Add ray and sphere structs and impl

src/main.rs

@@ -1,5 +1,6 @@
 use std::ops::{Add, Div, Mul, Sub};
 
+#[derive(Clone, Copy)]
 struct Vec3 {
     x: f64,
     y: f64,
@@ -61,5 +62,54 @@ impl Div for Vec3 {
     }
 }
 
-fn main() {
+// Aliased for use in arguments, no functional difference
+type Point = Vec3;
+type Color = Vec3;
+
+struct Ray {
+    origin: Point,
+    direction: Vec3,
 }
+
+struct Sphere {
+    center: Vec3,
+    radius: f64,
+    color: Color,
+}
+
+impl Sphere {
+    fn new(center: Vec3, radius: f64, color: Color) -> Self {
+        Self { center, radius, color }
+    }
+
+    // Ray/sphere intersection
+    // See: https://viclw17.github.io/2018/07/16/raytracing-ray-sphere-intersection/
+    fn intersect(&self, ray: &Ray) -> Option<f64> {
+        let epsilon = 1e-4;
+        let oc = ray.origin - self.center;
+        let a = ray.direction.dot(&ray.direction);
+        let b = 2. * oc.dot(&ray.direction);
+        let c = oc.dot(&oc) - self.radius * self.radius;
+        let discrimiant = b * b - 4. * a * c;
+
+        // The ray missed the sphere
+        if discrimiant < 0. {
+            None
+        } else {
+            let mut numerator = -b - discrimiant.sqrt();
+            if numerator > epsilon {
+                return Some(numerator / (2. * a));
+            }
+
+            numerator = -b + discrimiant.sqrt();
+            if numerator > epsilon {
+                Some(numerator / (2. * a))
+            } else {
+                // The intersection happened behind the ray's origin
+                None
+            }
+        }
+    }
+}
+
+fn main() {}