public SpecularTransmission(float indexOfRefractionIncident, float indexOfRefractionTransmitted,
SampledSpectrum s = null) : base(BxDFType.Transmission | BxDFType.Specular)
{
_fresnel = new FresnelDielectric(indexOfRefractionIncident, indexOfRefractionTransmitted);
_s = s ?? SampledSpectrum.Random();
IndexOfRefractionIncident = indexOfRefractionIncident;
IndexOfRefractionTransmitted = indexOfRefractionTransmitted;
}
public void ComputeScatteringFunctions(SurfaceInteraction inter, bool allowMultipleLobes)
{
inter.Bsdf = new BSDF(inter);
if (!diffuse.IsBlack())
{
inter.Bsdf.Add(new LambertianReflection(diffuse));
}
if (!specular.IsBlack())
{
var fresnel = new FresnelDielectric(1.5f, 1.0f);
var distribution = new TrowbridgeReitzDistribution(roughness);
inter.Bsdf.Add(new MicrofacetReflection(specular, distribution, fresnel));
}
}
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));
}
