Float BidirectionalMutator::Q(const Path &source, const Path &proposal,
const MutationRecord &muRec) const {
const int k = source.length(), l = muRec.l,
m = muRec.m, ka = muRec.ka, mPrime = l+ka;
Spectrum *importanceWeights = (Spectrum *) alloca(ka * sizeof(Spectrum)),
*radianceWeights = (Spectrum *) alloca(ka * sizeof(Spectrum));
/* Compute importance transport weights along the subpath */
importanceWeights[0] = Spectrum(1.0f);
for (int s=1; s<ka; ++s)
importanceWeights[s] = importanceWeights[s-1] *
proposal.vertex(l+s-1)->weight[EImportance] *
proposal.edge(l+s-1)->weight[EImportance];
/* Compute radiance transport weights along the subpath */
radianceWeights[0] = Spectrum(1.0f);
for (int t=1; t<ka; ++t)
radianceWeights[t] = radianceWeights[t-1] *
proposal.vertex(mPrime-t+1)->weight[ERadiance] *
proposal.edge(mPrime-t)->weight[ERadiance];
int sMin = 0, sMax = ka-1;
if (l == 0 && m_scene->hasDegenerateEmitters())
++sMin;
else if (m == k && m_scene->hasDegenerateSensor())
--sMax;
Float result = 0.0f;
for (int s = sMin; s <= sMax; ++s) {
const PathEdge *edge = proposal.edge(l+s);
const PathVertex *vs = proposal.vertex(l+s),
*vt = proposal.vertex(l+s+1);
int t = ka - s - 1;
/* Cannot connect endpoints with degenerate distributions */
if (!vs->isConnectable() || !vt->isConnectable())
continue;
Spectrum weight = importanceWeights[s]
* radianceWeights[t]
* edge->evalCached(vs, vt, PathEdge::EEverything)
* muRec.weight;
Float luminance = weight.getLuminance();
if (luminance <= 0 || !std::isfinite(luminance)) {
Log(EWarn, "Internal error: luminance = %f!", luminance);
continue;
}
result += 1 / luminance;
}
return result * pmfMutation(source, muRec);
}
Float CausticPerturbation::Q(const Path &source, const Path &proposal,
const MutationRecord &muRec) const {
int m = muRec.m, l = muRec.l;
/* Heuristic perturbation size computation (Veach, p.354) */
Float lengthE = source.edge(m-1)->length;
Float lengthL = 0;
for (int i=l; i<m-1; ++i)
lengthL += source.edge(i)->length;
Float factor = lengthE/lengthL,
theta1 = m_theta1 * factor,
theta2 = m_theta2 * factor;
Vector d1 = normalize(source.vertex(l+1)->getPosition() - source.vertex(l)->getPosition());
Vector d2 = normalize(proposal.vertex(l+1)->getPosition() - source.vertex(l)->getPosition());
Float theta = unitAngle(d1, d2);
if (theta >= theta2 || theta <= theta1)
return 0.0f;
Float solidAngleDensity = 1.0f / (2*M_PI * -m_logRatio * std::sin(theta) * theta);
Spectrum weight = muRec.weight * proposal.edge(m-1)->evalCached(
proposal.vertex(m-1), proposal.vertex(m), PathEdge::EEverything);
for (int i=l; i<m-1; ++i) {
const PathVertex *v0 = proposal.vertex(i),
*v1 = proposal.vertex(i+1);
const PathEdge *edge = proposal.edge(i);
weight *= edge->evalCached(v0, v1,
PathEdge::ETransmittance | PathEdge::EValueCosineImp);
if (v1->isMediumInteraction())
weight /= pdfMediumPerturbation(source.vertex(i+1),
source.edge(i), edge);
}
return solidAngleDensity / weight.getLuminance();
}