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Fix T39823: SSS scatter doesn't update volume stack, causing shading artifacts 

Basically the title says it all, we need to update volume stack when doing ray
scatter for SSS. This leads to speed regressions in cases scene does have both
volume and SSS (performance in case there's no SSS or no volume should be the
same).

We might try optimizing kernel_path_subsurface_update_volume_stack() a bit by
either recording all intersections or using some more appropriate visibility
flags.

Reviewers: brecht, juicyfruit, dingto

Differential Revision: https://developer.blender.org/D795
This commit is contained in:
Sergey Sharybin 2014-09-18 17:06:05 +06:00
parent 98153778b5
commit ccc5983e2b
Notes: blender-bot 2023-02-14 10:46:11 +01:00 
Referenced by issue #39823, SSS + volume rendering error
2 changed files with 83 additions and 3 deletions
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2
intern/cycles/kernel/kernel_bake.h
View File

@ -96,7 +96,7 @@ ccl_device void compute_light_pass(KernelGlobals *kg, ShaderData *sd, PathRadian
/* sample subsurface scattering */
if((is_combined || is_sss_sample) && (sd->flag & SD_BSSRDF)) {
/* when mixing BSSRDF and BSDF closures we should skip BSDF lighting if scattering was successful */
kernel_branched_path_subsurface_scatter(kg, sd, &L_sample, &state, &rng, throughput);
kernel_branched_path_subsurface_scatter(kg, sd, &L_sample, &state, &rng, &ray, throughput);
}
#endif

84
intern/cycles/kernel/kernel_path.h
View File

@ -359,6 +359,40 @@ ccl_device void kernel_branched_path_ao(KernelGlobals *kg, ShaderData *sd, PathR
}
#ifdef __SUBSURFACE__
# ifdef __VOLUME__
ccl_device void kernel_path_subsurface_update_volume_stack(KernelGlobals *kg,
Ray *ray,
VolumeStack *stack)
{
kernel_assert(kernel_data.integrator.use_volumes);
Ray volume_ray = *ray;
Intersection isect;
const float3 Pend = volume_ray.P + volume_ray.D*volume_ray.t;
while(
scene_intersect(kg, &volume_ray, PATH_RAY_ALL_VISIBILITY,
&isect, NULL, 0.0f, 0.0f)) {
ShaderData sd;
shader_setup_from_ray(kg, &sd, &isect, &volume_ray, 0, 0);
kernel_volume_stack_enter_exit(kg, &sd, stack);
/* Move ray forward. */
volume_ray.P = ray_offset(sd.P, -sd.Ng);
volume_ray.D = normalize_len(Pend - volume_ray.P,
&volume_ray.t);
/* TODO(sergey): Find a faster way detecting that ray_offset moved
* us pass through the end point.
*/
if(dot(ray->D, volume_ray.D) < 0.0f) {
break;
}
}
}
# endif
ccl_device bool kernel_path_subsurface_scatter(KernelGlobals *kg, ShaderData *sd, PathRadiance *L, PathState *state, RNG *rng, Ray *ray, float3 *throughput)
{
float bssrdf_probability;
@ -375,6 +409,9 @@ ccl_device bool kernel_path_subsurface_scatter(KernelGlobals *kg, ShaderData *sd
float bssrdf_u, bssrdf_v;
path_state_rng_2D(kg, rng, state, PRNG_BSDF_U, &bssrdf_u, &bssrdf_v);
int num_hits = subsurface_scatter_multi_step(kg, sd, bssrdf_sd, state->flag, sc, &lcg_state, bssrdf_u, bssrdf_v, false);
#ifdef __VOLUME__
Ray volume_ray = *ray;
#endif
/* compute lighting with the BSDF closure */
for(int hit = 0; hit < num_hits; hit++) {
@ -392,6 +429,22 @@ ccl_device bool kernel_path_subsurface_scatter(KernelGlobals *kg, ShaderData *sd
hit_state.ray_t = 0.0f;
#endif
#ifdef __VOLUME__
if(kernel_data.integrator.use_volumes) {
/* Setup ray from previous surface point to the new one. */
volume_ray.D = normalize_len(hit_ray.P - volume_ray.P,
&volume_ray.t);
kernel_path_subsurface_update_volume_stack(
kg,
&volume_ray,
hit_state.volume_stack);
/* Move volume ray forward. */
volume_ray.P = hit_ray.P;
}
#endif
kernel_path_indirect(kg, rng, hit_ray, tp, state->num_samples, hit_state, L);
/* for render passes, sum and reset indirect light pass variables
@ -718,7 +771,13 @@ ccl_device_noinline void kernel_branched_path_surface_indirect_light(KernelGloba
}
#ifdef __SUBSURFACE__
ccl_device void kernel_branched_path_subsurface_scatter(KernelGlobals *kg, ShaderData *sd, PathRadiance *L, PathState *state, RNG *rng, float3 throughput)
ccl_device void kernel_branched_path_subsurface_scatter(KernelGlobals *kg,
ShaderData *sd,
PathRadiance *L,
PathState *state,
RNG *rng,
Ray *ray,
float3 throughput)
{
for(int i = 0; i< sd->num_closure; i++) {
ShaderClosure *sc = &sd->closure[i];
@ -741,6 +800,9 @@ ccl_device void kernel_branched_path_subsurface_scatter(KernelGlobals *kg, Shade
float bssrdf_u, bssrdf_v;
path_branched_rng_2D(kg, &bssrdf_rng, state, j, num_samples, PRNG_BSDF_U, &bssrdf_u, &bssrdf_v);
int num_hits = subsurface_scatter_multi_step(kg, sd, bssrdf_sd, state->flag, sc, &lcg_state, bssrdf_u, bssrdf_v, true);
# ifdef __VOLUME__
Ray volume_ray = *ray;
# endif
/* compute lighting with the BSDF closure */
for(int hit = 0; hit < num_hits; hit++) {
@ -748,6 +810,23 @@ ccl_device void kernel_branched_path_subsurface_scatter(KernelGlobals *kg, Shade
path_state_branch(&hit_state, j, num_samples);
#ifdef __VOLUME__
if(kernel_data.integrator.use_volumes) {
/* Setup ray from previous surface point to the new one. */
float3 P = ray_offset(bssrdf_sd[hit].P, -bssrdf_sd[hit].Ng);
volume_ray.D = normalize_len(P - volume_ray.P,
&volume_ray.t);
kernel_path_subsurface_update_volume_stack(
kg,
&volume_ray,
hit_state.volume_stack);
/* Move volume ray forward. */
volume_ray.P = P;
}
#endif
#if defined(__EMISSION__) && defined(__BRANCHED_PATH__)
/* direct light */
if(kernel_data.integrator.use_direct_light) {
@ -1012,7 +1091,8 @@ ccl_device float4 kernel_branched_path_integrate(KernelGlobals *kg, RNG *rng, in
#ifdef __SUBSURFACE__
/* bssrdf scatter to a different location on the same object */
if(sd.flag & SD_BSSRDF) {
kernel_branched_path_subsurface_scatter(kg, &sd, &L, &state, rng, throughput);
kernel_branched_path_subsurface_scatter(kg, &sd, &L, &state,
rng, &ray, throughput);
}
#endif