matrices: moving another doctest to unit

transformations: moving another doctest to unit
lights: moving another doctest to unit
2021-07-30 21:59:40 -07:00 · 2021-07-30 21:58:32 -07:00 · 2021-07-30 21:51:35 -07:00 · 2021-07-30 21:49:48 -07:00 · 2021-07-30 21:44:58 -07:00 · 2021-07-30 21:33:43 -07:00
19 changed files with 2426 additions and 1418 deletions
--- a/rtchallenge/Cargo.toml
+++ b/rtchallenge/Cargo.toml
@ -8,7 +8,6 @@ edition = "2018"

 [features]
 default = [ "float-as-double" ]
-disable-inverse-cache = []
 float-as-double = []

 [dependencies]
--- a/rtchallenge/examples/eoc10.rs
+++ b/rtchallenge/examples/eoc10.rs
@ -0,0 +1,168 @@
+use std::time::Instant;
+
+use anyhow::Result;
+use structopt::StructOpt;
+
+use rtchallenge::prelude::*;
+
+use rtchallenge::{
+    camera::RenderStrategy, float::consts::PI, patterns::test_pattern, BLACK, 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, BLACK)
+                        .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, BLACK).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, BLACK)
+                        .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, BLACK)
+                        .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, BLACK)
+                        .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/eoc6.rs
+++ b/rtchallenge/examples/eoc6.rs
@ -22,7 +22,7 @@ fn main() -> Result<()> {
    let half = wall_size / 2.;
    let mut shape = Shape::sphere();
    shape.material = Material {
-        color: Color::new(1., 0.2, 1.),
+        color: Color::new(1., 0.2, 1.).into(),
        specular: 0.5,
        diffuse: 0.7,
        shininess: 30.,
@ -44,7 +44,15 @@ fn main() -> Result<()> {
                let point = r.position(hit.t);
                let normal = hit.object.normal_at(point);
                let eye = -r.direction;
-                let color = lighting(&hit.object.material, &light, point, eye, normal, in_shadow);
+                let color = lighting(
+                    &hit.object.material,
+                    &hit.object,
+                    &light,
+                    point,
+                    eye,
+                    normal,
+                    in_shadow,
+                );
                c.set(x, y, color);
            }
        }
--- a/rtchallenge/examples/eoc7.rs
+++ b/rtchallenge/examples/eoc7.rs
@ -42,7 +42,7 @@ fn main() -> Result<()> {
    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),
+        color: Color::new(1., 0.9, 0.9).into(),
        specular: 0.,
        ..Material::default()
    };
@ -68,7 +68,7 @@ fn main() -> Result<()> {
    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),
+        color: Color::new(0.1, 1., 0.5).into(),
        diffuse: 0.7,
        specular: 0.3,
        ..Material::default()
@ -77,7 +77,7 @@ fn main() -> Result<()> {
    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),
+        color: Color::new(0.5, 1., 0.1).into(),
        diffuse: 0.7,
        specular: 0.3,
        ..Material::default()
@ -88,7 +88,7 @@ fn main() -> Result<()> {
        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),
+        color: Color::new(1., 0.8, 0.1).into(),
        diffuse: 0.7,
        specular: 0.3,
        ..Material::default()
--- a/rtchallenge/examples/eoc8.rs
+++ b/rtchallenge/examples/eoc8.rs
@ -54,7 +54,7 @@ fn main() -> Result<()> {
    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),
+        color: Color::new(1., 0.9, 0.9).into(),
        specular: 0.,
        ..Material::default()
    };
@ -80,7 +80,7 @@ fn main() -> Result<()> {
    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),
+        color: Color::new(0.1, 1., 0.5).into(),
        diffuse: 0.7,
        specular: 0.3,
        ..Material::default()
@ -89,7 +89,7 @@ fn main() -> Result<()> {
    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.),
+        color: Color::new(1., 1., 1.).into(),
        diffuse: 0.7,
        specular: 0.0,
        ..Material::default()
@ -100,7 +100,7 @@ fn main() -> Result<()> {
        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),
+        color: Color::new(1., 0.8, 0.1).into(),
        diffuse: 0.7,
        specular: 0.3,
        ..Material::default()
--- a/rtchallenge/examples/eoc9-prelude.rs
+++ b/rtchallenge/examples/eoc9-prelude.rs
@ -11,19 +11,24 @@ use rtchallenge::{camera::RenderStrategy, float::consts::PI, WHITE};
 #[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 width = 2560;
-    let height = 1440;

    let light1 = PointLightBuilder::default()
        .position(point(-5., 5., -5.))
@ -42,8 +47,8 @@ fn main() -> Result<()> {
    let to = point(0., 1., 0.);
    let up = point(0., 1., 0.);
    let camera = CameraBuilder::default()
-        .hsize(width)
-        .vsize(height)
+        .hsize(opt.width)
+        .vsize(opt.height)
        .field_of_view(PI / 4.)
        .transform(view_transform(from, to, up))
        .render_strategy(opt.render_strategy)
--- a/rtchallenge/examples/eoc9.rs
+++ b/rtchallenge/examples/eoc9.rs
@ -20,19 +20,24 @@ use rtchallenge::{
 #[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 width = 2560;
-    let height = 1440;

    let light_position = Tuple::point(-5., 5., -5.);
    let light_color = WHITE;
@ -44,7 +49,7 @@ fn main() -> Result<()> {
    let light_color = Color::new(0.2, 0.2, 0.1);
    let light3 = PointLight::new(light_position, light_color);

-    let mut camera = Camera::new(width, height, PI / 4.);
+    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.);
@ -54,14 +59,14 @@ fn main() -> Result<()> {

    let mut floor = Shape::plane();
    floor.material = Material {
-        color: Color::new(1., 0.2, 0.2),
+        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),
+        color: Color::new(0.6, 0.6, 0.8).into(),
        specular: 0.2,
        ..Material::default()
    };
@ -69,7 +74,7 @@ fn main() -> Result<()> {
    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),
+        color: Color::new(0.1, 1., 0.5).into(),
        diffuse: 0.7,
        specular: 0.3,
        ..Material::default()
@ -78,7 +83,7 @@ fn main() -> Result<()> {
    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.),
+        color: Color::new(1., 1., 1.).into(),
        diffuse: 0.7,
        specular: 0.0,
        ..Material::default()
@ -89,7 +94,7 @@ fn main() -> Result<()> {
        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),
+        color: Color::new(1., 0.8, 0.1).into(),
        diffuse: 0.7,
        specular: 0.3,
        ..Material::default()
--- a/rtchallenge/src/camera.rs
+++ b/rtchallenge/src/camera.rs
@ -22,6 +22,8 @@ use crate::{
    Float, BLACK,
 };

+const MAX_DEPTH_RECURSION: usize = 5;
+
 #[derive(Copy, Clone, StructOpt, Debug, Deserialize)]
 #[serde(rename_all = "kebab-case")]
 pub enum RenderStrategy {
@ -116,27 +118,6 @@ enum Response {
 impl Camera {
    /// Create a camera with a canvas of pixel hsize (height) and vsize (width)
    /// with the given field of view (in radians).
-    ///
-    /// # Examples
-    /// ```
-    /// use rtchallenge::{camera::Camera, float::consts::PI, matrices::Matrix4x4, EPSILON};
-    ///
-    /// 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);
-    /// ```
    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;
@ -206,47 +187,17 @@ impl Camera {

    /// Calculate ray that starts at the camera and passes through the (x,y)
    /// pixel on the canvas.
-    ///
-    /// # Examples
-    /// ```
-    /// use rtchallenge::{
-    ///     camera::Camera, float::consts::PI, matrices::Matrix4x4, tuples::Tuple, Float,
-    /// };
-    ///
-    /// // 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, Tuple::point(0., 0., 0.));
-    /// assert_eq!(r.direction, Tuple::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, Tuple::point(0., 0., 0.));
-    /// assert_eq!(r.direction, Tuple::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, Tuple::point(0., 2., -5.));
-    /// assert_eq!(
-    ///     r.direction,
-    ///     Tuple::vector((2. as Float).sqrt() / 2., 0., -(2. as Float).sqrt() / 2.)
-    /// );
-    /// ```
-    #[cfg(not(feature = "disable-inverse-cache"))]
    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 pixle in world space.
+        // 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, transofmrm the canvas point and the origin,
+        // 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.);
@ -255,48 +206,8 @@ impl Camera {

        Ray::new(origin, direction)
    }
-    #[cfg(feature = "disable-inverse-cache")]
-    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 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.transform.inverse() * Tuple::point(world_x, world_y, -1.);
-        let origin = self.transform.inverse() * Tuple::point(0., 0., 0.);
-        let direction = (pixel - origin).normalize();
-
-        Ray::new(origin, direction)
-    }

    /// Use camera to render an image of the given world.
-    /// # Examples
-    /// ```
-    /// use rtchallenge::{
-    ///     camera::Camera,
-    ///     float::consts::PI,
-    ///     transformations::view_transform,
-    ///     tuples::{Color, Tuple},
-    ///     world::World,
-    /// };
-    ///
-    /// // Rendering a world with a camera.
-    /// let w = World::test_world();
-    /// let mut c = Camera::new(11, 11, PI / 2.);
-    /// let from = Tuple::point(0., 0., -5.);
-    /// let to = Tuple::point(0., 0., 0.);
-    /// let up = Tuple::vector(0., 1., 0.);
-    /// c.set_transform(view_transform(from, to, up));
-    /// let image = c.render(&w);
-    /// assert_eq!(image.get(5, 5), Color::new(0.38066, 0.47583, 0.2855));
-    /// ```
    pub fn render(&self, w: &World) -> Canvas {
        use RenderStrategy::*;

@ -416,12 +327,12 @@ impl Camera {
            let color = self
                .supersample_rays_for_pixel(x, y, self.samples_per_pixel)
                .iter()
-                .map(|ray| w.color_at(&ray))
+                .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)
+            w.color_at(&ray, MAX_DEPTH_RECURSION)
        }
    }
 }
@ -456,3 +367,70 @@ fn render_worker_task(
        }
    }
 }
+
+#[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/intersections.rs
+++ b/rtchallenge/src/intersections.rs
@ -3,7 +3,7 @@ use std::ops::Index;
 use crate::{
    rays::Ray,
    shapes::Shape,
-    tuples::{dot, Tuple},
+    tuples::{dot, reflect, Tuple},
    Float, EPSILON,
 };

@ -20,50 +20,22 @@ impl<'i> PartialEq for Intersection<'i> {

 impl<'i> Intersection<'i> {
    /// Create new `Intersection` at the given `t` that hits the given `object`.
-    ///
-    /// # Examples
-    /// ```
-    /// use rtchallenge::{intersections::Intersection, shapes::Shape};
-    ///
-    /// // 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);
-    /// ```
    pub fn new(t: Float, object: &Shape) -> Intersection {
        Intersection { t, object }
    }
 }

 /// Aggregates `Intersection`s.
-///
-/// # Examples
-/// ```
-/// use rtchallenge::{
-///     intersections::{Intersection, Intersections},
-///     rays::Ray,
-///     shapes::{intersect, Shape},
-///     tuples::Tuple,
-/// };
-///
-/// 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(Tuple::point(0., 0., -5.), Tuple::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);
-/// ```
 #[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)
@ -72,50 +44,6 @@ impl<'i> Intersections<'i> {
        self.0.len()
    }
    /// Finds nearest hit for this collection of intersections.
-    ///
-    /// # Examples
-    /// ```
-    /// use rtchallenge::{
-    ///     intersections::{Intersection, Intersections},
-    ///     rays::Ray,
-    ///     shapes::{intersect, Shape},
-    ///     tuples::Tuple,
-    /// };
-    ///
-    /// // The hit, 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));
-    ///
-    /// // The hit, 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));
-    ///
-    /// // The hit, 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);
-    ///
-    /// // The hit is 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));
-    /// ```
    pub fn hit(&self) -> Option<&Intersection> {
        self.0.iter().filter(|i| i.t > 0.).min_by(|i1, i2| {
            i1.t.partial_cmp(&i2.t)
@ -145,81 +73,358 @@ 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.
-///
-/// # Examples
-/// ```
-/// use rtchallenge::{
-///     intersections::{prepare_computations, Intersection, Intersections},
-///     rays::Ray,
-///     matrices::Matrix4x4,
-///     shapes::{intersect, Shape},
-///     tuples::Tuple,
-///     EPSILON
-/// };
-///
-/// // Precomputing the state of an intersection.
-/// let r = Ray::new(Tuple::point(0., 0., -5.), Tuple::vector(0., 0., 1.));
-/// let shape = Shape::sphere();
-/// let i = Intersection::new(4., &shape);
-/// let comps = prepare_computations(&i, &r);
-/// assert_eq!(comps.t, i.t);
-/// assert_eq!(comps.object, i.object);
-/// assert_eq!(comps.point, Tuple::point(0., 0., -1.));
-/// assert_eq!(comps.eyev, Tuple::vector(0., 0., -1.));
-/// assert_eq!(comps.normalv, Tuple::vector(0., 0., -1.));
-///
-/// // The hit, when an intersection occurs on the outside.
-/// let r = Ray::new(Tuple::point(0., 0., -5.), Tuple::vector(0., 0., 1.));
-/// let shape = Shape::sphere();
-/// let i = Intersection::new(4., &shape);
-/// let comps = prepare_computations(&i, &r);
-/// assert_eq!(comps.inside, false);
-///
-/// // The hit, when an intersection occurs on the inside.
-/// let r = Ray::new(Tuple::point(0., 0., 0.), Tuple::vector(0., 0., 1.));
-/// let shape = Shape::sphere();
-/// let i = Intersection::new(1., &shape);
-/// let comps = prepare_computations(&i, &r);
-/// assert_eq!(comps.point, Tuple::point(0., 0., 1.));
-/// assert_eq!(comps.eyev, Tuple::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, Tuple::vector(0., 0., -1.));
-///
-/// // The hit should offset the point.
-/// let r = Ray::new(Tuple::point(0., 0., -5.), Tuple::vector(0., 0., 1.));
-/// let mut shape = Shape::sphere();
-/// shape .set_transform(Matrix4x4::translation(0.,0.,1.));
-/// let i = Intersection::new(5., &shape);
-/// let comps = prepare_computations(&i, &r);
-/// assert!(comps.over_point.z< -EPSILON/2.);
-/// assert!(comps.point.z>comps.over_point.z);
-/// ```
-pub fn prepare_computations<'i>(i: &'i Intersection, r: &Ray) -> PrecomputedData<'i> {
-    let point = r.position(i.t);
-    let normalv = i.object.normal_at(point);
+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: i.t,
-        object: i.object,
+        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
@ -4,6 +4,7 @@ pub mod intersections;
 pub mod lights;
 pub mod materials;
 pub mod matrices;
+pub mod patterns;
 pub mod rays;
 pub mod shapes;
 pub mod transformations;
@ -44,6 +45,7 @@ pub mod prelude {
        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::{plane, sphere, test_shape},
        transformations::view_transform,
        tuples::{point, vector, Color},
--- a/rtchallenge/src/lights.rs
+++ b/rtchallenge/src/lights.rs
@ -13,21 +13,6 @@ pub struct PointLight {
 impl PointLight {
    /// Creates a new `PositionLight` at the given `position` and with the given
    /// `intensity`.
-    ///
-    /// # Examples
-    /// ```
-    /// use rtchallenge::{
-    ///     lights::PointLight,
-    ///     tuples::{Color, Tuple},
-    ///     WHITE,
-    /// };
-    ///
-    /// let intensity = WHITE;
-    /// let position = Tuple::point(0., 0., 0.);
-    /// let light = PointLight::new(position, intensity);
-    /// assert_eq!(light.position, position);
-    /// assert_eq!(light.intensity, intensity);
-    /// ```
    pub fn new<C>(position: Tuple, intensity: C) -> PointLight
    where
        C: Into<Color>,
@ -38,3 +23,17 @@ impl PointLight {
        }
    }
 }
+
+#[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/materials.rs
+++ b/rtchallenge/src/materials.rs
@ -2,8 +2,9 @@ use derive_builder::Builder;

 use crate::{
    lights::PointLight,
-    tuples::Color,
-    tuples::{dot, reflect, Tuple},
+    patterns::Pattern,
+    shapes::Shape,
+    tuples::{dot, reflect, Color, Tuple},
    Float, BLACK, WHITE,
 };

@ -11,103 +12,36 @@ use crate::{
 #[builder(default)]
 pub struct Material {
    #[builder(setter(into))]
-    pub color: Color,
+    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.
-    ///
-    /// # Examples
-    /// ```
-    /// use rtchallenge::{materials::Material, tuples::Color, WHITE};
-    ///
-    /// let m = Material::default();
-    /// assert_eq!(
-    ///     m,
-    ///     Material {
-    ///         color: WHITE,
-    ///         ambient: 0.1,
-    ///         diffuse: 0.9,
-    ///         specular: 0.9,
-    ///         shininess: 200.,
-    ///     }
-    /// );
-    /// ```
    fn default() -> Material {
        Material {
-            color: WHITE,
+            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.
-///
-/// # Examples
-/// ```
-/// use rtchallenge::{
-///     lights::PointLight,
-///     materials::{lighting, Material},
-///     tuples::{Color, Tuple},
-///     Float, WHITE,
-/// };
-///
-/// let in_shadow = false;
-/// let m = Material::default();
-/// let position = Tuple::point(0., 0., 0.);
-///
-/// // Lighting with the eye between the light and the surface.
-/// let eyev = Tuple::vector(0., 0., -1.);
-/// let normalv = Tuple::vector(0., 0., -1.);
-/// let light = PointLight::new(Tuple::point(0., 0., -10.), WHITE);
-/// let result = lighting(&m, &light, position, eyev, normalv, in_shadow);
-/// assert_eq!(result, Color::new(1.9, 1.9, 1.9));
-///
-/// // Lighting with the eye between the light and the surface, eye offset 45°.
-/// let eyev = Tuple::vector(0., (2. as Float).sqrt() / 2., -(2. as Float).sqrt() / 2.);
-/// let normalv = Tuple::vector(0., 0., -1.);
-/// let light = PointLight::new(Tuple::point(0., 0., -10.), WHITE);
-/// let result = lighting(&m, &light, position, eyev, normalv, in_shadow);
-/// assert_eq!(result, WHITE);
-///
-/// // Lighting with the eye opposite surface, light offset 45°.
-/// let eyev = Tuple::vector(0., 0., -1.);
-/// let normalv = Tuple::vector(0., 0., -1.);
-/// let light = PointLight::new(Tuple::point(0., 10., -10.), WHITE);
-/// let result = lighting(&m, &light, position, eyev, normalv, in_shadow);
-/// assert_eq!(result, Color::new(0.7364, 0.7364, 0.7364));
-///
-/// // Lighting with the eye in the path of the reflection vector.
-/// let eyev = Tuple::vector(0., -(2.0 as Float).sqrt() / 2., -(2.0 as Float).sqrt() / 2.);
-/// let normalv = Tuple::vector(0., 0., -1.);
-/// let light = PointLight::new(Tuple::point(0., 10., -10.), WHITE);
-/// let result = lighting(&m, &light, position, eyev, normalv, in_shadow);
-/// assert_eq!(result, Color::new(1.63639, 1.63639, 1.63639));
-///
-/// // Lighting with the light behind the surface.
-/// let eyev = Tuple::vector(0., 0., -1.);
-/// let normalv = Tuple::vector(0., 0., -1.);
-/// let light = PointLight::new(Tuple::point(0., 0., 10.), WHITE);
-/// let result = lighting(&m, &light, position, eyev, normalv, in_shadow);
-/// assert_eq!(result, Color::new(0.1, 0.1, 0.1));
-///
-/// // Lighting with the surface in shadow.
-/// let in_shadow = true;
-/// let eyev = Tuple::vector(0., 0., -1.);
-/// let normalv = Tuple::vector(0., 0., -1.);
-/// let light = PointLight::new(Tuple::point(0., 0., -10.), WHITE);
-/// let result = lighting(&m, &light, position, eyev, normalv, in_shadow);
-/// assert_eq!(result, Color::new(0.1, 0.1, 0.1));
-/// ```
 pub fn lighting(
    material: &Material,
+    object: &Shape,
    light: &PointLight,
    point: Tuple,
    eyev: Tuple,
@ -115,7 +49,8 @@ pub fn lighting(
    in_shadow: bool,
 ) -> Color {
    // Combine the surface color with the light's color.
-    let effective_color = material.color * light.intensity;
+    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.
@ -149,3 +84,153 @@ pub fn lighting(
        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,
+            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, BLACK),
+                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
@ -4,82 +4,30 @@ use std::ops::{Index, IndexMut, Mul, Sub};
 use crate::{tuples::Tuple, Float, EPSILON};

 /// Short hand for creating a Matrix4x4 set to the identity matrix.
-///
-/// # Examples
-/// ```
-/// use rtchallenge::matrices::{identity, Matrix4x4};
-///
-/// assert_eq!(identity(), Matrix4x4::identity());
-/// ```
 pub fn identity() -> Matrix4x4 {
    Matrix4x4::identity()
 }
 /// Short hand for creating a Matrix4x4 for rotating around the X-axis.
-///
-/// # Examples
-/// ```
-/// use rtchallenge::matrices::{rotation_x, Matrix4x4};
-///
-/// assert_eq!(rotation_x(10.), Matrix4x4::rotation_x(10.));
-/// ```
 pub fn rotation_x(radians: Float) -> Matrix4x4 {
    Matrix4x4::rotation_x(radians)
 }
 /// Short hand for creating a Matrix4x4 for rotating around the Y-axis.
-///
-/// # Examples
-/// ```
-/// use rtchallenge::matrices::{rotation_y, Matrix4x4};
-///
-/// assert_eq!(rotation_y(10.), Matrix4x4::rotation_y(10.));
-/// ```
 pub fn rotation_y(radians: Float) -> Matrix4x4 {
    Matrix4x4::rotation_y(radians)
 }
 /// Short hand for creating a Matrix4x4 for rotating around the Z-axis.
-///
-/// # Examples
-/// ```
-/// use rtchallenge::matrices::{rotation_z, Matrix4x4};
-///
-/// assert_eq!(rotation_z(10.), Matrix4x4::rotation_z(10.));
-/// ```
 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.
-///
-/// # Examples
-/// ```
-/// use rtchallenge::matrices::{scaling, Matrix4x4};
-///
-/// assert_eq!(scaling(1., 2., 3.), Matrix4x4::scaling(1., 2., 3.));
-/// ```
 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.
-///
-/// # Examples
-/// ```
-/// use rtchallenge::matrices::{shearing, Matrix4x4};
-///
-/// assert_eq!(
-///     shearing(1., 2., 3., 4., 5., 6.),
-///     Matrix4x4::shearing(1., 2., 3., 4., 5., 6.)
-/// );
-/// ```
 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.
-///
-/// # Examples
-/// ```
-/// use rtchallenge::matrices::{translation, Matrix4x4};
-///
-/// assert_eq!(translation(1., 2., 3.), Matrix4x4::translation(1., 2., 3.));
-/// ```
 pub fn translation(x: Float, y: Float, z: Float) -> Matrix4x4 {
    Matrix4x4::translation(x, y, z)
 }
@ -95,16 +43,6 @@ impl Matrix2x2 {
    }

    /// Calculate the determinant of a 2x2.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use rtchallenge::matrices::Matrix2x2;
-    ///
-    /// let a = Matrix2x2::new([1., 5.], [-3., 2.]);
-    ///
-    /// assert_eq!(a.determinant(), 17.);
-    /// ```
    pub fn determinant(&self) -> Float {
        let m = self;
        m[(0, 0)] * m[(1, 1)] - m[(0, 1)] * m[(1, 0)]
@ -142,16 +80,6 @@ impl Matrix3x3 {
        Matrix3x3 { m: [r0, r1, r2] }
    }
    /// submatrix extracts a 2x2 matrix ignoring the 0-based `row` and `col` given.
-    ///
-    /// # Examples
-    /// ```
-    /// use rtchallenge::matrices::{Matrix2x2, Matrix3x3};
-    ///
-    /// assert_eq!(
-    ///     Matrix3x3::new([1., 5., 0.], [-3., 2., 7.], [0., 6., -3.],).submatrix(0, 2),
-    ///     Matrix2x2::new([-3., 2.], [0., 6.])
-    /// );
-    /// ```
    pub fn submatrix(&self, row: usize, col: usize) -> Matrix2x2 {
        assert!(row < 3);
        assert!(col < 3);
@ -172,49 +100,17 @@ impl Matrix3x3 {
    }

    /// Compute minor of a 3x3 matrix.
-    ///
-    /// # Examples
-    /// ```
-    /// use rtchallenge::matrices::Matrix3x3;
-    ///
-    /// 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));
-    /// ```
    pub fn minor(&self, row: usize, col: usize) -> Float {
        self.submatrix(row, col).determinant()
    }

    /// Compute cofactor of a 3x3 matrix.
-    ///
-    /// # Examples
-    /// ```
-    /// use rtchallenge::matrices::Matrix3x3;
-    ///
-    /// 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.);
-    /// ```
    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.
-    ///
-    /// # Examples
-    /// ```
-    /// use rtchallenge::matrices::Matrix3x3;
-    ///
-    /// 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.);
-    /// ```
    pub fn determinant(&self) -> Float {
        (0..3).map(|i| self.cofactor(0, i) * self[(0, i)]).sum()
    }
@ -244,34 +140,6 @@ impl PartialEq for Matrix3x3 {

 /// 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.
-///
-/// # Examples
-/// ```
-/// use rtchallenge::{float::consts::PI, matrices::Matrix4x4, tuples::Tuple};
-///
-/// // Individual transformations are applied in sequence.
-/// let p = Tuple::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, Tuple::point(1., -1., 0.));
-/// // Then apply scaling.
-/// let p3 = b * p2;
-/// assert_eq!(p3, Tuple::point(5., -5., 0.));
-/// // Then apply translation.
-/// let p4 = c * p3;
-/// assert_eq!(p4, Tuple::point(15., 0., 7.));
-///
-/// // Chained transformations must be applied in reverse order.
-/// let p = Tuple::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, Tuple::point(15., 0., 7.));
-/// ```
 #[derive(Copy, Clone, Default)]
 pub struct Matrix4x4 {
    m: [[Float; 4]; 4],
@ -292,21 +160,6 @@ impl From<[Float; 16]> for Matrix4x4 {

 impl Matrix4x4 {
    /// Create a `Matrix4x4` containing the identity, all zeros with ones along the diagonal.
-    /// # Examples
-    ///
-    /// ```
-    /// use rtchallenge::matrices::Matrix4x4;
-    ///
-    /// let a = Matrix4x4::new(
-    ///     [0., 1., 2., 3.],
-    ///     [1., 2., 4., 8.],
-    ///     [2., 4., 8., 16.],
-    ///     [4., 8., 16., 32.],
-    /// );
-    /// let i = Matrix4x4::identity();
-    ///
-    /// assert_eq!(a * i, a);
-    /// ```
    pub fn identity() -> Matrix4x4 {
        Matrix4x4::new(
            [1., 0., 0., 0.],
@ -324,22 +177,6 @@ impl Matrix4x4 {
    }

    /// Creates a 4x4 matrix representing a translation of x,y,z.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use rtchallenge::{matrices::Matrix4x4, tuples::Tuple};
-    ///
-    /// let transform = Matrix4x4::translation(5., -3., 2.);
-    /// let p = Tuple::point(-3., 4., 5.);
-    /// assert_eq!(transform * p, Tuple::point(2., 1., 7.));
-    ///
-    /// let inv = transform.inverse();
-    /// assert_eq!(inv * p, Tuple::point(-8., 7., 3.));
-    ///
-    /// let v = Tuple::vector(-3., 4., 5.);
-    /// assert_eq!(transform * v, v);
-    /// ```
    pub fn translation(x: Float, y: Float, z: Float) -> Matrix4x4 {
        Matrix4x4::new(
            [1., 0., 0., x],
@ -350,30 +187,6 @@ impl Matrix4x4 {
    }

    /// Creates a 4x4 matrix representing a scaling of x,y,z.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use rtchallenge::{matrices::Matrix4x4, tuples::Tuple};
-    ///
-    /// // A scaling matrix applied to a point.
-    /// let transform = Matrix4x4::scaling(2., 3., 4.);
-    /// let p = Tuple::point(-4., 6., 8.);
-    /// assert_eq!(transform * p, Tuple::point(-8., 18., 32.));
-    ///
-    /// // A scaling matrix applied to a vector.
-    /// let v = Tuple::vector(-4., 6., 8.);
-    /// assert_eq!(transform * v, Tuple::vector(-8., 18., 32.));
-    ///
-    /// // Multiplying by the inverse of a scaling matrix.
-    /// let inv = transform.inverse();
-    /// assert_eq!(inv * v, Tuple::vector(-2., 2., 2.));
-    ///
-    /// // Reflection is scaling by a negative value.
-    /// let transform = Matrix4x4::scaling(-1., 1., 1.);
-    /// let p = Tuple::point(2., 3., 4.);
-    /// assert_eq!(transform * p, Tuple::point(-2., 3., 4.));
-    /// ```
    pub fn scaling(x: Float, y: Float, z: Float) -> Matrix4x4 {
        Matrix4x4::new(
            [x, 0., 0., 0.],
@ -384,23 +197,6 @@ impl Matrix4x4 {
    }

    /// Creates a 4x4 matrix representing a rotation around the x-axis.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use rtchallenge::{float::consts::PI, matrices::Matrix4x4, tuples::Tuple, Float};
-    ///
-    /// // A scaling matrix applied to a point.
-    /// let p = Tuple::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,
-    ///     Tuple::point(0., (2.0 as Float).sqrt() / 2., (2.0 as Float).sqrt() / 2.)
-    /// );
-    /// assert_eq!(full_quarter * p, Tuple::point(0., 0., 1.),);
-    /// ```
    pub fn rotation_x(radians: Float) -> Matrix4x4 {
        let r = radians;
        Matrix4x4::new(
@ -412,23 +208,6 @@ impl Matrix4x4 {
    }

    /// Creates a 4x4 matrix representing a rotation around the y-axis.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use rtchallenge::{float::consts::PI, matrices::Matrix4x4, tuples::Tuple, Float};
-    ///
-    /// // A scaling matrix applied to a point.
-    /// let p = Tuple::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,
-    ///     Tuple::point((2.0 as Float).sqrt() / 2., 0., (2.0 as Float).sqrt() / 2.)
-    /// );
-    /// assert_eq!(full_quarter * p, Tuple::point(1., 0., 0.,),);
-    /// ```
    pub fn rotation_y(radians: Float) -> Matrix4x4 {
        let r = radians;
        Matrix4x4::new(
@ -440,23 +219,6 @@ impl Matrix4x4 {
    }

    /// Creates a 4x4 matrix representing a rotation around the z-axis.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use rtchallenge::{float::consts::PI, matrices::Matrix4x4, tuples::Tuple, Float};
-    ///
-    /// // A scaling matrix applied to a point.
-    /// let p = Tuple::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,
-    ///     Tuple::point(-(2.0 as Float).sqrt() / 2., (2.0 as Float).sqrt() / 2., 0.)
-    /// );
-    /// assert_eq!(full_quarter * p, Tuple::point(-1., 0., 0.,),);
-    /// ```
    pub fn rotation_z(radians: Float) -> Matrix4x4 {
        let r = radians;
        Matrix4x4::new(
@ -468,26 +230,6 @@ impl Matrix4x4 {
    }

    /// Transpose self, returning a new matrix that has been reflected across the diagonal.
-    /// # Examples
-    ///
-    /// ```
-    /// use rtchallenge::matrices::Matrix4x4;
-    ///
-    /// 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());
    pub fn transpose(&self) -> Matrix4x4 {
        let m = self.m;
        Matrix4x4 {
@ -501,40 +243,6 @@ impl Matrix4x4 {
    }
    /// Create a transform matrix that will shear (skew) points.
    /// # Examples
-    ///
-    /// ```
-    /// use rtchallenge::{matrices::Matrix4x4, tuples::Tuple};
-    ///
-    /// // A shearing transform moves x in proportion to y.
-    /// let transform = Matrix4x4::shearing(1.,0.,0.,0.,0.,0.);
-    /// let p = Tuple::point(2.,3.,4.);
-    /// assert_eq!(transform * p, Tuple::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 = Tuple::point(2.,3.,4.);
-    /// assert_eq!(transform * p, Tuple::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 = Tuple::point(2.,3.,4.);
-    /// assert_eq!(transform * p, Tuple::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 = Tuple::point(2.,3.,4.);
-    /// assert_eq!(transform * p, Tuple::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 = Tuple::point(2.,3.,4.);
-    /// assert_eq!(transform * p, Tuple::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 = Tuple::point(2.,3.,4.);
-    /// assert_eq!(transform * p, Tuple::point(2.,3.,7.));
-
    pub fn shearing(xy: Float, xz: Float, yx: Float, yz: Float, zx: Float, zy: Float) -> Matrix4x4 {
        Matrix4x4::new(
            [1., xy, xz, 0.],
@ -547,24 +255,6 @@ impl Matrix4x4 {
    /// 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.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use rtchallenge::matrices::Matrix4x4;
-    ///
-    /// 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);
-    /// ```
    pub fn inverse_rtiow(&self) -> Matrix4x4 {
        // TODO(wathiede): how come the C++ version doesn't need to deal with non-invertable
        // matrix.
@ -639,22 +329,6 @@ impl Matrix4x4 {
        Matrix4x4 { m: minv }
    }
    /// submatrix extracts a 3x3 matrix ignoring the 0-based `row` and `col` given.
-    ///
-    /// # Examples
-    /// ```
-    /// use rtchallenge::matrices::{Matrix3x3, Matrix4x4};
-    ///
-    /// 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.],)
-    /// );
-    /// ```
    pub fn submatrix(&self, row: usize, col: usize) -> Matrix3x3 {
        assert!(row < 4);
        assert!(col < 4);
@ -688,133 +362,16 @@ impl Matrix4x4 {
        self.submatrix(row, col).determinant() * negate
    }
    /// Compute determinant of a 4x4 matrix.
-    ///
-    /// # Examples
-    /// ```
-    /// use rtchallenge::matrices::Matrix4x4;
-    ///
-    /// 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.);
-    /// ```
    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.
-    ///
-    /// # Examples
-    /// ```
-    /// use rtchallenge::matrices::Matrix4x4;
-    ///
-    /// 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);
-    /// ```
    pub fn invertable(&self) -> bool {
        self.determinant() != 0.
    }

    /// Compute the inverse of a 4x4 matrix.
-    ///
-    /// # Examples
-    /// ```
-    /// use rtchallenge::matrices::Matrix4x4;
-    ///
-    /// 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);
-    /// ```
    pub fn inverse(&self) -> Matrix4x4 {
        self.inverse_rtc()
    }
@ -857,17 +414,6 @@ impl Mul<Matrix4x4> for Matrix4x4 {
    type Output = Matrix4x4;

    /// Implement matrix multiplication for `Matrix4x4`.
-    ///
-    /// # Examples
-    /// ```
-    /// use rtchallenge::matrices::Matrix4x4;
-    ///
-    /// let i = Matrix4x4::identity();
-    /// let m1 = Matrix4x4::identity();
-    /// let m2 = Matrix4x4::identity();
-    ///
-    /// assert_eq!(m1 * m2, i);
-    /// ```
    fn mul(self, m2: Matrix4x4) -> Matrix4x4 {
        let m1 = self;
        let mut r: Matrix4x4 = Default::default();
@ -887,22 +433,6 @@ impl Mul<Tuple> for Matrix4x4 {
    type Output = Tuple;

    /// Implement matrix multiplication for `Matrix4x4` * `Tuple`.
-    ///
-    /// # Examples
-    /// ```
-    /// use rtchallenge::matrices::Matrix4x4;
-    /// use rtchallenge::tuples::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.));
-    /// ```
    fn mul(self, t: Tuple) -> Tuple {
        let m = self;
        Tuple {
@ -962,6 +492,235 @@ impl IndexMut<(usize, usize)> for Matrix4x4 {
 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.]);
@ -980,6 +739,100 @@ mod tests {
        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.],
@ -1052,4 +905,16 @@ mod tests {
            )
        );
    }
+    #[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 +1,361 @@
+use derive_builder::Builder;
+
+use crate::{
+    matrices::Matrix4x4,
+    shapes::Shape,
+    tuples::{Color, Tuple},
+    WHITE,
+};
+
+#[derive(Debug, PartialEq, Copy, 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 colors along each unit of the X-axis.  The strip
+    /// extends infinitely in the positive and negative Y and Z axes.
+    Stripe { a: Color, b: Color },
+    /// Linear blend between `a` and `b` along the X-axis.
+    Gradient { a: Color, b: Color },
+    /// Bullseye pattern in the XZ plane.
+    Ring { a: Color, b: Color },
+    /// Traditional ray tracer tile floor pattern.
+    Checkers { a: Color, b: Color },
+}
+
+#[derive(Builder, Debug, PartialEq, Clone)]
+#[builder(default, pattern = "owned")]
+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: Color, b: Color) -> PatternBuilder {
+    PatternBuilder::default().color(ColorMapper::Stripe { a, b })
+}
+
+/// Builder for creating a material pattern that gradually blends between the given colors along
+/// the X-axis.
+pub fn gradient_pattern(a: Color, b: Color) -> PatternBuilder {
+    PatternBuilder::default().color(ColorMapper::Gradient { a, b })
+}
+
+/// 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: Color, b: Color) -> PatternBuilder {
+    PatternBuilder::default().color(ColorMapper::Ring { a, b })
+}
+
+/// 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: Color, b: Color) -> PatternBuilder {
+    PatternBuilder::default().color(ColorMapper::Checkers { a, b })
+}
+
+/// 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 colors along each unit of the
+    /// X-axis.  The strip extends infinitely in the positive and negative Y and Z axes.
+    pub fn stripe(a: Color, b: Color) -> Pattern {
+        Pattern {
+            color: ColorMapper::Stripe { a, b },
+            ..Pattern::default()
+        }
+    }
+
+    /// Create a pattern that gradually blends between the given colors along the X-axis.
+    pub fn gradient(a: Color, b: Color) -> Pattern {
+        Pattern {
+            color: ColorMapper::Gradient { a, b },
+            ..Pattern::default()
+        }
+    }
+
+    /// Create a pattern that alternates between the given colors in a ring in the XZ plane.
+    pub fn ring(a: Color, b: Color) -> Pattern {
+        Pattern {
+            color: ColorMapper::Ring { a, b },
+            ..Pattern::default()
+        }
+    }
+
+    /// Create a pattern that alternates between the given colors along the X, Y and Z axis.
+    pub fn checkers(a: Color, b: Color) -> Pattern {
+        Pattern {
+            color: ColorMapper::Checkers { a, b },
+            ..Pattern::default()
+        }
+    }
+
+    /// Sample the color at the given point in untranslated object space.
+    pub fn pattern_at(&self, point: Tuple) -> Color {
+        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
+                } else {
+                    b
+                }
+            }
+            ColorMapper::Gradient { a, b } => {
+                let distance = b - a;
+                let fraction = point.x - point.x.floor();
+                a + distance * fraction
+            }
+            ColorMapper::Ring { a, b } => {
+                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 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;
+        let pattern_point = self.inverse_transform * object_point;
+        self.pattern_at(pattern_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, WHITE,
+    };
+
+    #[test]
+    fn test_create() {
+        let pattern = Pattern::test();
+        assert_eq!(pattern.transform(), identity());
+    }
+
+    #[test]
+    fn stripe_create() {
+        let pattern = Pattern::stripe(BLACK, WHITE);
+        assert_eq!(pattern.color, ColorMapper::Stripe { a: BLACK, b: WHITE });
+    }
+    #[test]
+    fn gradient_create() {
+        let pattern = Pattern::gradient(BLACK, WHITE);
+        assert_eq!(pattern.color, ColorMapper::Gradient { a: BLACK, b: WHITE });
+    }
+    #[test]
+    fn ring_create() {
+        let pattern = Pattern::ring(BLACK, WHITE);
+        assert_eq!(pattern.color, ColorMapper::Ring { a: BLACK, b: WHITE });
+    }
+    #[test]
+    fn checkers_create() {
+        let pattern = Pattern::checkers(BLACK, WHITE);
+        assert_eq!(pattern.color, ColorMapper::Checkers { a: BLACK, b: WHITE });
+    }
+
+    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, BLACK);
+            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, BLACK);
+            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, BLACK);
+            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, BLACK);
+            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, BLACK);
+            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, BLACK);
+            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,
+            shapes::{Shape, ShapeBuilder},
+            tuples::point,
+            BLACK, 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, BLACK).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, BLACK).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
@ -10,17 +10,6 @@ pub struct Ray {
 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.
-    ///
-    /// # Examples
-    /// ```
-    /// use rtchallenge::{rays::Ray, tuples::Tuple};
-    ///
-    /// let origin = Tuple::point(1., 2., 3.);
-    /// let direction = Tuple::vector(4., 5., 6.);
-    /// let r = Ray::new(origin, direction);
-    /// assert_eq!(r.origin, origin);
-    /// assert_eq!(r.direction, direction);
-    /// ```
    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");
@ -28,41 +17,11 @@ impl Ray {
    }

    /// Compute a point from the given distance along the `Ray`.
-    ///
-    /// # Examples
-    /// ```
-    /// use rtchallenge::{rays::Ray, tuples::Tuple};
-    ///
-    /// let r = Ray::new(Tuple::point(2., 3., 4.), Tuple::vector(1., 0., 0.));
-    /// assert_eq!(r.position(0.), Tuple::point(2., 3., 4.));
-    /// assert_eq!(r.position(1.), Tuple::point(3., 3., 4.));
-    /// assert_eq!(r.position(-1.), Tuple::point(1., 3., 4.));
-    /// assert_eq!(r.position(2.5), Tuple::point(4.5, 3., 4.));
-    /// ```
    pub fn position(&self, t: Float) -> Tuple {
        self.origin + self.direction * t
    }

    /// Apply Matrix4x4 transforms to Ray.
-    ///
-    /// # Examples
-    /// ```
-    /// use rtchallenge::{matrices::Matrix4x4, rays::Ray, tuples::Tuple};
-    ///
-    /// // Translating a ray
-    /// let r = Ray::new(Tuple::point(1., 2., 3.), Tuple::vector(0., 1., 0.));
-    /// let m = Matrix4x4::translation(3., 4., 5.);
-    /// let r2 = r.transform(m);
-    /// assert_eq!(r2.origin, Tuple::point(4., 6., 8.));
-    /// assert_eq!(r2.direction, Tuple::vector(0., 1., 0.));
-    ///
-    /// // Scaling a ray
-    /// let r = Ray::new(Tuple::point(1., 2., 3.), Tuple::vector(0., 1., 0.));
-    /// let m = Matrix4x4::scaling(2., 3., 4.);
-    /// let r2 = r.transform(m);
-    /// assert_eq!(r2.origin, Tuple::point(2., 6., 12.));
-    /// assert_eq!(r2.direction, Tuple::vector(0., 3., 0.));
-    /// ```
    pub fn transform(&self, m: Matrix4x4) -> Ray {
        Ray {
            origin: m * self.origin,
@ -70,3 +29,46 @@ impl Ray {
        }
    }
 }
+
+#[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
@ -3,7 +3,10 @@ use std::sync::{Arc, Mutex};
 use derive_builder::Builder;

 use crate::{
-    intersections::Intersections, materials::Material, matrices::Matrix4x4, rays::Ray,
+    intersections::Intersections,
+    materials::{Material, MaterialBuilder},
+    matrices::Matrix4x4,
+    rays::Ray,
    tuples::Tuple,
 };

@ -54,87 +57,39 @@ pub struct Shape {
 }

 /// Short hand for creating a ShapeBuilder with a plane geometry.
-///
-/// # Examples
-/// ```
-/// use rtchallenge::shapes::{plane, Shape};
-/// # fn main() -> Result<(), Box<std::error::Error>> {
-/// assert_eq!(plane().build()?, Shape::plane());
-/// # Ok(())
-/// # }
-/// ```
 pub fn plane() -> ShapeBuilder {
    ShapeBuilder::plane()
 }
 /// Short hand for creating a ShapeBuilder with a sphere geometry.
-///
-/// # Examples
-/// ```
-/// use rtchallenge::shapes::{sphere, Shape};
-///
-/// # fn main() -> Result<(), Box<std::error::Error>> {
-/// assert_eq!(sphere().build()?, Shape::sphere());
-/// # Ok(())
-/// # }
-/// ```
 pub fn sphere() -> ShapeBuilder {
    ShapeBuilder::sphere()
 }
+
 /// Short hand for creating a ShapeBuilder with a test shape geometry.
-///
-/// # Examples
-/// ```
-/// use rtchallenge::shapes::{test_shape, Shape};
-///
-/// # fn main() -> Result<(), Box<std::error::Error>> {
-/// assert_eq!(test_shape().build()?, Shape::test_shape());
-/// # Ok(())
-/// # }
-/// ```
 pub fn test_shape() -> ShapeBuilder {
    ShapeBuilder::test_shape()
 }

+/// 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.
-    ///
-    /// # Examples
-    /// ```
-    /// use rtchallenge::shapes::{plane, Shape};
-    ///
-    /// # fn main() -> Result<(), Box<std::error::Error>> {
-    /// assert_eq!(plane().build()?, Shape::plane());
-    /// # Ok(())
-    /// # }
-    /// ```
    pub fn plane() -> ShapeBuilder {
        ShapeBuilder::default().geometry(Geometry::Plane)
    }
    /// Short hand for creating a ShapeBuilder with a sphere geometry.
-    ///
-    /// # Examples
-    /// ```
-    /// use rtchallenge::shapes::{sphere, Shape};
-    ///
-    /// # fn main() -> Result<(), Box<std::error::Error>> {
-    /// assert_eq!(sphere().build()?, Shape::sphere());
-    /// # Ok(())
-    /// # }
-    /// ```
    pub fn sphere() -> ShapeBuilder {
        ShapeBuilder::default().geometry(Geometry::Sphere)
    }
    /// Short hand for creating a ShapeBuilder with a test shape geometry.
-    ///
-    /// # Examples
-    /// ```
-    /// use rtchallenge::shapes::{test_shape, Shape};
-    ///
-    /// # fn main() -> Result<(), Box<std::error::Error>> {
-    /// assert_eq!(test_shape().build()?, Shape::test_shape());
-    /// # Ok(())
-    /// # }
-    /// ```
    pub fn test_shape() -> ShapeBuilder {
        ShapeBuilder::default().geometry(Geometry::TestShape(Arc::new(Mutex::new(
            TestData::default(),
@ -158,24 +113,6 @@ impl Default for Shape {

 impl Shape {
    /// Create a test shape useful for debugging.
-    ///
-    /// # Examples
-    /// ```
-    /// use rtchallenge::{materials::Material, matrices::Matrix4x4, shapes::Shape};
-    ///
-    /// let mut s = Shape::test_shape();
-    /// // The default transform.
-    /// assert_eq!(s.transform(), Matrix4x4::identity());
-    /// // The default material.
-    /// assert_eq!(s.material, Material::default());
-    /// // Assigning a material.
-    /// let mut m = Material {
-    ///     ambient: 1.,
-    ///     ..Material::default()
-    /// };
-    /// s.material = m.clone();
-    /// assert_eq!(s.material, m);
-    /// ```
    pub fn test_shape() -> Shape {
        Shape {
            transform: Matrix4x4::identity(),
@ -185,28 +122,6 @@ impl Shape {
        }
    }
    /// # Examples
-    /// ```
-    /// use rtchallenge::{materials::Material, matrices::Matrix4x4, shapes::Shape};
-    ///
-    /// // A sphere's default transform is the identity matrix.
-    /// let s = Shape::sphere();
-    /// assert_eq!(s.transform(), Matrix4x4::identity());
-    ///
-    /// // It can be changed by directly setting the transform member.
-    /// let mut s = Shape::sphere();
-    /// let t = Matrix4x4::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);
-    /// ```
    pub fn sphere() -> Shape {
        Shape {
            transform: Matrix4x4::identity(),
@ -224,101 +139,6 @@ impl Shape {
        }
    }
    /// Find the normal at the point on the sphere.
-    ///
-    /// # Examples
-    /// ```
-    /// use rtchallenge::{
-    ///     float::consts::PI, materials::Material, matrices::Matrix4x4, shapes::Shape, tuples::Tuple,
-    ///     Float,
-    /// };
-    ///
-    /// // 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));
-    ///
-    /// // Computing the normal on a transform 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));
-    ///
-    /// // 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.));
-    ///
-    /// // 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.));
-    ///
-    /// // 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.));
-    ///
-    /// // 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.,
-    ///     )
-    /// );
-    /// // 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());
-    ///
-    /// // 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));
-    ///
-    /// // 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));
-    ///
-    /// // 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.)
-    /// );
-    /// ```
-    #[cfg(not(feature = "disable-inverse-cache"))]
    pub fn normal_at(&self, world_point: Tuple) -> Tuple {
        let object_point = self.inverse_transform * world_point;
        let object_normal = match self.geometry {
@ -330,23 +150,15 @@ impl Shape {
        world_normal.w = 0.;
        world_normal.normalize()
    }
-    #[cfg(feature = "disable-inverse-cache")]
-    pub fn normal_at(&self, world_point: Tuple) -> Tuple {
-        let object_point = self.transform.inverse() * 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(_) => todo!("test shape normal"),
-        };
-        let mut world_normal = self.transform.inverse().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();
@ -357,123 +169,6 @@ impl Shape {
 }

 /// Intersect a ray with a shapes.
-///
-/// # Examples
-/// ```
-/// use rtchallenge::{
-///     intersections::{Intersection, Intersections},
-///     matrices::Matrix4x4,
-///     rays::Ray,
-///     shapes::{intersect, Geometry, Shape},
-///     tuples::Tuple,
-/// };
-///
-/// // 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")
-/// };
-///
-/// // 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")
-/// };
-///
-/// // 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)])
-/// );
-///
-/// // 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());
-///
-/// // 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)])
-/// );
-///
-/// // 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)])
-/// );
-///
-/// // 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);
-///
-/// // 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);
-///
-/// // 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);
-///
-/// // Intersect with a coplanar.
-/// let r = Ray::new(Tuple::point(0., 0., 0.), Tuple::vector(0., 0., 1.));
-/// let xs = intersect(&p, &r);
-/// assert_eq!(xs.len(), 0);
-///
-/// // A ray intersecting a plane from above.
-/// 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 ray intersecting a plane from below.
-/// 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);
-/// ```
 pub fn intersect<'s>(shape: &'s Shape, ray: &Ray) -> Intersections<'s> {
    let local_ray = ray.transform(shape.inverse_transform);
    match shape.geometry {
@ -539,3 +234,325 @@ mod plane {
        )])
    }
 }
+
+#[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
@ -5,47 +5,6 @@ use crate::{

 /// Create a matrix representing a eye at `from` looking at `to`, with an `up`
 /// as the up vector.
-///
-/// # Examples
-/// ```
-/// use rtchallenge::{matrices::Matrix4x4, transformations::view_transform, tuples::Tuple};
-///
-/// // The transofrmation matrix for the default orientation.
-/// let from = Tuple::point(0., 0., 0.);
-/// let to = Tuple::point(0., 0., -1.);
-/// let up = Tuple::vector(0., 1., 0.);
-/// let t = view_transform(from, to, up);
-/// assert_eq!(t, Matrix4x4::identity());
-///
-/// // A view transformation matrix looking in positive z direction.
-/// let from = Tuple::point(0., 0., 0.);
-/// let to = Tuple::point(0., 0., 1.);
-/// let up = Tuple::vector(0., 1., 0.);
-/// let t = view_transform(from, to, up);
-/// assert_eq!(t, Matrix4x4::scaling(-1., 1., -1.));
-///
-/// // The view tranformation moves the world.
-/// let from = Tuple::point(0., 0., 8.);
-/// let to = Tuple::point(0., 0., 0.);
-/// let up = Tuple::vector(0., 1., 0.);
-/// let t = view_transform(from, to, up);
-/// assert_eq!(t, Matrix4x4::translation(0., 0., -8.));
-///
-/// // An arbitrary view transformation.
-/// let from = Tuple::point(1., 3., 2.);
-/// let to = Tuple::point(4., -2., 8.);
-/// let up = Tuple::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.],
-///     )
-/// );
-/// ```
 pub fn view_transform(from: Tuple, to: Tuple, up: Tuple) -> Matrix4x4 {
    let forward = (to - from).normalize();
    let left = cross(forward, up.normalize());
@ -57,3 +16,56 @@ pub fn view_transform(from: Tuple, to: Tuple, up: Tuple) -> Matrix4x4 {
        [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
@ -3,27 +3,11 @@ use std::ops::{Add, Div, Mul, Neg, Sub};
 use crate::{Float, EPSILON};

 /// Short hand for creating a Tuple that represents a point, w=1.
-///
-/// # Examples
-/// ```
-/// use rtchallenge::tuples::{point, Tuple};
-///
-/// assert_eq!(point(1., 2., 3.), Tuple::point(1., 2., 3.));
-/// assert_eq!(point(1., 2., 3.), Tuple::new(1., 2., 3., 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.
-///
-/// # Examples
-/// ```
-/// use rtchallenge::tuples::{vector, Tuple};
-///
-/// assert_eq!(vector(1., 2., 3.), Tuple::vector(1., 2., 3.));
-/// assert_eq!(vector(1., 2., 3.), Tuple::new(1., 2., 3., 0.));
-/// ```
 pub fn vector(x: Float, y: Float, z: Float) -> Tuple {
    Tuple::vector(x, y, z)
 }
@ -73,26 +57,6 @@ impl Tuple {
 }

 /// Reflects vector v across normal n.
-///
-/// # Examples
-/// ```
-/// use rtchallenge::{
-///     tuples::{reflect, Tuple},
-///     Float,
-/// };
-///
-/// // 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.));
-///
-/// // 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.));
-/// ```
 pub fn reflect(v: Tuple, n: Tuple) -> Tuple {
    v - n * 2. * dot(v, n)
 }
@ -297,7 +261,7 @@ impl Sub for Color {

 #[cfg(test)]
 mod tests {
-    use super::{cross, dot, Color, Float, Tuple, EPSILON};
+    use super::{cross, dot, reflect, Color, Float, Tuple, EPSILON};
    #[test]
    fn is_point() {
        // A tuple with w = 1 is a point
@ -456,4 +420,20 @@ mod tests {
        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
@ -1,27 +1,17 @@
 use derive_builder::Builder;

 use crate::{
-    intersections::{prepare_computations, Intersections, PrecomputedData},
+    intersections::{prepare_computations, schlick, Intersections, PrecomputedData},
    lights::PointLight,
    materials::{lighting, Material},
    matrices::Matrix4x4,
    rays::Ray,
    shapes::{intersect, Shape},
-    tuples::{Color, Tuple},
+    tuples::{dot, Color, Tuple},
    BLACK, WHITE,
 };

 /// World holds all drawable objects and the light(s) that illuminate them.
-///
-/// # Examples
-/// ```
-/// use rtchallenge::world::World;
-///
-/// let w = World::default();
-/// assert!(w.objects.is_empty());
-/// assert_eq!(w.lights.len(), 0);
-/// ```
-
 #[derive(Builder, Clone, Debug, Default)]
 #[builder(default)]
 pub struct World {
@ -31,20 +21,11 @@ pub struct World {

 impl World {
    /// Creates a world suitable for use across multiple tests in from the book.
-    ///
-    /// # Examples
-    /// ```
-    /// use rtchallenge::world::World;
-    ///
-    /// let w = World::test_world();
-    /// assert_eq!(w.objects.len(), 2);
-    /// assert!(!w.lights.is_empty());
-    /// ```
    pub fn test_world() -> World {
        let light = PointLight::new(Tuple::point(-10., 10., -10.), WHITE);
        let mut s1 = Shape::sphere();
        s1.material = Material {
-            color: Color::new(0.8, 1., 0.6),
+            color: [0.8, 1., 0.6].into(),
            diffuse: 0.7,
            specular: 0.2,
            ..Material::default()
@ -57,21 +38,7 @@ impl World {
        }
    }

-    /// Intesects the ray with this world.
-    ///
-    /// # Examples
-    /// ```
-    /// use rtchallenge::{rays::Ray, tuples::Tuple, world::World};
-    ///
-    /// let w = World::test_world();
-    /// let r = Ray::new(Tuple::point(0., 0., -5.), Tuple::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.);
-    /// ```
+    /// Intersects the ray with this world.
    pub fn intersect(&self, r: &Ray) -> Intersections {
        let mut xs: Vec<_> = self
            .objects
@ -87,147 +54,46 @@ impl World {
    }

    /// Compute shaded value for given precomputation.
-    ///
-    /// # Examples
-    /// ```
-    /// use rtchallenge::{
-    ///     intersections::{prepare_computations, Intersection},
-    ///     lights::PointLight,
-    ///     matrices::Matrix4x4,
-    ///     rays::Ray,
-    ///     shapes::Shape,
-    ///     tuples::{Color, Tuple},
-    ///     world::World,
-    ///     WHITE,
-    /// };
-    ///
-    /// // Shading an intersection.
-    /// let w = World::test_world();
-    /// let r = Ray::new(Tuple::point(0., 0., -5.), Tuple::vector(0., 0., 1.));
-    /// let s = &w.objects[0];
-    /// let i = Intersection::new(4., &s);
-    /// let comps = prepare_computations(&i, &r);
-    /// let c = w.shade_hit(&comps);
-    /// assert_eq!(c, Color::new(0.38066, 0.47583, 0.2855));
-    ///
-    /// // Shading an intersection from the inside.
-    /// let mut w = World::test_world();
-    /// w.lights = vec![PointLight::new(Tuple::point(0., 0.25, 0.), WHITE)];
-    /// let r = Ray::new(Tuple::point(0., 0., 0.), Tuple::vector(0., 0., 1.));
-    /// let s = &w.objects[1];
-    /// let i = Intersection::new(0.5, &s);
-    /// let comps = prepare_computations(&i, &r);
-    /// let c = w.shade_hit(&comps);
-    /// assert_eq!(c, Color::new(0.90498, 0.90498, 0.90498));
-    ///
-    /// // Shading with an intersection in shadow.
-    /// let mut w = World::default();
-    /// w.lights = vec![PointLight::new(Tuple::point(0., 0., -10.), WHITE)];
-    /// let s1 = Shape::sphere();
-    /// let mut s2 = Shape::sphere();
-    /// s2.set_transform(Matrix4x4::translation(0., 0., 10.));
-    /// w.objects = vec![s1, s2.clone()];
-    /// let r = Ray::new(Tuple::point(0., 0., 5.), Tuple::vector(0., 0., 1.));
-    /// let i = Intersection::new(4., &s2);
-    /// let comps = prepare_computations(&i, &r);
-    /// let c = w.shade_hit(&comps);
-    /// assert_eq!(c, Color::new(0.1, 0.1, 0.1));
-    /// ```
-    pub fn shade_hit(&self, comps: &PrecomputedData) -> Color {
-        let c = self
+    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);
-                acc + lighting(
+                let surface = lighting(
                    &comps.object.material,
+                    &comps.object,
                    light,
                    comps.over_point,
                    comps.eyev,
                    comps.normalv,
                    shadowed,
-                )
+                );
+                acc + surface
            });
-        c
+        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.
-    ///
-    /// # Examples
-    /// ```
-    /// use rtchallenge::{
-    ///     intersections::{prepare_computations, Intersection},
-    ///     lights::PointLight,
-    ///     rays::Ray,
-    ///     shapes::Shape,
-    ///     tuples::{Color, Tuple},
-    ///     world::World,
-    ///     BLACK,
-    /// };
-    ///
-    /// // The color when a ray misses.
-    /// let w = World::test_world();
-    /// let r = Ray::new(Tuple::point(0., 0., -5.), Tuple::vector(0., 1., 0.));
-    /// let c = w.color_at(&r);
-    /// assert_eq!(c, BLACK);
-    ///
-    /// // The color when a ray hits.
-    /// let w = World::test_world();
-    /// let r = Ray::new(Tuple::point(0., 0., -5.), Tuple::vector(0., 0., 1.));
-    /// let c = w.color_at(&r);
-    /// assert_eq!(c, Color::new(0.38066, 0.47583, 0.2855));
-    ///
-    /// // The color with an intersection behind the ray.
-    /// let w = {
-    ///     let mut w = World::test_world();
-    ///     let mut outer = &mut w.objects[0];
-    ///     let m = outer.material.ambient = 1.;
-    ///     let inner = &mut w.objects[1];
-    ///     inner.material.ambient = 1.;
-    ///     w
-    /// };
-    /// let inner = &w.objects[1];
-    /// let r = Ray::new(Tuple::point(0., 0., 0.75), Tuple::vector(0., 0., -1.));
-    /// let c = w.color_at(&r);
-    /// assert_eq!(c, inner.material.color);
-    /// ```
-    pub fn color_at(&self, r: &Ray) -> Color {
-        match self.intersect(r).hit() {
+    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);
-                self.shade_hit(&comps)
+                let comps = prepare_computations(&hit, r, &xs);
+                self.shade_hit(&comps, remaining)
            }
            None => BLACK,
        }
    }

    /// Determine if point in world is in a shadow.
-    ///
-    /// # Examples
-    /// ```
-    /// use rtchallenge::{
-    ///     tuples::{ Tuple},
-    ///     shapes::Shape,
-    ///     world::World,
-    /// };
-    ///
-    /// let w = World::test_world();
-    /// let light = &w.lights[0];
-    ///
-    /// // There is no shadow when nothing is collinear with point and light.
-    /// let p = Tuple::point(0.,10.,0.);
-    /// assert_eq!(w.is_shadowed(p,light), false);
-    ///
-    /// // There shadow when an object is between the point and the light.
-    /// let p = Tuple::point(10.,-10.,10.);
-    /// assert_eq!(w.is_shadowed(p,light), true);
-    ///
-    /// // There is no shadow when an object is behind the light.
-    /// let p = Tuple::point(-20.,20.,-20.);
-    /// assert_eq!(w.is_shadowed(p,light), false);
-    ///
-    /// // There is no shadow when an object is behind the point.
-    /// let p = Tuple::point(-2.,2.,-2.);
-    /// assert_eq!(w.is_shadowed(p,light), false);
    pub fn is_shadowed(&self, point: Tuple, light: &PointLight) -> bool {
        let v = light.position - point;
        let distance = v.magnitude();
@ -240,4 +106,455 @@ impl World {
        }
        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(())
+        }
+    }
 }
Author	SHA1	Message	Date
Bill Thiede	9befbd9ad2	matrices: moving another doctest to unit All checks were successful continuous-integration/drone/push Build is passing Details	2021-07-30 21:59:40 -07:00
Bill Thiede	c882fc81e5	transformations: moving another doctest to unit	2021-07-30 21:58:32 -07:00
Bill Thiede	1c2caf2cc5	lights: moving another doctest to unit	2021-07-30 21:51:35 -07:00
Bill Thiede	9006671a26	intersections: moving another doctest to unit	2021-07-30 21:49:48 -07:00
Bill Thiede	3838efd134	camera: moving another doctest to unit	2021-07-30 21:44:58 -07:00
Bill Thiede	e3d8988658	matrices: moving another doctest to unit	2021-07-30 21:33:43 -07:00
Bill Thiede	e4846de25b	rays: move tests from doctest to unit.	2021-07-30 21:28:13 -07:00
Bill Thiede	4352c03d20	tuples: move tests from doctest to unit.	2021-07-30 21:23:56 -07:00
Bill Thiede	1d5e5a164b	materials: move tests from doctest to unit.	2021-07-30 21:21:51 -07:00
Bill Thiede	f476822bcd	shapes: lint	2021-07-30 21:21:16 -07:00
Bill Thiede	135a519526	shapes: move tests from doctest to unit.	2021-07-30 20:58:05 -07:00
Bill Thiede	5d6b3e6d57	patterns: move tests from doctest to unit.	2021-07-30 20:00:08 -07:00
Bill Thiede	3aea76b35c	matrices: move tests from doctest to unit.	2021-07-29 20:33:03 -07:00
Bill Thiede	cd2a4770ca	world: move tests from doctest to unit.	2021-07-28 20:23:59 -07:00
Bill Thiede	5debb16d10	intersections: move tests from doctest to unit.	2021-07-27 21:51:26 -07:00
Bill Thiede	42e8ebe3bd	Implement transparency, reflections and refraction.	2021-07-26 21:46:04 -07:00
Bill Thiede	1d61f59935	materials: add transparency and refractive_index to Material.	2021-07-25 16:33:03 -07:00
Bill Thiede	7f36aecf5e	world: add reflection to ray tracer.	2021-07-25 16:28:34 -07:00
Bill Thiede	0c7bbae4a3	rtchallenge: remove disable-inverse-cache feature.	2021-07-25 14:54:00 -07:00
Bill Thiede	eaae65712b	eoc10: example showing concepts from the chapter.	2021-07-25 14:51:33 -07:00
Bill Thiede	68709da6c2	patterns: implement checker pattern.	2021-07-25 14:46:26 -07:00
Bill Thiede	77215193fa	patterns: implement ring pattern	2021-07-25 14:37:56 -07:00
Bill Thiede	74fe69188a	patterns: add Gradient pattern.	2021-07-25 14:11:44 -07:00
Bill Thiede	bdcee49d5a	patterns: add builder pattern for creating Patterns.	2021-07-25 13:50:13 -07:00
Bill Thiede	2e4e8b3dcd	patterns: make From for Pattern a little generic.	2021-07-25 13:35:14 -07:00
Bill Thiede	b9f2c3f0ec	patterns: create generic Pattern modeled after StripePattern. Add TestPattern to validate generic implementation. Make Material.color use Pattern.	2021-07-25 13:30:40 -07:00
Bill Thiede	8b79876aee	patterns: implement object and pattern transformation awareness.	2021-07-25 11:22:36 -07:00
Bill Thiede	bfa3282a37	materials: add StripePattern as a Material color option.	2021-07-24 19:36:32 -07:00
Bill Thiede	3e383c4dbd	patters: implemented basic stripe pattern.	2021-07-24 18:20:29 -07:00
Bill Thiede	c158d92252	eoc9: make width and height CLI flags.	2021-07-23 22:18:20 -07:00