Cycles: Use dedicated BVH for subsurface ray casting

This commit makes it so casting subsurface rays will totally ignore all
the BVH nodes and primitives which do not belong to a current object,
making it much simpler traversal code and reduces number of intersection
tests.

Reviewers: brecht, juicyfruit, dingto, lukasstockner97

Differential Revision: https://developer.blender.org/D1823

2 files changed, 7 insertions, 6 deletions

diff --git a/intern/cycles/bvh/bvh.cpp b/intern/cycles/bvh/bvh.cpp
index 4a5f8b1bda6..f78ad3e9ce2 100644
--- a/intern/cycles/bvh/bvh.cpp
+++ b/intern/cycles/bvh/bvh.cpp
@@ -233,7 +233,7 @@ void BVH::pack_instances(size_t nodes_size, size_t leaf_nodes_size)
 		Mesh *mesh = ob->mesh;
 		BVH *bvh = mesh->bvh;
 
-		if(!mesh->transform_applied) {
+		if(mesh->need_build_bvh()) {
 			if(mesh_map.find(mesh) == mesh_map.end()) {
 				prim_index_size += bvh->pack.prim_index.size();
 				tri_woop_size += bvh->pack.tri_woop.size();
@@ -268,9 +268,10 @@ void BVH::pack_instances(size_t nodes_size, size_t leaf_nodes_size)
 	foreach(Object *ob, objects) {
 		Mesh *mesh = ob->mesh;
 
-		/* if mesh transform is applied, that means it's already in the top
-		 * level BVH, and we don't need to merge it in */
-		if(mesh->transform_applied) {
+		/* We assume that if mesh doesn't need own BVH it was already included
+		 * into a top-level BVH and no packing here is needed.
+		 */
+		if(!mesh->need_build_bvh()) {
 			pack.object_node[object_offset++] = 0;
 			continue;
 		}
diff --git a/intern/cycles/bvh/bvh_build.cpp b/intern/cycles/bvh/bvh_build.cpp
index 45b0aaa2d63..a8b9fe0d52b 100644
--- a/intern/cycles/bvh/bvh_build.cpp
+++ b/intern/cycles/bvh/bvh_build.cpp
@@ -180,7 +180,7 @@ void BVHBuild::add_references(BVHRange& root)
 
 	foreach(Object *ob, objects) {
 		if(params.top_level) {
-			if(ob->mesh->transform_applied) {
+			if(!ob->mesh->is_instanced()) {
 				num_alloc_references += ob->mesh->triangles.size();
 				num_alloc_references += count_curve_segments(ob->mesh);
 			}
@@ -201,7 +201,7 @@ void BVHBuild::add_references(BVHRange& root)
 
 	foreach(Object *ob, objects) {
 		if(params.top_level) {
-			if(ob->mesh->transform_applied)
+			if(!ob->mesh->is_instanced())
 				add_reference_mesh(bounds, center, ob->mesh, i);
 			else
 				add_reference_object(bounds, center, ob, i);