zigrtiow: add metal material.

zigrtiow/src/main.zig

@@ -13,6 +13,7 @@ const Color = vec.Color;
 const Hittable = hittable.Hittable;
 const HittableList = hittable_list.HittableList;
 const Labertian = material.Labertian;
+const Metal = material.Metal;
 const Material = material.Material;
 const Point3 = vec.Point3;
 const Ray = ray.Ray;
@@ -50,9 +51,13 @@ pub fn main() anyerror!void {
 
     const material_ground = Material{ .labertian = Labertian{ .albedo = Color.init(0.8, 0.8, 0.0) } };
     const material_center = Material{ .labertian = Labertian{ .albedo = Color.init(0.7, 0.3, 0.3) } };
+    const material_left = Material{ .metal = Metal{ .albedo = Color.init(0.8, 0.8, 0.8) } };
+    const material_right = Material{ .metal = Metal{ .albedo = Color.init(0.8, 0.6, 0.2) } };
 
     try tmp_world.add(Hittable{ .sphere = Sphere.init(Point3.init(0, -100.5, -1), 100, material_ground) });
     try tmp_world.add(Hittable{ .sphere = Sphere.init(Point3.init(0, 0, -1), 0.5, material_center) });
+    try tmp_world.add(Hittable{ .sphere = Sphere.init(Point3.init(-1, 0, -1), 0.5, material_left) });
+    try tmp_world.add(Hittable{ .sphere = Sphere.init(Point3.init(1, 0, -1), 0.5, material_right) });
     const world = Hittable{ .hittable_list = tmp_world };
 
     // Camera

zigrtiow/src/material.zig

@@ -8,10 +8,12 @@ const random_unit_vector = vec.random_unit_vector;
 
 pub const Material = union(enum) {
     labertian: Labertian,
+    metal: Metal,
 
     pub fn scatter(material: Material, r_in: Ray, rec: HitRecord) ?ScatterRec {
         return switch (material) {
             .labertian => |labertian| labertian.scatter(r_in, rec),
+            .metal => |metal| metal.scatter(r_in, rec),
         };
     }
 };
@@ -32,3 +34,23 @@ pub const Labertian = struct {
         };
     }
 };
+
+pub const Metal = struct {
+    albedo: Vec3,
+    pub fn scatter(metal: Metal, r_in: Ray, rec: HitRecord) ?ScatterRec {
+        const reflected = reflect(r_in.direction().unit(), rec.normal);
+        const scattered = Ray.init(rec.p, reflected);
+        const attenuation = metal.albedo;
+        if (scattered.direction().dot(rec.normal) > 0) {
+            return ScatterRec{
+                .scattered = scattered,
+                .attenuation = attenuation,
+            };
+        } else {
+            return null;
+        }
+    }
+    fn reflect(v: Vec3, n: Vec3) Vec3 {
+        return v.sub(n.scale(v.dot(n) * 2));
+    }
+};