Add some reflections and native color mixing

src/lib.rs

@@ -185,6 +185,13 @@ impl Ray {
             dir: self.dir,
         }
     }
+
+    pub fn reflected(&self, position: Vector, normal: &UnitVector) -> Ray {
+        Ray {
+            pos: position,
+            dir: self.dir.reflected(normal),
+        }
+    }
 }
 
 impl AlmostEqual for Ray {
@@ -336,7 +343,13 @@ pub fn posunit_to_unit(value: f32) -> f32 {
 
 pub struct Radians(pub f32);
 
-pub fn render(spheres: &[Sphere], camera: &Camera, width: usize, height: usize) -> Image {
+pub fn render(
+    spheres: &[Sphere],
+    camera: &Camera,
+    width: usize,
+    height: usize,
+    bounces: usize,
+) -> Image {
     let mut image = Image::new(width, height);
     for i in 0..width {
         for j in 0..height {
@@ -345,19 +358,33 @@ pub fn render(spheres: &[Sphere], camera: &Camera, width: usize, height: usize)
                 i as f32 / (width - 1) as f32,
                 j as f32 / (height - 1) as f32,
             );
-            let color = match closest_intersection(&spheres, &ray) {
-                None => Color::new_black(),
-                Some(intersection) => {
-                    let brightness = intersection.normal.0.dot(&-ray.dir.0);
-                    intersection.sphere.color * brightness
-                }
-            };
+            let color = trace_ray(&spheres, &ray, bounces);
             image.set_color(i, j, color);
         }
     }
     image
 }
 
+pub fn trace_ray(spheres: &[Sphere], ray: &Ray, bounces: usize) -> Color {
+    match closest_intersection(&spheres, &ray) {
+        None => Color::new_black(),
+        Some(intersection) => {
+            let brightness = intersection.normal.0.dot(&-ray.dir.0);
+
+            let mut color = intersection.sphere.color;
+            if bounces > 0 {
+                color = color
+                    + trace_ray(
+                        &spheres,
+                        &ray.reflected(intersection.position, &intersection.normal),
+                        bounces - 1,
+                    );
+            }
+            color * brightness
+        }
+    }
+}
+
 pub fn closest_intersection<'a>(spheres: &'a [Sphere], ray: &Ray) -> Option<Intersection<'a>> {
     let mut closest_hit = None;
     let mut closest_hit_distance = f32::MAX;

src/main.rs

@@ -56,6 +56,6 @@ fn main() {
         aspect_ratio: 4.0 / 3.0,
         fovx: Radians(90.0f32.to_radians()),
     };
-    let image = render(&spheres, &camera, 800, 600);
+    let image = render(&spheres, &camera, 800, 600, 3);
     image_to_file(&image, &mut file);
 }

tests/lib.rs

@@ -1,6 +1,6 @@
 use raytracer::{
-    closest_intersection, image_to_file, AlmostEqual, Camera, Color, Image, Intersection, Radians,
-    Ray, Sphere, UnitVector, Vector,
+    closest_intersection, image_to_file, trace_ray, AlmostEqual, Camera, Color, Image,
+    Intersection, Radians, Ray, Sphere, UnitVector, Vector,
 };
 use std::str;
 
@@ -450,3 +450,48 @@ fn test_color_addition() {
     );
     assert_almost_eq!(Color::new_red() + Color::new_red(), Color::new_red());
 }
+
+#[test]
+fn test_trace_ray() {
+    let spheres = [
+        Sphere {
+            center: Vector {
+                x: 2.0,
+                y: 1.0,
+                z: 1.0,
+            },
+            radius: 1.0,
+            color: Color::new_red(),
+        },
+        Sphere {
+            center: Vector {
+                x: 4.0,
+                y: 4.0,
+                z: 1.0,
+            },
+            radius: 1.0,
+            color: Color::new_green(),
+        },
+    ];
+    let ray = Ray {
+        pos: Vector {
+            x: 1.0,
+            y: 3.0,
+            z: 1.0,
+        },
+        dir: Vector {
+            x: 1.0,
+            y: -1.0,
+            z: 0.0,
+        }
+        .normalized(),
+    };
+    assert_almost_eq!(
+        trace_ray(&spheres, &ray, 0),
+        45.0f32.to_radians().cos() * Color::new_red(),
+    );
+    assert_almost_eq!(
+        trace_ray(&spheres, &ray, 1),
+        45.0f32.to_radians().cos() * (Color::new_red() + Color::new_green()),
+    );
+}