world: implement World::color_at

rtchallenge/src/world.rs

@@ -1,11 +1,12 @@
 use crate::{
-    intersections::{Intersections, PrecomputedData},
+    intersections::{prepare_computations, Intersections, PrecomputedData},
     lights::PointLight,
     materials::{lighting, Material},
     matrices::Matrix4x4,
     rays::Ray,
     spheres::{intersect, Sphere},
     tuples::{Color, Tuple},
+    BLACK,
 };
 
 /// World holds all drawable objects and the light(s) that illuminate them.
@@ -118,6 +119,8 @@ impl World {
     /// 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"),
@@ -126,4 +129,51 @@ impl World {
             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,
+    /// };
+    ///
+    /// // 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, Color::new(0., 0., 0.));
+    ///
+    /// // 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,
+        }
+    }
 }