// Cheap shadows are hard. In fact, I'd almost say, shadowing particular scenes with limited
// iterations is impossible... However, I'd be very grateful if someone could prove me wrong. :)
private static float SoftShadow(Float3 ro, Float3 lp, Float3 n, float k)
{
const int iter = 24;
ro += n * 0.0015f;
Float3 rd = lp - ro;
float shade = 1.0f;
float t = 0;
float end = Hlsl.Max(Hlsl.Length(rd), 0.0001f);
rd /= end;
for (int i = 0; i < iter; i++)
{
float d = M(ro + rd * t);
shade = Hlsl.Min(shade, k * d / t);
t += Hlsl.Clamp(d, 0.01f, 0.25f);
if (d < 0.0f || t > end)
{
break;
}
}
return(Hlsl.Max(shade, 0.0f));
}