Fix T52021: Shadow catcher renders wrong when catcher object is behind transparent object

Tweaked the path radiance summing and alpha to accommodate for possible contribution of
light by transparent surface bounces happening prior to shadow catcher intersection.

This commit will change the way how shadow catcher results looks when was behind semi
transparent object, but the old result seemed to be fully wrong: there were big artifacts
when alpha-overing the result on some actual footage.

1 files changed, 7 insertions, 2 deletions

diff --git a/intern/cycles/kernel/kernel_path_branched.h b/intern/cycles/kernel/kernel_path_branched.h
index 5f7f1a2ef14..77d4f1df447 100644
--- a/intern/cycles/kernel/kernel_path_branched.h
+++ b/intern/cycles/kernel/kernel_path_branched.h
@@ -499,11 +499,16 @@ ccl_device float kernel_branched_path_integrate(KernelGlobals *kg,
 
 #ifdef __SHADOW_TRICKS__
 		if((sd.object_flag & SD_OBJECT_SHADOW_CATCHER)) {
-			state.flag |= (PATH_RAY_SHADOW_CATCHER | PATH_RAY_SHADOW_CATCHER_ONLY | PATH_RAY_STORE_SHADOW_INFO);
+			state.flag |= (PATH_RAY_SHADOW_CATCHER |
+			               PATH_RAY_SHADOW_CATCHER_ONLY |
+			               PATH_RAY_STORE_SHADOW_INFO);
 			state.catcher_object = sd.object;
 			if(!kernel_data.background.transparent) {
-				L->shadow_color = indirect_background(kg, &emission_sd, &state, &ray);
+				L->shadow_background_color =
+				        indirect_background(kg, &emission_sd, &state, &ray);
 			}
+			L->shadow_radiance_sum = path_radiance_clamp_and_sum(kg, L);
+			L->shadow_throughput = average(throughput);
 		}
 		else {
 			state.flag &= ~PATH_RAY_SHADOW_CATCHER_ONLY;