zigrtiow: add material property to hittable.

zigrtiow/src/hittable.zig

@@ -1,6 +1,8 @@
 const vec = @import("./vec.zig");
 const ray = @import("./ray.zig");
 
+const Material = @import("./material.zig").Material;
+
 const Sphere = @import("./sphere.zig").Sphere;
 const HittableList = @import("./hittable_list.zig").HittableList;
 
@@ -25,6 +27,7 @@ pub const HitRecord = struct {
     normal: Vec3,
     t: f32,
     front_face: bool,
+    material: Material,
 
     pub fn set_face_normal(hr: *HitRecord, r: Ray, outward_normal: Vec3) void {
         hr.front_face = r.direction().dot(outward_normal) < 0;

zigrtiow/src/main.zig

@@ -6,27 +6,31 @@ const vec = @import("./vec.zig");
 const sphere = @import("./sphere.zig");
 const hittable = @import("./hittable.zig");
 const hittable_list = @import("./hittable_list.zig");
+const material = @import("./material.zig");
 
 const Camera = camera.Camera;
 const Color = vec.Color;
 const Hittable = hittable.Hittable;
 const HittableList = hittable_list.HittableList;
+const Labertian = material.Labertian;
+const Material = material.Material;
 const Point3 = vec.Point3;
 const Ray = ray.Ray;
 const Sphere = sphere.Sphere;
 const Vec3 = vec.Vec3;
-const random_in_hemisphere = vec.random_in_hemisphere;
 const info = std.log.info;
+const random_in_hemisphere = vec.random_in_hemisphere;
 const write_color = color.write_color;
 
 fn ray_color(r: Ray, world: Hittable, depth: isize) Color {
     // If we've exceeded the ray bounce limit, no more light is gathered.
     if (depth <= 0) return Color.init(0, 0, 0);
 
-    var hit = world.hit(r, 0.0001, std.math.inf(f32));
-    if (hit) |rec| {
-        const target = rec.p.add(rec.normal.add(random_in_hemisphere(rec.normal)));
-        return ray_color(Ray.init(rec.p, target.sub(rec.p)), world, depth - 1).scale(0.5);
+    if (world.hit(r, 0.0001, std.math.inf(f32))) |hit_rec| {
+        if (hit_rec.material.scatter(r, hit_rec)) |scatter_rec| {
+            return scatter_rec.attenuation.mul(ray_color(scatter_rec.scattered, world, depth - 1));
+        }
+        return Color.init(0, 0, 0);
     }
     var unit_direction = r.direction().unit();
     const t = 0.5 * (unit_direction.y() + 1);
@@ -43,8 +47,12 @@ pub fn main() anyerror!void {
 
     // World
     var tmp_world = HittableList.init();
-    try tmp_world.add(Hittable{ .sphere = Sphere.init(Point3.init(0, 0, -1), 0.5) });
-    try tmp_world.add(Hittable{ .sphere = Sphere.init(Point3.init(0, -100.5, -1), 100) });
+
+    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) } };
+
+    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) });
     const world = Hittable{ .hittable_list = tmp_world };
 
     // Camera

zigrtiow/src/material.zig

@@ -0,0 +1,34 @@
+const vec = @import("./vec.zig");
+const Ray = @import("./ray.zig").Ray;
+const HitRecord = @import("./hittable.zig").HitRecord;
+
+const Vec3 = vec.Vec3;
+const Color = vec.Color;
+const random_unit_vector = vec.random_unit_vector;
+
+pub const Material = union(enum) {
+    labertian: Labertian,
+
+    pub fn scatter(material: Material, r_in: Ray, rec: HitRecord) ?ScatterRec {
+        return switch (material) {
+            .labertian => |labertian| labertian.scatter(r_in, rec),
+        };
+    }
+};
+
+pub const ScatterRec = struct { attenuation: Color, scattered: Ray };
+
+pub const Labertian = struct {
+    albedo: Vec3,
+    pub fn scatter(labertian: Labertian, r_in: Ray, rec: HitRecord) ?ScatterRec {
+        _ = r_in;
+        var scatter_direction = rec.normal.add(random_unit_vector());
+        if (scatter_direction.near_zero()) {
+            scatter_direction = rec.normal;
+        }
+        return ScatterRec{
+            .scattered = Ray.init(rec.p, scatter_direction),
+            .attenuation = labertian.albedo,
+        };
+    }
+};

zigrtiow/src/sphere.zig

@@ -2,6 +2,8 @@ const vec = @import("./vec.zig");
 const ray = @import("./ray.zig");
 const hittable = @import("./hittable.zig");
 
+const Material = @import("./material.zig").Material;
+
 const Vec3 = vec.Vec3;
 const Point3 = vec.Point3;
 const Ray = ray.Ray;
@@ -10,11 +12,13 @@ const HitRecord = hittable.HitRecord;
 pub const Sphere = struct {
     center: Point3,
     radius: f32,
+    material: Material,
 
-    pub fn init(center: Point3, radius: f32) Sphere {
+    pub fn init(center: Point3, radius: f32, material: Material) Sphere {
         return Sphere{
             .center = center,
             .radius = radius,
+            .material = material,
         };
     }
     pub fn hit(sphere: Sphere, r: Ray, t_min: f32, t_max: f32) ?HitRecord {
@@ -44,6 +48,7 @@ pub const Sphere = struct {
             .p = p,
             .normal = Vec3.init(0, 0, 0),
             .front_face = false,
+            .material = sphere.material,
         };
         hr.set_face_normal(r, outward_normal);
         return hr;

zigrtiow/src/vec.zig

@@ -34,6 +34,9 @@ pub const Vec3 = struct {
     pub fn sub(lhs: Vec3, rhs: Vec3) Vec3 {
         return Vec3{ .v = lhs.v - rhs.v };
     }
+    pub fn mul(lhs: Vec3, rhs: Vec3) Vec3 {
+        return Vec3{ .v = lhs.v * rhs.v };
+    }
     pub fn scale(vec: Vec3, t: f32) Vec3 {
         return Vec3{ .v = vec.v * @splat(3, t) };
     }
@@ -52,6 +55,12 @@ pub const Vec3 = struct {
             rand.float(f32) * 2 - 1,
         );
     }
+    pub fn near_zero(vec: Vec3) bool {
+        // Return true if the vector is close to zero in all dimensions.
+        const s = 1e-8;
+        const e = vec.v;
+        return (@fabs(e[0]) < s) and (@fabs(e[1]) < s) and (@fabs(e[2]) < s);
+    }
 };
 
 pub fn random_in_unit_sphere() Vec3 {