public override Spectrum f(Vector3 <float> wo, Vector3 <float> wi)
{
var cosThetaO = AbsCosTheta(wo);
var cosThetaI = AbsCosTheta(wi);
var wh = wi + wo;
// Handle degenerate cases at grazing angles
if (cosThetaI == 0 || cosThetaO == 0)
{
return(Spectrum.Zero);
}
if (wh.LengthSquared() == 0)
{
return(Spectrum.Zero);
}
wh = wh.Normalized();
var f = fresnel.Evaluate(wi.Dot(wh));
// Torrance-Sparrow model
return
((reflectance * distribution.D(wh) * distribution.G(wo, wi) * f) /
(4 * cosThetaI * cosThetaO));
}
public override Spectrum Sample_f(Vector3 <float> wo, out Vector3 <float> wi, Point2 <float> sample, out float pdf, out BxDFType type)
{
// Compute the perfect specular reflection direction
//
// In polar coordinates:
// phi_o = phi_i + pi
// theta_o = theta_i
wi = new Vector3 <float>(-wo.X, -wo.Y, wo.Z); // Simplified because we are in the BRDF coordinate frame
pdf = 1;
sample = null;
type = 0; // TODO?
return(fresnel.Evaluate(CosTheta(wi)) * reflectance * (1.0f / AbsCosTheta(wi)));
}
public override SampledSpectrum F(Vector3 incoming, Vector3 leaving)
{
var cosThetaO = AbsCosTheta(ref leaving);
var cosThetaI = AbsCosTheta(ref incoming);
if (cosThetaI == 0 || cosThetaO == 0)
{
return(new SampledSpectrum(0));
}
var wh = Vector3.Add(incoming, leaving).Normalized();
var cosThetaH = Vector3.Dot(incoming, leaving);
var f = _fresnel.Evaluate(cosThetaH);
return(_spectrum * _distribution.D(ref wh) * G(ref incoming, ref leaving, ref wh) * f / (4 * cosThetaI * cosThetaO));
}
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));
}
