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Cycles: use defensive sampling for picking BSDFs and BSSRDFs. 

For the first bounce we now give each BSDF or BSSRDF a minimum sample weight,
which helps reduce noise for a typical case where you have a glossy BSDF with
a small weight due to Fresnel, but not necessarily small contribution relative
to a diffuse or transmission BSDF below.

We can probably find a better heuristic that also enables this on further
bounces, for example when looking through a perfect mirror, but I wasn't able
to find a robust one so far.
This commit is contained in:
Brecht Van Lommel 2017-09-13 18:28:31 +02:00
parent 095a01a73a
commit 90d4b823d7
Notes: blender-bot 2023-02-14 06:00:46 +01:00 
Referenced by issue #62692, Cycles transparency shader
3 changed files with 38 additions and 5 deletions
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5
intern/cycles/kernel/kernel_path.h
View File

@ -435,9 +435,7 @@ ccl_device void kernel_path_indirect(KernelGlobals *kg,
&isect,
ray);
shader_eval_surface(kg, sd, state, state->flag);
#ifdef __BRANCHED_PATH__
shader_merge_closures(sd);
#endif /* __BRANCHED_PATH__ */
shader_prepare_closures(sd, state);
/* Apply shadow catcher, holdout, emission. */
if(!kernel_path_shader_apply(kg,
@ -588,6 +586,7 @@ ccl_device_forceinline void kernel_path_integrate(
/* Setup and evaluate shader. */
shader_setup_from_ray(kg, &sd, &isect, ray);
shader_eval_surface(kg, &sd, state, state->flag);
shader_prepare_closures(&sd, state);
/* Apply shadow catcher, holdout, emission. */
if(!kernel_path_shader_apply(kg,

28
intern/cycles/kernel/kernel_shader.h
View File

@ -494,6 +494,34 @@ ccl_device_inline void shader_merge_closures(ShaderData *sd)
}
#endif
/* Defensive sampling. */
ccl_device_inline void shader_prepare_closures(ShaderData *sd,
ccl_addr_space PathState *state)
{
/* We can likely also do defensive sampling at deeper bounces, particularly
* for cases like a perfect mirror but possibly also others. This will need
* a good heuristic. */
if(state->bounce + state->transparent_bounce == 0 && sd->num_closure > 1) {
float sum = 0.0f;
for(int i = 0; i < sd->num_closure; i++) {
ShaderClosure *sc = &sd->closure[i];
if(CLOSURE_IS_BSDF_OR_BSSRDF(sc->type)) {
sum += sc->sample_weight;
}
}
for(int i = 0; i < sd->num_closure; i++) {
ShaderClosure *sc = &sd->closure[i];
if(CLOSURE_IS_BSDF_OR_BSSRDF(sc->type)) {
sc->sample_weight = max(sc->sample_weight, 0.125f * sum);
}
}
}
}
/* BSDF */
ccl_device_inline void _shader_bsdf_multi_eval(KernelGlobals *kg, ShaderData *sd, const float3 omega_in, float *pdf,

10
intern/cycles/kernel/split/kernel_shader_eval.h
View File

@ -52,8 +52,14 @@ ccl_device void kernel_shader_eval(KernelGlobals *kg)
shader_eval_surface(kg, &kernel_split_state.sd[ray_index], state, state->flag);
#ifdef __BRANCHED_PATH__
shader_merge_closures(&kernel_split_state.sd[ray_index]);
#endif /* __BRANCHED_PATH__ */
if(kernel_data.integrator.branched) {
shader_merge_closures(&kernel_split_state.sd[ray_index]);
}
else
#endif
{
shader_prepare_closures(&kernel_split_state.sd[ray_index], state);
}
}
}