Adding dielectric material.

Makefile

@@ -9,7 +9,7 @@ TARGET = wtracer
 
 all: $(TARGET) run
 
-run:
+run: $(TARGET)
 	time -f '%E elapsed' ./wtracer > image.ppm
 	eog image.ppm
 

material.cpp

@@ -1,5 +1,7 @@
 #include "material.h"
 
+#include <cmath>
+
 bool Lambertian::scatter(const Ray& r_in, const hit_record& rec, Color& attenuation, Ray& scattered) const {
   //Vec3 scatter_direction = rec.normal + random_in_unit_sphere();
   Vec3 scatter_direction = rec.normal + random_unit_vector();
@@ -15,3 +17,28 @@ bool Metal::scatter(const Ray& r_in, const hit_record& rec, Color& attenuation,
   attenuation = albedo;
   return (dot(scattered.direction(), rec.normal) > 0);
 }
+
+double schlick(double cosine, double ref_idx) {
+  auto r0 = (1 - ref_idx) / (1 + ref_idx);
+  r0 = r0 * r0;
+  return r0 + (1 - r0) * std::pow((1 - cosine), 5);
+}
+
+bool Dielectric::scatter(const Ray& r_in, const hit_record& rec, Color& attenuation, Ray& scattered) const {
+    attenuation = Color(1.0, 1.0, 1.0);
+    double etai_over_etat = rec.front_face ? 1.0 / ref_idx : ref_idx;
+
+    Vec3 unit_direction = unit_vector(r_in.direction());
+    double cos_theta = std::fmin(dot(-unit_direction, rec.normal), 1.0);
+    double sin_theta = std::sqrt(1.0 - cos_theta*cos_theta);
+    double reflect_prob = schlick(cos_theta, etai_over_etat);
+    if (etai_over_etat * sin_theta > 1.0 || random_double() < reflect_prob) {
+        Vec3 reflected = reflect(unit_direction, rec.normal);
+        scattered = Ray(rec.p, reflected);
+        return true;
+    }
+
+    Vec3 refracted = refract(unit_direction, rec.normal, etai_over_etat);
+    scattered = Ray(rec.p, refracted);
+    return true;
+}

material.h

@@ -31,4 +31,14 @@ private:
   double fuzz;
 };
 
+double schlick(double cosine, double ref_idx);
+
+class Dielectric : public Material {
+public:
+  Dielectric(double ri) : ref_idx(ri) {}
+  virtual bool scatter(const Ray& r_in, const hit_record& rec, Color& attenuation, Ray& scattered) const;
+private:
+  double ref_idx;
+};
+
 #endif // MATERIAL_H

vec3.cpp

@@ -22,3 +22,10 @@ Vec3 random_in_hemisphere(const Vec3& normal) {
     else
         return -in_unit_sphere;
 }
+
+Vec3 refract(const Vec3& uv, const Vec3& n, double etai_over_etat) {
+    auto cos_theta = dot(-uv, n);
+    Vec3 r_out_parallel = etai_over_etat * (uv + cos_theta*n);
+    Vec3 r_out_perp = - std::sqrt(1.0 - r_out_parallel.length_squared()) * n;
+    return r_out_parallel + r_out_perp;
+}

vec3.h

@@ -122,4 +122,6 @@ Vec3 random_unit_vector();
 
 Vec3 random_in_hemisphere(const Vec3& normal);
 
+Vec3 refract(const Vec3& uv, const Vec3& n, double etai_over_etat);
+
 #endif  // VEC3_H

wtracer.cpp

@@ -41,14 +41,14 @@ int main() {
     std::cout << "P3\n" << image_width << " " << image_height << "\n255\n";
 
     Hittable_list world;
-    /*world.add(std::make_shared<Sphere>(Point3(0, 0, -1), 0.5));
-    world.add(std::make_shared<Sphere>(Point3(0, -100.5, -1), 100));*/
 
-    world.add(std::make_shared<Sphere>(Point3(0, 0, -1), 0.5, std::make_shared<Lambertian>(Color(0.7, 0.3, 0.3))));
+    world.add(std::make_shared<Sphere>(Point3(0, 0, -1), 0.5, std::make_shared<Lambertian>(Color(0.1, 0.2, 0.5))));
     world.add(std::make_shared<Sphere>(Point3(0, -100.5, -1), 100, std::make_shared<Lambertian>(Color(0.8, 0.8, 0.0))));
 
-    world.add(std::make_shared<Sphere>(Point3(1, 0, -1), 0.5, std::make_shared<Metal>(Color(0.8, 0.6, 0.2), 0.3)));
-    world.add(std::make_shared<Sphere>(Point3(-1, 0, -1), 0.5, std::make_shared<Metal>(Color(0.8, 0.8, 0.8), 1.0)));
+    world.add(std::make_shared<Sphere>(Point3(1, 0, -1), 0.5, std::make_shared<Metal>(Color(0.8, 0.6, 0.2), 0.0)));
+
+
+    world.add(std::make_shared<Sphere>(Point3(-1, 0, -1), 0.5, std::make_shared<Dielectric>(1.45)));
 
     Camera cam;