// 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));
}
static float SDBox(float3 p, float3 b)
{
float3 q = Hlsl.Abs(p) - b;
return(Hlsl.Length(Hlsl.Max(q, 0.0f)) +
Hlsl.Min(Hlsl.Max(q.X, Hlsl.Max(q.Y, q.Z)), 0.0f));
}
// Various distance metrics.
private static float Distance(Float2 p)
{
if (SHAPE == 0)
{
return(Hlsl.Length(p));
}
else
{
p = Hlsl.Abs(p);
}
switch (SHAPE)
{
case 1: return(Hlsl.Max(Hlsl.Length(p), (p.X + p.Y) * 0.7071f + 0.015f));
case 2: return(Hlsl.Max((p.X + p.Y) * 0.7071f, Hlsl.Max(p.X, p.Y)));
case 3: return(Hlsl.Pow(Hlsl.Dot(Hlsl.Pow(p, 3), 1), 1.0f / 3.0f));
default: return((p.X + p.Y) * 0.7071f);
}
}
// The scene's distance function: There'd be faster ways to do this, but it's
// more readable this way. Plus, this is a pretty simple scene, so it's
// efficient enough.
private static float M(Float3 p)
{
float fl = -p.Z;
float obj = Truchet(p.XY);
obj = Hlsl.Max(obj, Hlsl.Abs(p.Z) - 0.125f) - Hlsl.SmoothStep(0.03f, 0.25f, -obj) * 0.1f;
float studs = 1e5f;
const float sc = 0.5f;
Float2 q = p.XY + 0.5f * sc;
Float2 iq = Hlsl.Floor(q / sc) + 0.5f;
q -= iq * sc;
if (Mod(iq.X + iq.Y, 2.0f) > 0.5f)
{
studs = Hlsl.Max(Hlsl.Length(q) - 0.1f * sc - 0.02f, Hlsl.Abs(p.Z) - 0.26f);
}
objID = fl < obj && fl < studs ? 0 : obj < studs ? 1 : 2;
return(Hlsl.Min(Hlsl.Min(fl, obj), studs));
}