Spectrum SingleScatteringFluorescenceRWLIntegrator::Li(const Scene *scene, const Renderer *renderer, const RayDifferential &ray, const Sample *sample, RNG &rng, Spectrum *T, MemoryArena &arena) const { VolumeRegion *vr = scene->volumeRegion; float t0, t1; if (!vr || !vr->IntersectP(ray, &t0, &t1) || (t1-t0) == 0.f) { *T = 1.f; return 0.f; } // Do single scattering volume integration in _vr_ Spectrum Lv(0.); // Prepare for volume integration stepping int nSamples = Ceil2Int((t1-t0) / stepSize); float step = (t1 - t0) / nSamples; Spectrum Tr(1.f); Point p = ray(t0), pPrev; Vector w = -ray.d; t0 += sample->oneD[scatterSampleOffset][0] * step; // Compute sample patterns for single scattering samples float *lightNum = arena.Alloc<float>(nSamples); LDShuffleScrambled1D(1, nSamples, lightNum, rng); float *lightComp = arena.Alloc<float>(nSamples); LDShuffleScrambled1D(1, nSamples, lightComp, rng); float *lightPos = arena.Alloc<float>(2*nSamples); LDShuffleScrambled2D(1, nSamples, lightPos, rng); uint32_t sampOffset = 0; for (int i = 0; i < nSamples; ++i, t0 += step) { // Advance to sample at _t0_ and update _T_ pPrev = p; p = ray(t0); Ray tauRay(pPrev, p - pPrev, 0.f, 1.f, ray.time, ray.depth); Spectrum stepTau = vr->tau(tauRay, 0.5f * stepSize, rng.RandomFloat()); Tr *= Exp(-stepTau); // Possibly terminate ray marching if transmittance is small if (Tr.y() < 1e-3) { const float continueProb = .5f; if (rng.RandomFloat() > continueProb) { Tr = 0.f; break; } Tr /= continueProb; } // Compute fluorescence emission Spectrum sigma = vr->Mu(p, w, ray.time); if (!sigma.IsBlack() && scene->lights.size() > 0) { int nLights = scene->lights.size(); int ln = min(Floor2Int(lightNum[sampOffset] * nLights), nLights-1); Light *light = scene->lights[ln]; // Add contribution of _light_ due to the in-scattering at _p_ float pdf; VisibilityTester vis; Vector wo; LightSample ls(lightComp[sampOffset], lightPos[2*sampOffset], lightPos[2*sampOffset+1]); Spectrum L = light->Sample_L(p, 0.f, ls, ray.time, &wo, &pdf, &vis); if (!L.IsBlack() && pdf > 0.f && vis.Unoccluded(scene)) { Spectrum Ld = L * vis.Transmittance(scene, renderer, NULL, rng, arena); int lambdaExcIndex = light->GetLaserWavelengthIndex(); float Lpower = Ld.GetLaserEmissionPower(lambdaExcIndex); float yield = vr->Yeild(Point()); Spectrum fEx = vr->fEx(Point()); Spectrum fEm = vr->fEm(Point()); float scale = fEx.GetSampleValueAtWavelengthIndex(lambdaExcIndex); Lv += Lpower * Tr * sigma * vr->p(p, w, -wo, ray.time) * scale * fEm * yield * float(nLights) / pdf; } } ++sampOffset; } *T = Tr; return Lv * step; }