feat: add metal metarial

color.h

@@ -2,6 +2,7 @@
 #define COLOR_H
 
 #include "rtweekend.h"
+#include "vec3.h"
 
 #include <iostream>
 

hittable.h

@@ -1,11 +1,15 @@
 #ifndef HITTABLE_H
 #define HITTABLE_H
 
+#include "rtweekend.h"
 #include "ray.h"
 
+class material;
+
 struct hit_record {
 	point3 p;
 	vec3 normal;
+	shared_ptr<material> mat_ptr;
 	double t;
 	bool front_face;
 

main.cc

@@ -1,9 +1,10 @@
-#include "rtweekend.h"
 
 #include "color.h"
+#include "rtweekend.h"
 #include "hittable_list.h"
 #include "sphere.h"
 #include "camera.h"
+#include "material.h"
 
 #include <iostream>
 
@@ -15,8 +16,11 @@ color ray_color(const ray& r, const hittable& world, int depth) {
 		return color(0, 0, 0);
 
 	if (world.hit(r, 0.001, infinity, rec)) {
-		point3 target = rec.p + rec.normal + random_in_hemisphere(rec.normal);
-		return 0.5 * ray_color(ray(rec.p, target - rec.p), world, depth-1);
+		ray scattered;
+		color attenuation;
+		if (rec.mat_ptr->scatter(r, rec, attenuation, scattered))
+				return attenuation * ray_color(scattered, world, depth-1);
+		return color(0,0,0);
 	}
 
 	vec3 unit_direction = unit_vector(r.direction());
@@ -34,8 +38,16 @@ int main() {
 
 	// World
 	hittable_list world;
-	world.add(make_shared<sphere>(point3(0, 0, -1), 0.5));
-	world.add(make_shared<sphere>(point3(0, -100.5, -1), 100));
+
+	auto material_ground = make_shared<lambertian>(color(0.8, 0.8, 0.0));
+	auto material_center = make_shared<lambertian>(color(0.7, 0.3, 0.3));
+	auto material_left = make_shared<metal>(color(0.8, 0.8, 0.8), 0.3);
+	auto material_right = make_shared<metal>(color(0.8, 0.6, 0.2), 1.0);
+
+	world.add(make_shared<sphere>(point3(0, -100.5, -1), 100, material_ground));
+	world.add(make_shared<sphere>(point3(0, 0, -1), 0.5, material_center));
+	world.add(make_shared<sphere>(point3(-1, 0, -1), 0.5, material_left));
+	world.add(make_shared<sphere>(point3(1, 0, -1), 0.5, material_right));
 
 	// Camera
 	camera cam;

material.h

@@ -0,0 +1,56 @@
+#ifndef MATERIAL_H
+#define MATERIAL_H
+
+#include "hittable.h"
+#include "rtweekend.h"
+#include "vec3.h"
+
+struct hit_record;
+
+class material {
+	public:
+		virtual bool scatter(const ray& r_in, const hit_record& rec, color& attenuation, ray& scattered) const = 0;
+};
+
+
+class lambertian : public material {
+	public:
+		lambertian(const color& a) : albedo(a) {}
+
+		bool scatter(
+			const ray &r_in, const hit_record &rec, color &attenuation, ray &scattered
+		) const override {
+			auto scatter_direction = rec.normal + random_in_hemisphere(rec.normal);
+
+			// Catch degenerate scatter direction
+			if (scatter_direction.near_zero())
+				scatter_direction = rec.normal;
+
+			scattered = ray(rec.p, scatter_direction);
+			attenuation = albedo;
+			return true;
+		}
+
+	public:
+		color albedo;
+};
+
+class metal : public material {
+	public:
+		metal(const color& a, double f) : albedo(a), fuzz(f < 1 ? f : 1) {}
+
+		bool scatter(
+				const ray &r_in, const hit_record &rec, color &attenuation, ray &scattered
+		) const override {
+			vec3 reflected = reflect(unit_vector(r_in.direction()), rec.normal);
+			scattered = ray(rec.p, reflected + fuzz*random_in_hemisphere(rec.normal));
+			attenuation = albedo;
+			return (dot(scattered.direction(), rec.normal) > 0);
+		}
+
+	public:
+		color albedo;
+		double fuzz;
+};
+
+#endif

rtweekend.h

@@ -36,8 +36,4 @@ inline double random_double(double min, double max) {
 	return min + (max - min) * random_double();
 }
 
-// Common headers
-#include "ray.h"
-#include "vec3.h"
-
 #endif

sphere.h

@@ -7,7 +7,7 @@
 class sphere : public hittable {
 	public:
 		sphere() {}
-		sphere(point3 cen, double r) : center(cen), radius(r) {};
+		sphere(point3 cen, double r, shared_ptr<material> m) : center(cen), radius(r), mat_ptr(m) {};
 
 		virtual bool hit(
 				const ray& r, double t_min, double t_max, hit_record& rec) const override;
@@ -15,6 +15,7 @@ class sphere : public hittable {
 	public:
 		point3 center;
 		double radius;
+		shared_ptr<material> mat_ptr;
 };
 
 bool sphere::hit(const ray& r, double t_min, double t_max, hit_record& rec) const {
@@ -39,6 +40,7 @@ bool sphere::hit(const ray& r, double t_min, double t_max, hit_record& rec) cons
 	rec.p = r.at(rec.t);
 	vec3 outward_normal = (rec.p - center) / radius;
 	rec.set_face_normal(r, outward_normal);
+	rec.mat_ptr = mat_ptr;
 
 	return true;
 }

vec3.h

@@ -1,10 +1,11 @@
 #ifndef VEC3_H
 #define VEC3_H
 
-#include "rtweekend.h"
 #include <cmath>
 #include <iostream>
 
+#include "rtweekend.h"
+
 using std::sqrt;
 
 class vec3 {
@@ -54,6 +55,11 @@ class vec3 {
 			return vec3(random_double(min, max), random_double(min, max), random_double(min, max));
 		}
 
+		bool near_zero() const {
+			auto s = 1e-8;
+			return fabs(e[0]) < s && fabs(e[1]) < s && fabs(e[2]) < s;
+		}
+
 	public:
 		double e[3];
 };
@@ -128,4 +134,8 @@ vec3 random_in_hemisphere(const vec3& normal) {
 		return -in_unit_sphere;
 }
 
+vec3 reflect(const vec3& v, const vec3& n) {
+	return v - 2*dot(v,n)*n;
+}
+
 #endif