add glass

src/main.cpp

@@ -39,7 +39,7 @@ colour ray_colour(const ray& r, const hittable& world, int depth)
     auto t = 0.5 * (unit_direction.y() + 1.0);
 
     auto a = colour(0.5, 0.6, 0.7);
-    auto b = colour(1.0, 1.0, 1.0);
+    auto b = colour(0.5, 0.5, 0.5);
 
     return lerp(a, b, t);
 }
@@ -53,7 +53,7 @@ int main()
     world.add(make_shared<sphere>(
         point3(0,0,-1),
         0.5,
-        make_shared<lambertian>(colour(0.7,0.3,0.3))));
+        make_shared<lambertian>(colour(0.1,0.2,0.5))));
     world.add(make_shared<sphere>(
         point3(0,-100.5,-1),
         100,
@@ -62,11 +62,15 @@ int main()
     world.add(make_shared<sphere>(
         point3(1,0,-1),
         0.5,
-        make_shared<metal>(colour(0.8,0.6,0.2))));
+        make_shared<metal>(colour(0.8,0.6,0.2), 0.0)));
     world.add(make_shared<sphere>(
         point3(-1,0,-1),
         0.5,
-        make_shared<metal>(colour(0.8,0.8,0.8))));
+        make_shared<dielectric>(1.5)));
+    world.add(make_shared<sphere>(
+        point3(-1,0,-1),
+        -0.45,
+        make_shared<dielectric>(1.5)));
 
     camera cam;
 

src/material.h

@@ -13,6 +13,13 @@ class material
             ray& scattered) const = 0;
 };
 
+double schlick(double cosine, double refraction_index)
+{
+    auto r0 = (1-refraction_index) / (1+refraction_index);
+    r0 = r0*r0;
+    return r0 + (1-r0)*pow(1-cosine, 5);
+}
+
 class lambertian : public material
 {
     public:
@@ -37,7 +44,9 @@ class lambertian : public material
 class metal : public material
 {
     public:
-        metal(const colour& a) : albedo_(a) {}
+        metal(const colour& a, double f) : 
+            albedo_(a),
+            fuzz_(f < 1 ? f : 1) {}
 
     virtual bool scatter(
         const ray& r_in, 
@@ -46,11 +55,55 @@ class metal : public material
         ray& scattered) const 
     {
         vec3 reflected = reflect(unit_vector(r_in.direction()), rec.normal);
-        scattered = ray(rec.p, reflected);
+        scattered = ray(rec.p, reflected + fuzz_*random_in_unit_sphere());
         attenuation = albedo_;
         return dot(scattered.direction(), rec.normal) > 0;
     }
 
     private:
         colour albedo_;
+        double fuzz_;
+};
+
+class dielectric : public material
+{
+    public:
+        dielectric(double ri) : refraction_index_(ri) {}
+
+    virtual bool scatter(
+        const ray& r_in, 
+        const hit_record& rec, 
+        colour& attenuation, 
+        ray& scattered) const 
+    {
+        attenuation = colour(1.0,1.0,1.0);
+        double etai_over_etat = rec.front_face ? (1.0 / refraction_index_) : refraction_index_;
+
+        vec3 unit_direction = unit_vector(r_in.direction());
+
+        double cos_theta = fmin(dot(-unit_direction, rec.normal), 1.0);
+        double sin_theta = sqrt(1.0 - cos_theta*cos_theta);
+        if (etai_over_etat * sin_theta > 1.0)
+        {
+            vec3 reflected = reflect(unit_direction, rec.normal);
+            scattered = ray(rec.p, reflected);
+            return true;
+        }
+
+        double reflect_prob = schlick(cos_theta, etai_over_etat);
+        if (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;
+    }
+
+    private:
+        double refraction_index_;
 };

src/vec3.h

@@ -164,3 +164,12 @@ 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 = dot(-uv, n);
+    vec3 r_out_parallel = etai_over_etat * (uv + cos_theta*n);
+    vec3 r_out_perp = -sqrt(1.0 - r_out_parallel.length_squared()) * n;
+
+    return r_out_parallel + r_out_perp;
+}