6.3.An Abstraction for Hittable Objects

src/hittable.rs

@@ -0,0 +1,5 @@
+use crate::types_defined::{HitRecord, Ray};
+
+pub trait Hittable {
+    fn hit(self, r: &Ray, t_min: f32, t_max: f32) -> HitRecord;
+}

src/sphere.rs

@@ -0,0 +1,41 @@
+use crate::hittable;
+use crate::types_defined::{HitRecord, Point, Ray, Sphere};
+
+impl Sphere {
+    pub fn new(c: Point, r: f32) -> Self {
+        Self {
+            center: c,
+            radius: r,
+        }
+    }
+}
+
+impl hittable::Hittable for Sphere {
+    fn hit(self, r: &Ray, t_min: f32, t_max: f32) -> HitRecord {
+        let a: f32 = r.direction.length_squared();
+        let h = r.direction.dot(self.center - r.point);
+        // let b = -2.0 * r.direction.dot(sphere_center - r.point);
+        let c = (self.center - r.point).length_squared() - self.radius * self.radius;
+
+        let discriminant = h * h - a * c;
+
+        // // 两个焦点
+        let disc_sqrt = discriminant.sqrt();
+        let near = (h - disc_sqrt) / a;
+        let far = (h + disc_sqrt) / a;
+
+        let mut root = near;
+        if root <= t_min || root >= t_max {
+            root = far;
+            if root <= t_min || root >= t_max {
+                root = -1.0;
+            }
+        }
+        
+        HitRecord {
+            t: root,
+            p: r.at(root),
+            normal: r.at(root) - self.center,
+        }
+    }
+}