eoc7: implement end of chapter 7 challenge.

Mark Color::new const so it can be used in const expressions (like
predefining colors).

rtchallenge/examples/eoc5.rs

@@ -1,5 +1,3 @@
-use core::f32;
-
 use anyhow::Result;
 
 use rtchallenge::{

rtchallenge/examples/eoc6.rs

@@ -0,0 +1,57 @@
+use anyhow::Result;
+
+use rtchallenge::{
+    canvas::Canvas,
+    lights::PointLight,
+    materials::{lighting, Material},
+    rays::Ray,
+    spheres::{intersect, Sphere},
+    tuples::{Color, Tuple},
+    WHITE,
+};
+
+fn main() -> Result<()> {
+    let w = 640;
+    let h = w;
+    let bg = Color::new(0.2, 0.2, 0.2);
+    let mut c = Canvas::new(w, h, bg);
+    let ray_origin = Tuple::point(0., 0., -5.);
+    let wall_z = 10.;
+    let wall_size = 7.;
+    let pixel_size = wall_size / w as f32;
+    let half = wall_size / 2.;
+    let mut shape = Sphere::default();
+    shape.material = Material {
+        color: Color::new(1., 0.2, 1.),
+        specular: 0.5,
+        diffuse: 0.7,
+        shininess: 30.,
+        ..Material::default()
+    };
+    let light_position = Tuple::point(-10., 10., -10.);
+    let light_color = WHITE;
+    let light = PointLight::new(light_position, light_color);
+
+    for y in 0..h {
+        let world_y = half - pixel_size * y as f32;
+        for x in 0..w {
+            let world_x = -half + pixel_size * x as f32;
+            let position = Tuple::point(world_x, world_y, wall_z);
+            let direction = (position - ray_origin).normalize();
+            let r = Ray::new(ray_origin, direction);
+            let xs = intersect(&shape, &r);
+            if let Some(hit) = xs.hit() {
+                let point = r.position(hit.t);
+                let normal = hit.object.normal_at(point);
+                let eye = -r.direction;
+                let color = lighting(&hit.object.material, &light, point, eye, normal);
+                c.set(x, y, color);
+            }
+        }
+    }
+
+    let path = "/tmp/eoc6.png";
+    println!("saving output to {}", path);
+    c.write_to_file(path)?;
+    Ok(())
+}

rtchallenge/examples/eoc7.rs

@@ -0,0 +1,91 @@
+use std::{f32::consts::PI, time::Instant};
+
+use anyhow::Result;
+
+use rtchallenge::{
+    camera::Camera,
+    lights::PointLight,
+    materials::Material,
+    matrices::Matrix4x4,
+    spheres::Sphere,
+    transformations::view_transform,
+    tuples::{Color, Tuple},
+    world::World,
+    WHITE,
+};
+
+fn main() -> Result<()> {
+    let start = Instant::now();
+    let width = 640;
+    let height = 480;
+    let light_position = Tuple::point(-10., 10., -10.);
+    let light_color = WHITE;
+    let light = PointLight::new(light_position, light_color);
+    let mut camera = Camera::new(width, height, PI / 3.);
+    let from = Tuple::point(0., 1.5, -5.);
+    let to = Tuple::point(0., 1., 0.);
+    let up = Tuple::point(0., 1., 0.);
+    camera.transform = view_transform(from, to, up);
+
+    let mut floor = Sphere::default();
+    floor.transform = Matrix4x4::scaling(10., 0.01, 10.);
+    floor.material = Material {
+        color: Color::new(1., 0.9, 0.9),
+        specular: 0.,
+        ..Material::default()
+    };
+
+    let mut left_wall = Sphere::default();
+    left_wall.transform = Matrix4x4::translation(0., 0., 5.)
+        * Matrix4x4::rotation_y(-PI / 4.)
+        * Matrix4x4::rotation_x(PI / 2.)
+        * Matrix4x4::scaling(10., 0.01, 10.);
+    left_wall.material = floor.material.clone();
+
+    let mut right_wall = Sphere::default();
+    right_wall.transform = Matrix4x4::translation(0., 0., 5.)
+        * Matrix4x4::rotation_y(PI / 4.)
+        * Matrix4x4::rotation_x(PI / 2.)
+        * Matrix4x4::scaling(10., 0.01, 10.);
+    right_wall.material = floor.material.clone();
+
+    let mut middle = Sphere::default();
+    middle.transform = Matrix4x4::translation(-0.5, 1., 0.5);
+    middle.material = Material {
+        color: Color::new(0.1, 1., 0.5),
+        diffuse: 0.7,
+        specular: 0.3,
+        ..Material::default()
+    };
+
+    let mut right = Sphere::default();
+    right.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),
+        diffuse: 0.7,
+        specular: 0.3,
+        ..Material::default()
+    };
+
+    let mut left = Sphere::default();
+    left.transform =
+        Matrix4x4::translation(-1.5, 0.33, -0.75) * Matrix4x4::scaling(0.33, 0.33, 0.33);
+    left.material = Material {
+        color: Color::new(1., 0.8, 0.1),
+        diffuse: 0.7,
+        specular: 0.3,
+        ..Material::default()
+    };
+
+    let mut world = World::default();
+    world.light = Some(light);
+    world.objects = vec![floor, left_wall, right_wall, middle, right, left];
+
+    let image = camera.render(&world);
+
+    let path = "/tmp/eoc7.png";
+    println!("saving output to {}", path);
+    image.write_to_file(path)?;
+    println!("Render time {:.2} seconds", start.elapsed().as_secs_f32());
+    Ok(())
+}

rtchallenge/rustfmt.toml

@@ -0,0 +1 @@
+format_code_in_doc_comments = true

rtchallenge/src/camera.rs

@@ -0,0 +1,159 @@
+use crate::{canvas::Canvas, matrices::Matrix4x4, rays::Ray, tuples::Tuple, world::World, BLACK};
+
+pub struct Camera {
+    hsize: usize,
+    vsize: usize,
+    field_of_view: f32,
+    pub transform: Matrix4x4,
+    pixel_size: f32,
+    half_width: f32,
+    half_height: f32,
+}
+
+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 std::f32::consts::PI;
+    ///
+    /// use rtchallenge::{camera::Camera, matrices::Matrix4x4};
+    ///
+    /// 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_eq!(c.pixel_size(), 0.01);
+    ///
+    /// // Pixel size for a horizontal canvas.
+    /// let c = Camera::new(150, 200, PI / 2.);
+    /// assert_eq!(c.pixel_size(), 0.01);
+    /// ```
+    pub fn new(hsize: usize, vsize: usize, field_of_view: f32) -> Camera {
+        let half_view = (field_of_view / 2.).tan();
+        let aspect = hsize as f32 / vsize as f32;
+        let (half_width, half_height) = if aspect >= 1. {
+            (half_view, half_view / aspect)
+        } else {
+            (half_view * aspect, half_view)
+        };
+        let pixel_size = 2. * half_width / hsize as f32;
+        Camera {
+            hsize,
+            vsize,
+            field_of_view,
+            transform: Matrix4x4::identity(),
+            pixel_size,
+            half_height,
+            half_width,
+        }
+    }
+    pub fn hsize(&self) -> usize {
+        self.hsize
+    }
+    pub fn vsize(&self) -> usize {
+        self.vsize
+    }
+    pub fn field_of_view(&self) -> f32 {
+        self.field_of_view
+    }
+    pub fn transform(&self) -> Matrix4x4 {
+        self.transform
+    }
+    pub fn pixel_size(&self) -> f32 {
+        self.pixel_size
+    }
+
+    /// Calculate ray that starts at the camera and passes through the (x,y)
+    /// pixel on the canvas.
+    ///
+    /// # Examples
+    /// ```
+    /// use std::f32::consts::PI;
+    ///
+    /// use rtchallenge::{camera::Camera, matrices::Matrix4x4, tuples::Tuple};
+    ///
+    /// // 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.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_f32.sqrt() / 2., 0., -2_f32.sqrt() / 2.)
+    /// );
+    /// ```
+    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 f32 + 0.5) * self.pixel_size;
+        let yoffset = (py as f32 + 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 canves 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 std::f32::consts::PI;
+    ///
+    /// use rtchallenge::{
+    ///     camera::Camera,
+    ///     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.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 {
+        let mut image = Canvas::new(self.hsize, self.vsize, BLACK);
+        for y in 0..self.vsize {
+            for x in 0..self.hsize {
+                let ray = self.ray_for_pixel(x, y);
+                let color = w.color_at(&ray);
+                image.set(x, y, color);
+            }
+        }
+        image
+    }
+}

rtchallenge/src/canvas.rs

@@ -39,7 +39,7 @@ impl Canvas {
         }
         self.pixels[x + y * self.width] = c;
     }
-    pub fn get(&mut self, x: usize, y: usize) -> Color {
+    pub fn get(&self, x: usize, y: usize) -> Color {
         self.pixels[x + y * self.width]
     }
     pub fn write_to_file<P>(&self, path: P) -> Result<(), CanvasError>
@@ -74,17 +74,16 @@ impl Canvas {
 mod tests {
     use super::Canvas;
 
-    use crate::tuples::Color;
+    use crate::{tuples::Color, BLACK};
 
     #[test]
     fn create_canvas() {
-        let bg = Color::new(0.0, 0.0, 0.0);
+        let bg = BLACK;
         let c = Canvas::new(10, 20, bg);
         assert_eq!(c.width, 10);
         assert_eq!(c.height, 20);
-        let black = Color::new(0., 0., 0.);
         for (i, p) in c.pixels.iter().enumerate() {
-            assert_eq!(p, &black, "pixel {} not {:?}: {:?}", i, &black, p);
+            assert_eq!(p, &BLACK, "pixel {} not {:?}: {:?}", i, &BLACK, p);
         }
     }
 

rtchallenge/src/intersections.rs

@@ -1,6 +1,10 @@
 use std::ops::Index;
 
-use crate::spheres::Sphere;
+use crate::{
+    rays::Ray,
+    spheres::Sphere,
+    tuples::{dot, Tuple},
+};
 
 #[derive(Debug, Clone, PartialEq)]
 pub struct Intersection<'i> {
@@ -114,9 +118,86 @@ impl<'i> Intersections<'i> {
     }
 }
 
+impl<'i> IntoIterator for Intersections<'i> {
+    type Item = Intersection<'i>;
+    type IntoIter = std::vec::IntoIter<Self::Item>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        self.0.into_iter()
+    }
+}
+
 impl<'i> Index<usize> for Intersections<'i> {
     type Output = Intersection<'i>;
     fn index(&self, idx: usize) -> &Self::Output {
         &self.0[idx]
     }
 }
+
+pub struct PrecomputedData<'i> {
+    pub t: f32,
+    pub object: &'i Sphere,
+    pub point: Tuple,
+    pub eyev: Tuple,
+    pub normalv: Tuple,
+    pub inside: bool,
+}
+
+/// Precomputes data common to all intersections.
+///
+/// # Examples
+/// ```
+/// use rtchallenge::{
+///     intersections::{prepare_computations, Intersection, Intersections},
+///     rays::Ray,
+///     spheres::{intersect, Sphere},
+///     tuples::Tuple,
+/// };
+///
+/// // Precomputing the state of an intersection.
+/// let r = Ray::new(Tuple::point(0., 0., -5.), Tuple::vector(0., 0., 1.));
+/// let shape = Sphere::default();
+/// 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 = Sphere::default();
+/// 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 = Sphere::default();
+/// 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.));
+/// ```
+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);
+    let eyev = -r.direction;
+    let (inside, normalv) = if dot(normalv, eyev) < 0. {
+        (true, -normalv)
+    } else {
+        (false, normalv)
+    };
+    PrecomputedData {
+        t: i.t,
+        object: i.object,
+        point,
+        normalv,
+        inside,
+        eyev,
+    }
+}

rtchallenge/src/lib.rs

@@ -1,9 +1,17 @@
+pub mod camera;
 pub mod canvas;
 pub mod intersections;
+pub mod lights;
+pub mod materials;
 pub mod matrices;
 pub mod rays;
 pub mod spheres;
+pub mod transformations;
 pub mod tuples;
+pub mod world;
 
 /// Value considered close enough for PartialEq implementations.
 pub const EPSILON: f32 = 0.00001;
+
+pub const BLACK: tuples::Color = tuples::Color::new(0., 0., 0.);
+pub const WHITE: tuples::Color = tuples::Color::new(1., 1., 1.);

rtchallenge/src/lights.rs

@@ -0,0 +1,33 @@
+use crate::tuples::{Color, Tuple};
+
+#[derive(Debug, PartialEq)]
+pub struct PointLight {
+    pub position: Tuple,
+    pub intensity: Color,
+}
+
+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(position: Tuple, intensity: Color) -> PointLight {
+        PointLight {
+            position,
+            intensity,
+        }
+    }
+}

rtchallenge/src/materials.rs

@@ -0,0 +1,132 @@
+use crate::{
+    lights::PointLight,
+    tuples::Color,
+    tuples::{dot, reflect, Tuple},
+    BLACK, WHITE,
+};
+#[derive(Debug, PartialEq, Clone)]
+pub struct Material {
+    pub color: Color,
+    pub ambient: f32,
+    pub diffuse: f32,
+    pub specular: f32,
+    pub shininess: f32,
+}
+
+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,
+            ambient: 0.1,
+            diffuse: 0.9,
+            specular: 0.9,
+            shininess: 200.,
+        }
+    }
+}
+
+/// Compute lighting contributions using the Phong reflection model.
+///
+/// # Examples
+/// ```
+/// use rtchallenge::{
+///     lights::PointLight,
+///     materials::{lighting, Material},
+///     tuples::{Color, Tuple},
+///     WHITE,
+/// };
+///
+/// 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);
+/// 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_f32.sqrt() / 2., -2_f32.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);
+/// 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);
+/// 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_f32.sqrt() / 2., -2_f32.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);
+/// assert_eq!(result, Color::new(1.6363853, 1.6363853, 1.6363853));
+///
+/// // 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);
+/// assert_eq!(result, Color::new(0.1, 0.1, 0.1));
+/// ```
+pub fn lighting(
+    material: &Material,
+    light: &PointLight,
+    point: Tuple,
+    eyev: Tuple,
+    normalv: Tuple,
+) -> Color {
+    // Combine the surface color with the light's color.
+    let effective_color = material.color * light.intensity;
+    // Find the direciton of the light source.
+    let lightv = (light.position - point).normalize();
+    // Compute the ambient distribution.
+    let ambient = effective_color * material.ambient;
+    // This is the cosine of the angle between the light vector an the normal
+    // vector.  A negative number means the light is on the other side of the
+    // surface.
+    let light_dot_normal = dot(lightv, normalv);
+    let (diffuse, specular) = if light_dot_normal < 0. {
+        (BLACK, BLACK)
+    } else {
+        // Compute the diffuse contribution.
+        let diffuse = effective_color * material.diffuse * light_dot_normal;
+        // This represents the cosine of the angle between the relfection vector
+        // and the eye vector.  A negative number means the light reflects away
+        // from the eye.
+        let reflectv = reflect(-lightv, normalv);
+        let reflect_dot_eye = dot(reflectv, eyev);
+        let specular = if reflect_dot_eye <= 0. {
+            BLACK
+        } else {
+            // Compute the specular contribution.
+            let factor = reflect_dot_eye.powf(material.shininess);
+            light.intensity * material.specular * factor
+        };
+        (diffuse, specular)
+    };
+    ambient + diffuse + specular
+}

rtchallenge/src/matrices.rs

@@ -1,5 +1,5 @@
 use std::fmt;
-use std::ops::{Index, IndexMut, Mul};
+use std::ops::{Index, IndexMut, Mul, Sub};
 
 use crate::{tuples::Tuple, EPSILON};
 
@@ -161,7 +161,6 @@ impl PartialEq for Matrix3x3 {
     }
 }
 
-#[derive(Copy, Clone, Default)]
 /// 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.
 ///
@@ -194,6 +193,7 @@ impl PartialEq for Matrix3x3 {
 /// let t = c * b * a;
 /// assert_eq!(t * p, Tuple::point(15., 0., 7.));
 /// ```
+#[derive(Copy, Clone, Default)]
 pub struct Matrix4x4 {
     m: [[f32; 4]; 4],
 }
@@ -764,7 +764,7 @@ impl fmt::Debug for Matrix4x4 {
         if f.alternate() {
             write!(
                 f,
-                "{:?}\n  {:?}\n  {:?}\n  {:?}",
+                "\n  {:8.5?}\n  {:8.5?}\n  {:8.5?}\n  {:8.5?}",
                 self.m[0], self.m[1], self.m[2], self.m[3]
             )
         } else {
@@ -838,6 +838,21 @@ impl Mul<Tuple> for Matrix4x4 {
     }
 }
 
+impl Sub for Matrix4x4 {
+    type Output = Matrix4x4;
+
+    fn sub(self, m2: Matrix4x4) -> Matrix4x4 {
+        let m1 = self;
+        let mut r: Matrix4x4 = Default::default();
+        for i in 0..4 {
+            for j in 0..4 {
+                r.m[i][j] = m1.m[i][j] - m2.m[i][j];
+            }
+        }
+        r
+    }
+}
+
 impl PartialEq for Matrix4x4 {
     fn eq(&self, rhs: &Matrix4x4) -> bool {
         let l = self.m;

rtchallenge/src/spheres.rs

@@ -1,9 +1,9 @@
 use crate::{
     intersections::{Intersection, Intersections},
+    materials::Material,
     matrices::Matrix4x4,
     rays::Ray,
     tuples::{dot, Tuple},
-    EPSILON,
 };
 
 #[derive(Debug, PartialEq)]
@@ -11,12 +11,13 @@ use crate::{
 pub struct Sphere {
     // TODO(wathiede): cache inverse to speed up intersect.
     pub transform: Matrix4x4,
+    pub material: Material,
 }
 
 impl Default for Sphere {
     /// # Examples
     /// ```
-    /// use rtchallenge::{matrices::Matrix4x4, spheres::Sphere};
+    /// use rtchallenge::{materials::Material, matrices::Matrix4x4, spheres::Sphere};
     ///
     /// // A sphere's default transform is the identity matrix.
     /// let s = Sphere::default();
@@ -27,10 +28,21 @@ impl Default for Sphere {
     /// let t = Matrix4x4::translation(2., 3., 4.);
     /// s.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 = Sphere::default();
+    /// let mut m = Material::default();
+    /// m.ambient = 1.;
+    /// s.material = m.clone();
+    /// assert_eq!(s.material, m);
+
     /// ```
     fn default() -> Sphere {
         Sphere {
             transform: Matrix4x4::identity(),
+            material: Material::default(),
         }
     }
 }
@@ -76,21 +88,27 @@ impl Sphere {
     ///     3_f32.sqrt() / 3.,
     /// ));
     /// assert_eq!(n, n.normalize());
-    /// ```
-    /// ```should_panic
-    /// use rtchallenge::{spheres::Sphere, tuples::Tuple};
     ///
-    /// // In debug builds points not on the sphere should fail.
-    /// let s = Sphere::default();
-    /// let n = s.normal_at(Tuple::point(0., 0., 0.5));
+    /// // Compute the normal on a translated sphere.
+    /// let mut s = Sphere::default();
+    /// s.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.
+    /// use std::f32::consts::PI;
+    ///
+    /// let mut s = Sphere::default();
+    /// s.transform = Matrix4x4::scaling(1.,0.5,1.) * Matrix4x4::rotation_z(PI/5.);
+    /// let n = s.normal_at(Tuple::point(0., 2_f32.sqrt()/2., -2_f32.sqrt()/2.));
+    /// assert_eq!(n, Tuple::vector(0., 0.97014, -0.24254));
     /// ```
-    pub fn normal_at(&self, point: Tuple) -> Tuple {
-        debug_assert!(
-            ((point - Tuple::point(0., 0., 0.)).magnitude() - 1.).abs() < EPSILON,
-            "{} != 1.",
-            (point - Tuple::point(0., 0., 0.)).magnitude()
-        );
-        (point - Tuple::point(0., 0., 0.)).normalize()
+    pub fn normal_at(&self, world_point: Tuple) -> Tuple {
+        let object_point = self.transform.inverse() * world_point;
+        let object_normal = object_point - Tuple::point(0., 0., 0.);
+        let mut world_normal = self.transform.inverse().transpose() * object_normal;
+        world_normal.w = 0.;
+        world_normal.normalize()
     }
 }
 

rtchallenge/src/transformations.rs

@@ -0,0 +1,59 @@
+use crate::{
+    matrices::Matrix4x4,
+    tuples::{cross, Tuple},
+};
+
+/// Create a matrix representing a eye at `from` looking at `to`, with an `up`
+/// as the up vector.
+///
+/// # 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());
+    let true_up = cross(left, forward);
+    Matrix4x4::new(
+        [left.x, left.y, left.z, 0.],
+        [true_up.x, true_up.y, true_up.z, 0.],
+        [-forward.x, -forward.y, -forward.z, 0.],
+        [0., 0., 0., 1.],
+    ) * Matrix4x4::translation(-from.x, -from.y, -from.z)
+}

rtchallenge/src/tuples.rs

@@ -46,6 +46,28 @@ impl Tuple {
     }
 }
 
+/// Reflects vector v across normal n.
+///
+/// # Examples
+/// ```
+/// use rtchallenge::tuples::{reflect, Tuple};
+///
+/// // 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_f32.sqrt() / 2., 2_f32.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)
+}
+
 impl Add for Tuple {
     type Output = Self;
     fn add(self, other: Self) -> Self {
@@ -136,17 +158,24 @@ pub fn cross(a: Tuple, b: Tuple) -> Tuple {
     )
 }
 
-#[derive(Copy, Clone, Debug, PartialEq)]
+#[derive(Copy, Clone, Debug)]
 pub struct Color {
     pub red: f32,
     pub green: f32,
     pub blue: f32,
 }
 impl Color {
-    pub fn new(red: f32, green: f32, blue: f32) -> Color {
+    pub const fn new(red: f32, green: f32, blue: f32) -> Color {
         Color { red, green, blue }
     }
 }
+impl PartialEq for Color {
+    fn eq(&self, rhs: &Color) -> bool {
+        ((self.red - rhs.red).abs() < EPSILON)
+            && ((self.green - rhs.green).abs() < EPSILON)
+            && ((self.blue - rhs.blue).abs() < EPSILON)
+    }
+}
 impl Add for Color {
     type Output = Self;
     fn add(self, other: Self) -> Self {

rtchallenge/src/world.rs

@@ -0,0 +1,178 @@
+use crate::{
+    intersections::{prepare_computations, Intersections, PrecomputedData},
+    lights::PointLight,
+    materials::{lighting, Material},
+    matrices::Matrix4x4,
+    rays::Ray,
+    spheres::{intersect, Sphere},
+    tuples::{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.light, None);
+/// ```
+
+#[derive(Debug, Default)]
+pub struct World {
+    // TODO(wathiede): make this a list of abstract Light traits.
+    pub light: Option<PointLight>,
+    pub objects: Vec<Sphere>,
+}
+
+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.light.is_some());
+    /// ```
+    pub fn test_world() -> World {
+        let light = PointLight::new(Tuple::point(-10., 10., -10.), WHITE);
+        let mut s1 = Sphere::default();
+        s1.material = Material {
+            color: Color::new(0.8, 1., 0.6),
+            diffuse: 0.7,
+            specular: 0.2,
+            ..Material::default()
+        };
+        let mut s2 = Sphere::default();
+        s2.transform = Matrix4x4::scaling(0.5, 0.5, 0.5);
+        World {
+            light: Some(light),
+            objects: vec![s1, s2],
+        }
+    }
+
+    /// 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.);
+    /// ```
+    pub fn intersect(&self, r: &Ray) -> Intersections {
+        let mut xs: Vec<_> = self
+            .objects
+            .iter()
+            .map(|o| intersect(&o, &r))
+            .flatten()
+            .collect();
+        xs.sort_by(|i1, i2| {
+            i1.t.partial_cmp(&i2.t)
+                .expect("an intersection has a t value that is NaN")
+        });
+        Intersections::new(xs)
+    }
+
+    /// Compute shaded value for given precomputation.
+    ///
+    /// # Examples
+    /// ```
+    /// use rtchallenge::{
+    ///     intersections::{prepare_computations, Intersection},
+    ///     lights::PointLight,
+    ///     rays::Ray,
+    ///     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.light = Some(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));
+    /// ```
+    pub fn shade_hit(&self, comps: &PrecomputedData) -> Color {
+        // TODO(wathiede): support multiple light sources by iterating over all
+        // the light sources and summing the calls to lighting.
+        lighting(
+            &comps.object.material,
+            &self.light.as_ref().expect("World has no lights"),
+            comps.point,
+            comps.eyev,
+            comps.normalv,
+        )
+    }
+    /// Compute color for given ray fired at the world.
+    ///
+    /// # Examples
+    /// ```
+    /// use rtchallenge::{
+    ///     intersections::{prepare_computations, Intersection},
+    ///     lights::PointLight,
+    ///     rays::Ray,
+    ///     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];
+    ///     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() {
+            Some(hit) => {
+                let comps = prepare_computations(&hit, r);
+                self.shade_hit(&comps)
+            }
+            None => BLACK,
+        }
+    }
+}

rtiow/rustfmt.toml

@@ -0,0 +1 @@
+format_code_in_doc_comments = true