Implement motion blur

src/hittable.rs

@@ -62,3 +62,68 @@ impl Hittable for Sphere {
         })
     }
 }
+
+pub struct MovableSphere {
+    pub center0: Point3,
+    pub center1: Point3,
+    pub radius: f64,
+    pub material: Material,
+    pub time0: f64,
+    pub time1: f64,
+}
+impl MovableSphere {
+    pub fn new(
+        center0: Point3,
+        center1: Point3,
+        radius: f64,
+        material: Material,
+        time0: f64,
+        time1: f64) -> Self {
+        MovableSphere { center0, center1, radius, material, time0, time1 }
+    }
+    pub fn center(&self, time: f64) -> Point3 {
+        self.center0 + ((time - self.time0) / (self.time1 - self.time0))*(self.center1 - self.center0)
+    }
+}
+impl Default for MovableSphere {
+    fn default() -> Self {
+        MovableSphere {
+            center0: Point3::default(),
+            center1: Point3::default(),
+            radius: 0.0,
+            material: Material::default(),
+            time0: 0.0,
+            time1: 0.0
+        }
+    }
+}
+
+impl Hittable for MovableSphere {
+    fn hit(&self, ray: &Ray, t_min: f64, t_max: f64) -> Option<HitRecord> {
+        let oc = &ray.origin() - &self.center(ray.time());
+        let a = ray.direction().length_squared();
+        let half_b = oc.dot(&ray.direction());
+        let c = oc.length_squared() - &self.radius * &self.radius;
+        let discriminant = half_b * half_b - a * c;
+        if discriminant < 0.0 { return None; }
+
+        let sqrtd = discriminant.sqrt();
+        let mut root = (-half_b - sqrtd) / a;
+        if root < t_min || t_max < root {
+            root = (-half_b + sqrtd) / a;
+            if root < t_min || t_max < root { return None; }
+        }
+        let point = ray.at(root);
+        let normal = (point - self.center(ray.time())) / self.radius;
+        let dot = ray.direction().dot(&normal);
+        let front_face = dot < 0.0;
+        let normal = if front_face { normal } else { -normal };
+        Some(HitRecord {
+            point,
+            normal,
+            t: root,
+            front_face,
+            material: &self.material
+        })
+    }
+}