add Lambertian material

in_one_weekend/src/main.zig

@@ -1,6 +1,7 @@
 const std = @import("std");
 const print = std.debug.print;
 const Random = std.rand.Random;
+
 const sdl = @import("sdl.zig");
 const vec3 = @import("vec3.zig");
 const Vec3 = vec3.Vec3;
@@ -11,6 +12,10 @@ const Ray = @import("ray.zig").Ray;
 const Sphere = @import("sphere.zig").Sphere;
 const World = @import("world.zig").World;
 const Camera = @import("camera.zig").Camera;
+const material = @import("material.zig");
+const Material = material.Material;
+const MaterialType = material.MaterialType;
+const scatter = @import("material.zig").scatter;
 
 // From: https://github.com/Nelarius/weekend-raytracer-zig/blob/master/src/main.zig
 // See https://github.com/zig-lang/zig/issues/565
@@ -41,15 +46,16 @@ fn rayColor(ray: Ray, world: World, rng: *Random, depth: i32) Color {
     }
 
     if (world.hit(ray, 0.001, 99999)) |hit| {
-        const target = hit.p.add(vec3.random_in_hemisphere(rng, hit.normal));
-        const newRay = Ray{ .origin = hit.p, .direction = target.sub(hit.p)};
-        return rayColor(newRay, world, rng, depth - 1).div(2);
+        if (scatter(ray, hit, rng)) |sRay| {
+            return sRay.color.mul(rayColor(sRay.ray, world, rng, depth - 1));
+        }
+        return Color{ .x = 0, .y = 0, .z = 0 };
     }
-    const unitDirection = vec3.unitVector(ray.direction);
+    const unitDirection = ray.direction.unit();
     const t = 0.5 * (unitDirection.y + 1.0);
     const white = Color{ .x = 1.0, .y = 1.0, .z = 1.0 };
     const blue = Color{ .x = 0.5, .y = 0.7, .z = 1.0 };
-    return white.mul(1.0 - t).add(blue.mul(t));
+    return white.mul_s(1.0 - t).add(blue.mul_s(t));
 }
 
 fn setProgress(surface: *sdl.c.SDL_Surface, width: usize, height: usize, percent: f32) void {
@@ -87,9 +93,18 @@ pub fn main() anyerror!void {
     const maxDepth = 5;
 
     // World
+    const materialGround = Material{
+        .materialType = MaterialType.Lambertian,
+        .color = Color{ .x = 0.8, .y = 0.8, .z = 0.0 },
+    };
+    const materialCenter = Material{
+        .materialType = MaterialType.Lambertian,
+        .color = Color{ .x = 0.7, .y = 0.3, .z = 0.3 },
+    };
+
     const spheres = [_]Sphere{
-        Sphere{ .center = Point3{ .x = 0, .y = 0, .z = -1 }, .radius = 0.5 },
-        Sphere{ .center = Point3{ .x = 0, .y = -100.5, .z = -1 }, .radius = 100 },
+        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 },
      };
     const world = World{ .spheres = spheres[0..spheres.len] };