public RgbColor Evaluate(Vector3 outDir, Vector3 inDir, bool isOnLightSubpath)
{
if (!ShadingSpace.SameHemisphere(outDir, inDir))
{
return(RgbColor.Black);
}
float cosThetaO = ShadingSpace.AbsCosTheta(outDir);
float cosThetaI = ShadingSpace.AbsCosTheta(inDir);
Vector3 halfVector = inDir + outDir;
// Handle degenerate cases for microfacet reflection
if (cosThetaI == 0 || cosThetaO == 0)
{
return(RgbColor.Black);
}
if (halfVector.X == 0 && halfVector.Y == 0 && halfVector.Z == 0)
{
return(RgbColor.Black);
}
// For the Fresnel call, make sure that wh is in the same hemisphere
// as the surface normal, so that total internal reflection is handled correctly.
halfVector = Vector3.Normalize(halfVector);
if (ShadingSpace.CosTheta(halfVector) < 0)
{
halfVector = -halfVector;
}
var cosine = Vector3.Dot(inDir, halfVector);
var f = fresnel.Evaluate(cosine);
var nd = distribution.NormalDistribution(halfVector);
var ms = distribution.MaskingShadowing(outDir, inDir);
return(tint * nd * ms * f / (4 * cosThetaI * cosThetaO));
}
/// <summary> /// The Pdf that is used for importance sampling microfacet normals from this distribution. /// This usually importance samples the portion of normals that are in the hemisphere of the outgoing direction. /// </summary> /// <param name="outDir">The outgoing direction in shading space.</param> /// <param name="inDir">The incoming direction in shading space.</param> /// <returns>The pdf value.</returns> public float Pdf(Vector3 outDir, Vector3 normal) => NormalDistribution(normal) * MaskingShadowing(outDir) * MathF.Abs(Vector3.Dot(outDir, normal)) / ShadingSpace.AbsCosTheta(outDir);
