Code refactor: tweaks in SSS code to prepare for coming changes.

This also fixes a subtle bug in the split kernel branched path SSS, the
volume stack update can't be shared between multiple hit points.

6 files changed, 38 insertions, 53 deletions

diff --git a/intern/cycles/kernel/kernel_path.h b/intern/cycles/kernel/kernel_path.h
index 1e98bca66ad..afca4575331 100644
--- a/intern/cycles/kernel/kernel_path.h
+++ b/intern/cycles/kernel/kernel_path.h
@@ -504,7 +504,6 @@ ccl_device void kernel_path_indirect(KernelGlobals *kg,
 				subsurface_scatter_step(kg,
 				                        sd,
 				                        state,
-				                        state->flag,
 				                        sc,
 				                        &lcg_state,
 				                        bssrdf_u, bssrdf_v,
diff --git a/intern/cycles/kernel/kernel_path_branched.h b/intern/cycles/kernel/kernel_path_branched.h
index 70d0292c5a5..5f917d509ec 100644
--- a/intern/cycles/kernel/kernel_path_branched.h
+++ b/intern/cycles/kernel/kernel_path_branched.h
@@ -340,9 +340,13 @@ ccl_device void kernel_branched_path_subsurface_scatter(KernelGlobals *kg,
 		/* do subsurface scatter step with copy of shader data, this will
 		 * replace the BSSRDF with a diffuse BSDF closure */
 		for(int j = 0; j < num_samples; j++) {
+			PathState hit_state = *state;
+			path_state_branch(&hit_state, j, num_samples);
+			hit_state.rng_hash = bssrdf_rng_hash;
+
 			LocalIntersection ss_isect;
 			float bssrdf_u, bssrdf_v;
-			path_branched_rng_2D(kg, bssrdf_rng_hash, state, j, num_samples, PRNG_BSDF_U, &bssrdf_u, &bssrdf_v);
+			path_state_rng_2D(kg, &hit_state, PRNG_BSDF_U, &bssrdf_u, &bssrdf_v);
 			int num_hits = subsurface_scatter_multi_intersect(kg,
 			                                                  &ss_isect,
 			                                                  sd,
@@ -350,6 +354,9 @@ ccl_device void kernel_branched_path_subsurface_scatter(KernelGlobals *kg,
 			                                                  &lcg_state,
 			                                                  bssrdf_u, bssrdf_v,
 			                                                  true);
+
+			hit_state.rng_offset += PRNG_BOUNCE_NUM;
+
 #ifdef __VOLUME__
 			Ray volume_ray = *ray;
 			bool need_update_volume_stack =
@@ -364,15 +371,8 @@ ccl_device void kernel_branched_path_subsurface_scatter(KernelGlobals *kg,
 				                               &ss_isect,
 				                               hit,
 				                               &bssrdf_sd,
-				                               state,
-				                               state->flag,
-				                               sc,
-				                               true);
-
-				PathState hit_state = *state;
-
-				path_state_branch(&hit_state, j, num_samples);
-				hit_state.rng_offset += PRNG_BOUNCE_NUM;
+				                               &hit_state,
+				                               sc);
 
 #ifdef __VOLUME__
 				if(need_update_volume_stack) {
@@ -381,6 +381,10 @@ ccl_device void kernel_branched_path_subsurface_scatter(KernelGlobals *kg,
 					volume_ray.D = normalize_len(P - volume_ray.P,
 					                             &volume_ray.t);
 
+					for(int k = 0; k < VOLUME_STACK_SIZE; k++) {
+						hit_state.volume_stack[k] = state->volume_stack[k];
+					}
+
 					kernel_volume_stack_update_for_subsurface(
 					    kg,
 					    emission_sd,
@@ -393,7 +397,7 @@ ccl_device void kernel_branched_path_subsurface_scatter(KernelGlobals *kg,
 				/* direct light */
 				if(kernel_data.integrator.use_direct_light) {
 					int all = (kernel_data.integrator.sample_all_lights_direct) ||
-					          (state->flag & PATH_RAY_SHADOW_CATCHER);
+					          (hit_state.flag & PATH_RAY_SHADOW_CATCHER);
 					kernel_branched_path_surface_connect_light(
 					        kg,
 					        &bssrdf_sd,
diff --git a/intern/cycles/kernel/kernel_path_subsurface.h b/intern/cycles/kernel/kernel_path_subsurface.h
index c29b41e4222..a48bde6443e 100644
--- a/intern/cycles/kernel/kernel_path_subsurface.h
+++ b/intern/cycles/kernel/kernel_path_subsurface.h
@@ -71,9 +71,7 @@ bool kernel_path_subsurface_scatter(
 			                               hit,
 			                               sd,
 			                               state,
-			                               state->flag,
-			                               sc,
-			                               false);
+			                               sc);
 
 			kernel_path_surface_connect_light(kg, sd, emission_sd, *throughput, state, L);
 
diff --git a/intern/cycles/kernel/kernel_subsurface.h b/intern/cycles/kernel/kernel_subsurface.h
index 582a20704d3..f4759b26191 100644
--- a/intern/cycles/kernel/kernel_subsurface.h
+++ b/intern/cycles/kernel/kernel_subsurface.h
@@ -135,7 +135,6 @@ ccl_device float3 subsurface_color_pow(float3 color, float exponent)
 ccl_device void subsurface_color_bump_blur(KernelGlobals *kg,
                                            ShaderData *sd,
                                            ccl_addr_space PathState *state,
-                                           int state_flag,
                                            float3 *eval,
                                            float3 *N)
 {
@@ -148,7 +147,7 @@ ccl_device void subsurface_color_bump_blur(KernelGlobals *kg,
 
 	if(bump || texture_blur > 0.0f) {
 		/* average color and normal at incoming point */
-		shader_eval_surface(kg, sd, state, state_flag, kernel_data.integrator.max_closures);
+		shader_eval_surface(kg, sd, state, state->flag, kernel_data.integrator.max_closures);
 		float3 in_color = shader_bssrdf_sum(sd, (bump)? N: NULL, NULL);
 
 		/* we simply divide out the average color and multiply with the average
@@ -311,9 +310,7 @@ ccl_device_noinline void subsurface_scatter_multi_setup(
         int hit,
         ShaderData *sd,
         ccl_addr_space PathState *state,
-        int state_flag,
-        const ShaderClosure *sc,
-        bool all)
+        const ShaderClosure *sc)
 {
 #ifdef __SPLIT_KERNEL__
 	Ray ray_object = ss_isect->ray;
@@ -333,7 +330,7 @@ ccl_device_noinline void subsurface_scatter_multi_setup(
 	/* Optionally blur colors and bump mapping. */
 	float3 weight = ss_isect->weight[hit];
 	float3 N = sd->N;
-	subsurface_color_bump_blur(kg, sd, state, state_flag, &weight, &N);
+	subsurface_color_bump_blur(kg, sd, state, &weight, &N);
 
 	/* Setup diffuse BSDF. */
 	subsurface_scatter_setup_diffuse_bsdf(kg, sd, sc, weight, true, N);
@@ -341,7 +338,7 @@ ccl_device_noinline void subsurface_scatter_multi_setup(
 
 /* subsurface scattering step, from a point on the surface to another nearby point on the same object */
 ccl_device void subsurface_scatter_step(KernelGlobals *kg, ShaderData *sd, ccl_addr_space PathState *state,
-	int state_flag, const ShaderClosure *sc, uint *lcg_state, float disk_u, float disk_v, bool all)
+	const ShaderClosure *sc, uint *lcg_state, float disk_u, float disk_v, bool all)
 {
 	float3 eval = make_float3(0.0f, 0.0f, 0.0f);
 
@@ -430,7 +427,7 @@ ccl_device void subsurface_scatter_step(KernelGlobals *kg, ShaderData *sd, ccl_a
 
 	/* optionally blur colors and bump mapping */
 	float3 N = sd->N;
-	subsurface_color_bump_blur(kg, sd, state, state_flag, &eval, &N);
+	subsurface_color_bump_blur(kg, sd, state, &eval, &N);
 
 	/* setup diffuse bsdf */
 	subsurface_scatter_setup_diffuse_bsdf(kg, sd, sc, eval, (ss_isect.num_hits > 0), N);
diff --git a/intern/cycles/kernel/split/kernel_split_data_types.h b/intern/cycles/kernel/split/kernel_split_data_types.h
index 5f40fdc9240..56194d9f857 100644
--- a/intern/cycles/kernel/split/kernel_split_data_types.h
+++ b/intern/cycles/kernel/split/kernel_split_data_types.h
@@ -67,10 +67,6 @@ typedef ccl_global struct SplitBranchedState {
 
 	uint lcg_state;
 	LocalIntersection ss_isect;
-
-#  ifdef __VOLUME__
-	VolumeStack volume_stack[VOLUME_STACK_SIZE];
-#  endif  /* __VOLUME__ */
 #endif  /*__SUBSURFACE__ */
 
 	int shared_sample_count; /* number of branched samples shared with other threads */
diff --git a/intern/cycles/kernel/split/kernel_subsurface_scatter.h b/intern/cycles/kernel/split/kernel_subsurface_scatter.h
index 993e8d4d477..f902d000918 100644
--- a/intern/cycles/kernel/split/kernel_subsurface_scatter.h
+++ b/intern/cycles/kernel/split/kernel_subsurface_scatter.h
@@ -61,11 +61,16 @@ ccl_device_noinline bool kernel_split_branched_path_subsurface_indirect_light_it
 		/* do subsurface scatter step with copy of shader data, this will
 		 * replace the BSSRDF with a diffuse BSDF closure */
 		for(int j = branched_state->ss_next_sample; j < num_samples; j++) {
+			ccl_global PathState *hit_state = &kernel_split_state.path_state[ray_index];
+			*hit_state = branched_state->path_state;
+			hit_state->rng_hash = bssrdf_rng_hash;
+			path_state_branch(hit_state, j, num_samples);
+
 			ccl_global LocalIntersection *ss_isect = &branched_state->ss_isect;
 			float bssrdf_u, bssrdf_v;
 			path_branched_rng_2D(kg,
 			                     bssrdf_rng_hash,
-			                     &branched_state->path_state,
+			                     hit_state,
 			                     j,
 			                     num_samples,
 			                     PRNG_BSDF_U,
@@ -89,6 +94,8 @@ ccl_device_noinline bool kernel_split_branched_path_subsurface_indirect_light_it
 				*ss_isect = ss_isect_private;
 			}
 
+			hit_state->rng_offset += PRNG_BOUNCE_NUM;
+
 #ifdef __VOLUME__
 			Ray volume_ray = branched_state->ray;
 			bool need_update_volume_stack =
@@ -107,39 +114,24 @@ ccl_device_noinline bool kernel_split_branched_path_subsurface_indirect_light_it
 				                               &ss_isect_private,
 				                               hit,
 				                               bssrdf_sd,
-				                               &branched_state->path_state,
-				                               branched_state->path_state.flag,
-				                               sc,
-				                               true);
+				                               hit_state,
+				                               sc);
 				*ss_isect = ss_isect_private;
 
-				ccl_global PathState *hit_state = &kernel_split_state.path_state[ray_index];
-				*hit_state = branched_state->path_state;
-
-				path_state_branch(hit_state, j, num_samples);
-				hit_state->rng_offset += PRNG_BOUNCE_NUM;
-
 #ifdef __VOLUME__
 				if(need_update_volume_stack) {
 					/* Setup ray from previous surface point to the new one. */
 					float3 P = ray_offset(bssrdf_sd->P, -bssrdf_sd->Ng);
 					volume_ray.D = normalize_len(P - volume_ray.P, &volume_ray.t);
 
-					/* this next part is expensive as it does scene intersection so only do once */
-					if(branched_state->next_closure == 0 && branched_state->next_sample == 0) {
-						for(int k = 0; k < VOLUME_STACK_SIZE; k++) {
-							branched_state->volume_stack[k] = hit_state->volume_stack[k];
-						}
-
-						kernel_volume_stack_update_for_subsurface(kg,
-						                                          emission_sd,
-						                                          &volume_ray,
-						                                          branched_state->volume_stack);
-					}
-
 					for(int k = 0; k < VOLUME_STACK_SIZE; k++) {
-						hit_state->volume_stack[k] = branched_state->volume_stack[k];
+						hit_state->volume_stack[k] = branched_state->path_state.volume_stack[k];
 					}
+
+					kernel_volume_stack_update_for_subsurface(kg,
+					                                          emission_sd,
+					                                          &volume_ray,
+					                                          hit_state->volume_stack);
 				}
 #endif  /* __VOLUME__ */
 
@@ -148,7 +140,7 @@ ccl_device_noinline bool kernel_split_branched_path_subsurface_indirect_light_it
 					/* direct light */
 					if(kernel_data.integrator.use_direct_light) {
 						int all = (kernel_data.integrator.sample_all_lights_direct) ||
-							      (branched_state->path_state.flag & PATH_RAY_SHADOW_CATCHER);
+							      (hit_state->flag & PATH_RAY_SHADOW_CATCHER);
 						kernel_branched_path_surface_connect_light(kg,
 						                                           bssrdf_sd,
 						                                           emission_sd,
@@ -265,7 +257,6 @@ ccl_device void kernel_subsurface_scatter(KernelGlobals *kg)
 					subsurface_scatter_step(kg,
 					                        sd,
 					                        state,
-					                        state->flag,
 					                        sc,
 					                        &lcg_state,
 					                        bssrdf_u, bssrdf_v,