bool MultiQuadLight::sampleDirect(uint32 threadIndex, const Vec3f &p, PathSampleGenerator &pathSampler, LightSample &sample) const
{
float xi = pathSampler.next1D(EmitterSample);
ThreadlocalSampleInfo &sampler = *_samplers[threadIndex];
std::pair<int, float> result = _sampleBvh->sampleLight(p, &sampler.sampleWeights[0],
&sampler.insideIds[0], xi, [&](uint32 id) {
return approximateQuadContribution(p, id);
});
if (result.first == -1)
return false;
int idx = pathSampler.next1D(EmitterSample) < 0.5f ? result.first*2 : result.first*2 + 1;
const QuadGeometry::TriangleInfo &t = _geometry.triangle(idx);
Vec3f q = SampleWarp::uniformTriangle(pathSampler.next2D(EmitterSample), t.p0, t.p1, t.p2);
Vec3f L = q - p;
float rSq = L.lengthSq();
sample.dist = std::sqrt(rSq);
sample.d = L/sample.dist;
float cosTheta = -(t.Ng.dot(sample.d));
if (cosTheta <= 0.0f)
return false;
sample.pdf = result.second*0.5f*rSq/(cosTheta*_triangleAreas[idx]);
return true;
}
bool Cube::samplePosition(PathSampleGenerator &sampler, PositionSample &sample) const
{
float u = sampler.next1D();
int dim = sampleFace(u);
float s = (dim + 1) % 3;
float t = (dim + 2) % 3;
Vec2f xi = sampler.next2D();
Vec3f n(0.0f);
n[dim] = u < 0.5f ? -1.0f : 1.0f;
Vec3f p(0.0f);
p[dim] = n[dim]*_scale[dim];
p[s] = (xi.x()*2.0f - 1.0f)*_scale[s];
p[t] = (xi.y()*2.0f - 1.0f)*_scale[t];
sample.p = _rot*p + _pos;
sample.pdf = _invArea;
sample.uv = xi;
sample.weight = PI*_area*(*_emission)[sample.uv];
sample.Ng = _rot*n;
return true;
}
bool IsotropicPhaseFunction::sample(PathSampleGenerator &sampler, const Vec3f &/*wi*/, PhaseSample &sample) const
{
sample.w = SampleWarp::uniformSphere(sampler.next2D());
sample.weight = Vec3f(1.0f);
sample.pdf = SampleWarp::uniformSpherePdf();
return true;
}
bool Cube::sampleDirection(PathSampleGenerator &sampler, const PositionSample &point, DirectionSample &sample) const
{
Vec3f d = SampleWarp::cosineHemisphere(sampler.next2D());
sample.d = TangentFrame(point.Ng).toGlobal(d);
sample.weight = Vec3f(1.0f);
sample.pdf = SampleWarp::cosineHemispherePdf(d);
return true;
}
bool Quad::sampleDirection(PathSampleGenerator &sampler, const PositionSample &/*point*/, DirectionSample &sample) const
{
Vec3f d = SampleWarp::cosineHemisphere(sampler.next2D(EmitterSample));
sample.d = _frame.toGlobal(d);
sample.weight = Vec3f(1.0f);
sample.pdf = SampleWarp::cosineHemispherePdf(d);
return true;
}
bool ExponentialMedium::sampleDistance(PathSampleGenerator &sampler, const Ray &ray,
MediumState &state, MediumSample &sample) const
{
if (state.bounce > _maxBounce)
return false;
float x = _falloffScale*(ray.pos() - _unitPoint).dot(_unitFalloffDirection);
float dx = _falloffScale*ray.dir().dot(_unitFalloffDirection);
float maxT = ray.farT();
if (_absorptionOnly) {
if (maxT == Ray::infinity() && dx <= 0.0f)
return false;
sample.t = maxT;
sample.weight = std::exp(-_sigmaT*densityIntegral(x, dx, ray.farT()));
sample.pdf = 1.0f;
sample.exited = true;
} else {
int component = sampler.nextDiscrete(3);
float sigmaTc = _sigmaT[component];
float xi = 1.0f - sampler.next1D();
float logXi = std::log(xi);
float t = inverseOpticalDepth(x, dx, sigmaTc, logXi);
sample.t = min(t, maxT);
sample.weight = std::exp(-_sigmaT*densityIntegral(x, dx, sample.t));
sample.exited = (t >= maxT);
if (sample.exited) {
sample.pdf = sample.weight.avg();
} else {
float rho = density(x, dx, sample.t);
sample.pdf = (rho*_sigmaT*sample.weight).avg();
sample.weight *= rho*_sigmaS;
}
sample.weight /= sample.pdf;
state.advance();
}
sample.p = ray.pos() + sample.t*ray.dir();
sample.phase = _phaseFunction.get();
return true;
}
float ErlangTransmittance::sampleSurface(PathSampleGenerator &sampler) const
{
float xi = sampler.next1D();
float x = 0.5f;
for (int i = 0; i < 10; ++i) {
x += (xi - (1.0f - surfaceSurface(Vec3f(x))[0]))/surfaceMedium(Vec3f(x))[0];
x = max(x, 0.0f);
}
return x;
}
bool AtmosphericMedium::sampleDistance(PathSampleGenerator &sampler, const Ray &ray,
MediumState &state, MediumSample &sample) const
{
if (state.bounce > _maxBounce)
return false;
Vec3f p = (ray.pos() - _center);
float t0 = p.dot(ray.dir());
float h = (p - t0*ray.dir()).length();
float maxT = ray.farT() + t0;
if (_absorptionOnly) {
sample.t = ray.farT();
sample.weight = std::exp(-_sigmaT*densityIntegral(h, t0, maxT));
sample.pdf = 1.0f;
sample.exited = true;
} else {
int component = sampler.nextDiscrete(3);
float sigmaTc = _sigmaT[component];
float xi = 1.0f - sampler.next1D();
float t = inverseOpticalDepth(h, t0, sigmaTc, xi);
sample.t = min(t, maxT);
sample.weight = std::exp(-_sigmaT*densityIntegral(h, t0, sample.t));
sample.exited = (t >= maxT);
if (sample.exited) {
sample.pdf = sample.weight.avg();
} else {
float rho = density(h, sample.t);
sample.pdf = (rho*_sigmaT*sample.weight).avg();
sample.weight *= rho*_sigmaS;
}
sample.weight /= sample.pdf;
sample.t -= t0;
state.advance();
}
sample.p = ray.pos() + sample.t*ray.dir();
sample.phase = _phaseFunction.get();
return true;
}
bool Quad::samplePosition(PathSampleGenerator &sampler, PositionSample &sample) const
{
Vec2f xi = sampler.next2D(EmitterSample);
sample.p = _base + xi.x()*_edge0 + xi.y()*_edge1;
sample.pdf = _invArea;
sample.uv = xi;
sample.weight = PI*_area*(*_emission)[sample.uv];
sample.Ng = _frame.normal;
return true;
}
bool EquirectangularCamera::sampleDirection(PathSampleGenerator &sampler, const PositionSample &/*point*/, Vec2u pixel,
DirectionSample &sample) const
{
float pdf;
Vec2f uv = (Vec2f(pixel) + 0.5f + _filter.sample(sampler.next2D(), pdf))*_pixelSize;
float sinTheta;
sample.d = uvToDirection(uv, sinTheta);
sample.weight = Vec3f(1.0f);
sample.pdf = INV_PI*INV_TWO_PI/sinTheta;
return true;
}
bool HomogeneousMedium::sampleDistance(PathSampleGenerator &sampler, const Ray &ray,
MediumState &state, MediumSample &sample) const
{
if (state.bounce > _maxBounce)
return false;
float maxT = ray.farT();
if (_absorptionOnly) {
if (maxT == Ray::infinity())
return false;
sample.t = maxT;
sample.weight = std::exp(-_sigmaT*maxT);
sample.pdf = 1.0f;
sample.exited = true;
} else {
int component = sampler.nextDiscrete(3);
float sigmaTc = _sigmaT[component];
float t = -std::log(1.0f - sampler.next1D())/sigmaTc;
sample.t = min(t, maxT);
sample.weight = std::exp(-sample.t*_sigmaT);
sample.exited = (t >= maxT);
if (sample.exited) {
sample.pdf = sample.weight.avg();
} else {
sample.pdf = (_sigmaT*sample.weight).avg();
sample.weight *= _sigmaS;
}
sample.weight /= sample.pdf;
state.advance();
}
sample.p = ray.pos() + sample.t*ray.dir();
sample.phase = _phaseFunction.get();
return true;
}
bool Quad::sampleDirect(uint32 /*threadIndex*/, const Vec3f &p, PathSampleGenerator &sampler, LightSample &sample) const
{
if (_frame.normal.dot(p - _base) <= 0.0f)
return false;
Vec2f xi = sampler.next2D(EmitterSample);
Vec3f q = _base + xi.x()*_edge0 + xi.y()*_edge1;
sample.d = q - p;
float rSq = sample.d.lengthSq();
sample.dist = std::sqrt(rSq);
sample.d /= sample.dist;
float cosTheta = -_frame.normal.dot(sample.d);
sample.pdf = rSq/(cosTheta*_area);
return true;
}
bool PinholeCamera::sampleDirection(PathSampleGenerator &sampler, const PositionSample &/*point*/, Vec2u pixel,
DirectionSample &sample) const
{
float pdf;
Vec2f uv = _filter.sample(sampler.next2D(CameraSample), pdf);
Vec3f localD = Vec3f(
-1.0f + (float(pixel.x()) + 0.5f + uv.x())*2.0f*_pixelSize.x(),
_ratio - (float(pixel.y()) + 0.5f + uv.y())*2.0f*_pixelSize.x(),
_planeDist
).normalized();
sample.d = _transform.transformVector(localD);
sample.weight = Vec3f(1.0f);
sample.pdf = _invPlaneArea/cube(localD.z());
return true;
}
bool CubemapCamera::sampleDirection(PathSampleGenerator &sampler, const PositionSample &/*point*/, Vec2u pixel,
DirectionSample &sample) const
{
Vec2f uv = (Vec2f(pixel) + 0.5f)*_pixelSize;
int face;
if (!uvToFace(uv, face))
return false;
float filterPdf;
uv += _filter.sample(sampler.next2D(CameraSample), filterPdf)*_pixelSize;
sample.d = uvToDirection(face, uv, sample.pdf);
sample.weight = Vec3f(1.0f);
return true;
}
bool HenyeyGreensteinPhaseFunction::sample(PathSampleGenerator &sampler, const Vec3f &wi, PhaseSample &sample) const
{
Vec2f xi = sampler.next2D(MediumPhaseSample);
if (_g == 0.0f) {
sample.w = SampleWarp::uniformSphere(xi);
sample.weight = Vec3f(1.0f);
sample.pdf = SampleWarp::uniformSpherePdf();
} else {
float phi = xi.x()*TWO_PI;
float cosTheta = (1.0f + _g*_g - sqr((1.0f - _g*_g)/(1.0f + _g*(xi.y()*2.0f - 1.0f))))/(2.0f*_g);
float sinTheta = std::sqrt(max(1.0f - cosTheta*cosTheta, 0.0f));
sample.w = TangentFrame(wi).toGlobal(Vec3f(
std::cos(phi)*sinTheta,
std::sin(phi)*sinTheta,
cosTheta
));
sample.weight = Vec3f(1.0f);
sample.pdf = henyeyGreenstein(cosTheta);
}
return true;
}
Vec3f PhotonTracer::traceSample(Vec2u pixel, const KdTree<Photon> &surfaceTree,
const KdTree<VolumePhoton> *mediumTree, PathSampleGenerator &sampler,
float gatherRadius)
{
PositionSample point;
if (!_scene->cam().samplePosition(sampler, point))
return Vec3f(0.0f);
DirectionSample direction;
if (!_scene->cam().sampleDirection(sampler, point, pixel, direction))
return Vec3f(0.0f);
sampler.advancePath();
Vec3f throughput = point.weight*direction.weight;
Ray ray(point.p, direction.d);
ray.setPrimaryRay(true);
IntersectionTemporary data;
IntersectionInfo info;
const Medium *medium = _scene->cam().medium().get();
Vec3f result(0.0f);
int bounce = 0;
bool didHit = _scene->intersect(ray, data, info);
while ((medium || didHit) && bounce < _settings.maxBounces - 1) {
if (medium) {
if (mediumTree) {
Vec3f beamEstimate(0.0f);
mediumTree->beamQuery(ray.pos(), ray.dir(), ray.farT(), [&](const VolumePhoton &p, float t, float distSq) {
Ray mediumQuery(ray);
mediumQuery.setFarT(t);
beamEstimate += (3.0f*INV_PI*sqr(1.0f - distSq/p.radiusSq))/p.radiusSq
*medium->phaseFunction(p.pos)->eval(ray.dir(), -p.dir)
*medium->transmittance(mediumQuery)*p.power;
});
result += throughput*beamEstimate;
}
throughput *= medium->transmittance(ray);
}
if (!didHit)
break;
const Bsdf &bsdf = *info.bsdf;
SurfaceScatterEvent event = makeLocalScatterEvent(data, info, ray, &sampler);
Vec3f transparency = bsdf.eval(event.makeForwardEvent(), false);
float transparencyScalar = transparency.avg();
Vec3f wo;
if (sampler.nextBoolean(DiscreteTransparencySample, transparencyScalar)) {
wo = ray.dir();
throughput *= transparency/transparencyScalar;
} else {
event.requestedLobe = BsdfLobes::SpecularLobe;
if (!bsdf.sample(event, false))
break;
wo = event.frame.toGlobal(event.wo);
throughput *= event.weight;
}
bool geometricBackside = (wo.dot(info.Ng) < 0.0f);
medium = info.primitive->selectMedium(medium, geometricBackside);
ray = ray.scatter(ray.hitpoint(), wo, info.epsilon);
if (std::isnan(ray.dir().sum() + ray.pos().sum()))
break;
if (std::isnan(throughput.sum()))
break;
sampler.advancePath();
bounce++;
if (bounce < _settings.maxBounces)
didHit = _scene->intersect(ray, data, info);
}
if (!didHit) {
if (!medium && _scene->intersectInfinites(ray, data, info))
result += throughput*info.primitive->evalDirect(data, info);
return result;
}
if (info.primitive->isEmissive())
result += throughput*info.primitive->evalDirect(data, info);
int count = surfaceTree.nearestNeighbours(ray.hitpoint(), _photonQuery.get(), _distanceQuery.get(),
_settings.gatherCount, gatherRadius);
if (count == 0)
return result;
const Bsdf &bsdf = *info.bsdf;
SurfaceScatterEvent event = makeLocalScatterEvent(data, info, ray, &sampler);
Vec3f surfaceEstimate(0.0f);
for (int i = 0; i < count; ++i) {
event.wo = event.frame.toLocal(-_photonQuery[i]->dir);
// Asymmetry due to shading normals already compensated for when storing the photon,
// so we don't use the adjoint BSDF here
surfaceEstimate += _photonQuery[i]->power*bsdf.eval(event, false)/std::abs(event.wo.z());
}
float radiusSq = count == int(_settings.gatherCount) ? _distanceQuery[0] : gatherRadius*gatherRadius;
result += throughput*surfaceEstimate*(INV_PI/radiusSq);
return result;
}
bool PinholeCamera::sampleDirection(PathSampleGenerator &sampler, const PositionSample &point,
DirectionSample &sample) const
{
Vec2u pixel(sampler.next2D(CameraSample)*Vec2f(_res));
return sampleDirection(sampler, point, pixel, sample);
}
void PhotonTracer::tracePhoton(SurfacePhotonRange &surfaceRange, VolumePhotonRange &volumeRange,
PathSampleGenerator &sampler)
{
float lightPdf;
const Primitive *light = chooseLightAdjoint(sampler, lightPdf);
PositionSample point;
if (!light->samplePosition(sampler, point))
return;
DirectionSample direction;
if (!light->sampleDirection(sampler, point, direction))
return;
sampler.advancePath();
Ray ray(point.p, direction.d);
Vec3f throughput(point.weight*direction.weight/lightPdf);
SurfaceScatterEvent event;
IntersectionTemporary data;
IntersectionInfo info;
Medium::MediumState state;
state.reset();
Vec3f emission(0.0f);
const Medium *medium = nullptr; // TODO: Media
int bounce = 0;
bool wasSpecular = true;
bool hitSurface = true;
bool didHit = _scene->intersect(ray, data, info);
while ((didHit || medium) && bounce < _settings.maxBounces - 1) {
if (medium) {
MediumSample mediumSample;
if (!medium->sampleDistance(sampler, ray, state, mediumSample))
break;
throughput *= mediumSample.weight;
hitSurface = mediumSample.exited;
if (!hitSurface) {
if (!volumeRange.full()) {
VolumePhoton &p = volumeRange.addPhoton();
p.pos = mediumSample.p;
p.dir = ray.dir();
p.power = throughput;
}
PhaseSample phaseSample;
if (!mediumSample.phase->sample(sampler, ray.dir(), phaseSample))
break;
ray = ray.scatter(mediumSample.p, phaseSample.w, 0.0f);
ray.setPrimaryRay(false);
throughput *= phaseSample.weight;
}
}
if (hitSurface) {
if (!info.bsdf->lobes().isPureSpecular() && !surfaceRange.full()) {
Photon &p = surfaceRange.addPhoton();
p.pos = info.p;
p.dir = ray.dir();
p.power = throughput*std::abs(info.Ns.dot(ray.dir())/info.Ng.dot(ray.dir()));
}
}
if (volumeRange.full() && surfaceRange.full())
break;
if (hitSurface) {
event = makeLocalScatterEvent(data, info, ray, &sampler);
if (!handleSurface(event, data, info, medium, bounce,
true, false, ray, throughput, emission, wasSpecular, state))
break;
}
if (throughput.max() == 0.0f)
break;
if (std::isnan(ray.dir().sum() + ray.pos().sum()))
break;
if (std::isnan(throughput.sum()))
break;
sampler.advancePath();
bounce++;
if (bounce < _settings.maxBounces)
didHit = _scene->intersect(ray, data, info);
}
}
void LightTracer::traceSample(PathSampleGenerator &sampler)
{
float lightPdf;
const Primitive *light = chooseLightAdjoint(sampler, lightPdf);
const Medium *medium = light->extMedium().get();
PositionSample point;
if (!light->samplePosition(sampler, point))
return;
DirectionSample direction;
if (!light->sampleDirection(sampler, point, direction))
return;
sampler.advancePath();
Vec3f throughput(point.weight/lightPdf);
LensSample splat;
if (_settings.minBounces == 0 && !light->isInfinite() && _scene->cam().sampleDirect(point.p, sampler, splat)) {
Ray shadowRay(point.p, splat.d);
shadowRay.setFarT(splat.dist);
Vec3f transmission = generalizedShadowRay(shadowRay, medium, nullptr, 0);
if (transmission != 0.0f) {
Vec3f value = throughput*transmission*splat.weight
*light->evalDirectionalEmission(point, DirectionSample(splat.d));
_splatBuffer->splatFiltered(splat.pixel, value);
}
}
sampler.advancePath();
Ray ray(point.p, direction.d);
throughput *= direction.weight;
VolumeScatterEvent volumeEvent;
SurfaceScatterEvent surfaceEvent;
IntersectionTemporary data;
IntersectionInfo info;
Medium::MediumState state;
state.reset();
Vec3f emission(0.0f);
int bounce = 0;
bool wasSpecular = true;
bool didHit = _scene->intersect(ray, data, info);
while ((didHit || medium) && bounce < _settings.maxBounces - 1) {
bool hitSurface = true;
if (medium) {
volumeEvent = VolumeScatterEvent(&sampler, throughput, ray.pos(), ray.dir(), ray.farT());
if (!medium->sampleDistance(volumeEvent, state))
break;
throughput *= volumeEvent.weight;
volumeEvent.weight = Vec3f(1.0f);
hitSurface = volumeEvent.t == volumeEvent.maxT;
if (hitSurface && !didHit)
break;
}
if (hitSurface) {
surfaceEvent = makeLocalScatterEvent(data, info, ray, &sampler);
Vec3f weight;
Vec2f pixel;
if (surfaceLensSample(_scene->cam(), surfaceEvent, medium, bounce + 1, ray, weight, pixel))
_splatBuffer->splatFiltered(pixel, weight*throughput);
if (!handleSurface(surfaceEvent, data, info, medium, bounce,
true, false, ray, throughput, emission, wasSpecular, state))
break;
} else {
volumeEvent.p += volumeEvent.t*volumeEvent.wi;
Vec3f weight;
Vec2f pixel;
if (volumeLensSample(_scene->cam(), volumeEvent, medium, bounce + 1, ray, weight, pixel))
_splatBuffer->splatFiltered(pixel, weight*throughput);
if (!handleVolume(volumeEvent, medium, bounce,
true, false, ray, throughput, emission, wasSpecular, state))
break;
}
if (throughput.max() == 0.0f)
break;
if (std::isnan(ray.dir().sum() + ray.pos().sum()))
break;
if (std::isnan(throughput.sum()))
break;
sampler.advancePath();
bounce++;
if (bounce < _settings.maxBounces)
didHit = _scene->intersect(ray, data, info);
}
}
Vec2f VdbGrid::inverseOpticalDepth(PathSampleGenerator &sampler, Vec3f p, Vec3f w, float t0, float t1,
float sigmaT, float xi) const
{
auto accessor = _grid->getConstAccessor();
if (_sampleMethod == SampleMethod::ExactNearest) {
VdbRaymarcher<openvdb::FloatGrid::TreeType, 3> dda;
float integral = 0.0f;
Vec2f result(t1, 0.0f);
bool exited = !dda.march(DdaRay(p + 0.5f, w), t0, t1, accessor, [&](openvdb::Coord voxel, float ta, float tb) {
float v = accessor.getValue(voxel);
float delta = v*sigmaT*(tb - ta);
if (integral + delta >= xi) {
result = Vec2f(ta + (tb - ta)*(xi - integral)/delta, v);
return true;
}
integral += delta;
return false;
});
return exited ? Vec2f(t1, integral) : result;
} else if (_sampleMethod == SampleMethod::ExactLinear) {
VdbRaymarcher<openvdb::FloatGrid::TreeType, 3> dda;
float integral = 0.0f;
float fa = gridAt(accessor, p + w*t0);
Vec2f result(t1, 0.0f);
bool exited = !dda.march(DdaRay(p + 0.5f, w), t0, t1, accessor, [&](openvdb::Coord /*voxel*/, float ta, float tb) {
float fb = gridAt(accessor, p + tb*w);
float delta = (fb + fa)*0.5f*sigmaT*(tb - ta);
if (integral + delta >= xi) {
float a = (fb - fa)*sigmaT;
float b = fa*sigmaT;
float c = (integral - xi)/(tb - ta);
float mantissa = max(b*b - 2.0f*a*c, 0.0f);
float x1 = (-b + std::sqrt(mantissa))/a;
result = Vec2f(ta + (tb - ta)*x1, fa + (fb - fa)*x1);
return true;
}
integral += delta;
fa = fb;
return false;
});
return exited ? Vec2f(t1, integral) : result;
} else {
float ta = t0;
float fa = gridAt(accessor, p + w*t0);
float integral = 0.0f;
float dT = sampler.next1D()*_stepSize;
do {
float tb = min(ta + dT, t1);
float fb = gridAt(accessor, p + w*tb);
float delta = (fa + fb)*sigmaT*0.5f*(tb - ta);
if (integral + delta >= xi) {
float a = (fb - fa)*sigmaT;
float b = fa*sigmaT;
float c = (integral - xi)/(tb - ta);
float mantissa = max(b*b - 2.0f*a*c, 0.0f);
float x1 = (-b + std::sqrt(mantissa))/a;
return Vec2f(ta + (tb - ta)*x1, fa + (fb - fa)*x1);
}
integral += delta;
ta = tb;
fa = fb;
dT = _stepSize;
} while (ta < t1);
return Vec2f(t1, integral);
}
}
Vec3f VdbGrid::transmittance(PathSampleGenerator &sampler, Vec3f p, Vec3f w, float t0, float t1, Vec3f sigmaT) const
{
auto accessor = _grid->getConstAccessor();
if (_integrationMethod == IntegrationMethod::ExactNearest) {
VdbRaymarcher<openvdb::FloatGrid::TreeType, 3> dda;
float integral = 0.0f;
dda.march(DdaRay(p + 0.5f, w), t0, t1, accessor, [&](openvdb::Coord voxel, float ta, float tb) {
integral += accessor.getValue(voxel)*(tb - ta);
return false;
});
return std::exp(-integral*sigmaT);
} else if (_integrationMethod == IntegrationMethod::ExactLinear) {
VdbRaymarcher<openvdb::FloatGrid::TreeType, 3> dda;
float integral = 0.0f;
float fa = gridAt(accessor, p + w*t0);
dda.march(DdaRay(p, w), t0, t1, accessor, [&](openvdb::Coord /*voxel*/, float ta, float tb) {
float fb = gridAt(accessor, p + w*tb);
integral += (fa + fb)*0.5f*(tb - ta);
fa = fb;
return false;
});
return std::exp(-integral*sigmaT);
} else if (_integrationMethod == IntegrationMethod::ResidualRatio) {
VdbRaymarcher<Vec2fGrid::TreeType, 3> dda;
float scale = _supergridSubsample;
float invScale = 1.0f/scale;
sigmaT *= scale;
float sigmaTc = sigmaT.max();
auto superAccessor = _superGrid->getConstAccessor();
UniformSampler &generator = sampler.uniformGenerator();
float controlIntegral = 0.0f;
Vec3f Tr(1.0f);
dda.march(DdaRay(p*invScale + 0.5f, w), t0*invScale, t1*invScale, superAccessor, [&](openvdb::Coord voxel, float ta, float tb) {
openvdb::Vec2s v = superAccessor.getValue(voxel);
float muC = v.x();
float muR = v.y();
muR *= sigmaTc;
controlIntegral += muC*(tb - ta);
while (true) {
ta -= BitManip::normalizedLog(generator.nextI())/muR;
if (ta >= tb)
break;
Tr *= 1.0f - sigmaT*((gridAt(accessor, p + w*ta*scale) - muC)/muR);
}
return false;
});
return std::exp(-controlIntegral*sigmaT)*Tr;
} else {
float ta = t0;
float fa = gridAt(accessor, p + w*t0);
float integral = 0.0f;
float dT = sampler.next1D()*_stepSize;
do {
float tb = min(ta + dT, t1);
float fb = gridAt(accessor, p + w*tb);
integral += (fa + fb)*0.5f*(tb - ta);
ta = tb;
fa = fb;
dT = _stepSize;
} while (ta < t1);
return std::exp(-integral*sigmaT);
}
}
float ErlangTransmittance::sampleMedium(PathSampleGenerator &sampler) const
{
return -1.0f/_lambda*std::log(sampler.next1D()*sampler.next1D());
}
