const Distribution1D *SpatialLightDistribution::Lookup(const Point3f &p) const {
ProfilePhase _(Prof::LightDistribLookup);
++nLookups;
// Compute integer voxel coordinates for the given point |p| with
// respect to the overall voxel grid.
Vector3f offset = scene.WorldBound().Offset(p); // offset in [0,1].
Point3i pi;
for (int i = 0; i < 3; ++i) pi[i] = int(offset[i] * nVoxels[i]);
// Create the per-thread cache of sampling distributions if needed.
LocalBucketHash *localVoxelDistribution =
localVoxelDistributions[ThreadIndex].get();
if (!localVoxelDistribution) {
LOG(INFO) << "Created per-thread SpatialLightDistribution for thread" <<
ThreadIndex;
localVoxelDistribution = new LocalBucketHash;
localVoxelDistributions[ThreadIndex].reset(localVoxelDistribution);
}
else {
// Otherwise see if we have a sampling distribution for the voxel
// that |p| is in already available in the local cache.
auto iter = localVoxelDistribution->find(pi);
if (iter != localVoxelDistribution->end())
return iter->second;
}
// Now we need to either get the distribution from the shared hash
// table (if another thread has already created it), or create it
// ourselves and add it to the shared table.
ProfilePhase __(Prof::LightDistribLookupL2);
// First, compute a hash into the first-level hash table.
size_t hash = std::hash<int>{}(pi[0] + nVoxels[0] * pi[1] +
nVoxels[0] * nVoxels[1] * pi[2]);
hash &= (nBuckets - 1);
// Acquire the lock for the corresponding second-level hash table.
std::lock_guard<std::mutex> lock(mutexes[hash]);
// See if we can find it.
auto iter = voxelDistribution[hash].find(pi);
if (iter != voxelDistribution[hash].end()) {
// Success. Add the pointer to the thread-specific hash table so
// that we can look up this distribution more efficiently in the
// future.
(*localVoxelDistribution)[pi] = iter->second.get();
return iter->second.get();
}
// We need to compute a new sampling distriibution for this voxel. Note
// that we're holding the lock for the first-level hash table bucket
// throughout the following; in general, we'd like to do the following
// quickly so that other threads don't get held up waiting for that
// lock (for this or other voxels that share it).
ProfilePhase ___(Prof::LightDistribCreation);
++nCreated;
++nDistributions;
// Compute the world-space bounding box of the voxel.
Point3f p0(Float(pi[0]) / Float(nVoxels[0]),
Float(pi[1]) / Float(nVoxels[1]),
Float(pi[2]) / Float(nVoxels[2]));
Point3f p1(Float(pi[0] + 1) / Float(nVoxels[0]),
Float(pi[1] + 1) / Float(nVoxels[1]),
Float(pi[2] + 1) / Float(nVoxels[2]));
Bounds3f voxelBounds(scene.WorldBound().Lerp(p0),
scene.WorldBound().Lerp(p1));
// Compute the sampling distribution. Sample a number of points inside
// voxelBounds using a 3D Halton sequence; at each one, sample each
// light source and compute a weight based on Li/pdf for the light's
// sample (ignoring visibility between the point in the voxel and the
// point on the light source) as an approximation to how much the light
// is likely to contribute to illumination in the voxel.
int nSamples = 128;
std::vector<Float> lightContrib(scene.lights.size(), Float(0));
for (int i = 0; i < nSamples; ++i) {
Point3f po = voxelBounds.Lerp(Point3f(
RadicalInverse(0, i), RadicalInverse(1, i), RadicalInverse(2, i)));
Interaction intr(po, Normal3f(), Vector3f(), Vector3f(1, 0, 0),
0 /* time */, MediumInterface());
// Use the next two Halton dimensions to sample a point on the
// light source.
Point2f u(RadicalInverse(3, i), RadicalInverse(4, i));
for (size_t j = 0; j < scene.lights.size(); ++j) {
Float pdf;
Vector3f wi;
VisibilityTester vis;
Spectrum Li = scene.lights[j]->Sample_Li(intr, u, &wi, &pdf, &vis);
if (pdf > 0) {
// TODO: look at tracing shadow rays / computing beam
// transmittance. Probably shouldn't give those full weight
// but instead e.g. have an occluded shadow ray scale down
// the contribution by 10 or something.
lightContrib[j] += Li.y() / pdf;
}
}
}
// We don't want to leave any lights with a zero probability; it's
// possible that a light contributes to points in the voxel even though
// we didn't find such a point when sampling above. Therefore, compute
// a minimum (small) weight and ensure that all lights are given at
// least the corresponding probability.
Float sumContrib =
std::accumulate(lightContrib.begin(), lightContrib.end(), Float(0));
Float avgContrib = sumContrib / (nSamples * lightContrib.size());
Float minContrib = (avgContrib > 0) ? .001 * avgContrib : 1;
for (size_t i = 0; i < lightContrib.size(); ++i) {
VLOG(2) << "Voxel pi = " << pi << ", light " << i << " contrib = "
<< lightContrib[i];
lightContrib[i] = std::max(lightContrib[i], minContrib);
}
LOG(INFO) << "Initialized light distribution in voxel pi= " << pi <<
", avgContrib = " << avgContrib;
// Compute a sampling distribution from the accumulated
// contributions.
std::unique_ptr<Distribution1D> distrib(
new Distribution1D(&lightContrib[0], lightContrib.size()));
// Store a pointer to it in the per-thread cache for the future.
(*localVoxelDistribution)[pi] = distrib.get();
// Store the canonical unique_ptr for it in the global hash table so
// other threads can use it.
voxelDistribution[hash][pi] = std::move(distrib);
return (*localVoxelDistribution)[pi];
}
Distribution1D *
SpatialLightDistribution::ComputeDistribution(Point3i pi) const {
ProfilePhase _(Prof::LightDistribCreation);
++nCreated;
++nDistributions;
// Compute the world-space bounding box of the voxel corresponding to
// |pi|.
Point3f p0(Float(pi[0]) / Float(nVoxels[0]),
Float(pi[1]) / Float(nVoxels[1]),
Float(pi[2]) / Float(nVoxels[2]));
Point3f p1(Float(pi[0] + 1) / Float(nVoxels[0]),
Float(pi[1] + 1) / Float(nVoxels[1]),
Float(pi[2] + 1) / Float(nVoxels[2]));
Bounds3f voxelBounds(scene.WorldBound().Lerp(p0),
scene.WorldBound().Lerp(p1));
// Compute the sampling distribution. Sample a number of points inside
// voxelBounds using a 3D Halton sequence; at each one, sample each
// light source and compute a weight based on Li/pdf for the light's
// sample (ignoring visibility between the point in the voxel and the
// point on the light source) as an approximation to how much the light
// is likely to contribute to illumination in the voxel.
int nSamples = 128;
std::vector<Float> lightContrib(scene.lights.size(), Float(0));
for (int i = 0; i < nSamples; ++i) {
Point3f po = voxelBounds.Lerp(Point3f(
RadicalInverse(0, i), RadicalInverse(1, i), RadicalInverse(2, i)));
Interaction intr(po, Normal3f(), Vector3f(), Vector3f(1, 0, 0),
0 /* time */, MediumInterface());
// Use the next two Halton dimensions to sample a point on the
// light source.
Point2f u(RadicalInverse(3, i), RadicalInverse(4, i));
for (size_t j = 0; j < scene.lights.size(); ++j) {
Float pdf;
Vector3f wi;
VisibilityTester vis;
Spectrum Li = scene.lights[j]->Sample_Li(intr, u, &wi, &pdf, &vis);
if (pdf > 0) {
// TODO: look at tracing shadow rays / computing beam
// transmittance. Probably shouldn't give those full weight
// but instead e.g. have an occluded shadow ray scale down
// the contribution by 10 or something.
lightContrib[j] += Li.y() / pdf;
}
}
}
// We don't want to leave any lights with a zero probability; it's
// possible that a light contributes to points in the voxel even though
// we didn't find such a point when sampling above. Therefore, compute
// a minimum (small) weight and ensure that all lights are given at
// least the corresponding probability.
Float sumContrib =
std::accumulate(lightContrib.begin(), lightContrib.end(), Float(0));
Float avgContrib = sumContrib / (nSamples * lightContrib.size());
Float minContrib = (avgContrib > 0) ? .001 * avgContrib : 1;
for (size_t i = 0; i < lightContrib.size(); ++i) {
VLOG(2) << "Voxel pi = " << pi << ", light " << i << " contrib = "
<< lightContrib[i];
lightContrib[i] = std::max(lightContrib[i], minContrib);
}
LOG(INFO) << "Initialized light distribution in voxel pi= " << pi <<
", avgContrib = " << avgContrib;
// Compute a sampling distribution from the accumulated contributions.
return new Distribution1D(&lightContrib[0], lightContrib.size());
}