bool BidirPathTracing::sampleScattering(BSDF& bsdf ,
const Vector3& hitPos , BidirPathState& pathState)
{
Real bsdfDirPdf , cosWo;
int sampledBSDFType;
Color3 bsdfFactor = bsdf.sample(scene , rng.randVector3() ,
pathState.dir , bsdfDirPdf , cosWo , &sampledBSDFType);
if (bsdfFactor.isBlack())
return 0;
Real bsdfRevPdf = bsdfDirPdf;
if ((sampledBSDFType & BSDF_SPECULAR) == 0)
bsdfRevPdf = bsdf.pdf(scene , pathState.dir , 1);
Real contProb = bsdf.continueProb;
if (rng.randFloat() > contProb)
return 0;
bsdfDirPdf *= contProb;
bsdfRevPdf *= contProb;
// Partial sub-path MIS quantities
// the evaluation is completed when the actual hit point is known!
// i.e. after tracing the ray, out of the procedure
if (sampledBSDFType & BSDF_SPECULAR)
{
pathState.specularVertexNum++;
pathState.dVCM = 0.f;
pathState.dVC *= mis(cosWo);
}
else
{
pathState.specularPath &= 0;
pathState.dVC = mis(1.f / bsdfDirPdf) * (pathState.dVCM +
pathState.dVC * mis(bsdfRevPdf));
pathState.dVCM = mis(1.f / bsdfDirPdf);
}
pathState.origin = hitPos;
pathState.throughput = (pathState.throughput | bsdfFactor) *
(cosWo / bsdfDirPdf);
return 1;
}
bool extend(BDPTPathVertex& next,
const Scene& scene,
uint32_t pathCount,
bool sampleAdjoint, // Number of paths sampled with the strategies s/t = m_nDepth + 1, t/s = *
RandomGenerator&& rng,
MisFunctor&& mis) {
if(!m_Intersection) {
return false; // Can't sample from infinity
}
Sample3f woSample;
float cosThetaOutDir;
uint32_t sampledEvent;
auto fs = m_BSDF.sample(Vec3f(getFloat(rng), getFloat2(rng)), woSample, cosThetaOutDir, &sampledEvent, sampleAdjoint);
if(woSample.pdf == 0.f || fs == zero<Vec3f>()) {
return false;
}
float reversePdf = m_BSDF.pdf(woSample.value, true);
auto nextI = scene.intersect(Ray(m_Intersection, woSample.value));
if(!nextI) {
next.m_Intersection = nextI;
next.m_BSDF.init(-woSample.value, scene);
next.m_fPdfWrtArea = woSample.pdf;
next.m_fPathPdf = m_fPathPdf * woSample.pdf;
next.m_Power = m_Power * abs(cosThetaOutDir) * fs / woSample.pdf;
next.m_nDepth = m_nDepth + 1;
auto previousPointToIncidentDirectionJacobian = abs(cosThetaOutDir); // No division by squared distance since the point is at infinity
if((sampledEvent & ScatteringEvent::Specular) && m_BSDF.isDelta()) {
next.m_fdVC = mis(previousPointToIncidentDirectionJacobian) * m_fdVC;
next.m_fdVCM = 0.f;
} else {
// We set dVC first in case next == *this, so that the dVCM is unchanged until next line
next.m_fdVC = mis(previousPointToIncidentDirectionJacobian / next.m_fPdfWrtArea) * (m_fdVCM + mis(reversePdf) * m_fdVC);
next.m_fdVCM = mis(pathCount / next.m_fPdfWrtArea);
}
} else {
auto incidentDirection = -woSample.value;
auto sqrLength = sqr(nextI.distance);
if(sqrLength == 0.f) {
return false;
}
auto pdfWrtArea = woSample.pdf * abs(dot(nextI.Ns, incidentDirection)) / sqrLength;
if(pdfWrtArea == 0.f) {
return false;
}
next.m_Intersection = nextI;
next.m_BSDF.init(incidentDirection, nextI, scene);
next.m_fPdfWrtArea = pdfWrtArea;
next.m_fPathPdf = m_fPathPdf * pdfWrtArea;
next.m_Power = m_Power * abs(cosThetaOutDir) * fs / woSample.pdf;
next.m_nDepth = m_nDepth + 1;
auto previousPointToIncidentDirectionJacobian = abs(cosThetaOutDir) / sqrLength;
if((sampledEvent & ScatteringEvent::Specular) && m_BSDF.isDelta()) {
next.m_fdVC = mis(previousPointToIncidentDirectionJacobian) * m_fdVC;
next.m_fdVCM = 0.f;
} else {
// We set dVC first in case next == *this, so that the dVCM is unchanged until next line
next.m_fdVC = mis(previousPointToIncidentDirectionJacobian / next.m_fPdfWrtArea) * (m_fdVCM + mis(reversePdf) * m_fdVC);
next.m_fdVCM = mis(pathCount / next.m_fPdfWrtArea);
}
}
return true;
}
