public void NDF_Orthogonal()
{
float ax = 0.5f;
float ay = 0.3f;
var dist = new TrowbridgeReitzDistribution()
{
AlphaX = ax, AlphaY = ay
};
var ndf = dist.NormalDistribution(new System.Numerics.Vector3(0, 0, 1));
float expectedNdf = 1 / (MathF.PI * ax * ay);
Assert.Equal(expectedNdf, ndf, 4);
}
public void NDF_GrazingAngle()
{
float ax = 0.5f;
float ay = 0.3f;
var dist = new TrowbridgeReitzDistribution()
{
AlphaX = ax, AlphaY = ay
};
var ndf = dist.NormalDistribution(new System.Numerics.Vector3(1, 0, 0));
float expectedNdf = 0;
Assert.Equal(expectedNdf, ndf, 4);
}
public RgbColor Evaluate(Vector3 outDir, Vector3 inDir, bool isOnLightSubpath)
{
if (ShadingSpace.SameHemisphere(outDir, inDir))
{
return(RgbColor.Black); // transmission only
}
float cosThetaO = ShadingSpace.CosTheta(outDir);
float cosThetaI = ShadingSpace.CosTheta(inDir);
if (cosThetaI == 0 || cosThetaO == 0)
{
return(RgbColor.Black);
}
// Compute the half vector
float eta = ShadingSpace.CosTheta(outDir) > 0 ? (insideIOR / outsideIOR) : (outsideIOR / insideIOR);
Vector3 wh = Vector3.Normalize(outDir + inDir * eta);
if (ShadingSpace.CosTheta(wh) < 0)
{
wh = -wh;
}
if (Vector3.Dot(outDir, wh) * Vector3.Dot(inDir, wh) > 0)
{
return(RgbColor.Black);
}
var F = new RgbColor(FresnelDielectric.Evaluate(Vector3.Dot(outDir, wh), outsideIOR, insideIOR));
float sqrtDenom = Vector3.Dot(outDir, wh) + eta * Vector3.Dot(inDir, wh);
float factor = isOnLightSubpath ? (1 / eta) : 1;
var numerator = distribution.NormalDistribution(wh) * distribution.MaskingShadowing(outDir, inDir);
numerator *= eta * eta * Math.Abs(Vector3.Dot(inDir, wh)) * Math.Abs(Vector3.Dot(outDir, wh));
numerator *= factor * factor;
var denom = (cosThetaI * cosThetaO * sqrtDenom * sqrtDenom);
Debug.Assert(float.IsFinite(denom));
return((RgbColor.White - F) * transmittance * Math.Abs(numerator / denom));
}
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));
}