public static Vector3 Radiance(Ray ray, RNG rng)
{
Ray r = ray;
Vector3 L = new Vector3();
Vector3 F = new Vector3(1.0);
while (true)
{
int id;
if (!Intersect(r, out id))
{
return(L);
}
Sphere shape = spheres[id];
Vector3 p = r.Eval(r.tmax);
Vector3 n = (p - shape.p).Normalize();
L += F * shape.e;
F *= shape.f;
// Russian roulette
if (r.depth > 4)
{
double continue_probability = shape.f.Max();
if (rng.UniformFloat() >= continue_probability)
{
return(L);
}
F /= continue_probability;
}
// Next path segment
switch (shape.reflection_t)
{
case Sphere.Reflection_t.SPECULAR: {
Vector3 d = Specular.IdealSpecularReflect(r.d, n);
r = new Ray(p, d, Sphere.EPSILON_SPHERE, double.PositiveInfinity, r.depth + 1);
break;
}
case Sphere.Reflection_t.REFRACTIVE: {
double pr;
Vector3 d = Specular.IdealSpecularTransmit(r.d, n, REFRACTIVE_INDEX_OUT, REFRACTIVE_INDEX_IN, out pr, rng);
F *= pr;
r = new Ray(p, d, Sphere.EPSILON_SPHERE, double.PositiveInfinity, r.depth + 1);
break;
}
default: {
Vector3 w = n.Dot(r.d) < 0 ? n : -n;
Vector3 u = ((Math.Abs(w[0]) > 0.1 ? new Vector3(0.0, 1.0, 0.0) : new Vector3(1.0, 0.0, 0.0)).Cross(w)).Normalize();
Vector3 v = w.Cross(u);
Vector3 sample_d = Sampling.CosineWeightedSampleOnHemisphere(rng.UniformFloat(), rng.UniformFloat());
Vector3 d = (sample_d[0] * u + sample_d[1] * v + sample_d[2] * w).Normalize();
r = new Ray(p, d, Sphere.EPSILON_SPHERE, double.PositiveInfinity, r.depth + 1);
break;
}
}
}
}
public static Vector3 IdealSpecularTransmit(Vector3 d, Vector3 n, double n_out, double n_in, out double pr, RNG rng)
{
Vector3 d_Re = IdealSpecularReflect(d, n);
bool out_to_in = n.Dot(d) < 0;
Vector3 nl = out_to_in ? n : -n;
double nn = out_to_in ? n_out / n_in : n_in / n_out;
double cos_theta = d.Dot(nl);
double cos2_phi = 1.0 - nn * nn * (1.0 - cos_theta * cos_theta);
// Total Internal Reflection
if (cos2_phi < 0)
{
pr = 1.0;
return(d_Re);
}
Vector3 d_Tr = (nn * d - nl * (nn * cos_theta + Math.Sqrt(cos2_phi))).Normalize();
double c = 1.0 - (out_to_in ? -cos_theta : d_Tr.Dot(n));
double Re = SchlickReflectance(n_out, n_in, c);
double p_Re = 0.25 + 0.5 * Re;
if (rng.UniformFloat() < p_Re)
{
pr = (Re / p_Re);
return(d_Re);
}
else
{
double Tr = 1.0 - Re;
double p_Tr = 1.0 - p_Re;
pr = (Tr / p_Tr);
return(d_Tr);
}
}