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Fix T72791: Cycles wrong results when mixing multiple random walk BSSRDFs

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Take into account the closure sample weight for the throughput.

Differential Revision: https://developer.blender.org/D10936
This commit is contained in:
Chris Eveleigh 2021-05-11 22:06:10 +02:00 committed by Brecht Van Lommel
parent 0830458bcc
commit e637149166
1 changed files with 31 additions and 5 deletions
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36
intern/cycles/kernel/kernel_subsurface.h
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@ -25,8 +25,9 @@ CCL_NAMESPACE_BEGIN
ccl_device_inline float3
subsurface_scatter_eval(ShaderData *sd, const ShaderClosure *sc, float disk_r, float r, bool all)
{
/* this is the veach one-sample model with balance heuristic, some pdf
* factors drop out when using balance heuristic weighting */
/* This is the Veach one-sample model with balance heuristic, some pdf
* factors drop out when using balance heuristic weighting. For branched
* path tracing (all) we sample all closure and don't use MIS. */
float3 eval_sum = zero_float3();
float pdf_sum = 0.0f;
float sample_weight_inv = 0.0f;
@ -65,6 +66,30 @@ subsurface_scatter_eval(ShaderData *sd, const ShaderClosure *sc, float disk_r, f
return (pdf_sum > 0.0f) ? eval_sum / pdf_sum : zero_float3();
}
ccl_device_inline float3 subsurface_scatter_walk_eval(ShaderData *sd,
const ShaderClosure *sc,
float3 throughput,
bool all)
{
/* This is the Veach one-sample model with balance heuristic, some pdf
* factors drop out when using balance heuristic weighting. For branched
* path tracing (all) we sample all closure and don't use MIS. */
if (!all) {
float bssrdf_weight = 0.0f;
float weight = sc->sample_weight;
for (int i = 0; i < sd->num_closure; i++) {
sc = &sd->closure[i];
if (CLOSURE_IS_BSSRDF(sc->type)) {
bssrdf_weight += sc->sample_weight;
}
}
throughput *= bssrdf_weight / weight;
}
return throughput;
}
/* replace closures with a single diffuse bsdf closure after scatter step */
ccl_device void subsurface_scatter_setup_diffuse_bsdf(
KernelGlobals *kg, ShaderData *sd, ClosureType type, float roughness, float3 weight, float3 N)
@ -437,7 +462,8 @@ ccl_device_noinline
ccl_addr_space PathState *state,
const ShaderClosure *sc,
const float bssrdf_u,
const float bssrdf_v)
const float bssrdf_v,
bool all)
{
/* Sample diffuse surface scatter into the object. */
float3 D;
@ -669,7 +695,7 @@ ccl_device_noinline
/* TODO: gain back performance lost from merging with disk BSSRDF. We
* only need to return on hit so this indirect ray push/pop overhead
* is not actually needed, but it does keep the code simpler. */
ss_isect->weight[0] = throughput;
ss_isect->weight[0] = subsurface_scatter_walk_eval(sd, sc, throughput, all);
#ifdef __SPLIT_KERNEL__
ss_isect->ray = *ray;
#endif
@ -691,7 +717,7 @@ ccl_device_inline int subsurface_scatter_multi_intersect(KernelGlobals *kg,
return subsurface_scatter_disk(kg, ss_isect, sd, sc, lcg_state, bssrdf_u, bssrdf_v, all);
}
else {
return subsurface_random_walk(kg, ss_isect, sd, state, sc, bssrdf_u, bssrdf_v);
return subsurface_random_walk(kg, ss_isect, sd, state, sc, bssrdf_u, bssrdf_v, all);
}
}