public virtual RgbColor StartFromEmitter(EmitterSample emitterSample, RgbColor initialWeight)
{
isOnLightSubpath = true;
Ray ray = Raytracer.SpawnRay(emitterSample.Point, emitterSample.Direction);
return(ContinueWalk(ray, emitterSample.Point, emitterSample.Pdf, initialWeight, 1));
}
public virtual RgbColor StartFromBackground(Ray ray, RgbColor initialWeight, float pdf)
{
isOnLightSubpath = true;
// Find the first actual hitpoint on scene geometry
var hit = scene.Raytracer.Trace(ray);
if (!hit)
{
return(OnInvalidHit(ray, pdf, initialWeight, 1));
}
// Sample the next direction (required to know the reverse pdf)
var(pdfNext, pdfReverse, weight, direction) = SampleNextDirection(hit, ray, initialWeight, 1);
// Both pdfs have unit sr-1
float pdfFromAncestor = pdf;
float pdfToAncestor = pdfReverse;
RgbColor estimate = OnHit(ray, hit, pdfFromAncestor, initialWeight, 1, 1.0f);
OnContinue(pdfToAncestor, 1);
// Terminate if the maximum depth has been reached
if (maxDepth <= 1)
{
return(estimate);
}
// Terminate absorbed paths and invalid samples
if (pdfNext == 0 || weight == RgbColor.Black)
{
return(estimate);
}
// Continue the path with the next ray
ray = Raytracer.SpawnRay(hit, direction);
return(estimate + ContinueWalk(ray, hit, pdfNext, initialWeight * weight, 2));
}
RgbColor ContinueWalk(Ray ray, SurfacePoint previousPoint, float pdfDirection, RgbColor throughput,
int depth)
{
// Terminate if the maximum depth has been reached
if (depth >= maxDepth)
{
OnTerminate();
return(RgbColor.Black);
}
var hit = scene.Raytracer.Trace(ray);
if (!hit)
{
var result = OnInvalidHit(ray, pdfDirection, throughput, depth);
OnTerminate();
return(result);
}
// Convert the PDF of the previous hemispherical sample to surface area
float pdfFromAncestor = pdfDirection * SampleWarp.SurfaceAreaToSolidAngle(previousPoint, hit);
// Geometry term might be zero due to, e.g., shading normal issues
// Avoid NaNs in that case by terminating early
if (pdfFromAncestor == 0)
{
OnTerminate();
return(RgbColor.Black);
}
RgbColor estimate = OnHit(ray, hit, pdfFromAncestor, throughput, depth,
SampleWarp.SurfaceAreaToSolidAngle(hit, previousPoint));
// Terminate with Russian roulette
float survivalProb = ComputeSurvivalProbability(hit, ray, throughput, depth);
if (rng.NextFloat() > survivalProb)
{
OnTerminate();
return(estimate);
}
// Continue based on the splitting factor
int numSplits = ComputeSplitFactor(hit, ray, throughput, depth);
for (int i = 0; i < numSplits; ++i)
{
// Sample the next direction and convert the reverse pdf
var(pdfNext, pdfReverse, weight, direction) = SampleNextDirection(hit, ray, throughput, depth);
float pdfToAncestor = pdfReverse * SampleWarp.SurfaceAreaToSolidAngle(hit, previousPoint);
if (pdfToAncestor == 0)
{
Debug.Assert(pdfNext == 0);
}
OnContinue(pdfToAncestor, depth);
if (pdfNext == 0 || weight == RgbColor.Black)
{
OnTerminate();
continue;
}
// Account for splitting and roulette in the weight
weight *= 1.0f / (survivalProb * numSplits);
// Continue the path with the next ray
var nextRay = Raytracer.SpawnRay(hit, direction);
estimate += ContinueWalk(nextRay, hit, pdfNext, throughput * weight, depth + 1);
}
return(estimate);
}
