2 files changed, 39 insertions, 4 deletions
diff --git a/src/scene/shapes/mod.rs b/src/scene/shapes/mod.rs
index 76fb6f2..7fbb8db 100644
--- a/src/scene/shapes/mod.rs
+++ b/src/scene/shapes/mod.rs
@@ -5,8 +5,6 @@ pub use sphere::Sphere;
 use crate::core::Ray;
 use crate::Float;
 
-trait Shape {
-    // 
-    fn intersect(ray: Ray) -> Float;
-    fn intersect_
+pub trait Shape {
+    fn intersect(&self, ray: &Ray) -> Option<Float>;
 }
diff --git a/src/scene/shapes/sphere.rs b/src/scene/shapes/sphere.rs
index 9598422..f8ae11e 100644
--- a/src/scene/shapes/sphere.rs
+++ b/src/scene/shapes/sphere.rs
@@ -1,5 +1,6 @@
 use crate::Float;
 use crate::core::{Ray, Vector3f};
+use super::Shape;
 
 pub struct Sphere {
     radius: Float,
@@ -14,3 +15,39 @@ impl Sphere {
         }
     }
 }
+
+impl Shape for Sphere {
+    // Implementation from ray tracing in a weekend
+    fn intersect(&self, ray: &Ray) -> Option<Float> {
+        let oc = ray.origin - self.center;
+        let a = ray.direction.len_squared();
+        let half_b = oc.dot(&ray.direction);
+        let c = oc.len_squared() - self.radius * self.radius;
+        let disc = half_b*half_b - a*c;
+
+        if disc < 0.0 {
+            None
+        } else {
+            Some( (-half_b - disc.sqrt()) / a)
+        }
+
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn sphere_intersect() {
+        let sph = Sphere::new(2.0, Vector3f::new_xyz(2.0, 3.0, 4.0));
+
+        let ray = Ray {
+            origin: Vector3f::new_xyz(1.0, 0.0, 0.0),
+            direction: Vector3f::new_xyz(0.0, 1.0, 1.5).norm(),
+        };
+
+        let dist = sph.intersect(&ray);
+        assert!((dist.unwrap() - 3.28).abs() < 0.01);
+    }
+}