feat: add dialectric material

main.cc

@@ -33,21 +33,22 @@ int main() {
 	const auto aspect_ratio = 16.0 / 9.0;
 	const int image_width = 400;
 	const int image_height = static_cast<int>(image_width / aspect_ratio);
-	const int samples_per_pixel = 16;
+	const int samples_per_pixel = 32;
-	const int max_depth = 25;
+	const int max_depth = 32;
 
 	// World
 	hittable_list world;
 
 	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_center = make_shared<lambertian>(color(0.1, 0.2, 0.5));
-	auto material_left = make_shared<metal>(color(0.8, 0.8, 0.8), 0.3);
+	auto material_left = make_shared<dialectric>(1.5);
-	auto material_right = make_shared<metal>(color(0.8, 0.6, 0.2), 1.0);
+	auto material_right = make_shared<metal>(color(0.8, 0.6, 0.2), 0.1);
 
-	world.add(make_shared<sphere>(point3(0, -100.5, -1), 100, material_ground));
+	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( 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_left));
-	world.add(make_shared<sphere>(point3(1, 0, -1), 0.5, material_right));
+	world.add(make_shared<sphere>(point3(-1,      0, -1), -0.4, material_left));
+	world.add(make_shared<sphere>(point3( 1,      0, -1), 0.5, material_right));
 
 	// Camera
 	camera cam;

material.h

@@ -53,4 +53,42 @@ class metal : public material {
 		double fuzz;
 };
 
+class dialectric : public material {
+	public:
+		dialectric(double index_of_refraction): ir(index_of_refraction) {}
+
+		bool scatter(
+			const ray &r_in, const hit_record &rec, color &attenuation, ray &scattered
+		) const override {
+			attenuation = color(1.0, 1.0, 1.0);
+			double refraction_ratio = rec.front_face ? (1.0/ir) : ir;
+
+			vec3 unit_direction = unit_vector(r_in.direction());
+			double cos_theta = fmin(dot(-unit_direction, rec.normal), 1.0);
+			double sin_theta = sqrt(1 - cos_theta*cos_theta);
+
+			bool cannot_refract = refraction_ratio * sin_theta > 1.0;
+			vec3 direction;
+			if (cannot_refract || reflectance(cos_theta, refraction_ratio) > random_double())
+				direction = reflect(unit_direction, rec.normal);
+			else
+				direction = refract(unit_direction, rec.normal, refraction_ratio);
+
+			scattered = ray(rec.p, direction);
+			return true;
+		}
+
+
+	public:
+		double ir; // Index of Refraction
+
+	private:
+		static double reflectance(double cosine, double ref_idx) {
+			// Use Schlick's approximation for reflectance
+			auto r0 = (1-ref_idx) /(1+ref_idx);
+			r0 = r0*r0;
+			return r0 + (1-r0)*pow((1 - cosine), 5);
+		}
+};
+
 #endif

vec3.h

@@ -138,4 +138,11 @@ vec3 reflect(const vec3& v, const vec3& n) {
 	return v - 2*dot(v,n)*n;
 }
 
+vec3 refract(const vec3& uv, const vec3& n, double etai_over_etat) {
+	auto cos_theta = fmin(dot(-uv, n), 1.0);
+	vec3 r_out_perp = etai_over_etat * (uv + cos_theta*n);
+	vec3 r_out_parrallel = -sqrt(fabs(1.0 - r_out_perp.length_squared())) * n;
+	return r_out_perp + r_out_parrallel;
+}
+
 #endif