Cycles: Revert previous fixes to intersect_all functions

While they prevent legit write past the array boundary error
those fixes introduced regression in behavior when having exact
max_hits transparent intersections and nothing else.

Previous code would have considered such case a totally opaque,
but it's not correct.

Fixes T48941: Some materials don't get transparent shadows anymore

5 files changed, 28 insertions, 38 deletions

diff --git a/intern/cycles/kernel/bvh/bvh_shadow_all.h b/intern/cycles/kernel/bvh/bvh_shadow_all.h
index b27afaa9869..1d6fa303d3e 100644
--- a/intern/cycles/kernel/bvh/bvh_shadow_all.h
+++ b/intern/cycles/kernel/bvh/bvh_shadow_all.h
@@ -254,9 +254,6 @@ ccl_device bool BVH_FUNCTION_FULL_NAME(BVH)(KernelGlobals *kg,
 
 						/* shadow ray early termination */
 						if(hit) {
-							/* Update number of hits now, so we do proper check on max bounces. */
-							(*num_hits)++;
-
 							/* detect if this surface has a shader with transparent shadows */
 
 							/* todo: optimize so primitive visibility flag indicates if
@@ -283,15 +280,18 @@ ccl_device bool BVH_FUNCTION_FULL_NAME(BVH)(KernelGlobals *kg,
 								return true;
 							}
 							/* if maximum number of hits reached, block all light */
-							else if(*num_hits >= max_hits) {
+							else if(*num_hits == max_hits) {
 								return true;
 							}
 
+							/* move on to next entry in intersections array */
+							isect_array++;
+							(*num_hits)++;
 #if BVH_FEATURE(BVH_INSTANCING)
 							num_hits_in_instance++;
 #endif
-							/* Move on to next entry in intersections array */
-							isect_array++;
+
+							isect_array->t = isect_t;
 						}
 
 						prim_addr++;
diff --git a/intern/cycles/kernel/bvh/bvh_volume_all.h b/intern/cycles/kernel/bvh/bvh_volume_all.h
index d7f6bf86c71..7eddc2891d0 100644
--- a/intern/cycles/kernel/bvh/bvh_volume_all.h
+++ b/intern/cycles/kernel/bvh/bvh_volume_all.h
@@ -201,12 +201,14 @@ ccl_device uint BVH_FUNCTION_FULL_NAME(BVH)(KernelGlobals *kg,
 								                         object,
 								                         prim_addr);
 								if(hit) {
-									/* Update number of hits now, so we do proper check on max bounces. */
+									/* Move on to next entry in intersections array. */
+									isect_array++;
 									num_hits++;
 #if BVH_FEATURE(BVH_INSTANCING)
 									num_hits_in_instance++;
 #endif
-									if(num_hits >= max_hits) {
+									isect_array->t = isect_t;
+									if(num_hits == max_hits) {
 #if BVH_FEATURE(BVH_INSTANCING)
 #  if BVH_FEATURE(BVH_MOTION)
 										float t_fac = 1.0f / len(transform_direction(&ob_itfm, dir));
@@ -220,9 +222,6 @@ ccl_device uint BVH_FUNCTION_FULL_NAME(BVH)(KernelGlobals *kg,
 #endif  /* BVH_FEATURE(BVH_INSTANCING) */
 										return num_hits;
 									}
-									/* Move on to next entry in intersections array */
-									isect_array++;
-									isect_array->t = isect_t;
 								}
 							}
 							break;
@@ -247,12 +246,14 @@ ccl_device uint BVH_FUNCTION_FULL_NAME(BVH)(KernelGlobals *kg,
 								                                object,
 								                                prim_addr);
 								if(hit) {
-									/* Update number of hits now, so we do proper check on max bounces. */
+									/* Move on to next entry in intersections array. */
+									isect_array++;
 									num_hits++;
 #  if BVH_FEATURE(BVH_INSTANCING)
 									num_hits_in_instance++;
 #  endif
-									if(num_hits >= max_hits) {
+									isect_array->t = isect_t;
+									if(num_hits == max_hits) {
 #  if BVH_FEATURE(BVH_INSTANCING)
 #    if BVH_FEATURE(BVH_MOTION)
 										float t_fac = 1.0f / len(transform_direction(&ob_itfm, dir));
@@ -266,9 +267,6 @@ ccl_device uint BVH_FUNCTION_FULL_NAME(BVH)(KernelGlobals *kg,
 #  endif  /* BVH_FEATURE(BVH_INSTANCING) */
 										return num_hits;
 									}
-									/* Move on to next entry in intersections array */
-									isect_array++;
-									isect_array->t = isect_t;
 								}
 							}
 							break;
diff --git a/intern/cycles/kernel/bvh/qbvh_shadow_all.h b/intern/cycles/kernel/bvh/qbvh_shadow_all.h
index eb98eaf7455..3a728b388eb 100644
--- a/intern/cycles/kernel/bvh/qbvh_shadow_all.h
+++ b/intern/cycles/kernel/bvh/qbvh_shadow_all.h
@@ -337,9 +337,6 @@ ccl_device bool BVH_FUNCTION_FULL_NAME(QBVH)(KernelGlobals *kg,
 
 						/* Shadow ray early termination. */
 						if(hit) {
-							/* Update number of hits now, so we do proper check on max bounces. */
-							(*num_hits)++;
-
 							/* detect if this surface has a shader with transparent shadows */
 
 							/* todo: optimize so primitive visibility flag indicates if
@@ -366,15 +363,17 @@ ccl_device bool BVH_FUNCTION_FULL_NAME(QBVH)(KernelGlobals *kg,
 								return true;
 							}
 							/* if maximum number of hits reached, block all light */
-							else if(*num_hits >= max_hits) {
+							else if(*num_hits == max_hits) {
 								return true;
 							}
 
+							/* move on to next entry in intersections array */
+							isect_array++;
+							(*num_hits)++;
 #if BVH_FEATURE(BVH_INSTANCING)
 							num_hits_in_instance++;
 #endif
-							/* Move on to next entry in intersections array */
-							isect_array++;
+
 							isect_array->t = isect_t;
 						}
 
diff --git a/intern/cycles/kernel/bvh/qbvh_volume_all.h b/intern/cycles/kernel/bvh/qbvh_volume_all.h
index 90cad9d91c0..4d3028b37bf 100644
--- a/intern/cycles/kernel/bvh/qbvh_volume_all.h
+++ b/intern/cycles/kernel/bvh/qbvh_volume_all.h
@@ -268,12 +268,14 @@ ccl_device uint BVH_FUNCTION_FULL_NAME(QBVH)(KernelGlobals *kg,
 								/* Intersect ray against primitive. */
 								hit = triangle_intersect(kg, &isect_precalc, isect_array, P, visibility, object, prim_addr);
 								if(hit) {
-									/* Update number of hits now, so we do proper check on max bounces. */
+									/* Move on to next entry in intersections array. */
+									isect_array++;
 									num_hits++;
 #if BVH_FEATURE(BVH_INSTANCING)
 									num_hits_in_instance++;
 #endif
-									if(num_hits >= max_hits) {
+									isect_array->t = isect_t;
+									if(num_hits == max_hits) {
 #if BVH_FEATURE(BVH_INSTANCING)
 #  if BVH_FEATURE(BVH_MOTION)
 										float t_fac = 1.0f / len(transform_direction(&ob_itfm, dir));
@@ -287,9 +289,6 @@ ccl_device uint BVH_FUNCTION_FULL_NAME(QBVH)(KernelGlobals *kg,
 #endif  /* BVH_FEATURE(BVH_INSTANCING) */
 										return num_hits;
 									}
-									/* Move on to next entry in intersections array */
-									isect_array++;
-									isect_array->t = isect_t;
 								}
 							}
 							break;
@@ -307,12 +306,14 @@ ccl_device uint BVH_FUNCTION_FULL_NAME(QBVH)(KernelGlobals *kg,
 								/* Intersect ray against primitive. */
 								hit = motion_triangle_intersect(kg, isect_array, P, dir, ray->time, visibility, object, prim_addr);
 								if(hit) {
-									/* Update number of hits now, so we do proper check on max bounces. */
+									/* Move on to next entry in intersections array. */
+									isect_array++;
 									num_hits++;
 #  if BVH_FEATURE(BVH_INSTANCING)
 									num_hits_in_instance++;
 #  endif
-									if(num_hits >= max_hits) {
+									isect_array->t = isect_t;
+									if(num_hits == max_hits) {
 #  if BVH_FEATURE(BVH_INSTANCING)
 #    if BVH_FEATURE(BVH_MOTION)
 										float t_fac = 1.0f / len(transform_direction(&ob_itfm, dir));
@@ -326,9 +327,6 @@ ccl_device uint BVH_FUNCTION_FULL_NAME(QBVH)(KernelGlobals *kg,
 #  endif  /* BVH_FEATURE(BVH_INSTANCING) */
 										return num_hits;
 									}
-									/* Move on to next entry in intersections array */
-									isect_array++;
-									isect_array->t = isect_t;
 								}
 							}
 							break;
diff --git a/intern/cycles/kernel/kernel_shadow.h b/intern/cycles/kernel/kernel_shadow.h
index d1576754d2e..db2fc84834a 100644
--- a/intern/cycles/kernel/kernel_shadow.h
+++ b/intern/cycles/kernel/kernel_shadow.h
@@ -75,12 +75,7 @@ ccl_device_inline bool shadow_blocked(KernelGlobals *kg, ShaderData *shadow_sd,
 		}
 
 		uint num_hits;
-		if(max_hits == 0) {
-			blocked = true;
-			num_hits = 0;
-		} else {
-			blocked = scene_intersect_shadow_all(kg, ray, hits, max_hits, &num_hits);
-		}
+		blocked = scene_intersect_shadow_all(kg, ray, hits, max_hits, &num_hits);
 
 		/* if no opaque surface found but we did find transparent hits, shade them */
 		if(!blocked && num_hits > 0) {