feat: add diffusion with gamma-correction

color.h

@@ -1,16 +1,20 @@
 #ifndef COLOR_H
 #define COLOR_H
 
-#include "vec3.h"
 #include "rtweekend.h"
 
 #include <iostream>
 
 void write_color(std::ostream &out, color pixel_color, int samples_per_pixel) {
+	auto r = pixel_color.x();
+	auto g = pixel_color.y();
+	auto b = pixel_color.z();
+
+	// Divide the color by the number of samples and gamma-correct for gamma=2.0
 	auto scale = 1.0 / samples_per_pixel;
-	auto r = pixel_color.x() * scale;
-	auto g = pixel_color.y() * scale;
-	auto b = pixel_color.z() * scale;
+	r = sqrt(scale * r);
+	g = sqrt(scale * g);
+	b = sqrt(scale * b);
 
 	// Write the translated [0,255] value of each color component
 	out << static_cast<int>(256 * clamp(r, 0.0, 0.999)) << " "

main.cc

@@ -7,10 +7,16 @@
 
 #include <iostream>
 
-color ray_color(const ray& r, const hittable& world) {
+color ray_color(const ray& r, const hittable& world, int depth) {
 	hit_record rec;
+
+	// If we've exceeded the ray bounce limit, no more light is gathered.
+	if (depth <= 0)
+		return color(0, 0, 0);
+
 	if (world.hit(r, 0, infinity, rec)) {
-		return 0.5 * (rec.normal + color(1, 1, 1));
+		point3 target = rec.p + rec.normal + random_in_unit_sphere();
+		return 0.5 * ray_color(ray(rec.p, target - rec.p), world, depth-1);
 	}
 
 	vec3 unit_direction = unit_vector(r.direction());
@@ -23,7 +29,8 @@ 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 = 10;
+	const int samples_per_pixel = 32;
+	const int max_depth = 25;
 
 	// World
 	hittable_list world;
@@ -34,7 +41,7 @@ int main() {
 	camera cam;
 
 	// Render
-	std::cout<<"P3\n"<<image_width<<" "<<image_height<<"\n255\n";
+	std::cout<<"P3\n" <<image_width<<" "<<image_height<<"\n255\n";
 	for (int j = image_height-1; j >= 0; --j) {
 		std::cerr<<"\rScanlines remaining: "<<j<<" "<<std::flush;
 		for (int i = 0; i < image_width; ++i) {
@@ -43,7 +50,7 @@ int main() {
 				auto u = (i + random_double()) / (image_width-1);
 				auto v = (j + random_double()) / (image_height-1);
 				ray r = cam.get_ray(u, v);
-				pixel_color += ray_color(r, world);
+				pixel_color += ray_color(r, world, max_depth);
 			}
 			write_color(std::cout, pixel_color, samples_per_pixel);
 		}

vec3.h

@@ -1,6 +1,7 @@
 #ifndef VEC3_H
 #define VEC3_H
 
+#include "rtweekend.h"
 #include <cmath>
 #include <iostream>
 
@@ -45,6 +46,14 @@ class vec3 {
 			return e[0]*e[0] + e[1]*e[1] + e[2]*e[2];
 		}
 
+		inline static vec3 random() {
+			return vec3(random_double(), random_double(), random_double());
+		}
+
+		inline static vec3 random(double min, double max) {
+			return vec3(random_double(min, max), random_double(min, max), random_double(min, max));
+		}
+
 	public:
 		double e[3];
 };
@@ -95,6 +104,14 @@ inline vec3 cross(const vec3 &u, const vec3 &v) {
 	            u.e[0] * v.e[1] - u.e[1] * v.e[0]);
 }
 
+vec3 random_in_unit_sphere() {
+	while(true) {
+		auto p = vec3::random(-1, 1);
+		if (p.length_squared() >= 1) continue;
+		return p;
+	}
+}
+
 inline vec3 unit_vector(vec3 v) {
 	return v / v.length();
 }