[Bf-blender-cvs] [ffe115d1a8f] blender-v3.0-release: Fix T92450: Cycles wrong render with overlapping glass, transparency and volumes

[Brecht Van Lommel]

Commit: ffe115d1a8f625bb5a6b72616fa2f955448869ff
Author: Brecht Van Lommel
Date:   Thu Nov 4 16:39:49 2021 +0100
Branches: blender-v3.0-release
https://developer.blender.org/rBffe115d1a8f625bb5a6b72616fa2f955448869ff

Fix T92450: Cycles wrong render with overlapping glass, transparency and volumes

We need to store the continuation probability used to make the termination
decision in intersect_closest, instead of recomputing it in shade_surface.
Because otherwise a shade_volume in between can change the throughput and
change the probability.

===================================================================

M	intern/cycles/kernel/integrator/intersect_closest.h
M	intern/cycles/kernel/integrator/path_state.h
M	intern/cycles/kernel/integrator/shade_surface.h
M	intern/cycles/kernel/integrator/shade_volume.h
M	intern/cycles/kernel/integrator/state_template.h

===================================================================

diff --git a/intern/cycles/kernel/integrator/intersect_closest.h b/intern/cycles/kernel/integrator/intersect_closest.h
index 7fb88fc2804..2cac18ed889 100644
--- a/intern/cycles/kernel/integrator/intersect_closest.h
+++ b/intern/cycles/kernel/integrator/intersect_closest.h
@@ -63,6 +63,7 @@ ccl_device_forceinline bool integrator_intersect_terminate(KernelGlobals kg,
    * perform MIS as part of indirect rays. */
   const uint32_t path_flag = INTEGRATOR_STATE(state, path, flag);
   const float probability = path_state_continuation_probability(kg, state, path_flag);
+  INTEGRATOR_STATE_WRITE(state, path, continuation_probability) = probability;
 
   if (probability != 1.0f) {
     const float terminate = path_state_rng_1D(kg, &rng_state, PRNG_TERMINATE);
diff --git a/intern/cycles/kernel/integrator/path_state.h b/intern/cycles/kernel/integrator/path_state.h
index 8311b97dedb..c325d829b5c 100644
--- a/intern/cycles/kernel/integrator/path_state.h
+++ b/intern/cycles/kernel/integrator/path_state.h
@@ -67,6 +67,7 @@ ccl_device_inline void path_state_init_integrator(KernelGlobals kg,
   INTEGRATOR_STATE_WRITE(state, path, mis_ray_pdf) = 0.0f;
   INTEGRATOR_STATE_WRITE(state, path, mis_ray_t) = 0.0f;
   INTEGRATOR_STATE_WRITE(state, path, min_ray_pdf) = FLT_MAX;
+  INTEGRATOR_STATE_WRITE(state, path, continuation_probability) = 1.0f;
   INTEGRATOR_STATE_WRITE(state, path, throughput) = make_float3(1.0f, 1.0f, 1.0f);
 
   if (kernel_data.kernel_features & KERNEL_FEATURE_VOLUME) {
diff --git a/intern/cycles/kernel/integrator/shade_surface.h b/intern/cycles/kernel/integrator/shade_surface.h
index cce591eb219..d9006e71ce0 100644
--- a/intern/cycles/kernel/integrator/shade_surface.h
+++ b/intern/cycles/kernel/integrator/shade_surface.h
@@ -479,7 +479,7 @@ ccl_device bool integrate_surface(KernelGlobals kg,
     if (!(path_flag & PATH_RAY_SUBSURFACE)) {
       const float probability = (path_flag & PATH_RAY_TERMINATE_ON_NEXT_SURFACE) ?
                                     0.0f :
-                                    path_state_continuation_probability(kg, state, path_flag);
+                                    INTEGRATOR_STATE(state, path, continuation_probability);
       if (probability == 0.0f) {
         return false;
       }
diff --git a/intern/cycles/kernel/integrator/shade_volume.h b/intern/cycles/kernel/integrator/shade_volume.h
index f455152dcf9..05959bef220 100644
--- a/intern/cycles/kernel/integrator/shade_volume.h
+++ b/intern/cycles/kernel/integrator/shade_volume.h
@@ -941,7 +941,7 @@ ccl_device VolumeIntegrateEvent volume_integrate(KernelGlobals kg,
   const uint32_t path_flag = INTEGRATOR_STATE(state, path, flag);
   const float probability = (path_flag & PATH_RAY_TERMINATE_IN_NEXT_VOLUME) ?
                                 0.0f :
-                                path_state_continuation_probability(kg, state, path_flag);
+                                INTEGRATOR_STATE(state, path, continuation_probability);
   if (probability == 0.0f) {
     return VOLUME_PATH_MISSED;
   }
diff --git a/intern/cycles/kernel/integrator/state_template.h b/intern/cycles/kernel/integrator/state_template.h
index e082424fabd..25475883915 100644
--- a/intern/cycles/kernel/integrator/state_template.h
+++ b/intern/cycles/kernel/integrator/state_template.h
@@ -56,6 +56,8 @@ KERNEL_STRUCT_MEMBER(path, float, mis_ray_pdf, KERNEL_FEATURE_PATH_TRACING)
 KERNEL_STRUCT_MEMBER(path, float, mis_ray_t, KERNEL_FEATURE_PATH_TRACING)
 /* Filter glossy. */
 KERNEL_STRUCT_MEMBER(path, float, min_ray_pdf, KERNEL_FEATURE_PATH_TRACING)
+/* Continuation probability for path termination. */
+KERNEL_STRUCT_MEMBER(path, float, continuation_probability, KERNEL_FEATURE_PATH_TRACING)
 /* Throughput. */
 KERNEL_STRUCT_MEMBER(path, float3, throughput, KERNEL_FEATURE_PATH_TRACING)
 /* Ratio of throughput to distinguish diffuse and glossy render passes. */