public override SampledSpectrum Sample(Vector3 leaving, out Vector3 incoming)
{
var entering = CosTheta(ref leaving) > 0;
float ei, et;
if (entering)
{
ei = IndexOfRefractionIncident;
et = IndexOfRefractionTransmitted;
}
else
{
et = IndexOfRefractionIncident;
ei = IndexOfRefractionTransmitted;
}
var sinIncidentSquared = SinThetaSquared(ref leaving);
var eta = ei / et;
var sinTransmittedSquared = eta * eta * sinIncidentSquared;
var cosTransmitted = (float)Math.Sqrt(1 - sinTransmittedSquared);
if (entering)
{
cosTransmitted = -cosTransmitted;
}
var sinTOversinI = eta;
incoming = new Vector3(sinTOversinI * -leaving.X, sinTOversinI * -leaving.Y, cosTransmitted);
if (sinTransmittedSquared >= 1)
{
return(SampledSpectrum.Black());
}
var f = _fresnel.Evaluate(CosTheta(ref leaving));
return((new SampledSpectrum(1) - f) * _s / AbsCosTheta(ref incoming) * (et * et) / (ei * ei));
}
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));
}