world: implement World::intersect.

rtchallenge/src/intersections.rs

@@ -114,6 +114,15 @@ 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 {

rtchallenge/src/world.rs

@@ -1,8 +1,10 @@
 use crate::{
+    intersections::Intersections,
     lights::PointLight,
     materials::Material,
     matrices::{Matrix2x2, Matrix4x4},
-    spheres::Sphere,
+    rays::Ray,
+    spheres::{intersect, Sphere},
     tuples::{Color, Tuple},
 };
 
@@ -51,4 +53,32 @@ impl World {
             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)
+    }
 }