Refraction

rtiww/src/main.cpp

@@ -46,11 +46,12 @@ 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_center = make_shared<dielectric>(1.5);
-    auto material_left   = make_shared<metal>(color(0.8, 0.8, 0.8), 0.3);
+  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, -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));

rtiww/src/material.h

@@ -13,15 +13,12 @@ public:
                        color &attenuation, ray &scattered) const = 0;
 };
 
-
-
 class lambertian : public material {
 public:
   lambertian(const color &a) : albedo(a) {}
 
-    virtual bool scatter(
+  virtual bool scatter(const ray &r_in, const hit_record &rec,
-            const ray& r_in, const hit_record& rec, color& attenuation, ray& scattered
+                       color &attenuation, ray &scattered) const override {
-    ) const override {
     auto scatter_direction = rec.normal + random_in_unit_sphere();
 
     // Catch degenerate scatter direction
@@ -41,9 +38,8 @@ class metal : public material {
 public:
   metal(const color &a, double f) : albedo(a), fuzz(f < 1 ? f : 1) {}
 
-    virtual bool scatter(
+  virtual bool scatter(const ray &r_in, const hit_record &rec,
-            const ray& r_in, const hit_record& rec, color& attenuation, ray& scattered
+                       color &attenuation, ray &scattered) const override {
-    ) const override {
     vec3 reflected = reflect(unit_vector(r_in.direction()), rec.normal);
     scattered = ray(rec.p, reflected + fuzz * random_in_unit_sphere());
     attenuation = albedo;
@@ -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