1 files changed, 70 insertions, 0 deletions
diff --git a/src/world/shapes/sphere.rs b/src/world/shapes/sphere.rs
new file mode 100644
index 0000000..8e0816b
--- /dev/null
+++ b/src/world/shapes/sphere.rs
@@ -0,0 +1,70 @@
+//! Implements sphere
+//!
+//! Spheres are relatively easy to calculate intersections between
+use crate::Float;
+use crate::core::{Ray, Vector3f, Hittable, Intersection};
+
+pub struct Sphere {
+    radius: Float,
+    center: Vector3f,
+}
+
+impl Sphere {
+    pub fn new(radius: Float, center: Vector3f) -> Sphere {
+        Sphere {
+            radius,
+            center,
+        }
+    }
+
+    fn norm_at(&self, point: &Vector3f) -> Vector3f {
+        let mut v = *point - self.center;
+        v /= self.radius;
+        v
+    }
+}
+
+impl Hittable for Sphere {
+    // Implementation from ray tracing in a weekend
+    fn intersect(&self, ray: &Ray) -> Option<Intersection> {
+        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 {
+            let distance = (-half_b - disc.sqrt()) / a;
+            if distance < 0.0 {
+                return None
+            }
+            let w = ray.at(distance);
+            Some(Intersection {
+                n: self.norm_at(&w),
+                p: w,
+                t: distance,
+            })
+        }
+
+    }
+}
+
+#[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).unwrap();
+        assert!((dist.t - 3.28).abs() < 0.01);
+    }
+}