private Vector CalculateRefractionRadiance(Ray ray, int depth, Point x, Vector n, Vector nl, Sphere obj, Color f)
{
var reflRay = new Ray(x, ray.Direction - n * 2 * n.Dot(ray.Direction)); // Ideal dielectric REFRACTION
var into = n.Dot(nl) > 0; // Ray from outside going in?
const int Nc = 1;
const double Nt = 1.5;
var nnt = @into ? Nc / Nt : Nt / Nc;
var ddn = ray.Direction.Dot(nl);
double cos2T;
if((cos2T = 1 - nnt * nnt * (1 - ddn * ddn)) < 0) { // Total internal reflection
return obj.Emission + f.Multiply(Radiance(reflRay, depth));
}
var tdir = (ray.Direction * nnt - n * ((@into ? 1 : -1) * (ddn * nnt + Math.Sqrt(cos2T)))).Normalize();
const double A = Nt - Nc;
const double B = Nt + Nc;
const double R0 = A * A / (B * B);
var c = 1 - (@into ? -ddn : tdir.Dot(n));
var re = R0 + (1 - R0) * c * c * c * c * c;
var tr = 1 - re;
var pp = .25 + .5 * re;
var rp = re / pp;
var tp = tr / (1 - pp);
return obj.Emission + f.Multiply(depth > 2 ? (random.NextDouble() < pp ? // Russian roulette
Radiance(reflRay, depth) * rp : Radiance(new Ray(x, tdir), depth) * tp) :
Radiance(reflRay, depth) * re + Radiance(new Ray(x, tdir), depth) * tr);
}
// --- Private Methods ---
private Vector CalculateDiffuseRadiance(int depth, Vector nl, Sphere obj, Color f, Point x)
{
var r1 = 2 * Math.PI * random.NextDouble();
var r2 = random.NextDouble();
var r2SquareRoot = Math.Sqrt(r2);
var w = nl;
var u = ((Math.Abs(w.X) > .1 ? Vector.UnitY : Vector.UnitX) % w).Normalize();
var v = w % u;
var d = (u * Math.Cos(r1) * r2SquareRoot + v * Math.Sin(r1) * r2SquareRoot + w * Math.Sqrt(1 - r2)).Normalize();
return obj.Emission + f.Multiply(Radiance(new Ray(x, d), depth));
}
private Vector CalculateSpecularRadiance(Ray ray, int depth, Sphere obj, Color f, Point x, Vector n)
{
return obj.Emission + f.Multiply(Radiance(new Ray(x, ray.Direction - n * 2 * n.Dot(ray.Direction)), depth));
}
