodes.len() as u32;
+        let right_child_idx = left_child_idx + 1 as u32;
+        let left = BVHNode {
+            aabb: AABB::default(),
+            left_first,
+            tri_count: left_count as u32,
+        };
+        let right = BVHNode {
+            aabb: AABB::default(),
+            left_first: i as u32,
+            tri_count: (tri_count - left_count) as u32,
+        };
+        self.bvh_nodes.push(left);
+        self.bvh_nodes.push(right);
+        let node = &mut self.bvh_nodes[idx];
+        node.left_first = left_child_idx;
+        node.tri_count = 0;
+
+        // Recurse
+        self.update_node_bounds(left_child_idx as usize);
+        self.subdivide(left_child_idx as usize);
+        self.update_node_bounds(right_child_idx as usize);
+        self.subdivide(right_child_idx as usize);
+    }
+
+    fn intersect_bvh(&self, r: Ray, t_min: f32, t_max: f32) -> Option<HitRecord> {
+        let mut node = &self.bvh_nodes[ROOT_NODE_IDX];
+        let mut stack = Vec::with_capacity(2);
+        let mut nearest = None;
+        loop {
+            if node.is_leaf() {
+                let canditate = (node.left_first..(node.left_first + node.tri_count))
+                    // Map from idx to Triangle
+                    .map(|idx| &self.triangles[self.triangle_index[idx as usize]])
+                    // Try to hit all triangles for this node, filtering out misses.
+                    .filter_map(|tri| intersect_tri(r, &tri))
+                    // Find the nearest hit (if any).
+                    .min_by(|a, b| a.t.partial_cmp(&b.t).unwrap());
+
+                // merge candidate with nearest.
+                nearest = match (&canditate, &nearest) {
+                    (Some(_), None) => canditate,
+                    (None, Some(_)) => nearest,
+                    (Some(c), Some(n)) => {
+                        //info!("merging {c:#?} and {n:#?}");
+                        if c.t < n.t {
+                            canditate
+                        } else {
+                            nearest
+                        }
+                    }
+                    (None, None) => None,
+                };
+                if stack.is_empty() {
+                    break;
+                }
+                node = stack.pop().unwrap();
+                continue;
+            }
+
+            let child1 = &self.bvh_nodes[node.left_first as usize];
+            let child2 = &self.bvh_nodes[node.left_first as usize + 1];
+            let dist1 = child1.aabb.hit_distance(r, t_min, t_max);
+            let dist2 = child2.aabb.hit_distance(r, t_min, t_max);
+            // Swap c1/c2 & d1/d2 based on d1/d2.
+            let (child1, child2, dist1, dist2) = match (dist1, dist2) {
+                (Some(d1), Some(d2)) if d1 > d2 => (child2, child1, dist2, dist1),
+                (None, Some(_)) => (child2, child1, dist2, dist1),
+                _ => (child1, child2, dist1, dist2),
+            };
+
+            // dist1/child1 should now be the nearest hit.
+
+            // If we missed dist1/child1, then we implicitly missed dist2/child2, so pop a child
+            // from the stack or exit the function.
+            if dist1.is_none() {
+                if stack.is_empty() {
+                    break;
+                }
+                node = stack.pop().unwrap();
+            } else {
+                // We hit child1, so process it next.
+                node = child1;
+                // If we also hit child2 save it on the stack so we can process it later.
+                if dist2.is_some() {
+                    stack.push(child2);
+                }
+            }
+        }
+        nearest
+            .and_then(|rtr: RayTriangleResult| Some(rtr.hit_record_with_material(&self.material)))
+    }
+}
+
+/// Based on https://www.scratchapixel.com/lessons/3d-basic-rendering/ray-tracing-rendering-a-triangle/moller-trumbore-ray-triangle-intersection.html
+fn intersect_tri(r: Ray, tri: &Triangle) -> Option<RayTriangleResult> {
+    // #ifdef MOLLER_TRUMBORE
+    //     Vec3f v0v1 = v1 - v0;
+    //     Vec3f v0v2 = v2 - v0;
+    //     Vec3f pvec = dir.crossProduct(v0v2);
+    //     float det = v0v1.dotProduct(pvec);
+    // #ifdef CULLING
+    //     // if the determinant is negative, the triangle is 'back facing'
+    //     // if the determinant is close to 0, the ray misses the triangle
+    //     if (det < kEpsilon) return false;
+    // #else
+    //     // ray and triangle are parallel if det is close to 0
+    //     if (fabs(det) < kEpsilon) return false;
+    // #endif
+    //     float invDet = 1 / det;
+    //
+    //     Vec3f tvec = orig - v0;
+    //     u = tvec.dotProduct(pvec) * invDet;
+    //     if (u < 0 || u > 1) return false;
+    //
+    //     Vec3f qvec = tvec.crossProduct(v0v1);
+    //     v = dir.dotProduct(qvec) * invDet;
+    //     if (v < 0 || u + v > 1) return false;
+    //
+    //     t = v0v2.dotProduct(qvec) * invDet;
+    //
+    let v0 = tri.verts[0];
+    let v1 = tri.verts[1];
+    let v2 = tri.verts[2];
+
+    let v0v1 = v1 - v0;
+    let v0v2 = v2 - v0;
+    let p = cross(r.direction, v0v2);
+    let det = dot(v0v1, p);
+    if det.abs() < EPSILON {
+        return None;
+    }
+
+    let inv_det = 1. / det;
+
+    let t = r.origin - v0;
+    let u = dot(t, p) * inv_det;
+    if u < 0. || u > 1. {
+        return None;
+    }
+
+    let q = cross(t, v0v1);
+    let v = dot(r.direction, q) * inv_det;
+    if v < 0. || u + v > 1. {
+        return None;
+    }
+    let t = dot(v0v2, q) * inv_det;
+
+    if t > EPSILON {
+        return Some(RayTriangleResult {
+            t,
+            p: r.point_at_parameter(t),
+            tri: tri.clone(),
+        });
+    }
+    None
+}
+
+impl<M> Hit for BVHTriangles<M>
+where
+    M: Material,
+{
+    fn hit(&self, r: Ray, t_min: f32, t_max: f32) -> Option<HitRecord> {
+        self.intersect_bvh(r, t_min, t_max)
+    }
+
+    fn bounding_box(&self, _t_min: f32, _t_max: f32) -> Option<AABB> {
+        Some(self.bvh_nodes[ROOT_NODE_IDX].aabb)
+    }
+}
+
+#[derive(Debug)]
+struct RayTriangleResult {
+    t: f32,
+    p: Vec3,
+    tri: Triangle,
+}
+
+impl RayTriangleResult {
+    fn hit_record_with_material<'m>(self, material: &'m dyn Material) -> HitRecord<'m> {
+        // We don't support UV (yet?).
+        let uv = (0.5, 0.5);
+        let v0 = self.tri.verts[0];
+        let v1 = self.tri.verts[1];
+        let v2 = self.tri.verts[2];
+
+        let v0v1 = v1 - v0;
+        let v0v2 = v2 - v0;
+        let normal = cross(v0v1, v0v2).unit_vector();
+        //println!("hit triangle {tri:?}");
+        HitRecord {
+            t: self.t,
+            uv,
+            p: self.p,
+            normal,
+            material,
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::{
+        bvh_triangles::BVHTriangles,
+        cuboid::Cuboid,
+        hitable::Hit,
+        material::{Dielectric, Lambertian},
+        ray::Ray,
+        texture::ConstantTexture,
+    };
+    use pretty_assertions::assert_eq;
+    use proptest::prelude::*;
+    use std::{
+        io::{BufReader, Cursor},
+        sync::Arc,
+    };
+    use stl::STL;
+
+    #[test]
+    fn compare_cuboid() {
+        let c = Cuboid::new(
+            [0., 0., 0.].into(),
+            [20., 20., 20.].into(),
+            Arc::new(Dielectric::new(1.5)),
+        );
+        let stl_cube = STL::parse(
+            BufReader::new(Cursor::new(include_bytes!("../stls/cube.stl"))),
+            false,
+        )
+        .expect("failed to parse cube");
+
+        let s = BVHTriangles::new(
+            &stl_cube,
+            Dielectric::new(1.5),
+            //Metal::new(Vec3::new(0.8, 0.8, 0.8), 0.2),
+            //Lambertian::new(ConstantTexture::new(Vec3::new(1.0, 0.2, 0.2))),
+        );
+        //dbg!(&s);
+        let mut rays: Vec<_> = (1..20)
+            .flat_map(|y| {
+                (1..20).flat_map(move |x| {
+                    let x = x as f32;
+                    let y = y as f32;
+                    vec![
+                        // Outward in angle
+                        Ray::new([-1., x, y], [1., 0., 0.], 0.),
+                        Ray::new([21., x, y], [-1., 0., 0.], 0.),
+                        Ray::new([x, -1., y], [0., 1., 0.], 0.),
+                        Ray::new([x, 21., y], [0., -1., 0.], 0.),
+                        Ray::new([x, y, -1.], [0., 0., 1.], 0.),
+                        Ray::new([x, y, 21.], [0., 0., -1.], 0.),
+                        // Inward out (
+                        Ray::new([x, y, 10.], [1., 0., 0.], 0.),
+                        Ray::new([x, y, 10.], [-1., 0., 0.], 0.),
+                        Ray::new([x, 10., y], [1., 0., 0.], 0.),
+                        Ray::new([x, 10., y], [-1., 0., 0.], 0.),
+                        Ray::new([10., x, y], [1., 0., 0.], 0.),
+                        Ray::new([10., x, y], [-1., 0., 0.], 0.),
+                        Ray::new([x, y, 10.], [0., 1., 0.], 0.),
+                        Ray::new([x, y, 10.], [0., -1., 0.], 0.),
+                        Ray::new([x, 10., y], [0., 1., 0.], 0.),
+                        Ray::new([x, 10., y], [0., -1., 0.], 0.),
+                        Ray::new([10., x, y], [0., 1., 0.], 0.),
+                        Ray::new([10., x, y], [0., -1., 0.], 0.),
+                        Ray::new([x, y, 10.], [0., 0., 1.], 0.),
+                        Ray::new([x, y, 10.], [0., 0., -1.], 0.),
+                        Ray::new([x, 10., y], [0., 0., 1.], 0.),
+                        Ray::new([x, 10., y], [0., 0., -1.], 0.),
+                        Ray::new([10., x, y], [0., 0., 1.], 0.),
+                        Ray::new([10., x, y], [0., 0., -1.], 0.),
+                    ]
+                    .into_iter()
+                })
+            })
+            .collect();
+        if false {
+            // Outward in at an angle.
+            let sqrt2 = 2f32.sqrt();
+            rays.extend(vec![
+                Ray::new([-1., 10., 10.], [sqrt2, sqrt2, 0.], 0.),
+                Ray::new([-1., 10., 10.], [sqrt2, -sqrt2, 0.], 0.),
+                Ray::new([-1., 10., 10.], [sqrt2, 0., sqrt2], 0.),
+                Ray::new([-1., 10., 10.], [sqrt2, 0., -sqrt2], 0.),
+            ]);
+        }
+
+        for r in rays.into_iter() {
+            let c_hit = c
+                .hit(r, 0., f32::MAX)
+                .expect(&format!("c_hit missed {r:#?}"));
+            let s_hit = s
+                .hit(r, 0., f32::MAX)
+                .expect(&format!("s_hit missed {r:#?}"));
+            assert!(
+                (c_hit.t - s_hit.t).abs() < EPSILON,
+                "{r:?} [t] c_hit: {c_hit:#?}, s_hit: {s_hit:#?}"
+            );
+            // uv isn't valid for BVHTriangles.
+            // assert_eq!( c_hit.uv, s_hit.uv, "{i}: [uv] c_hit: {c_hit:?}, s_hit: {s_hit:?}");
+            assert_eq!(
+                c_hit.p, s_hit.p,
+                "{r:?}: [p] c_hit: {c_hit:#?}, s_hit: {s_hit:#?}"
+            );
+            assert_eq!(
+                c_hit.normal, s_hit.normal,
+                "{r:?}: [normal] c_hit: {c_hit:?}, s_hit: {s_hit:?}"
+            );
+        }
+    }
+
+    proptest! {
+        // TODO(wathiede): make this work.
+        //#[test]
+        fn compare_cuboid_proptest(
+            ox in -20.0f32..40.0,
+            oy in -20.0f32..40.0,
+            oz in -20.0f32..40.0,
+            dx in -1.0f32..1.0,
+            dy in -1.0f32..1.0,
+            dz in -1.0f32..1.0,
+        ) {
+            let r = Ray::new([ox,oy,oz].into(), Vec3::new(dx, dy, dz).unit_vector(), 0.5);
+            let c = Cuboid::new(
+                [0., 0., 0.].into(),
+                [20., 20., 20.].into(),
+                Arc::new(Dielectric::new(1.5)),
+            );
+            let stl_cube = STL::parse(
+                BufReader::new(Cursor::new(include_bytes!("../stls/cube.stl"))),
+                false,
+            )
+                .expect("failed to parse cube");
+
+            let s = BVHTriangles::new(
+                &stl_cube,
+                Dielectric::new(1.5),
+                //Metal::new(Vec3::new(0.8, 0.8, 0.8), 0.2),
+                //Lambertian::new(ConstantTexture::new(Vec3::new(1.0, 0.2, 0.2))),
+            );
+
+            let c_hit = c .hit(r, 0., f32::MAX);
+            let s_hit = s .hit(r, 0., f32::MAX);
+
+            match (c_hit, s_hit) {
+                (Some(_), None)=>assert!(false, "hit cuboid but not STL"),
+                (None, Some(_))=>assert!(false, "hit STL but not cuboid"),
+                (Some(c_hit), Some(s_hit))=> {
+                    assert!(
+                        (c_hit.t - s_hit.t).abs() < 0.00001,
+                        "{r:?} [t] c_hit: {c_hit:#?}, s_hit: {s_hit:#?}"
+                    );
+                    // uv isn't valid for BVHTriangles.
+                    // assert_eq!( c_hit.uv, s_hit.uv, "{i}: [uv] c_hit: {c_hit:?}, s_hit: {s_hit:?}");
+                    assert_eq!(
+                        c_hit.p, s_hit.p,
+                        "{r:?}: [p] c_hit: {c_hit:#?}, s_hit: {s_hit:#?}"
+                    );
+                    assert_eq!(
+                        c_hit.normal, s_hit.normal,
+                        "{r:?}: [normal] c_hit: {c_hit:?}, s_hit: {s_hit:?}"
+                    );
+                },
+                // It's okay if they both miss.
+                (None,None)=>(),
+            }
+        }
+    }
+}
--- a/rtiow/renderer/src/camera.rs
+++ b/rtiow/renderer/src/camera.rs
@@ -1,28 +1,24 @@
-extern crate rand;
 use std::f32::consts::PI;

-use self::rand::Rng;
+use rand::{self, Rng};

-use crate::ray::Ray;
-use crate::vec3::cross;
-use crate::vec3::Vec3;
+use crate::{
+    ray::Ray,
+    vec3::{cross, Vec3},
+};

 fn random_in_unit_disk() -> Vec3 {
    let mut rng = rand::thread_rng();
    let v = Vec3::new(1., 1., 0.);
    loop {
-        let p =
-            2. * Vec3::new(
-                rng.gen_range::<f32>(0., 1.),
-                rng.gen_range::<f32>(0., 1.),
-                0.,
-            ) - v;
+        let p = 2. * Vec3::new(rng.gen(), rng.gen(), 0.) - v;
        if p.squared_length() < 1. {
            return p;
        }
    }
 }

+#[derive(Debug)]
 pub struct Camera {
    origin: Vec3,
    lower_left_corner: Vec3,
@@ -77,7 +73,7 @@ impl Camera {
        let mut rng = rand::thread_rng();
        let rd = self.lens_radius * random_in_unit_disk();
        let offset = self.u * rd.x + self.v * rd.y;
-        let time = self.time_min + rng.gen_range::<f32>(0., 1.) * (self.time_max - self.time_min);
+        let time = self.time_min + rng.gen::<f32>() * (self.time_max - self.time_min);
        Ray::new(
            self.origin + offset,
            self.lower_left_corner + self.horizontal * u + self.vertical * v - self.origin - offset,
--- a/rtiow/renderer/src/colors.rs
+++ b/rtiow/renderer/src/colors.rs
@@ -0,0 +1,46 @@
+use rand::{self, Rng};
+
+use crate::vec3::Vec3;
+
+// HSV values in [0..1]
+// returns [r, g, b] values from 0 to 255
+//From https://martin.ankerl.com/2009/12/09/how-to-create-random-colors-programmatically/
+pub fn hsv_to_rgb(h: f32, s: f32, v: f32) -> Vec3 {
+    let h_i = (h * 6.) as i32;
+    let f = h * 6. - h_i as f32;
+    let p = v * (1. - s);
+    let q = v * (1. - f * s);
+    let t = v * (1. - (1. - f) * s);
+    match h_i {
+        0 => Vec3::new(v, t, p),
+        1 => Vec3::new(q, v, p),
+        2 => Vec3::new(p, v, t),
+        3 => Vec3::new(p, q, v),
+        4 => Vec3::new(t, p, v),
+        5 => Vec3::new(v, p, q),
+        _ => panic!("Unknown H value {}", h_i),
+    }
+}
+
+pub fn generate_rainbow(num: usize) -> Vec<Vec3> {
+    (0..num)
+        .map(|n| {
+            let h = n as f32 / num as f32;
+            hsv_to_rgb(h, 0.99, 0.99)
+        })
+        .collect()
+}
+pub fn generate_palette(num: usize) -> Vec<Vec3> {
+    let mut rng = rand::thread_rng();
+    let mut random = || rng.gen();
+    // use golden ratio
+    let golden_ratio_conjugate = 0.618_034;
+    let mut h = random();
+    (0..num)
+        .map(|_| {
+            h += golden_ratio_conjugate;
+            h %= 1.0;
+            hsv_to_rgb(h, 0.99, 0.99)
+        })
+        .collect()
+}
--- a/rtiow/renderer/src/constant_medium.rs
+++ b/rtiow/renderer/src/constant_medium.rs
@@ -1,16 +1,17 @@
 use std;

-use rand;
-use rand::Rng;
+use rand::{self, Rng};

-use crate::aabb::AABB;
-use crate::hitable::Hit;
-use crate::hitable::HitRecord;
-use crate::material::Isotropic;
-use crate::ray::Ray;
-use crate::texture::Texture;
-use crate::vec3::Vec3;
+use crate::{
+    aabb::AABB,
+    hitable::{Hit, HitRecord},
+    material::Isotropic,
+    ray::Ray,
+    texture::Texture,
+    vec3::Vec3,
+};

+#[derive(Debug)]
 pub struct ConstantMedium<H, T>
 where
    H: Hit,
@@ -60,14 +61,10 @@ where
                    rec1.t = 0.;
                }
                let distance_inside_boundary = (rec2.t - rec1.t) * r.direction.length();
-                let hit_distance = -(1. / self.density) * rng.gen_range::<f32>(0., 1.).ln();
+                let hit_distance: f32 = -(1. / self.density) * rng.gen::<f32>().ln();
                if hit_distance < distance_inside_boundary {
                    let t = rec1.t + hit_distance / r.direction.length();
-                    let normal = Vec3::new(
-                        rng.gen_range::<f32>(0., 1.),
-                        rng.gen_range::<f32>(0., 1.),
-                        rng.gen_range::<f32>(0., 1.),
-                    ).unit_vector();
+                    let normal = Vec3::new(rng.gen(), rng.gen(), rng.gen()).unit_vector();
                    return Some(HitRecord {
                        t,
                        p: r.point_at_parameter(t),
--- a/rtiow/renderer/src/cuboid.rs
+++ b/rtiow/renderer/src/cuboid.rs
@@ -1,17 +1,17 @@
 use std::sync::Arc;

-use crate::aabb::AABB;
-use crate::flip_normals::FlipNormals;
-use crate::hitable::Hit;
-use crate::hitable::HitRecord;
-use crate::hitable_list::HitableList;
-use crate::material::Material;
-use crate::ray::Ray;
-use crate::rect::XYRect;
-use crate::rect::XZRect;
-use crate::rect::YZRect;
-use crate::vec3::Vec3;
+use crate::{
+    aabb::AABB,
+    flip_normals::FlipNormals,
+    hitable::{Hit, HitRecord},
+    hitable_list::HitableList,
+    material::Material,
+    ray::Ray,
+    rect::{XYRect, XZRect, YZRect},
+    vec3::Vec3,
+};

+#[derive(Debug)]
 pub struct Cuboid {
    p_min: Vec3,
    p_max: Vec3,
@@ -22,6 +22,9 @@ impl Cuboid {
    // This clippy doesn't work right with Arc.
    #[allow(clippy::needless_pass_by_value)]
    pub fn new(p_min: Vec3, p_max: Vec3, material: Arc<dyn Material>) -> Cuboid {
+        assert!(p_min.x <= p_max.x);
+        assert!(p_min.y <= p_max.y);
+        assert!(p_min.z <= p_max.z);
        Cuboid {
            p_min,
            p_max,
--- a/rtiow/renderer/src/debug_hit.rs
+++ b/rtiow/renderer/src/debug_hit.rs
@@ -0,0 +1,44 @@
+use crate::{
+    aabb::AABB,
+    hitable::{Hit, HitRecord},
+    material::Lambertian,
+    ray::Ray,
+};
+
+#[derive(Debug)]
+pub struct DebugHit<H>
+where
+    H: Hit,
+{
+    hitable: H,
+    material: Lambertian<[f32; 3]>,
+}
+
+impl<H> DebugHit<H>
+where
+    H: Hit,
+{
+    pub fn new(hitable: H) -> DebugHit<H>
+where {
+        DebugHit {
+            hitable,
+            material: Lambertian::new([0.2, 0.2, 0.2]),
+        }
+    }
+}
+
+impl<H> Hit for DebugHit<H>
+where
+    H: Hit,
+{
+    fn hit(&self, r: Ray, t_min: f32, t_max: f32) -> Option<HitRecord> {
+        if let Some(hit) = self.hitable.hit(r, t_min, t_max) {
+            return Some(HitRecord { t: hit.t, ..hit });
+        }
+        None
+    }
+
+    fn bounding_box(&self, t_min: f32, t_max: f32) -> Option<AABB> {
+        self.hitable.bounding_box(t_min, t_max)
+    }
+}
--- a/rtiow/renderer/src/flip_normals.rs
+++ b/rtiow/renderer/src/flip_normals.rs
@@ -1,8 +1,10 @@
-use crate::aabb::AABB;
-use crate::hitable::Hit;
-use crate::hitable::HitRecord;
-use crate::ray::Ray;
+use crate::{
+    aabb::AABB,
+    hitable::{Hit, HitRecord},
+    ray::Ray,
+};

+#[derive(Debug)]
 pub struct FlipNormals<H>
 where
    H: Hit,
--- a/rtiow/renderer/src/glowybox.rs
+++ b/rtiow/renderer/src/glowybox.rs
@@ -0,0 +1,139 @@
+use std::sync::Arc;
+
+use crate::{
+    aabb::AABB,
+    cuboid::Cuboid,
+    hitable::{Hit, HitRecord},
+    material::Material,
+    ray::Ray,
+    vec3::Vec3,
+};
+
+#[derive(Debug)]
+pub struct Glowybox {
+    p_min: Vec3,
+    p_max: Vec3,
+    main: Cuboid,
+    edges: [Cuboid; 12],
+}
+
+impl Glowybox {
+    // This clippy doesn't work right with Arc.
+    #[allow(clippy::needless_pass_by_value)]
+    pub fn new(
+        p_min: Vec3,
+        p_max: Vec3,
+        edge_thickness: f32,
+        main_material: Arc<dyn Material>,
+        edge_material: Arc<dyn Material>,
+    ) -> Glowybox {
+        assert!(p_min.x < p_max.x);
+        assert!(p_min.y < p_max.y);
+        assert!(p_min.z < p_max.z);
+        let main = Cuboid::new(p_min, p_max, main_material);
+        // Top edges
+        let ht = edge_thickness / 2.;
+        let edges = [
+            // Top edges
+            Cuboid::new(
+                [p_min.x - ht, p_max.y - ht, p_min.z - ht].into(),
+                [p_min.x + ht, p_max.y + ht, p_max.z + ht].into(),
+                Arc::clone(&edge_material),
+            ),
+            Cuboid::new(
+                [p_min.x - ht, p_max.y - ht, p_min.z - ht].into(),
+                [p_max.x + ht, p_max.y + ht, p_min.z + ht].into(),
+                Arc::clone(&edge_material),
+            ),
+            Cuboid::new(
+                [p_max.x - ht, p_max.y - ht, p_min.z - ht].into(),
+                [p_max.x + ht, p_max.y + ht, p_max.z + ht].into(),
+                Arc::clone(&edge_material),
+            ),
+            Cuboid::new(
+                [p_min.x - ht, p_max.y - ht, p_max.z - ht].into(),
+                [p_max.x + ht, p_max.y + ht, p_max.z + ht].into(),
+                Arc::clone(&edge_material),
+            ),
+            // Bottom edges
+            Cuboid::new(
+                [p_min.x - ht, p_min.y - ht, p_min.z - ht].into(),
+                [p_min.x + ht, p_min.y + ht, p_max.z + ht].into(),
+                Arc::clone(&edge_material),
+            ),
+            Cuboid::new(
+                [p_min.x - ht, p_min.y - ht, p_min.z - ht].into(),
+                [p_max.x + ht, p_min.y + ht, p_min.z + ht].into(),
+                Arc::clone(&edge_material),
+            ),
+            Cuboid::new(
+                [p_max.x - ht, p_min.y - ht, p_min.z - ht].into(),
+                [p_max.x + ht, p_min.y + ht, p_max.z + ht].into(),
+                Arc::clone(&edge_material),
+            ),
+            Cuboid::new(
+                [p_min.x - ht, p_min.y - ht, p_max.z - ht].into(),
+                [p_max.x + ht, p_min.y + ht, p_max.z + ht].into(),
+                Arc::clone(&edge_material),
+            ),
+            // Middle edges
+            Cuboid::new(
+                [p_min.x - ht, p_min.y - ht, p_min.z - ht].into(),
+                [p_min.x + ht, p_max.y + ht, p_min.z + ht].into(),
+                Arc::clone(&edge_material),
+            ),
+            Cuboid::new(
+                [p_min.x - ht, p_min.y - ht, p_max.z - ht].into(),
+                [p_min.x + ht, p_max.y + ht, p_max.z + ht].into(),
+                Arc::clone(&edge_material),
+            ),
+            Cuboid::new(
+                [p_max.x - ht, p_min.y - ht, p_min.z - ht].into(),
+                [p_max.x + ht, p_max.y + ht, p_min.z + ht].into(),
+                Arc::clone(&edge_material),
+            ),
+            Cuboid::new(
+                [p_max.x - ht, p_min.y - ht, p_max.z - ht].into(),
+                [p_max.x + ht, p_max.y + ht, p_max.z + ht].into(),
+                Arc::clone(&edge_material),
+            ),
+        ];
+        let p_min = [p_min.x - ht, p_min.y - ht, p_min.z - ht].into();
+        let p_max = [p_max.x + ht, p_max.y + ht, p_max.z + ht].into();
+        Glowybox {
+            p_min,
+            p_max,
+            main,
+            edges,
+        }
+    }
+}
+
+impl Hit for Glowybox {
+    fn hit(&self, r: Ray, t_min: f32, t_max: f32) -> Option<HitRecord> {
+        let mut edge_hit = None;
+        for edge in &self.edges {
+            if let Some(hit) = edge.hit(r, t_min, t_max) {
+                edge_hit = Some(hit);
+                break;
+            }
+        }
+        let main_hit = self.main.hit(r, t_min, t_max);
+        match (edge_hit, main_hit) {
+            (Some(ehit), Some(mhit)) => {
+                if mhit.t < ehit.t {
+                    Some(mhit)
+                } else {
+                    Some(ehit)
+                }
+            }
+            (Some(ehit), None) => Some(ehit),
+            (None, Some(mhit)) => Some(mhit),
+            _ => None,
+        }
+    }
+
+    fn bounding_box(&self, _t_min: f32, _t_max: f32) -> Option<AABB> {
+        Some(AABB::new(self.p_min, self.p_max))
+    }
+}
--- a/rtiow/renderer/src/hitable.rs
+++ b/rtiow/renderer/src/hitable.rs
@@ -1,10 +1,8 @@
-use std::sync::Arc;
+use std::{fmt::Debug, sync::Arc};

-use crate::aabb::AABB;
-use crate::material::Material;
-use crate::ray::Ray;
-use crate::vec3::Vec3;
+use crate::{aabb::AABB, material::Material, ray::Ray, vec3::Vec3};

+#[derive(Debug)]
 pub struct HitRecord<'m> {
    pub t: f32,
    pub uv: (f32, f32),
@@ -13,7 +11,7 @@ pub struct HitRecord<'m> {
    pub material: &'m dyn Material,
 }

-pub trait Hit: Send + Sync {
+pub trait Hit: Send + Sync + Debug {
    fn hit(&self, r: Ray, t_min: f32, t_max: f32) -> Option<HitRecord>;
    fn bounding_box(&self, t_min: f32, t_max: f32) -> Option<AABB>;
 }
@@ -26,3 +24,12 @@ impl Hit for Arc<dyn Hit> {
        (**self).bounding_box(t_min, t_max)
    }
 }
+
+impl Hit for Box<dyn Hit> {
+    fn hit(&self, r: Ray, t_min: f32, t_max: f32) -> Option<HitRecord> {
+        (**self).hit(r, t_min, t_max)
+    }
+    fn bounding_box(&self, t_min: f32, t_max: f32) -> Option<AABB> {
+        (**self).bounding_box(t_min, t_max)
+    }
+}
--- a/rtiow/renderer/src/hitable_list.rs
+++ b/rtiow/renderer/src/hitable_list.rs
@@ -1,13 +1,13 @@
 use std;

-use crate::aabb::surrounding_box;
-use crate::aabb::AABB;
-use crate::hitable::Hit;
-use crate::hitable::HitRecord;
-use crate::ray::Ray;
-use crate::vec3::Vec3;
+use crate::{
+    aabb::{surrounding_box, AABB},
+    hitable::{Hit, HitRecord},
+    ray::Ray,
+    vec3::Vec3,
+};

-#[derive(Default)]
+#[derive(Debug, Default)]
 pub struct HitableList {
    list: Vec<Box<dyn Hit>>,
 }
--- a/rtiow/renderer/src/human.rs
+++ b/rtiow/renderer/src/human.rs
@@ -6,28 +6,24 @@
 //! Print some human readable strings
 //!
 //! ```rust
-//! use rtiow::human;
+//! use renderer::human;
 //!
 //! // "1.00 k"
-//! let tmpStr = human::Formatter::new()
-//!     .format(1000.0);
+//! let tmpStr = human::Formatter::new().format(1000.0);
 //! # assert_eq!(tmpStr, "1.00 k");
 //!
 //! // "1.00 M"
-//! let tmpStr2 = human::Formatter::new()
-//!     .format(1000000.0);
+//! let tmpStr2 = human::Formatter::new().format(1000000.0);
 //! # assert_eq!(tmpStr2, "1.00 M");
 //!
 //! // "1.00 B"
-//! let tmpStr3 = human::Formatter::new()
-//!     .format(1000000000.0);
+//! let tmpStr3 = human::Formatter::new().format(1000000000.0);
 //! # assert_eq!(tmpStr3, "1.00 B");
 //! ```
 //!
 //! If you are so inspired you can even try playing with units and customizing your `Scales`
 //!
 //! For more examples you should review the examples on github: [tests/demo.rs](https://github.com/BobGneu/human-format-rs/blob/master/tests/demo.rs)
-//!

 #[derive(Debug)]
 struct ScaledValue {
@@ -130,7 +126,13 @@ impl Formatter {

        let magnitude_multiplier = self.scales.get_magnitude_multipler(&suffix);

-        (result * magnitude_multiplier)
+        result * magnitude_multiplier
+    }
+}
+
+impl Default for Formatter {
+    fn default() -> Self {
+        Self::new()
    }
 }

@@ -203,7 +205,7 @@ impl Scales {
            }
        }

-        return 0.0;
+        0.0
    }

    fn to_scaled_value(&self, value: f64) -> ScaledValue {
@@ -225,3 +227,9 @@ impl Scales {
        }
    }
 }
+
+impl Default for Scales {
+    fn default() -> Self {
+        Self::new()
+    }
+}
--- a/rtiow/renderer/src/kdtree.rs
+++ b/rtiow/renderer/src/kdtree.rs
@@ -1,11 +1,15 @@
 use std::fmt;

-use crate::aabb::surrounding_box;
-use crate::aabb::AABB;
-use crate::hitable::Hit;
-use crate::hitable::HitRecord;
-use crate::ray::Ray;
+use log::info;

+use crate::{
+    aabb::{surrounding_box, AABB},
+    hitable::{Hit, HitRecord},
+    hitable_list::HitableList,
+    ray::Ray,
+};
+
+#[derive(Debug)]
 pub enum KDTree {
    Leaf(Box<dyn Hit>),
    Branch {
@@ -20,10 +24,10 @@ pub enum KDTree {
 // returns a reference.)
 fn vec_first_into<T>(v: Vec<T>) -> T {
    if v.len() != 1 {
-        panic!(format!(
+        panic!(
            "vec_first_into called for vector length != 1, length {}",
            v.len()
-        ));
+        );
    }
    v.into_iter().next().unwrap()
 }
@@ -100,6 +104,14 @@ impl KDTree {
            }),
            _ => panic!("Unreachable"),
        };
+        //info!("left_half {:?}", left_half);
+        //info!("right_half {:?}", right_half);
+        if left_half.is_empty() {
+            return KDTree::Leaf(Box::new(HitableList::new(right_half)));
+        };
+        if right_half.is_empty() {
+            return KDTree::Leaf(Box::new(HitableList::new(left_half)));
+        };
        KDTree::Branch {
            left: Box::new(KDTree::new(left_half, t_min, t_max)),
            right: Box::new(KDTree::new(right_half, t_min, t_max)),
@@ -144,7 +156,7 @@ fn print_tree(f: &mut fmt::Formatter, depth: usize, kdt: &KDTree) -> fmt::Result
 impl fmt::Display for KDTree {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        writeln!(f, "kd-tree")?;
-        print_tree(f, 1, &self)
+        print_tree(f, 1, self)
    }
 }
 impl Hit for KDTree {
--- a/rtiow/renderer/src/lib.rs
+++ b/rtiow/renderer/src/lib.rs
@@ -1,9 +1,13 @@
 pub mod aabb;
 pub mod bvh;
+pub mod bvh_triangles;
 pub mod camera;
+pub mod colors;
 pub mod constant_medium;
 pub mod cuboid;
+pub mod debug_hit;
 pub mod flip_normals;
+pub mod glowybox;
 pub mod hitable;
 pub mod hitable_list;
 pub mod human;
@@ -12,22 +16,15 @@ pub mod material;
 pub mod moving_sphere;
 pub mod noise;
 pub mod output;
+pub mod parser;
 pub mod ray;
 pub mod rect;
 pub mod renderer;
 pub mod rotate;
+pub mod scale;
 pub mod scenes;
 pub mod sphere;
 pub mod texture;
 pub mod translate;
+pub mod triangles;
 pub mod vec3;
-
-extern crate image;
-#[macro_use]
-extern crate log;
-extern crate num_cpus;
-extern crate rand;
-#[macro_use]
-extern crate structopt;
-#[macro_use]
-extern crate serde_derive;
--- a/rtiow/renderer/src/material.rs
+++ b/rtiow/renderer/src/material.rs
@@ -1,38 +1,33 @@
-use std::sync::Arc;
+use std::{fmt::Debug, sync::Arc};

-extern crate rand;
-use self::rand::Rng;
+use rand::{self, Rng};

-use crate::hitable::HitRecord;
-use crate::ray::Ray;
-use crate::texture::Texture;
-use crate::vec3::dot;
-use crate::vec3::Vec3;
+use crate::{
+    hitable::HitRecord,
+    ray::Ray,
+    texture::Texture,
+    vec3::{dot, Vec3},
+};

 fn random_in_unit_sphere() -> Vec3 {
    let mut rng = rand::thread_rng();
    let v = Vec3::new(1., 1., 1.);
    loop {
-        let p =
-            2. * Vec3::new(
-                rng.gen_range::<f32>(0., 1.),
-                rng.gen_range::<f32>(0., 1.),
-                rng.gen_range::<f32>(0., 1.),
-            ) - v;
+        let p = 2. * Vec3::new(rng.gen(), rng.gen(), rng.gen()) - v;
        if p.squared_length() < 1. {
            return p;
        }
    }
 }

-#[derive(Default)]
+#[derive(Default, Debug)]
 pub struct ScatterResponse {
    pub scattered: Ray,
    pub attenutation: Vec3,
    pub reflected: bool,
 }

-pub trait Material: Send + Sync {
+pub trait Material: Send + Sync + Debug {
    fn scatter(&self, r_in: &Ray, rec: &HitRecord) -> ScatterResponse;
    fn emitted(&self, _u: f32, _v: f32, _p: Vec3) -> Vec3 {
        Vec3::new(0., 0., 0.)
@@ -57,6 +52,7 @@ impl Material for Box<dyn Material> {
    }
 }

+#[derive(Clone, Debug)]
 pub struct Isotropic<T>
 where
    T: Texture,
@@ -87,6 +83,7 @@ where
    }
 }

+#[derive(Clone, Debug)]
 pub struct Lambertian<T>
 where
    T: Texture,
@@ -118,6 +115,7 @@ where
    }
 }

+#[derive(Clone, Debug)]
 pub struct Metal {
    albedo: Vec3,
    fuzzy: f32,
@@ -172,6 +170,7 @@ fn schlick(cosine: f32, ref_idx: f32) -> f32 {
    r0 + (1. - r0) * (1. - cosine).powf(5.)
 }

+#[derive(Clone, Debug)]
 pub struct Dielectric {
    ref_idx: f32,
 }
@@ -201,7 +200,7 @@ impl Material for Dielectric {
        let scattered = if let Some(refracted) = refract(r_in.direction, outward_normal, ni_over_nt)
        {
            let mut rng = rand::thread_rng();
-            if rng.gen_range::<f32>(0., 1.) < schlick(cosine, self.ref_idx) {
+            if rng.gen::<f32>() < schlick(cosine, self.ref_idx) {
                Ray::new(rec.p, reflected, r_in.time)
            } else {
                Ray::new(rec.p, refracted, r_in.time)
@@ -218,6 +217,7 @@ impl Material for Dielectric {
    }
 }

+#[derive(Debug)]
 pub struct DiffuseLight<T>
 where
    T: Texture,
@@ -251,6 +251,20 @@ where
    }
 }

+#[derive(Debug)]
+pub struct DebugMaterial {}
+
+impl Material for DebugMaterial {
+    fn scatter(&self, _r_in: &Ray, rec: &HitRecord) -> ScatterResponse {
+        let dir = Vec3::new(0., -1., -1.).unit_vector();
+        ScatterResponse {
+            scattered: Ray::new(rec.p, dir, 0.),
+            attenutation: [1., 1., 1.].into(),
+            reflected: true,
+        }
+    }
+}
+
 #[cfg(test)]
 mod tests {
    use super::*;
--- a/rtiow/renderer/src/moving_sphere.rs
+++ b/rtiow/renderer/src/moving_sphere.rs
@@ -1,13 +1,13 @@
-use crate::aabb::surrounding_box;
-use crate::aabb::AABB;
-use crate::hitable::Hit;
-use crate::hitable::HitRecord;
-use crate::material::Material;
-use crate::ray::Ray;
-use crate::sphere::get_sphere_uv;
-use crate::vec3::dot;
-use crate::vec3::Vec3;
+use crate::{
+    aabb::{surrounding_box, AABB},
+    hitable::{Hit, HitRecord},
+    material::Material,
+    ray::Ray,
+    sphere::get_sphere_uv,
+    vec3::{dot, Vec3},
+};

+#[derive(Debug)]
 pub struct MovingSphere<M>
 where
    M: Material,
--- a/rtiow/renderer/src/noise/lode.rs
+++ b/rtiow/renderer/src/noise/lode.rs
@@ -1,10 +1,11 @@
+use log::trace;
 /// Implements the concepts from https://lodev.org/cgtutor/randomnoise.html
 use rand;

-use crate::noise::NoiseSource;
-use crate::vec3::Vec3;
+use crate::{noise::NoiseSource, vec3::Vec3};

 const NOISE_SIZE: usize = 128;
+#[derive(Debug)]
 pub struct Lode {
    // Using fixed array causes stack overflow.
    noise: Vec<Vec<Vec<f32>>>, //[[[f32; NOISE_SIZE]; NOISE_SIZE]; NOISE_SIZE],
@@ -21,7 +22,7 @@ impl Lode {
        for x in 0..NOISE_SIZE {
            for y in 0..NOISE_SIZE {
                for z in 0..NOISE_SIZE {
-                    noise[x][y][z] = rng.gen_range::<f32>(0., 1.);
+                    noise[x][y][z] = rng.gen();
                }
            }
        }
--- a/rtiow/renderer/src/noise/mod.rs
+++ b/rtiow/renderer/src/noise/mod.rs
@@ -1,11 +1,13 @@
 pub mod lode;
 pub mod perlin;

-use std::f32::consts::PI;
+use std::{f32::consts::PI, fmt::Debug};
+
+use serde_derive::Deserialize;

 use crate::vec3::Vec3;

-pub trait NoiseSource: Send + Sync {
+pub trait NoiseSource: Send + Sync + Debug {
    /// value returns noise on the interval [0., 1.).
    fn value(&self, p: Vec3) -> f32;

--- a/rtiow/renderer/src/noise/perlin.rs
+++ b/rtiow/renderer/src/noise/perlin.rs
@@ -1,11 +1,14 @@
 // There are many math functions in this file, so we allow single letter variable names.
 #![allow(clippy::many_single_char_names)]
-use rand::Rng;
+use log::trace;
+use rand::{seq::SliceRandom, Rng};

-use crate::noise::NoiseSource;
-use crate::vec3::dot;
-use crate::vec3::Vec3;
+use crate::{
+    noise::NoiseSource,
+    vec3::{dot, Vec3},
+};

+#[derive(Debug)]
 pub struct Perlin {
    ran_vec: Vec<Vec3>,
    perm_x: Vec<usize>,
@@ -20,9 +23,9 @@ where
    (0..256)
        .map(|_| {
            Vec3::new(
-                rng.gen_range::<f32>(-1., 1.),
-                rng.gen_range::<f32>(-1., 1.),
-                rng.gen_range::<f32>(-1., 1.),
+                rng.gen_range(-1. ..1.),
+                rng.gen_range(-1. ..1.),
+                rng.gen_range(-1. ..1.),
            )
            .unit_vector()
        })
@@ -33,8 +36,8 @@ fn perlin_generate_perm<R>(rng: &mut R) -> Vec<usize>
 where
    R: Rng,
 {
-    let mut p: Vec<usize> = (0..256).map(|i| i).collect();
-    rng.shuffle(&mut p);
+    let mut p: Vec<usize> = (0..256).collect();
+    p.shuffle(rng);
    p
 }

--- a/rtiow/renderer/src/output.rs
+++ b/rtiow/renderer/src/output.rs
@@ -0,0 +1,250 @@
+use std::{
+    collections::HashMap,
+    fs::File,
+    io::BufWriter,
+    net::TcpStream,
+    path::Path,
+    sync::{Arc, Mutex},
+    time,
+};
+
+use chrono::Local;
+use image;
+use log::info;
+use serde_derive::Serialize;
+use tev_client::{PacketCreateImage, PacketUpdateImage, TevClient};
+
+use crate::{renderer::Scene, vec3::Vec3};
+
+// Main RGB image output from rendering the scene.
+pub const MAIN_IMAGE: &str = "@final";
+// Debug image for adaptive pixels subsampling.
+// Red indicates recursion hit maximum depth splitting the pixel.
+// Green indicates no subdivision necessary
+pub const ADAPTIVE_DEPTH: &str = "adaptive_depth";
+// Grey scale showing rays cast per pixel.
+pub const RAYS_PER_PIXEL: &str = "rays_per_pixel";
+
+#[derive(Serialize)]
+struct ImageMetadata {
+    name: String,
+    image: String,
+    binary: String,
+    ratio: f32,
+    size: (usize, usize),
+    format: ImageType,
+}
+#[derive(Serialize)]
+#[serde(rename_all = "camelCase")]
+struct Data<'s> {
+    timestamp: i64,
+    render_time_seconds: f32,
+    scene: &'s Scene,
+    image_metadata: Vec<ImageMetadata>,
+}
+
+#[derive(Clone, Copy, Serialize)]
+pub enum ImageType {
+    RGB01,
+    Grey01,
+    GreyNormalized,
+}
+
+struct Image {
+    w: usize,
+    h: usize,
+    pix: Vec<Vec3>,
+}
+
+impl Image {
+    fn new(w: usize, h: usize) -> Image {
+        Image {
+            w,
+            h,
+            pix: (0..w * h).map(|_| [0., 0., 0.].into()).collect(),
+        }
+    }
+
+    fn put_pixel(&mut self, x: usize, y: usize, p: Vec3) {
+        let offset = x + y * self.w;
+        self.pix[offset] = p;
+    }
+}
+
+pub struct OutputManager {
+    images: Arc<Mutex<HashMap<String, (ImageType, Image)>>>,
+    tev_client: Option<Arc<Mutex<TevClient>>>,
+}
+
+impl OutputManager {
+    pub fn new(tev_addr: &Option<String>) -> std::io::Result<OutputManager> {
+        let tev_client = if let Some(addr) = tev_addr {
+            Some(Arc::new(Mutex::new(TevClient::wrap(TcpStream::connect(
+                addr,
+            )?))))
+        } else {
+            None
+        };
+        Ok(OutputManager {
+            images: Arc::new(Mutex::new(HashMap::new())),
+            tev_client,
+        })
+    }
+
+    pub fn register_image(&self, name: String, dimensions: (usize, usize), it: ImageType) {
+        let mut images = self.images.lock().unwrap();
+        images.insert(name.clone(), (it, Image::new(dimensions.0, dimensions.1)));
+        self.tev_client.clone().map(|c| {
+            c.lock().unwrap().send(PacketCreateImage {
+                image_name: &name,
+                grab_focus: false,
+                width: dimensions.0 as u32,
+                height: dimensions.1 as u32,
+                channel_names: &["R", "G", "B"],
+            })
+        });
+    }
+
+    pub fn set_pixel(&self, name: &str, x: usize, y: usize, pixel: Vec3) {
+        let mut images = self.images.lock().unwrap();
+        let (_it, img) = images
+            .get_mut(name)
+            .unwrap_or_else(|| panic!("couldn't find image named '{}'", name));
+        let y_inv = img.h - y - 1;
+        img.put_pixel(x, y_inv, pixel);
+        self.tev_client.clone().map(|c| {
+            c.lock().unwrap().send(PacketUpdateImage {
+                image_name: &name,
+                grab_focus: false,
+                channel_names: &["R", "G", "B"],
+                channel_offsets: &[0, 1, 2],
+                channel_strides: &[0, 0, 0],
+                x: x as u32,
+                y: y_inv as u32,
+                width: 1,
+                height: 1,
+                data: &[pixel.x, pixel.y, pixel.z],
+            })
+        });
+    }
+
+    pub fn set_pixel_grey(&self, name: &str, x: usize, y: usize, grey: f32) {
+        let mut images = self.images.lock().unwrap();
+        let (_it, img) = images
+            .get_mut(name)
+            .unwrap_or_else(|| panic!("couldn't find image named '{}'", name));
+        let y_inv = img.h - y - 1;
+        img.put_pixel(x, y_inv, [grey, grey, grey].into());
+    }
+    pub fn write_images<P: AsRef<Path>>(
+        &self,
+        scene: &Scene,
+        render_time: time::Duration,
+        output_dir: P,
+    ) -> std::io::Result<()> {
+        let output_dir: &Path = output_dir.as_ref();
+        let now = Local::now();
+        let images = self.images.lock().unwrap();
+        // Write out images in consistent order.
+        let mut names = images.keys().collect::<Vec<_>>();
+        names.sort();
+        let mut image_metadata = Vec::new();
+        for name in &names {
+            let (it, img) = images.get(*name).unwrap();
+            let image = format!("{}.png", name);
+            let binary = format!("{}.json", name);
+            let ratio = img.w as f32 / img.h as f32;
+            let size = (img.w, img.h);
+            let image_path = output_dir.join(&image);
+            let binary_path = output_dir.join(&binary);
+            image_metadata.push(ImageMetadata {
+                name: name.to_string(),
+                image,
+                binary,
+                ratio,
+                size,
+                format: *it,
+            });
+            info!("Saving {}", image_path.to_string_lossy());
+            match it {
+                ImageType::RGB01 => {
+                    let mut out_img = image::RgbImage::new(img.w as u32, img.h as u32);
+                    out_img
+                        .enumerate_pixels_mut()
+                        .enumerate()
+                        .for_each(|(i, (_x, _y, p))| {
+                            let pixel = img.pix[i];
+                            *p = image::Rgb([
+                                (pixel[0] * 255.).min(255.) as u8,
+                                (pixel[1] * 255.).min(255.) as u8,
+                                (pixel[2] * 255.).min(255.) as u8,
+                            ])
+                        });
+                    out_img.save(image_path)?;
+                }
+                ImageType::Grey01 => {
+                    let mut out_img = image::GrayImage::new(img.w as u32, img.h as u32);
+                    out_img
+                        .enumerate_pixels_mut()
+                        .enumerate()
+                        .for_each(|(i, (_x, _y, p))| {
+                            let pixel = img.pix[i];
+                            *p = image::Luma([(pixel[0] * 255.).min(255.) as u8])
+                        });
+                    out_img.save(image_path)?;
+                }
+                ImageType::GreyNormalized => {
+                    let mut out_img = image::GrayImage::new(img.w as u32, img.h as u32);
+
+                    let max_val = img.pix.iter().map(|v| v.x).fold(0., f32::max);
+                    out_img
+                        .enumerate_pixels_mut()
+                        .enumerate()
+                        .for_each(|(i, (_x, _y, p))| {
+                            let pixel = img.pix[i];
+                            *p = image::Luma([(pixel[0] / max_val * 255.).min(255.) as u8])
+                        });
+                    out_img.save(image_path)?;
+                }
+            };
+            info!("Saving {}", binary_path.to_string_lossy());
+            let f = File::create(output_dir.join(binary_path))?;
+            let f = BufWriter::new(f);
+            match it {
+                ImageType::RGB01 => {
+                    serde_json::ser::to_writer(
+                        f,
+                        &img.pix
+                            .iter()
+                            .map(|v| [v.x, v.y, v.z])
+                            .collect::<Vec<[f32; 3]>>(),
+                    )?;
+                }
+                ImageType::Grey01 | ImageType::GreyNormalized => {
+                    serde_json::ser::to_writer(
+                        f,
+                        &img.pix.iter().map(|v| v.x).collect::<Vec<f32>>(),
+                    )?;
+                }
+            };
+        }
+        let f = File::create(output_dir.join("data.json"))?;
+        let f = BufWriter::new(f);
+        serde_json::ser::to_writer(
+            f,
+            &Data {
+                timestamp: now.timestamp(),
+                render_time_seconds: render_time.as_secs_f32(),
+                scene,
+                image_metadata,
+            },
+        )?;
+        Ok(())
+    }
+}
+
+trait ImageSaver {
+    fn save<Q>(&self, path: Q) -> std::io::Result<()>
+    where
+        Q: AsRef<Path> + Sized;
+}
--- a/rtiow/renderer/src/parser.rs
+++ b/rtiow/renderer/src/parser.rs
@@ -0,0 +1,206 @@
+use crate::{
+    bvh_triangles::BVHTriangles,
+    camera::Camera,
+    cuboid::Cuboid,
+    hitable::Hit,
+    hitable_list::HitableList,
+    material::{Dielectric, DiffuseLight, Isotropic, Lambertian, Material, Metal},
+    renderer::Scene,
+    sphere::Sphere,
+    texture::{EnvMap, Texture},
+};
+use chrono::IsoWeek;
+use serde::Deserialize;
+use std::{collections::HashMap, fs::File, io::BufReader, path::PathBuf, sync::Arc};
+use stl::STL;
+use thiserror::Error;
+use vec3::Vec3;
+
+#[derive(Debug, Deserialize)]
+pub struct Config {
+    scene: SceneConfig,
+    camera: CameraConfig,
+    materials: Vec<MaterialConfig>,
+    hitables: Vec<HitableConfig>,
+    envmap: Option<EnvMapConfig>,
+}
+
+#[derive(Error, Debug)]
+pub enum ConfigError {
+    #[error("failed to load image")]
+    ImageError(#[from] image::ImageError),
+    #[error("failed to parser STL")]
+    STLError(#[from] stl::ParseError),
+    #[error("I/O error")]
+    IOError(#[from] std::io::Error),
+    #[error("duplication material named '{0}'")]
+    DuplicateMaterial(String),
+    #[error("unkown material named '{0}'")]
+    UnknownMaterial(String),
+}
+
+impl TryFrom<Config> for Scene {
+    type Error = ConfigError;
+
+    fn try_from(c: Config) -> Result<Scene, Self::Error> {
+        let mut materials = HashMap::new();
+        for mc in c.materials {
+            let v: Arc<dyn Material> = match mc.material {
+                Materials::Metal { albedo, fuzzy } => Arc::new(Metal::new(albedo, fuzzy)),
+                Materials::Dielectric { ref_idx } => Arc::new(Dielectric::new(ref_idx)),
+                Materials::DiffuseLight { texture } => Arc::new(DiffuseLight::new(texture)),
+                Materials::Isotropic { texture } => Arc::new(Isotropic::new(texture)),
+                Materials::Lambertian { texture } => Arc::new(Lambertian::new(texture)),
+            };
+            if materials.insert(mc.name.clone(), v).is_some() {
+                return Err(ConfigError::DuplicateMaterial(mc.name));
+            }
+        }
+
+        let hitables: Result<Vec<Box<dyn Hit>>, Self::Error> = c
+            .hitables
+            .into_iter()
+            .map(|hc| -> Result<Box<dyn Hit>, Self::Error> {
+                match hc.hitable {
+                    Hitables::Sphere { center, radius } => Ok(Box::new(Sphere::new(
+                        center,
+                        radius,
+                        Arc::clone(
+                            materials
+                                .get(&hc.material_name)
+                                .ok_or(ConfigError::UnknownMaterial(hc.material_name))?,
+                        ),
+                    ))),
+                    Hitables::Cuboid { min, max } => Ok(Box::new(Cuboid::new(
+                        min.into(),
+                        max.into(),
+                        Arc::clone(
+                            materials
+                                .get(&hc.material_name)
+                                .ok_or(ConfigError::UnknownMaterial(hc.material_name))?,
+                        ),
+                    ))),
+                    Hitables::STL { path, scale } => {
+                        let r = BufReader::new(File::open(path)?);
+                        let stl = STL::parse(r, false)?;
+                        Ok(Box::new(BVHTriangles::new(
+                            &stl,
+                            Arc::clone(
+                                materials
+                                    .get(&hc.material_name)
+                                    .ok_or(ConfigError::UnknownMaterial(hc.material_name))?,
+                            ),
+                            scale.unwrap_or(1.),
+                        )))
+                    }
+                }
+            })
+            .collect();
+        let hitables = hitables?;
+
+        let world: Box<dyn Hit> = Box::new(HitableList::new(hitables));
+        let mut env_map: Option<EnvMap> = None;
+
+        if let Some(em) = c.envmap {
+            let im = image::open(em.path)?.into_rgb();
+            env_map = Some(EnvMap::new(im));
+        };
+
+        let camera = make_camera(&c.camera, c.scene.width, c.scene.height);
+
+        let scene = Scene {
+            world,
+            camera,
+            env_map,
+            subsamples: c.scene.subsamples.unwrap_or(8),
+            adaptive_subsampling: c.scene.adaptive_subsampling,
+            num_threads: c.scene.num_threads,
+            width: c.scene.width,
+            height: c.scene.height,
+            global_illumination: c.scene.global_illumination.unwrap_or(true),
+        };
+        Ok(scene)
+    }
+}
+
+fn make_camera(cfg: &CameraConfig, width: usize, height: usize) -> Camera {
+    Camera::new(
+        cfg.lookfrom.into(),
+        cfg.lookat.into(),
+        Vec3::new(0., 1., 0.),
+        cfg.fov,
+        width as f32 / height as f32,
+        cfg.aperture,
+        cfg.focus_dist,
+        cfg.time_min,
+        cfg.time_max,
+    )
+}
+
+#[derive(Debug, Deserialize)]
+struct SceneConfig {
+    subsamples: Option<usize>,
+    adaptive_subsampling: Option<f32>,
+    num_threads: Option<usize>,
+    width: usize,
+    height: usize,
+    global_illumination: Option<bool>,
+}
+
+#[derive(Debug, Deserialize)]
+#[serde(tag = "type")]
+struct HitableConfig {
+    material_name: String,
+    #[serde(flatten)]
+    hitable: Hitables,
+}
+
+#[derive(Debug, Deserialize)]
+#[serde(tag = "type")]
+enum Hitables {
+    #[serde(rename = "sphere")]
+    Sphere { center: [f32; 3], radius: f32 },
+    #[serde(rename = "cuboid")]
+    Cuboid { min: [f32; 3], max: [f32; 3] },
+    #[serde(rename = "stl")]
+    STL { path: PathBuf, scale: Option<f32> },
+}
+
+#[derive(Debug, Deserialize)]
+struct MaterialConfig {
+    name: String,
+    #[serde(flatten)]
+    material: Materials,
+}
+
+#[derive(Debug, Deserialize)]
+#[serde(tag = "type")]
+enum Materials {
+    #[serde(rename = "metal")]
+    Metal { albedo: [f32; 3], fuzzy: f32 },
+    #[serde(rename = "dielectric")]
+    Dielectric { ref_idx: f32 },
+    // TODO(wathiede): these all take Textures, for now, only support RGB
+    #[serde(rename = "diffuse_light")]
+    DiffuseLight { texture: [f32; 3] },
+    #[serde(rename = "isotropic")]
+    Isotropic { texture: [f32; 3] },
+    #[serde(rename = "lambertian")]
+    Lambertian { texture: [f32; 3] },
+}
+
+#[derive(Debug, Deserialize)]
+pub struct CameraConfig {
+    lookfrom: [f32; 3],
+    lookat: [f32; 3],
+    fov: f32,
+    aperture: f32,
+    focus_dist: f32,
+    time_min: f32,
+    time_max: f32,
+}
+
+#[derive(Debug, Deserialize)]
+struct EnvMapConfig {
+    path: PathBuf,
+}
--- a/rtiow/renderer/src/ray.rs
+++ b/rtiow/renderer/src/ray.rs
@@ -5,6 +5,9 @@ pub struct Ray {
    pub origin: Vec3,
    pub direction: Vec3,
    pub time: f32,
+
+    // Precache 1/direction, a single ray intersects multiple AABB's, and divides are more
+    // expensive than multiplies.
    pub inv_direction: Vec3,
    pub sign: [usize; 3],
 }
@@ -14,7 +17,7 @@ impl Ray {
    where
        V: Into<Vec3>,
    {
-        let direction = direction.into();
+        let direction: Vec3 = direction.into();
        let origin = origin.into();
        let inv = 1. / direction;
        Ray {
--- a/rtiow/renderer/src/rect.rs
+++ b/rtiow/renderer/src/rect.rs
@@ -1,12 +1,14 @@
 // There are many math functions in this file, so we allow single letter variable names.
 #![allow(clippy::many_single_char_names)]
-use crate::aabb::AABB;
-use crate::hitable::Hit;
-use crate::hitable::HitRecord;
-use crate::material::Material;
-use crate::ray::Ray;
-use crate::vec3::Vec3;
+use crate::{
+    aabb::AABB,
+    hitable::{Hit, HitRecord},
+    material::Material,
+    ray::Ray,
+    vec3::Vec3,
+};

+#[derive(Debug)]
 pub struct XYRect<M>
 where
    M: Material,
@@ -68,6 +70,7 @@ where
    }
 }

+#[derive(Debug)]
 pub struct XZRect<M>
 where
    M: Material,
@@ -129,6 +132,7 @@ where
    }
 }

+#[derive(Debug)]
 pub struct YZRect<M>
 where
    M: Material,
--- a/rtiow/renderer/src/renderer.rs
+++ b/rtiow/renderer/src/renderer.rs
@@ -1,36 +1,41 @@
-use std::fmt;
-use std::ops::AddAssign;
-use std::ops::Range;
-use std::path::Path;
-use std::path::PathBuf;
-use std::str;
-use std::sync;
-use std::sync::mpsc::sync_channel;
-use std::sync::mpsc::Receiver;
-use std::sync::mpsc::SyncSender;
-use std::sync::Arc;
-use std::sync::Mutex;
-use std::thread;
-use std::time;
+use std::{
+    collections::HashMap,
+    fmt,
+    ops::{AddAssign, Range},
+    path::{Path, PathBuf},
+    str, sync,
+    sync::{
+        mpsc::{sync_channel, Receiver, SyncSender},
+        Arc, Mutex,
+    },
+    thread,
+    time::{Duration, Instant},
+};

 use core_affinity;
+use log::{info, trace};
 use num_cpus;
-use rand;
-use rand::Rng;
+use rand::{self, Rng};
+use serde_derive::Serialize;
+use structopt::StructOpt;

-use crate::camera::Camera;
-use crate::hitable::Hit;
-use crate::human;
-use crate::material::Lambertian;
-use crate::output;
-use crate::ray::Ray;
-use crate::scenes;
-use crate::sphere::Sphere;
-use crate::texture::ConstantTexture;
-use crate::texture::EnvMap;
-use crate::vec3::Vec3;
+use crate::{
+    camera::Camera,
+    hitable::Hit,
+    human,
+    material::{Lambertian, Material},
+    output,
+    output::OutputManager,
+    ray::Ray,
+    scenes,
+    sphere::Sphere,
+    texture::{ConstantTexture, EnvMap},
+    vec3::Vec3,
+};
+use strum::{EnumString, EnumVariantNames};

-#[derive(Debug)]
+#[derive(Debug, EnumString, EnumVariantNames, strum::Display)]
+#[strum(serialize_all = "snake_case")]
 pub enum Model {
    BVH,
    Bench,
@@ -41,24 +46,30 @@ pub enum Model {
    Mandelbrot,
    PerlinDebug,
    Spheramid,
+    Stltest,
    Test,
+    Tron,
    Tutorial,
+    Dragon,
 }

 impl Model {
    pub fn scene(&self, opt: &Opt) -> Scene {
        match self {
-            Model::BVH => scenes::bvh::new(&opt),
-            Model::Bench => scenes::bench::new(&opt),
-            Model::Book => scenes::book::new(&opt),
-            Model::CornellBox => scenes::cornell_box::new(&opt),
-            Model::CornellSmoke => scenes::cornell_smoke::new(&opt),
-            Model::Final => scenes::final_scene::new(&opt),
-            Model::Mandelbrot => scenes::mandelbrot::new(&opt),
-            Model::PerlinDebug => scenes::perlin_debug::new(&opt),
-            Model::Spheramid => scenes::spheramid::new(&opt),
-            Model::Test => scenes::test::new(&opt),
-            Model::Tutorial => scenes::tutorial::new(&opt),
+            Model::BVH => scenes::bvh::new(opt),
+            Model::Bench => scenes::bench::new(opt),
+            Model::Book => scenes::book::new(opt),
+            Model::CornellBox => scenes::cornell_box::new(opt),
+            Model::CornellSmoke => scenes::cornell_smoke::new(opt),
+            Model::Dragon => scenes::dragon::new(opt),
+            Model::Final => scenes::final_scene::new(opt),
+            Model::Mandelbrot => scenes::mandelbrot::new(opt),
+            Model::PerlinDebug => scenes::perlin_debug::new(opt),
+            Model::Spheramid => scenes::spheramid::new(opt),
+            Model::Stltest => scenes::stltest::new(opt),
+            Model::Test => scenes::test::new(opt),
+            Model::Tron => scenes::tron::new(opt),
+            Model::Tutorial => scenes::tutorial::new(opt),
        }
    }
 }
@@ -72,44 +83,6 @@ impl fmt::Display for ModelParseError {
    }
 }

-impl str::FromStr for Model {
-    type Err = ModelParseError;
-    fn from_str(s: &str) -> std::result::Result<Self, Self::Err> {
-        match s {
-            "bench" => Ok(Model::Bench),
-            "book" => Ok(Model::Book),
-            "bvh" => Ok(Model::BVH),
-            "cornell_box" => Ok(Model::CornellBox),
-            "cornell_smoke" => Ok(Model::CornellSmoke),
-            "final" => Ok(Model::Final),
-            "mandelbrot" => Ok(Model::Mandelbrot),
-            "perlin_debug" => Ok(Model::PerlinDebug),
-            "spheramid" => Ok(Model::Spheramid),
-            "test" => Ok(Model::Test),
-            "tutorial" => Ok(Model::Tutorial),
-            _ => Err(ModelParseError(s.to_owned())),
-        }
-    }
-}
-
-impl std::string::ToString for Model {
-    fn to_string(&self) -> String {
-        match self {
-            Model::BVH => "bvh".to_string(),
-            Model::Bench => "bench".to_string(),
-            Model::Book => "book".to_string(),
-            Model::CornellBox => "cornell_box".to_string(),
-            Model::CornellSmoke => "cornell_smoke".to_string(),
-            Model::Final => "final".to_string(),
-            Model::Mandelbrot => "mandelbrot".to_string(),
-            Model::PerlinDebug => "perlin_debug".to_string(),
-            Model::Spheramid => "spheramid".to_string(),
-            Model::Test => "test".to_string(),
-            Model::Tutorial => "tutorial".to_string(),
-        }
-    }
-}
-
 #[derive(Debug, StructOpt)]
 #[structopt(name = "tracer", about = "An experimental ray tracer.")]
 pub struct Opt {
@@ -125,19 +98,29 @@ pub struct Opt {
    /// Sub-samples per pixel
    #[structopt(short = "s", long = "subsample", default_value = "8")]
    pub subsamples: usize,
-    /// Select scene to render, one of: "bench", "book", "tutorial", "bvh", "test", "cornell_box",
-    /// "cornell_smoke", "perlin_debug", "final"
-    #[structopt(long = "model", default_value = "book")]
-    pub model: Model,
+    /// Select scene to render.
+    #[structopt(long = "model")]
+    pub model: Option<Model>,
+    /// Toml config describing scene.
+    #[structopt(long = "config")]
+    pub config: Option<PathBuf>,
    /// Path to store pprof profile data, i.e. /tmp/cpuprofile.pprof
    #[structopt(long = "pprof", parse(from_os_str))]
    pub pprof: Option<PathBuf>,
    /// Use acceleration data structure, may be BVH or kd-tree depending on scene.
    #[structopt(long = "use_accel")]
    pub use_accel: bool,
+    /// Host:port of running tev instance.
+    #[structopt(long = "tev_addr")]
+    pub tev_addr: Option<String>,

    /// Output directory
-    #[structopt(parse(from_os_str), default_value = "/tmp/tracer")]
+    #[structopt(
+        short = "o",
+        long = "output",
+        parse(from_os_str),
+        default_value = "/tmp/tracer"
+    )]
    pub output: PathBuf,
 }

@@ -149,18 +132,20 @@ pub fn opt_hash(opt: &Opt) -> String {
        opt.height,
        opt.subsamples,
        opt.pprof.is_some(),
-        opt.model.to_string(),
+        opt.model.as_ref().unwrap().to_string(),
        opt.use_accel,
-        opt.output.display().to_string().replace("/", "_")
+        opt.output.display().to_string().replace('/', "_")
    )
 }

 // TODO(wathiede): implement the skips and then the renderer could use json as an input file type.
-#[derive(Serialize)]
+#[derive(Debug, Serialize)]
 #[serde(rename_all = "camelCase")]
 pub struct Scene {
    #[serde(skip)]
    pub world: Box<dyn Hit>,
+    //#[serde(skip)]
+    //pub materials: HashMap<String, Box<dyn Material>>,
    #[serde(skip)]
    pub camera: Camera,
    pub subsamples: usize,
@@ -265,6 +250,7 @@ fn trace_pixel_adaptive(
    x_range: Range<f32>,
    y_range: Range<f32>,
    scene: &Scene,
+    output: &OutputManager,
 ) -> (Vec3, usize) {
    let w = scene.width as f32;
    let h = scene.height as f32;
@@ -279,7 +265,7 @@ fn trace_pixel_adaptive(
        &scene.env_map,
    );
    if depth == 0 {
-        output::set_pixel(output::ADAPTIVE_DEPTH, x, y, [1., 0., 0.].into());
+        output.set_pixel(output::ADAPTIVE_DEPTH, x, y, [1., 0., 0.].into());
        return (center, rays);
    }
    // t = top
@@ -321,6 +307,7 @@ fn trace_pixel_adaptive(
            x_range.start..x_mid,
            y_range.start..y_mid,
            scene,
+            output,
        );
        let tr = trace_pixel_adaptive(
            depth - 1,
@@ -330,6 +317,7 @@ fn trace_pixel_adaptive(
            x_mid..x_range.end,
            y_range.start..y_mid,
            scene,
+            output,
        );
        let bl = trace_pixel_adaptive(
            depth - 1,
@@ -339,6 +327,7 @@ fn trace_pixel_adaptive(
            x_range.start..x_mid,
            y_mid..y_range.end,
            scene,
+            output,
        );
        let br = trace_pixel_adaptive(
            depth - 1,
@@ -348,13 +337,14 @@ fn trace_pixel_adaptive(
            x_mid..x_range.end,
            y_mid..y_range.end,
            scene,
+            output,
        );
        let pixel = (tl.0 + tr.0 + bl.0 + br.0) / 4.;
        let rays = tl.1 + tr.1 + bl.1 + br.1;
        (pixel, rays)
    } else {
        if depth == MAX_ADAPTIVE_DEPTH {
-            output::set_pixel(output::ADAPTIVE_DEPTH, x, y, [0., 1., 0.].into());
+            output.set_pixel(output::ADAPTIVE_DEPTH, x, y, [0., 1., 0.].into());
        }
        (corners, rays)
    }
@@ -362,8 +352,8 @@ fn trace_pixel_adaptive(

 fn trace_pixel_random(x: usize, y: usize, scene: &Scene) -> (Vec3, usize) {
    let mut rng = rand::thread_rng();
-    let u = (rng.gen_range::<f32>(0., 1.) + x as f32) / scene.width as f32;
-    let v = (rng.gen_range::<f32>(0., 1.) + y as f32) / scene.height as f32;
+    let u = (rng.gen::<f32>() + x as f32) / scene.width as f32;
+    let v = (rng.gen::<f32>() + y as f32) / scene.height as f32;
    let ray = scene.camera.get_ray(u, v);
    color(
        ray,
@@ -374,7 +364,7 @@ fn trace_pixel_random(x: usize, y: usize, scene: &Scene) -> (Vec3, usize) {
    )
 }

-#[derive(Clone, Copy)]
+#[derive(Clone, Copy, Default)]
 struct RenderStats {
    rays: usize,
    pixels: usize,
@@ -390,33 +380,37 @@ impl AddAssign for RenderStats {
 }

 fn progress(
+    start_time: Instant,
    last_stat: &RenderStats,
    current_stat: &RenderStats,
-    time_diff: time::Duration,
+    time_diff: Duration,
    pixel_total: usize,
 ) -> String {
    let human = human::Formatter::new();
    let pixel_diff = current_stat.pixels - last_stat.pixels;
    let ray_diff = current_stat.rays - last_stat.rays;
+    let now = Instant::now();
+    let start_diff = now - start_time;
+    let ratio = current_stat.pixels as f32 / pixel_total as f32;
+    let percent = ratio * 100.;
+    let elapsed = start_diff.as_secs_f32();
+    let total = elapsed * (1. / ratio);
+    let eta = total - elapsed;
    format!(
-        "{:7} / {:7}pixels ({:2}%) {:7}pixels/s {:7}rays/s",
+        "{:7} / {:7}pixels ({:2.0}%) {:7}pixels/s {:7}rays/s eta {:.0}s",
        human.format(current_stat.pixels as f64),
        human.format(pixel_total as f64),
-        100 * current_stat.pixels / pixel_total,
+        percent,
        human.format(pixel_diff as f64 / time_diff.as_secs_f64()),
-        human.format(ray_diff as f64 / time_diff.as_secs_f64())
+        human.format(ray_diff as f64 / time_diff.as_secs_f64()),
+        eta
    )
 }

-impl Default for RenderStats {
-    fn default() -> Self {
-        RenderStats { rays: 0, pixels: 0 }
-    }
-}
-
 enum Request {
    Pixel { x: usize, y: usize },
    Line { width: usize, y: usize },
+    // TODO(wathiede): add Cohort that does 4x4 or 8x8 pixel chunks.
 }

 enum Response {
@@ -433,7 +427,7 @@ enum Response {
    },
 }

-fn render_pixel(scene: &Scene, x: usize, y: usize) -> (Vec3, usize) {
+fn render_pixel(scene: &Scene, x: usize, y: usize, output: &OutputManager) -> (Vec3, usize) {
    let (pixel, rays) = if let Some(threshold) = scene.adaptive_subsampling {
        trace_pixel_adaptive(
            MAX_ADAPTIVE_DEPTH,
@@ -443,6 +437,7 @@ fn render_pixel(scene: &Scene, x: usize, y: usize) -> (Vec3, usize) {
            0.0..1.0,
            0.0..1.0,
            scene,
+            output,
        )
    } else {
        let (pixel, rays) = (0..scene.subsamples)
@@ -451,7 +446,7 @@ fn render_pixel(scene: &Scene, x: usize, y: usize) -> (Vec3, usize) {
                ([0., 0., 0.].into(), 0),
                |(p1, r1): (Vec3, usize), (p2, r2): (Vec3, usize)| ((p1 + p2), (r1 + r2)),
            );
-        output::set_pixel_grey(output::RAYS_PER_PIXEL, x, y, rays as f32);
+        output.set_pixel_grey(output::RAYS_PER_PIXEL, x, y, rays as f32);
        (pixel / scene.subsamples as f32, rays)
    };
    // Gamma correct, use gamma 2 correction, which is 1/gamma where gamma=2 which is 1/2 or
@@ -467,6 +462,7 @@ fn render_worker(
    scene: &Scene,
    input_chan: Arc<Mutex<Receiver<Request>>>,
    output_chan: &SyncSender<Response>,
+    output: &OutputManager,
 ) {
    loop {
        let job = { input_chan.lock().unwrap().recv() };
@@ -481,7 +477,7 @@ fn render_worker(
                    let batch = false;
                    if batch {
                        let (pixels, rays): (Vec<Vec3>, Vec<usize>) = (0..width)
-                            .map(|x| render_pixel(scene, x, y))
+                            .map(|x| render_pixel(scene, x, y, output))
                            .collect::<Vec<(_, _)>>()
                            .into_iter()
                            .unzip();
@@ -498,7 +494,7 @@ fn render_worker(
                            .expect("failed to send pixel response");
                    } else {
                        (0..width).for_each(|x| {
-                            let (pixel, rays) = render_pixel(scene, x, y);
+                            let (pixel, rays) = render_pixel(scene, x, y, output);
                            output_chan
                                .send(Response::Pixel {
                                    x,
@@ -512,7 +508,7 @@ fn render_worker(
                }
                Request::Pixel { x, y } => {
                    trace!("tid {} x {} y {}", tid, x, y);
-                    let (pixel, rays) = render_pixel(scene, x, y);
+                    let (pixel, rays) = render_pixel(scene, x, y, output);
                    output_chan
                        .send(Response::Pixel {
                            x,
@@ -527,8 +523,19 @@ fn render_worker(
    }
 }

-pub fn render(scene: Scene, output_dir: &Path) -> std::result::Result<(), std::io::Error> {
-    let num_threads = scene.num_threads.unwrap_or_else(num_cpus::get);
+/*
+lazy_static! {
+    static ref DEBUGGER: Arc<Mutex<OutputManager>> = Arc::new(Mutex::new(OutputManager::new()));
+}
+*/
+
+pub fn render(
+    scene: Scene,
+    output_dir: &Path,
+    tev_addr: &Option<String>,
+) -> std::result::Result<(), std::io::Error> {
+    // Default to half the cores to disable hyperthreading.
+    let num_threads = scene.num_threads.unwrap_or_else(|| num_cpus::get() / 2);
    let (pixel_req_tx, pixel_req_rx) = sync_channel(2 * num_threads);
    let (pixel_resp_tx, pixel_resp_rx) = sync_channel(2 * num_threads);

@@ -542,20 +549,23 @@ pub fn render(scene: Scene, output_dir: &Path) -> std::result::Result<(), std::i
    } else {
        core_ids
    };
+    let output = output::OutputManager::new(tev_addr)?;
+    let output = Arc::new(output);
+
    info!("Creating {} render threads", core_ids.len());
-    output::register_image(
+    output.register_image(
        output::MAIN_IMAGE.to_string(),
        (scene.width, scene.height),
        output::ImageType::RGB01,
    );
    if scene.adaptive_subsampling.is_some() {
-        output::register_image(
+        output.register_image(
            output::ADAPTIVE_DEPTH.to_string(),
            (scene.width, scene.height),
            output::ImageType::RGB01,
        );
    }
-    output::register_image(
+    output.register_image(
        output::RAYS_PER_PIXEL.to_string(),
        (scene.width, scene.height),
        output::ImageType::GreyNormalized,
@@ -569,19 +579,19 @@ pub fn render(scene: Scene, output_dir: &Path) -> std::result::Result<(), std::i
            let s = sync::Arc::clone(&scene);
            let pixel_req_rx = pixel_req_rx.clone();
            let pixel_resp_tx = pixel_resp_tx.clone();
+            let output = sync::Arc::clone(&output);
            thread::spawn(move || {
                core_affinity::set_for_current(id);
-                render_worker(i, &s, pixel_req_rx, &pixel_resp_tx);
+                render_worker(i, &s, pixel_req_rx, &pixel_resp_tx, &output);
            })
        })
        .collect::<Vec<_>>();
    drop(pixel_req_rx);
    drop(pixel_resp_tx);

-    let start_time = time::Instant::now();
    let (w, h) = (scene.width, scene.height);
    handles.push(thread::spawn(move || {
-        let batch_line_requests = true;
+        let batch_line_requests = false;
        if batch_line_requests {
            for y in 0..h {
                pixel_req_tx
@@ -603,29 +613,36 @@ pub fn render(scene: Scene, output_dir: &Path) -> std::result::Result<(), std::i
    info!("Rendering with {} subsamples", scene.subsamples);

    let pixel_total = scene.width * scene.height;
-    let mut last_time = time::Instant::now();
+    let mut last_time = Instant::now();
    let mut last_stat: RenderStats = Default::default();
    let mut current_stat: RenderStats = Default::default();
+    let render_start_time = Instant::now();
    for resp in pixel_resp_rx {
        match resp {
            Response::Pixel { x, y, pixel, rs } => {
                current_stat += rs;
-                output::set_pixel(output::MAIN_IMAGE, x, y, pixel);
+                output.set_pixel(output::MAIN_IMAGE, x, y, pixel);
            }
            Response::Line { y, pixels, rs } => {
                current_stat += rs;
                for (x, pixel) in pixels.iter().enumerate() {
-                    output::set_pixel(output::MAIN_IMAGE, x, y, *pixel);
+                    output.set_pixel(output::MAIN_IMAGE, x, y, *pixel);
                }
            }
        }

-        let now = time::Instant::now();
+        let now = Instant::now();
        let time_diff = now - last_time;
-        if time_diff > time::Duration::from_secs(1) {
-            info!(
+        if time_diff > Duration::from_secs(5) {
+            println!(
                "{}",
-                progress(&last_stat, &current_stat, time_diff, pixel_total)
+                progress(
+                    render_start_time,
+                    &last_stat,
+                    &current_stat,
+                    time_diff,
+                    pixel_total
+                )
            );
            last_stat = current_stat;
            last_time = now;
@@ -634,12 +651,18 @@ pub fn render(scene: Scene, output_dir: &Path) -> std::result::Result<(), std::i
    for thr in handles {
        thr.join().expect("thread join");
    }
-    let time_diff = time::Instant::now() - start_time;
-    info!(
-        "Runtime {} seconds {}",
+    let time_diff = Instant::now() - render_start_time;
+    println!(
+        "Render {} seconds {}",
        time_diff.as_secs_f32(),
-        progress(&Default::default(), &current_stat, time_diff, pixel_total)
+        progress(
+            render_start_time,
+            &Default::default(),
+            &current_stat,
+            time_diff,
+            pixel_total
+        )
    );

-    output::write_images(&scene, time_diff, output_dir)
+    output.write_images(&scene, time_diff, output_dir)
 }
--- a/rtiow/renderer/src/rotate.rs
+++ b/rtiow/renderer/src/rotate.rs
@@ -1,13 +1,13 @@
-use std::f32::consts::PI;
-use std::f32::MAX;
-use std::f32::MIN;
+use std::f32::{consts::PI, MAX, MIN};

-use crate::aabb::AABB;
-use crate::hitable::Hit;
-use crate::hitable::HitRecord;
-use crate::ray::Ray;
-use crate::vec3::Vec3;
+use crate::{
+    aabb::AABB,
+    hitable::{Hit, HitRecord},
+    ray::Ray,
+    vec3::Vec3,
+};

+#[derive(Debug)]
 pub struct RotateY<H>
 where
    H: Hit,
--- a/rtiow/renderer/src/scale.rs
+++ b/rtiow/renderer/src/scale.rs
@@ -0,0 +1,47 @@
+use crate::{
+    aabb::AABB,
+    hitable::{Hit, HitRecord},
+    ray::Ray,
+};
+
+#[derive(Debug)]
+pub struct Scale<H>
+where
+    H: Hit,
+{
+    hitable: H,
+    scale: f32,
+}
+
+impl<H> Scale<H>
+where
+    H: Hit,
+{
+    pub fn new(hitable: H, scale: f32) -> Scale<H> {
+        Scale { hitable, scale }
+    }
+}
+
+impl<H> Hit for Scale<H>
+where
+    H: Hit,
+{
+    fn hit(&self, r: Ray, t_min: f32, t_max: f32) -> Option<HitRecord> {
+        let moved_r = Ray::new(r.origin / self.scale, r.direction, r.time);
+        if let Some(rec) = self.hitable.hit(moved_r, t_min, t_max) {
+            return Some(HitRecord {
+                p: rec.p * self.scale,
+                t: rec.t * self.scale,
+                ..rec
+            });
+        }
+        None
+    }
+
+    fn bounding_box(&self, t_min: f32, t_max: f32) -> Option<AABB> {
+        if let Some(bbox) = self.hitable.bounding_box(t_min, t_max) {
+            return Some(AABB::new(bbox.min() * self.scale, bbox.max() * self.scale));
+        }
+        None
+    }
+}
--- a/rtiow/renderer/src/scenes/bench.rs
+++ b/rtiow/renderer/src/scenes/bench.rs
@@ -1,17 +1,18 @@
-use rand;
-use rand::Rng;
+use log::trace;
+use rand::{self, Rng};

-use crate::bvh::BVH;
-use crate::camera::Camera;
-use crate::hitable::Hit;
-use crate::hitable_list::HitableList;
-use crate::kdtree::KDTree;
-use crate::material::Lambertian;
-use crate::renderer::Opt;
-use crate::renderer::Scene;
-use crate::sphere::Sphere;
-use crate::texture::ConstantTexture;
-use crate::vec3::Vec3;
+use crate::{
+    bvh::BVH,
+    camera::Camera,
+    hitable::Hit,
+    hitable_list::HitableList,
+    kdtree::KDTree,
+    material::Lambertian,
+    renderer::{Opt, Scene},
+    sphere::Sphere,
+    texture::ConstantTexture,
+    vec3::Vec3,
+};

 pub fn new(opt: &Opt) -> Scene {
    let lookfrom = Vec3::new(20., 20., 20.);
@@ -36,12 +37,12 @@ pub fn new(opt: &Opt) -> Scene {
    let len = 1000;
    for x in 0..len {
        for z in 0..len {
-            let r = rng.gen_range::<f32>(0., 1.);
-            let g = rng.gen_range::<f32>(0., 1.);
-            let b = rng.gen_range::<f32>(0., 1.);
+            let r = rng.gen();
+            let g = rng.gen();
+            let b = rng.gen();

-            let x_pos = (x - len / 2) as f32 + rng.gen_range(-0.1, 0.1);
-            let z_pos = (z - len / 2) as f32 + rng.gen_range(-0.1, 0.1);
+            let x_pos = (x - len / 2) as f32 + rng.gen_range(-0.1..0.1);
+            let z_pos = (z - len / 2) as f32 + rng.gen_range(-0.1..0.1);

            grid.push(Box::new(Sphere::new(
                Vec3::new(x_pos, 0., z_pos),
--- a/rtiow/renderer/src/scenes/book.rs
+++ b/rtiow/renderer/src/scenes/book.rs
@@ -1,21 +1,16 @@
-use rand;
-use rand::Rng;
+use rand::{self, Rng};

-use crate::camera::Camera;
-use crate::hitable::Hit;
-use crate::hitable_list::HitableList;
-use crate::kdtree::KDTree;
-use crate::material::Dielectric;
-use crate::material::Lambertian;
-use crate::material::Material;
-use crate::material::Metal;
-use crate::renderer::Opt;
-use crate::renderer::Scene;
-use crate::sphere::Sphere;
-use crate::texture::CheckerTexture;
-use crate::texture::ConstantTexture;
-use crate::texture::EnvMap;
-use crate::vec3::Vec3;
+use crate::{
+    camera::Camera,
+    hitable::Hit,
+    hitable_list::HitableList,
+    kdtree::KDTree,
+    material::{Dielectric, Lambertian, Material, Metal},
+    renderer::{Opt, Scene},
+    sphere::Sphere,
+    texture::{CheckerTexture, ConstantTexture, EnvMap},
+    vec3::Vec3,
+};

 pub fn new(opt: &Opt) -> Scene {
    let lookfrom = Vec3::new(13., 2., 3.);
@@ -81,7 +76,7 @@ where
        1000.,
        ground_material,
    ))];
-    let mut random = || rng.gen_range::<f32>(0., 1.);
+    let mut random = || rng.gen::<f32>();

    for a in -11..11 {
        for b in -11..11 {
--- a/rtiow/renderer/src/scenes/bvh.rs
+++ b/rtiow/renderer/src/scenes/bvh.rs
@@ -1,14 +1,16 @@
-use crate::bvh::BVH;
-use crate::camera::Camera;
-use crate::hitable::Hit;
-use crate::material::Lambertian;
-use crate::material::Metal;
-use crate::moving_sphere::MovingSphere;
-use crate::renderer::Opt;
-use crate::renderer::Scene;
-use crate::sphere::Sphere;
-use crate::texture::ConstantTexture;
-use crate::vec3::Vec3;
+use log::trace;
+
+use crate::{
+    bvh::BVH,
+    camera::Camera,
+    hitable::Hit,
+    material::{Lambertian, Metal},
+    moving_sphere::MovingSphere,
+    renderer::{Opt, Scene},
+    sphere::Sphere,
+    texture::ConstantTexture,
+    vec3::Vec3,
+};

 pub fn new(opt: &Opt) -> Scene {
    let lookfrom = Vec3::new(3., 3., 2.);
--- a/rtiow/renderer/src/scenes/cornell_box.rs
+++ b/rtiow/renderer/src/scenes/cornell_box.rs
@@ -1,22 +1,20 @@
 use std::sync::Arc;

-use crate::camera::Camera;
-use crate::cuboid::Cuboid;
-use crate::flip_normals::FlipNormals;
-use crate::hitable::Hit;
-use crate::hitable_list::HitableList;
-use crate::kdtree::KDTree;
-use crate::material::DiffuseLight;
-use crate::material::Lambertian;
-use crate::rect::XYRect;
-use crate::rect::XZRect;
-use crate::rect::YZRect;
-use crate::renderer::Opt;
-use crate::renderer::Scene;
-use crate::rotate::RotateY;
-use crate::texture::ConstantTexture;
-use crate::translate::Translate;
-use crate::vec3::Vec3;
+use crate::{
+    camera::Camera,
+    cuboid::Cuboid,
+    flip_normals::FlipNormals,
+    hitable::Hit,
+    hitable_list::HitableList,
+    kdtree::KDTree,
+    material::{DiffuseLight, Lambertian},
+    rect::{XYRect, XZRect, YZRect},
+    renderer::{Opt, Scene},
+    rotate::RotateY,
+    texture::ConstantTexture,
+    translate::Translate,
+    vec3::Vec3,
+};

 pub fn new(opt: &Opt) -> Scene {
    let lookfrom = Vec3::new(278., 278., -800.);
--- a/rtiow/renderer/src/scenes/cornell_smoke.rs
+++ b/rtiow/renderer/src/scenes/cornell_smoke.rs
@@ -1,24 +1,21 @@
 use std::sync::Arc;

-use crate::camera::Camera;
-use crate::constant_medium::ConstantMedium;
-use crate::cuboid::Cuboid;
-use crate::flip_normals::FlipNormals;
-use crate::hitable::Hit;
-use crate::hitable_list::HitableList;
-use crate::kdtree::KDTree;
-use crate::material::DiffuseLight;
-use crate::material::Lambertian;
-use crate::material::Material;
-use crate::rect::XYRect;
-use crate::rect::XZRect;
-use crate::rect::YZRect;
-use crate::renderer::Opt;
-use crate::renderer::Scene;
-use crate::rotate::RotateY;
-use crate::texture::ConstantTexture;
-use crate::translate::Translate;
-use crate::vec3::Vec3;
+use crate::{
+    camera::Camera,
+    constant_medium::ConstantMedium,
+    cuboid::Cuboid,
+    flip_normals::FlipNormals,
+    hitable::Hit,
+    hitable_list::HitableList,
+    kdtree::KDTree,
+    material::{DiffuseLight, Lambertian, Material},
+    rect::{XYRect, XZRect, YZRect},
+    renderer::{Opt, Scene},
+    rotate::RotateY,
+    texture::ConstantTexture,
+    translate::Translate,
+    vec3::Vec3,
+};

 pub fn new(opt: &Opt) -> Scene {
    let lookfrom = Vec3::new(278., 278., -800.);
--- a/rtiow/renderer/src/scenes/dragon.rs
+++ b/rtiow/renderer/src/scenes/dragon.rs
@@ -0,0 +1,116 @@
+use std::{
+    f32::consts::PI,
+    io::{BufReader, Cursor},
+};
+
+use stl::STL;
+
+use crate::{
+    bvh_triangles::BVHTriangles,
+    camera::Camera,
+    colors::generate_rainbow,
+    hitable::Hit,
+    hitable_list::HitableList,
+    kdtree::KDTree,
+    material::{Lambertian, Metal},
+    renderer::{Opt, Scene},
+    rotate::RotateY,
+    scale::Scale,
+    sphere::Sphere,
+    texture::{ConstantTexture, EnvMap},
+    translate::Translate,
+    vec3::Vec3,
+};
+
+pub fn new(opt: &Opt) -> Scene {
+    let lookfrom = Vec3::new(0., 80., 80.);
+    let lookat = Vec3::new(0., 0., 0.);
+    let dist_to_focus = 10.0;
+    let aperture = 0.0;
+    let time_min = 0.;
+    let time_max = 1.;
+    let camera = Camera::new(
+        lookfrom,
+        lookat,
+        Vec3::new(0., 1., 0.),
+        45.,
+        opt.width as f32 / opt.height as f32,
+        aperture,
+        dist_to_focus,
+        time_min,
+        time_max,
+    );
+    //let dragon_material = Dielectric::new(1.5);
+    let dragon_material = Metal::new(Vec3::new(0.6, 0.6, 0.6), 0.0);
+    //let dragon_material = Lambertian::new(ConstantTexture::new(Vec3::new(1.0, 1.0, 0.2)));
+
+    let ground_color = if opt.use_accel {
+        ConstantTexture::new(Vec3::new(1.0, 0.4, 0.4))
+    } else {
+        ConstantTexture::new(Vec3::new(0.4, 0.4, 0.4))
+    };
+
+    let stl_cube = STL::parse(
+        BufReader::new(Cursor::new(include_bytes!("../../stls/dragon.stl"))),
+        false,
+    )
+    .expect("failed to parse cube");
+    let _light_size = 50.;
+    let _light_height = 200.;
+    let sphere_radius = 5.;
+    let circle_radius = 40.;
+    let num_spheres = 16;
+    let palette = generate_rainbow(num_spheres);
+    let spheres: Vec<Box<dyn Hit>> = (0..num_spheres)
+        .map(|i| (i, i as f32, num_spheres as f32))
+        .map(|(idx, idx_f, n)| (idx, idx_f * 2. * PI / n))
+        .map(|(idx, rad)| -> Box<dyn Hit> {
+            let x = circle_radius * rad.cos();
+            let y = 4. * sphere_radius;
+            let z = circle_radius * rad.sin();
+            let c = palette[idx];
+            Box::new(Sphere::new(
+                [x, y, z],
+                sphere_radius,
+                Lambertian::new(ConstantTexture::new(c)),
+            ))
+        })
+        .collect();
+    let mut objects: Vec<Box<dyn Hit>> = vec![
+        Box::new(Sphere::new(
+            Vec3::new(0., 0.1, -0.5),
+            0.1,
+            Lambertian::new([0., 1., 1.]),
+        )),
+        // Earth sized sphere
+        //Box::new(Sphere::new( Vec3::new(0., -10000., 0.), 10000., Lambertian::new(ground_color),)),
+        // STL Mesh
+        Box::new(crate::debug_hit::DebugHit::new(RotateY::new(
+            Translate::new(
+                BVHTriangles::new(&stl_cube, dragon_material, 250.),
+                [0., -10., 0.],
+            ),
+            180.,
+        ))),
+    ];
+    objects.extend(spheres);
+
+    let world: Box<dyn Hit> = if opt.use_accel {
+        Box::new(KDTree::new(objects, time_min, time_max))
+    } else {
+        Box::new(HitableList::new(objects))
+    };
+    let skybox_bytes = include_bytes!("../../images/envmap.jpg");
+    let skybox = image::load_from_memory(skybox_bytes).unwrap().to_rgb();
+    Scene {
+        camera,
+        world,
+        subsamples: opt.subsamples,
+        num_threads: opt.num_threads,
+        width: opt.width,
+        height: opt.height,
+        global_illumination: true,
+        env_map: Some(EnvMap::new(skybox)),
+        ..Default::default()
+    }
+}
--- a/rtiow/renderer/src/scenes/final_scene.rs
+++ b/rtiow/renderer/src/scenes/final_scene.rs
@@ -1,33 +1,26 @@
 use std::sync::Arc;

 use image;
-use rand;
-use rand::Rng;
+use rand::{self, Rng};

-use crate::camera::Camera;
-use crate::constant_medium::ConstantMedium;
-use crate::cuboid::Cuboid;
-use crate::hitable::Hit;
-use crate::hitable_list::HitableList;
-use crate::kdtree::KDTree;
-use crate::material::Dielectric;
-use crate::material::DiffuseLight;
-use crate::material::Lambertian;
-use crate::material::Material;
-use crate::material::Metal;
-use crate::moving_sphere::MovingSphere;
-use crate::noise::perlin::Perlin;
-use crate::noise::NoiseType;
-use crate::rect::XZRect;
-use crate::renderer::Opt;
-use crate::renderer::Scene;
-use crate::rotate::RotateY;
-use crate::sphere::Sphere;
-use crate::texture::ConstantTexture;
-use crate::texture::ImageTexture;
-use crate::texture::NoiseTexture;
-use crate::translate::Translate;
-use crate::vec3::Vec3;
+use crate::{
+    camera::Camera,
+    constant_medium::ConstantMedium,
+    cuboid::Cuboid,
+    hitable::Hit,
+    hitable_list::HitableList,
+    kdtree::KDTree,
+    material::{Dielectric, DiffuseLight, Lambertian, Material, Metal},
+    moving_sphere::MovingSphere,
+    noise::{perlin::Perlin, NoiseType},
+    rect::XZRect,
+    renderer::{Opt, Scene},
+    rotate::RotateY,
+    sphere::Sphere,
+    texture::{ConstantTexture, ImageTexture, NoiseTexture},
+    translate::Translate,
+    vec3::Vec3,
+};

 pub fn new(opt: &Opt) -> Scene {
    let lookfrom = Vec3::new(478., 278., -600.);
@@ -64,7 +57,7 @@ pub fn new(opt: &Opt) -> Scene {
            let z0 = -1000. + j as f32 * w;
            let y0 = 0.;
            let x1 = x0 + w;
-            let y1 = 100. * (rng.gen_range::<f32>(0., 1.) + 0.01);
+            let y1 = 100. * (rng.gen::<f32>() + 0.01);
            let z1 = z0 + w;
            boxlist.push(Box::new(Cuboid::new(
                Vec3::new(x0, y0, z0),
@@ -152,9 +145,9 @@ pub fn new(opt: &Opt) -> Scene {
    for _ in 0..ns {
        boxlist.push(Box::new(Sphere::new(
            [
-                165. * rng.gen_range::<f32>(0., 1.),
-                165. * rng.gen_range::<f32>(0., 1.),
-                165. * rng.gen_range::<f32>(0., 1.),
+                165. * rng.gen::<f32>(),
+                165. * rng.gen::<f32>(),
+                165. * rng.gen::<f32>(),
            ],
            10.,
            Arc::clone(&white),
--- a/rtiow/renderer/src/scenes/mandelbrot.rs
+++ b/rtiow/renderer/src/scenes/mandelbrot.rs
@@ -1,24 +1,18 @@
 use rand;

-use crate::camera::Camera;
-use crate::hitable::Hit;
-use crate::hitable_list::HitableList;
-use crate::kdtree::KDTree;
-use crate::material::DiffuseLight;
-use crate::material::Lambertian;
-use crate::noise::perlin::Perlin;
-use crate::noise::NoiseType;
-use crate::rect::XYRect;
-use crate::rect::XZRect;
-use crate::rect::YZRect;
-use crate::renderer::Opt;
-use crate::renderer::Scene;
-use crate::sphere::Sphere;
-use crate::texture::ConstantTexture;
-use crate::texture::ImageTexture;
-use crate::texture::Mandelbrot;
-use crate::texture::NoiseTexture;
-use crate::vec3::Vec3;
+use crate::{
+    camera::Camera,
+    hitable::Hit,
+    hitable_list::HitableList,
+    kdtree::KDTree,
+    material::{DiffuseLight, Lambertian},
+    noise::{perlin::Perlin, NoiseType},
+    rect::{XYRect, XZRect, YZRect},
+    renderer::{Opt, Scene},
+    sphere::Sphere,
+    texture::{ConstantTexture, ImageTexture, Mandelbrot, NoiseTexture},
+    vec3::Vec3,
+};

 pub fn new(opt: &Opt) -> Scene {
    let lookfrom = Vec3::new(20., 20., 20.);
--- a/rtiow/renderer/src/scenes/mod.rs
+++ b/rtiow/renderer/src/scenes/mod.rs
@@ -3,9 +3,12 @@ pub mod book;
 pub mod bvh;
 pub mod cornell_box;
 pub mod cornell_smoke;
+pub mod dragon;
 pub mod final_scene;
 pub mod mandelbrot;
 pub mod perlin_debug;
 pub mod spheramid;
+pub mod stltest;
 pub mod test;
+pub mod tron;
 pub mod tutorial;
--- a/Show More
+++ b/Show More