public Vector3?Sample(Vector3 outDir, bool isOnLightSubpath, Vector2 primarySample)
{
if (outDir.Z == 0)
{
return(null);
}
Vector3 wh = distribution.Sample(outDir, primarySample);
if (Vector3.Dot(outDir, wh) < 0)
{
return(null);
}
float eta = ShadingSpace.CosTheta(outDir) > 0 ? (outsideIOR / insideIOR) : (insideIOR / outsideIOR);
var inDir = ShadingSpace.Refract(outDir, wh, eta);
return(inDir);
}