float ComputeOneDir(Vector3 outDir, Vector3 inDir)
{
// Compute the half vector
float eta = ShadingSpace.CosTheta(outDir) > 0 ? (insideIOR / outsideIOR) : (outsideIOR / insideIOR);
Vector3 wh = outDir + inDir * eta;
if (wh == Vector3.Zero)
{
return(0); // Prevent NaN if outDir and inDir exactly align
}
wh = Vector3.Normalize(wh);
if (Vector3.Dot(outDir, wh) * Vector3.Dot(inDir, wh) > 0)
{
return(0);
}
// Compute change of variables _dwh\_dinDir_ for microfacet transmission
float sqrtDenom = Vector3.Dot(outDir, wh) + eta * Vector3.Dot(inDir, wh);
if (sqrtDenom == 0)
{
return(0); // Prevent NaN in corner case
}
float dwh_dinDir = Math.Abs((eta * eta * Vector3.Dot(inDir, wh)) / (sqrtDenom * sqrtDenom));
float result = distribution.Pdf(outDir, wh) * dwh_dinDir;
Debug.Assert(float.IsFinite(result));
return(result);
}
public (float, float) Pdf(Vector3 outDir, Vector3 inDir, bool isOnLightSubpath)
{
if (!ShadingSpace.SameHemisphere(outDir, inDir))
{
return(0, 0);
}
var halfVector = outDir + inDir;
// catch NaN causing corner cases
if (halfVector == Vector3.Zero)
{
return(0, 0);
}
halfVector = Vector3.Normalize(halfVector);
var pdfForward = distribution.Pdf(outDir, halfVector) / Math.Abs(4 * Vector3.Dot(outDir, halfVector));
var pdfReverse = distribution.Pdf(inDir, halfVector) / Math.Abs(4 * Vector3.Dot(inDir, halfVector));
return(pdfForward, pdfReverse);
}