void VolumePatIntegrator::EyeRandomWalk(const Scene *scene, const Ray &eyeRay,
VolumeVertexList& vertexList, RNG &rng) const {
// Do a random walk for the eye ray in the volume
Spectrum cummulative(1.f);
// Find the intersection between the eye ray and the volume
VolumeRegion *vr = scene->volumeRegion;
float t0, t1;
if (!vr || !vr->IntersectP(eyeRay, &t0, &t1) || (t1-t0) == 0.f || t0 < 0.f) {
return;
}
// Find the intersection point between the sampled light ray and the volume
RayDifferential ray(eyeRay);
Point p = ray(t0), pPrev;
uint64_t bounces = 0;
while(vr->WorldBound().Inside(p)) {
Vector wi = -ray.d;
const Spectrum sigma_a = vr->Sigma_a(p, wi, eyeRay.time);
const Spectrum sigma_s = vr->Sigma_s(p, wi, eyeRay.time);
const Spectrum STER = vr->STER(p, wi, eyeRay.time);
// Construct and add the _eyeVertex_ to the _vertexList_
VolumeVertex eyeVertex(p, wi, sigma_a, sigma_s, cummulative, 1.0);
vertexList.push_back(eyeVertex);
// Sample the direction of the next event
float directionPdf = 1.f;
Vector wo;
if(STER.y() > rng.RandomFloat()) {
// Change the ray direction due to a scattering event at _p_
if(!vr->SampleDirection(p, wi, wo, &directionPdf, rng)) {
break; // Direction error
}
// Account for the losses due to the scattering event at _p_
cummulative *= sigma_s * vr->p(p, wi, wo, ray.time);
} else {
// Account only for the trnsmittance between the previous and the
// next events becuse there is no direction change.
wo = ray.d;
}
// Sample the distance of the next event
ray = RayDifferential(p, wo, 0, INFINITY);
float tDist;
float distancePdf = 1.f;
Point Psample;
if(!vr->SampleDistance(ray, &tDist, Psample, &distancePdf, rng)) {
break; // The sampled point is outside the volume
}
// Account for the sampling Pdfs from sampling a direction and/or distance
const float pdf = distancePdf * directionPdf;
cummulative *= 1 / pdf;
// Update the events and account for the transmittance between the events
pPrev = p;
p = Psample;
const Ray tauRay(pPrev, p - pPrev, 0.f, 1.f, ray.time, ray.depth);
const Spectrum stepTau = vr->tau(tauRay, .5f * stepSize, rng.RandomFloat());
const Spectrum TrPP = Exp(-stepTau);
cummulative *= TrPP;
// Possibly terminate ray marching if _cummulative_ is small
if (cummulative.y() < 1e-3) {
const float continueProb = .5f;
if (rng.RandomFloat() > continueProb) {
cummulative = 0.f;
break;
}
cummulative /= continueProb;
}
// Terminate if bounces are more than requested
bounces++;
if (bounces > maxDepth) {
break;
}
}
}
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;
}
