void RoughCoatBsdf::substrateEvalAndPdf(const SurfaceScatterEvent &event, float eta,
float Fi, float cosThetaTi, float &pdf, Vec3f &brdf) const
{
const Vec3f &wi = event.wi;
const Vec3f &wo = event.wo;
float cosThetaTo;
float Fo = Fresnel::dielectricReflectance(eta, wo.z(), cosThetaTo);
if (Fi == 1.0f || Fo == 1.0f) {
pdf = 0.0f;
brdf = Vec3f(0.0f);
return;
}
Vec3f wiSubstrate(wi.x()*eta, wi.y()*eta, std::copysign(cosThetaTi, wi.z()));
Vec3f woSubstrate(wo.x()*eta, wo.y()*eta, std::copysign(cosThetaTo, wo.z()));
pdf = _substrate->pdf(event.makeWarpedQuery(wiSubstrate, woSubstrate));
pdf *= eta*eta*std::abs(wo.z()/cosThetaTo);
float compressionProjection = eta*eta*wo.z()/cosThetaTo;
Vec3f substrateF = _substrate->eval(event.makeWarpedQuery(wiSubstrate, woSubstrate));
if (_scaledSigmaA.max() > 0.0f)
substrateF *= std::exp(_scaledSigmaA*(-1.0f/cosThetaTo - 1.0f/cosThetaTi));
brdf = compressionProjection*(1.0f - Fi)*(1.0f - Fo)*substrateF;
}
float RoughCoatBsdf::pdf(const SurfaceScatterEvent &event) const
{
bool sampleR = event.requestedLobe.test(BsdfLobes::GlossyReflectionLobe);
bool sampleT = event.requestedLobe.test(_substrate->lobes());
if (!sampleT && !sampleR)
return 0.0f;
if (event.wi.z() <= 0.0f || event.wo.z() <= 0.0f)
return 0.0f;
const Vec3f &wi = event.wi;
const Vec3f &wo = event.wo;
float eta = 1.0f/_ior;
float cosThetaTi, cosThetaTo;
float Fi = Fresnel::dielectricReflectance(eta, wi.z(), cosThetaTi);
float Fo = Fresnel::dielectricReflectance(eta, wo.z(), cosThetaTo);
float specularProbability;
if (sampleR && sampleT) {
float substrateWeight = _avgTransmittance*(1.0f - Fi);
float specularWeight = Fi;
specularProbability = specularWeight/(specularWeight + substrateWeight);
} else {
specularProbability = sampleR ? 1.0f : 0.0f;
}
float glossyPdf = 0.0f;
if (sampleR)
glossyPdf = RoughDielectricBsdf::pdfBase(event, true, false, (*_roughness)[*event.info].x(), _ior, _distribution);
float substratePdf = 0.0f;
if (sampleT) {
if (Fi < 1.0f && Fo < 1.0f) {
Vec3f wiSubstrate(wi.x()*eta, wi.y()*eta, std::copysign(cosThetaTi, wi.z()));
Vec3f woSubstrate(wo.x()*eta, wo.y()*eta, std::copysign(cosThetaTo, wo.z()));
substratePdf = _substrate->pdf(event.makeWarpedQuery(wiSubstrate, woSubstrate));
substratePdf *= eta*eta*std::abs(wo.z()/cosThetaTo);
}
}
return glossyPdf*specularProbability + substratePdf*(1.0f - specularProbability);
}
Vec3f RoughCoatBsdf::eval(const SurfaceScatterEvent &event) const
{
bool sampleR = event.requestedLobe.test(BsdfLobes::GlossyReflectionLobe);
bool sampleT = event.requestedLobe.test(_substrate->lobes());
if (!sampleT && !sampleR)
return Vec3f(0.0f);
if (event.wi.z() <= 0.0f || event.wo.z() <= 0.0f)
return Vec3f(0.0f);
Vec3f glossyR(0.0f);
if (sampleR)
glossyR = RoughDielectricBsdf::evalBase(event, true, false, (*_roughness)[*event.info].x(), _ior, _distribution);
Vec3f substrateR(0.0f);
if (sampleT) {
const Vec3f &wi = event.wi;
const Vec3f &wo = event.wo;
float eta = 1.0f/_ior;
float cosThetaTi, cosThetaTo;
float Fi = Fresnel::dielectricReflectance(eta, wi.z(), cosThetaTi);
float Fo = Fresnel::dielectricReflectance(eta, wo.z(), cosThetaTo);
if (Fi == 1.0f || Fo == 1.0f)
return glossyR;
Vec3f wiSubstrate(wi.x()*eta, wi.y()*eta, std::copysign(cosThetaTi, wi.z()));
Vec3f woSubstrate(wo.x()*eta, wo.y()*eta, std::copysign(cosThetaTo, wo.z()));
float compressionProjection = eta*eta*wo.z()/cosThetaTo;
Vec3f substrateF = _substrate->eval(event.makeWarpedQuery(wiSubstrate, woSubstrate));
if (_scaledSigmaA.max() > 0.0f)
substrateF *= std::exp(_scaledSigmaA*(-1.0f/cosThetaTo - 1.0f/cosThetaTi));
substrateR = compressionProjection*(1.0f - Fi)*(1.0f - Fo)*substrateF;
}
return glossyR + substrateR;
}