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Refactor: Cycles: use reservoir sampling to pick phase function in volume

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so that we loop through the volumes only once.

Pull Request: https://projects.blender.org/blender/blender/pulls/125676
This commit is contained in:
Weizhen Huang
2024-07-30 18:20:28 +02:00
committed by Gitea
parent 7e40d567d4
commit e981389bdd
1 changed files with 15 additions and 21 deletions
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36
intern/cycles/kernel/integrator/volume_shader.h
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@@ -164,40 +164,34 @@ ccl_device_inline void volume_shader_prepare_guiding(KernelGlobals kg,
/* Phase Evaluation & Sampling */
/* Randomly sample a volume phase function proportional to ShaderClosure.sample_weight. */
/* TODO: this isn't quite correct, we don't weight anisotropy properly depending on color channels,
* even if this is perhaps not a common case */
ccl_device_inline ccl_private const ShaderVolumeClosure *volume_shader_phase_pick(
ccl_private const ShaderVolumePhases *phases, ccl_private float2 *rand_phase)
{
int sampled = 0;
if (phases->num_closure > 1) {
/* pick a phase closure based on sample weights */
float sum = 0.0f;
/* Pick a phase closure based on sample weights. */
/* For reservoir sampling, always accept the first in the stream. */
float sum = phases->closure[0].sample_weight;
for (int i = 0; i < phases->num_closure; i++) {
ccl_private const ShaderVolumeClosure *svc = &phases->closure[i];
sum += svc->sample_weight;
}
for (int i = 1; i < phases->num_closure; i++) {
const float sample_weight = phases->closure[i].sample_weight;
sum += sample_weight;
const float thresh = sample_weight / sum;
float r = (*rand_phase).x * sum;
float partial_sum = 0.0f;
for (int i = 0; i < phases->num_closure; i++) {
ccl_private const ShaderVolumeClosure *svc = &phases->closure[i];
float next_sum = partial_sum + svc->sample_weight;
if (r <= next_sum) {
/* Rescale to reuse for volume phase direction sample. */
/* Rescale random number to reuse for volume phase direction sample. */
if (rand_phase->x < thresh) {
sampled = i;
(*rand_phase).x = (r - partial_sum) / svc->sample_weight;
break;
rand_phase->x /= thresh;
}
else {
rand_phase->x = (rand_phase->x - thresh) / (1.0f - thresh);
}
partial_sum = next_sum;
}
}
/* TODO: this isn't quite correct, we don't weight anisotropy properly
* depending on color channels, even if this is perhaps not a common case */
return &phases->closure[sampled];
}