add Metal material

in_one_weekend/src/main.zig

@@ -94,17 +94,27 @@ pub fn main() anyerror!void {
 
     // World
     const materialGround = Material{
-        .materialType = MaterialType.Lambertian,
+        .materialType = .Lambertian,
         .color = Color{ .x = 0.8, .y = 0.8, .z = 0.0 },
     };
     const materialCenter = Material{
-        .materialType = MaterialType.Lambertian,
+        .materialType = .Lambertian,
         .color = Color{ .x = 0.7, .y = 0.3, .z = 0.3 },
     };
+    const materialLeft = Material{
+        .materialType = .Metal,
+        .color = Color{ .x = 0.8, .y = 0.8, .z = 0.8 },
+    };
+    const materialRight = Material{
+        .materialType = .Metal,
+        .color = Color{ .x = 0.8, .y = 0.6, .z = 0.2 },
+    };
 
     const spheres = [_]Sphere{
-        Sphere{ .center = Point3{ .x = 0, .y = 0, .z = -1 }, .radius = 0.5, .material = materialCenter },
         Sphere{ .center = Point3{ .x = 0, .y = -100.5, .z = -1 }, .radius = 100, .material = materialGround },
+        Sphere{ .center = Point3{ .x = 0, .y = 0, .z = -1 }, .radius = 0.5, .material = materialCenter },
+        Sphere{ .center = Point3{ .x = -1, .y = 0, .z = -1 }, .radius = 0.5, .material = materialLeft },
+        Sphere{ .center = Point3{ .x = 1, .y = 0, .z = -1 }, .radius = 0.5, .material = materialRight },
      };
     const world = World{ .spheres = spheres[0..spheres.len] };
 

in_one_weekend/src/material.zig

@@ -8,6 +8,7 @@ const HitRecord = @import("hittable.zig").HitRecord;
 
 pub const MaterialType = enum {
     Lambertian,
+    Metal,
 };
 
 pub const Material = struct {
@@ -21,15 +22,34 @@ pub const ScatteredRay = struct {
 };
 
 pub fn scatter(ray: Ray, hit: HitRecord, rng: *Random) ?ScatteredRay {
-    var scatterDirection = hit.normal.add(vec3.random_unit_vector(rng));
+    const scatteredDirection = switch (hit.material.materialType) {
 
-    // Catch degenerate scatter direction
-    if (scatterDirection.nearZero()) {
-        scatterDirection = hit.normal;
+        .Lambertian => blk: {
+            var scatterDirection = hit.normal.add(vec3.random_unit_vector(rng));
+            // Catch degenerate scatter direction
+            if (scatterDirection.nearZero()) {
+                scatterDirection = hit.normal;
+            }
+            break :blk scatterDirection;
+        },
+
+        .Metal => blk: {
+            const reflected = ray.direction.unit().reflect(hit.normal);
+            const scattered = Ray{ .origin = hit.p, .direction = reflected };
+            if (scattered.direction.dot(hit.normal) <= 0) {
+                break :blk null;
+            }
+            break :blk scattered.direction;
+        },
+
+    };
+
+    if (scatteredDirection) |dir| {
+        return ScatteredRay{
+            .ray = Ray{ .origin = hit.p, .direction = dir},
+            .color = hit.material.color,
+        };
     }
 
-    return ScatteredRay{
-        .ray = Ray{ .origin = hit.p, .direction = scatterDirection},
-        .color = hit.material.color,
-    };
+    return null;
 }

in_one_weekend/src/vec3.zig

@@ -78,6 +78,10 @@ pub const Vec3 = packed struct {
             and math.absFloat(self.y) < t
             and math.absFloat(self.z) < t;
     }
+
+    pub fn reflect(self: Vec3, n: Vec3) Vec3 {
+        return self.sub(n.mul_s(self.dot(n) * 2));
+    }
 };
 
 pub fn random(rng: *Random, min: f32, max: f32) Vec3 {