world: add default empty World constructor.

rtchallenge/src/lib.rs

@@ -6,6 +6,7 @@ pub mod matrices;
 pub mod rays;
 pub mod spheres;
 pub mod tuples;
+pub mod world;
 
 /// Value considered close enough for PartialEq implementations.
 pub const EPSILON: f32 = 0.00001;

rtchallenge/src/lights.rs

@@ -1,5 +1,6 @@
 use crate::tuples::{Color, Tuple};
 
+#[derive(Debug, PartialEq)]
 pub struct PointLight {
     pub position: Tuple,
     pub intensity: Color,

rtchallenge/src/world.rs

@@ -0,0 +1,19 @@
+use crate::{lights::PointLight, spheres::Sphere};
+
+/// 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>,
+}