Spectrum VolumePatIntegrator::EstimateDirectLight(const Scene *scene,
const Renderer *renderer, MemoryArena &arena, const Light *light,
const Point &p, const Normal &n, const Vector &wo, float rayEpsilon,
float time, RNG &rng, const LightSample &lightSample) const {
VolumeRegion *vr = scene->volumeRegion;
if (!vr) Spectrum(0.);
Spectrum Ld(0.);
// Sample light source.
Vector wi;
float lightPdf;
VisibilityTester visibility;
Spectrum Li = light->Sample_L(p, rayEpsilon, lightSample, time,
&wi, &lightPdf, &visibility);
if (lightPdf > 0. && !Li.IsBlack() && visibility.Unoccluded(scene)) {
// Add light's contribution to reflected radiance
Li *= visibility.Transmittance(scene, renderer, NULL, rng, arena);
// Li *= PowerHeuristic(1, lightPdf, 1, (1/M_PI_4));
Ld += vr->p(p, -wi, wo, time) * vr->Sigma_s(p, wo, time) * Li / lightPdf;
}
return Ld;
}
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 VolumePatIntegrator::Li_Single(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,
.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 single-scattering source term at _p_
Lv += Tr * vr->Lve(p, w, ray.time);
Spectrum ss = vr->Sigma_s(p, w, ray.time);
if (!ss.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 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);
Lv += Tr * ss * vr->p(p, w, -wo, ray.time) * Ld * float(nLights) /
pdf;
}
}
++sampOffset;
}
*T = Tr;
return Lv * step;
}