Fix T52433: Volume Absorption color tint

Need to exit the volume stack when shadow ray laves the medium.

Thanks Brecht for review and help in troubleshooting!

1 files changed, 68 insertions, 16 deletions

diff --git a/intern/cycles/kernel/kernel_shadow.h b/intern/cycles/kernel/kernel_shadow.h
index bb6bdc7fbd0..b409aca7674 100644
--- a/intern/cycles/kernel/kernel_shadow.h
+++ b/intern/cycles/kernel/kernel_shadow.h
@@ -119,12 +119,46 @@ ccl_device bool shadow_blocked_opaque(KernelGlobals *kg,
 
 #    define SHADOW_STACK_MAX_HITS 64
 
+#    ifdef __VOLUME__
+struct VolumeState {
+#      ifdef __SPLIT_KERNEL__
+#      else
+		PathState ps;
+#      endif
+};
+
+/* Get PathState ready for use for volume stack evaluation. */
+ccl_device_inline PathState *shadow_blocked_volume_path_state(
+        KernelGlobals *kg,
+        VolumeState *volume_state,
+        ccl_addr_space PathState *state,
+        ShaderData *sd,
+        Ray *ray)
+{
+#      ifdef __SPLIT_KERNEL__
+	ccl_addr_space PathState *ps =
+	        &kernel_split_state.state_shadow[ccl_global_id(1) * ccl_global_size(0) + ccl_global_id(0)];
+#      else
+	PathState *ps = &volume_state->ps;
+#      endif
+	*ps = *state;
+	/* We are checking for shadow on the "other" side of the surface, so need
+	 * to discard volume we are currently at.
+	 */
+	if(dot(sd->Ng, ray->D) < 0.0f) {
+		kernel_volume_stack_enter_exit(kg, sd, ps->volume_stack);
+	}
+	return ps;
+}
+#endif  //   __VOLUME__
+
 /* Actual logic with traversal loop implementation which is free from device
  * specific tweaks.
  *
  * Note that hits array should be as big as max_hits+1.
  */
 ccl_device bool shadow_blocked_transparent_all_loop(KernelGlobals *kg,
+                                                    ShaderData *sd,
                                                     ShaderData *shadow_sd,
                                                     ccl_addr_space PathState *state,
                                                     const uint visibility,
@@ -143,6 +177,9 @@ ccl_device bool shadow_blocked_transparent_all_loop(KernelGlobals *kg,
 	                                                visibility,
 	                                                max_hits,
 	                                                &num_hits);
+#    ifdef __VOLUME__
+	VolumeState volume_state;
+#    endif
 	/* If no opaque surface found but we did find transparent hits,
 	 * shade them.
 	 */
@@ -153,13 +190,11 @@ ccl_device bool shadow_blocked_transparent_all_loop(KernelGlobals *kg,
 		int bounce = state->transparent_bounce;
 		Intersection *isect = hits;
 #    ifdef __VOLUME__
-#      ifdef __SPLIT_KERNEL__
-		ccl_addr_space PathState *ps = &kernel_split_state.state_shadow[ccl_global_id(1) * ccl_global_size(0) + ccl_global_id(0)];
-#      else
-		PathState ps_object;
-		PathState *ps = &ps_object;
-#      endif
-		*ps = *state;
+		PathState *ps = shadow_blocked_volume_path_state(kg,
+		                                                 &volume_state,
+		                                                 state,
+		                                                 sd,
+		                                                 ray);
 #    endif
 		sort_intersections(hits, num_hits);
 		for(int hit = 0; hit < num_hits; hit++, isect++) {
@@ -205,7 +240,12 @@ ccl_device bool shadow_blocked_transparent_all_loop(KernelGlobals *kg,
 #    ifdef __VOLUME__
 	if(!blocked && state->volume_stack[0].shader != SHADER_NONE) {
 		/* Apply attenuation from current volume shader. */
-		kernel_volume_shadow(kg, shadow_sd, state, ray, shadow);
+		PathState *ps = shadow_blocked_volume_path_state(kg,
+		                                                 &volume_state,
+		                                                 state,
+		                                                 sd,
+		                                                 ray);
+		kernel_volume_shadow(kg, shadow_sd, ps, ray, shadow);
 	}
 #    endif
 	return blocked;
@@ -215,6 +255,7 @@ ccl_device bool shadow_blocked_transparent_all_loop(KernelGlobals *kg,
  * loop to help readability of the actual logic.
  */
 ccl_device bool shadow_blocked_transparent_all(KernelGlobals *kg,
+                                               ShaderData *sd,
                                                ShaderData *shadow_sd,
                                                ccl_addr_space PathState *state,
                                                const uint visibility,
@@ -250,6 +291,7 @@ ccl_device bool shadow_blocked_transparent_all(KernelGlobals *kg,
 #    endif  /* __KERNEL_GPU__ */
 	/* Invoke actual traversal. */
 	return shadow_blocked_transparent_all_loop(kg,
+	                                           sd,
 	                                           shadow_sd,
 	                                           state,
 	                                           visibility,
@@ -275,6 +317,7 @@ ccl_device bool shadow_blocked_transparent_all(KernelGlobals *kg,
  */
 ccl_device bool shadow_blocked_transparent_stepped_loop(
         KernelGlobals *kg,
+        ShaderData *sd,
         ShaderData *shadow_sd,
         ccl_addr_space PathState *state,
         const uint visibility,
@@ -284,18 +327,18 @@ ccl_device bool shadow_blocked_transparent_stepped_loop(
         const bool is_transparent_isect,
         float3 *shadow)
 {
+#    ifdef __VOLUME__
+	VolumeState volume_state;
+#    endif
 	if(blocked && is_transparent_isect) {
 		float3 throughput = make_float3(1.0f, 1.0f, 1.0f);
 		float3 Pend = ray->P + ray->D*ray->t;
 		int bounce = state->transparent_bounce;
 #    ifdef __VOLUME__
-#      ifdef __SPLIT_KERNEL__
-		ccl_addr_space PathState *ps = &kernel_split_state.state_shadow[ccl_global_id(1) * ccl_global_size(0) + ccl_global_id(0)];
-#      else
-		PathState ps_object;
-		PathState *ps = &ps_object;
-#      endif
-		*ps = *state;
+		PathState *ps = shadow_blocked_volume_path_state(kg,
+		                                                 &volume_state,
+		                                                 state,
+		                                                 sd);
 #    endif
 		for(;;) {
 			if(bounce >= kernel_data.integrator.transparent_max_bounce) {
@@ -345,7 +388,11 @@ ccl_device bool shadow_blocked_transparent_stepped_loop(
 #    ifdef __VOLUME__
 	if(!blocked && state->volume_stack[0].shader != SHADER_NONE) {
 		/* Apply attenuation from current volume shader. */
-		kernel_volume_shadow(kg, shadow_sd, state, ray, shadow);
+		PathState *ps = shadow_blocked_volume_path_state(kg,
+		                                                 &volume_state,
+		                                                 state,
+		                                                 sd);
+		kernel_volume_shadow(kg, shadow_sd, ps, ray, shadow);
 	}
 #    endif
 	return blocked;
@@ -353,6 +400,7 @@ ccl_device bool shadow_blocked_transparent_stepped_loop(
 
 ccl_device bool shadow_blocked_transparent_stepped(
         KernelGlobals *kg,
+        ShaderData *sd,
         ShaderData *shadow_sd,
         ccl_addr_space PathState *state,
         const uint visibility,
@@ -370,6 +418,7 @@ ccl_device bool shadow_blocked_transparent_stepped(
 		? shader_transparent_shadow(kg, isect)
 		: false;
 	return shadow_blocked_transparent_stepped_loop(kg,
+	                                               sd,
 	                                               shadow_sd,
 	                                               state,
 	                                               visibility,
@@ -384,6 +433,7 @@ ccl_device bool shadow_blocked_transparent_stepped(
 #endif /* __TRANSPARENT_SHADOWS__ */
 
 ccl_device_inline bool shadow_blocked(KernelGlobals *kg,
+                                      ShaderData *sd,
                                       ShaderData *shadow_sd,
                                       ccl_addr_space PathState *state,
                                       Ray *ray_input,
@@ -452,6 +502,7 @@ ccl_device_inline bool shadow_blocked(KernelGlobals *kg,
 	   max_hits + 1 >= SHADOW_STACK_MAX_HITS)
 	{
 		return shadow_blocked_transparent_stepped_loop(kg,
+		                                               sd,
 		                                               shadow_sd,
 		                                               state,
 		                                               visibility,
@@ -463,6 +514,7 @@ ccl_device_inline bool shadow_blocked(KernelGlobals *kg,
 	}
 #    endif  /* __KERNEL_GPU__ */
 	return shadow_blocked_transparent_all(kg,
+	                                      sd,
 	                                      shadow_sd,
 	                                      state,
 	                                      visibility,