Spectrum VSDScatteringIntegrator::LiSingle(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;
vr->IntersectP(ray, &t0, &t1);
// 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;
t0 += sample->oneD[scatterSampleOffset][0] * step;
// Compute the emission from the voxels, not from the light sources
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,
.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 emission term at _p_
Lv += Tr * vr->PhotonDensity(p);
}
*T = Tr;
return Lv * step;
}
Spectrum VSDScatteringIntegrator::LiMultiple(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;
vr->IntersectP(ray, &t0, &t1);
// Do multiple scattering volume integration in _vr_
Spectrum Lv(0.);
// Prepare for random walk
Spectrum Tr(1.f);
Point p = ray(t0), pPrev = ray.o;
// printf("%f %f %f, ", p.x, p.y, p.z);
int steps = 0;
// Sample the events in a random walk
// BBox bb = vr->WorldBound();
// printf("%f %f %f & %f %f %f \n",
// bb.pMin.x, bb.pMin.y, bb.pMin.z, bb.pMax.x, bb.pMax.y, bb.pMax.z);
while(vr->WorldBound().Inside(p)) {
//printf("%f %f %f %d \n", p.x, p.y, p.z, steps);
steps++;
// Sample direction
Vector wi = -ray.d, wo;
float pdfDirection = 0.f;
if(!vr->SampleDirection(p, wi, wo, &pdfDirection, rng)) {
// printf("return 1 \n");
return Lv;
}
Ray r(p, wo, 0);
// Sample a distance
float pdfDistance = 0.f;
float tDist;
Point pSample;
if(!vr->SampleDistance(r, &tDist, pSample, &pdfDistance, rng)) {
// printf("return 2 \n");
return Lv;
}
// Compute the transmittance
pPrev = p;
p = r(tDist);
Ray tauRay(pPrev, p - pPrev, 0.f, 1.f, r.time, r.depth);
Spectrum stepTau = vr->tau(tauRay, .5f * stepSize, rng.RandomFloat());
Tr *= Exp(-stepTau);
// Possibly terminate random walk if transmittance is small
if (Tr.y() < 1e-3) {
const float continueProb = .5f;
if (rng.RandomFloat() > continueProb) {
Tr = 0.f;
// printf("return 3 \n");
break;
}
Tr /= continueProb;
}
// Compute emission term at _p_
Lv += Tr * vr->PhotonDensity(p) / (pdfDistance * pdfDirection);
}
// printf("%f %f %f %d \n", p.x, p.y, p.z, steps);
// printf("%d, ", steps);
return Lv;
}