Refraction

rtiww/src/main.cpp

@@ -16,19 +16,19 @@ color ray_color(const ray &r, const hittable &world, int depth) {
 
   // If we've exceeded the ray bounce limit, no more light is gathered.
   if (depth <= 0)
-        return color(0,0,0);
+    return color(0, 0, 0);
 
   if (world.hit(r, 0.000001, infinity, rec)) {
     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);
+      return attenuation * ray_color(scattered, world, depth - 1);
+    return color(0, 0, 0);
   }
 
   vec3 unit_direction = unit_vector(r.direction());
-    auto t = 0.5*(unit_direction.y() + 1.0);
-    return (1.0-t)*color(1.0, 1.0, 1.0) + t*color(0.5, 0.7, 1.0);
+  auto t = 0.5 * (unit_direction.y() + 1.0);
+  return (1.0 - t) * color(1.0, 1.0, 1.0) + t * color(0.5, 0.7, 1.0);
 }
 
 int main() {
@@ -46,14 +46,15 @@ int main() {
   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_left   = make_shared<metal>(color(0.8, 0.8, 0.8), 0.3);
+  auto material_center = make_shared<dielectric>(1.5);
+  auto material_left = make_shared<dielectric>(1.5);
   auto material_right = make_shared<metal>(color(0.8, 0.6, 0.2), 1.0);
 
-    world.add(make_shared<sphere>(point3( 0.0, -100.5, -1.0), 100.0, material_ground));
-    world.add(make_shared<sphere>(point3( 0.0,    0.0, -1.0),   0.5, material_center));
+  world.add(
+      make_shared<sphere>(point3(0.0, -100.5, -1.0), 100.0, material_ground));
+  world.add(make_shared<sphere>(point3(0.0, 0.0, -1.0), 0.5, material_center));
   world.add(make_shared<sphere>(point3(-1.0, 0.0, -1.0), 0.5, material_left));
-    world.add(make_shared<sphere>(point3( 1.0,    0.0, -1.0),   0.5, material_right));
+  world.add(make_shared<sphere>(point3(1.0, 0.0, -1.0), 0.5, material_right));
 
   // Camera
 
@@ -63,13 +64,13 @@ int main() {
 
   std::cout << "P3\n" << image_width << " " << image_height << "\n255\n";
 
-    for (int j = image_height-1; j >= 0; --j) {
+  for (int j = image_height - 1; j >= 0; --j) {
     std::cerr << "\rScanlines remaining: " << j << ' ' << std::flush;
     for (int i = 0; i < image_width; ++i) {
       color pixel_color(0, 0, 0);
       for (int s = 0; s < samples_per_pixel; ++s) {
-                auto u = (i + random_double()) / (image_width-1);
-                auto v = (j + random_double()) / (image_height-1);
+        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, max_depth);
       }

rtiww/src/material.h

@@ -13,16 +13,13 @@ public:
                        color &attenuation, ray &scattered) const = 0;
 };
 
-
-
 class lambertian : public material {
 public:
-    lambertian(const color& a) : albedo(a) {}
+  lambertian(const color &a) : albedo(a) {}
 
-    virtual bool scatter(
-            const ray& r_in, const hit_record& rec, color& attenuation, ray& scattered
-    ) const override {
-        auto scatter_direction = rec.normal+random_in_unit_sphere();
+  virtual bool scatter(const ray &r_in, const hit_record &rec,
+                       color &attenuation, ray &scattered) const override {
+    auto scatter_direction = rec.normal + random_in_unit_sphere();
 
     // Catch degenerate scatter direction
     if (scatter_direction.near_zero())
@@ -39,13 +36,12 @@ public:
 
 class metal : public material {
 public:
-    metal(const color& a, double f) : albedo(a), fuzz(f<1 ? f: 1) {}
+  metal(const color &a, double f) : albedo(a), fuzz(f < 1 ? f : 1) {}
 
-    virtual bool scatter(
-            const ray& r_in, const hit_record& rec, color& attenuation, ray& scattered
-    ) const override {
+  virtual 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_unit_sphere());
+    scattered = ray(rec.p, reflected + fuzz * random_in_unit_sphere());
     attenuation = albedo;
     return true;
   }
@@ -55,4 +51,24 @@ public:
   double fuzz;
 };
 
+class dielectric : public material {
+public:
+  dielectric(double index_of_refraction) : ir(index_of_refraction) {}
+
+  virtual 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());
+    vec3 refracted = refract(unit_direction, rec.normal, refraction_ratio);
+
+    scattered = ray(rec.p, refracted);
+    return true;
+  }
+
+public:
+  double ir;
+};
+
 #endif // MATERIAL_H_

rtiww/src/vec3.h

@@ -124,4 +124,11 @@ vec3 random_in_hemisphere(const vec3 &normal) {
 
 vec3 reflect(const vec3 &v, const vec3 &n) { return v - 2 * dot(v, n) * n; }
 
+vec3 refract(const vec3 &v, const vec3 &n, double etai_over_etat) {
+  auto cos_theta = fmin(dot(-v, n), 1.0);
+  vec3 r_out_perp = etai_over_etat * (v + cos_theta * n);
+  vec3 r_out_parallel = -sqrt(fabs(1.0 - r_out_perp.length_squared())) * n;
+  return r_out_perp + r_out_parallel;
+}
+
 #endif // RTIWW_VEC3_H