OpenSubdiv: Resolve crashes when other object depends on subsurf-ed object

Cases like using subsurfed object as a boolean operand can't be evaluated
on GPU and needs to have all the CCG on CPU.

This commit resolves existing configuration to survive, but new configurations
would need to have some sort of forced object update so all the data is being
moved on CPU if it was previously on GPU.

source/blender/blenkernel/BKE_depsgraph.h

@@ -72,6 +72,10 @@ enum {
 	 * who're using curve deform, where_on_path and so.
 	 */
 	DAG_EVAL_NEED_CURVE_PATH = 1,
+	/* Scene evaluation would need to have object's data on CPU,
+	 * meaning no GPU shortcuts is allowed.
+	 */
+	DAG_EVAL_NEED_CPU        = 2,
 };
 
 /* Global initialization/deinitialization */

source/blender/blenkernel/intern/depsgraph.c

@@ -1138,6 +1138,13 @@ void dag_add_relation(DagForest *forest, DagNode *fob1, DagNode *fob2, short rel
 	/* parent relation is for cycle checking */
 	dag_add_parent_relation(forest, fob1, fob2, rel, name);
 
+	/* TODO(sergey): Find a better place for this. */
+#ifdef WITH_OPENSUBDIV
+	if ((rel & DAG_RL_DATA_DATA) != 0) {
+		fob1->eval_flags |= DAG_EVAL_NEED_CPU;
+	}
+#endif
+
 	while (itA) { /* search if relation exist already */
 		if (itA->node == fob2) {
 			itA->type |= rel;

source/blender/depsgraph/CMakeLists.txt

@@ -115,4 +115,8 @@ if(WITH_BOOST)
 	add_definitions(-DHAVE_BOOST_FUNCTION_BINDINGS)
 endif()
 
+if(WITH_OPENSUBDIV)
+	add_definitions(-DWITH_OPENSUBDIV)
+endif()
+
 blender_add_lib(bf_depsgraph "${SRC}" "${INC}" "${INC_SYS}")

source/blender/depsgraph/SConscript

@@ -69,6 +69,9 @@ else:
 if env['WITH_BF_LEGACY_DEPSGRAPH']:
     defs.append('WITH_LEGACY_DEPSGRAPH')
 
+if env['WITH_BF_OPENSUBDIV']:
+    defs.append('WITH_OPENSUBDIV')
+
 env.BlenderLib(libname='bf_depsgraph', sources=sources,
                includes=incs, defines=defs,
                libtype=['core', 'player'], priority=[200, 40])

source/blender/depsgraph/intern/depsgraph.cc

@@ -44,6 +44,8 @@ extern "C" {
 #include "DNA_object_types.h"
 #include "DNA_sequence_types.h"
 
+#include "BKE_depsgraph.h"
+
 #include "RNA_access.h"
 }
 
@@ -351,6 +353,13 @@ DepsRelation *Depsgraph::add_new_relation(OperationDepsNode *from,
 {
 	/* Create new relation, and add it to the graph. */
 	DepsRelation *rel = OBJECT_GUARDED_NEW(DepsRelation, from, to, type, description);
+	/* TODO(sergey): Find a better place for this. */
+#ifdef WITH_OPENSUBDIV
+	if (type == DEPSREL_TYPE_GEOMETRY_EVAL) {
+		IDDepsNode *id_to = to->owner->owner;
+		id_to->eval_flags |= DAG_EVAL_NEED_CPU;
+	}
+#endif
 	return rel;
 }
 

source/blender/modifiers/intern/MOD_subsurf.c

@@ -42,6 +42,7 @@
 
 
 #include "BKE_cdderivedmesh.h"
+#include "BKE_depsgraph.h"
 #include "BKE_scene.h"
 #include "BKE_subsurf.h"
 
@@ -120,7 +121,9 @@ static DerivedMesh *applyModifier(ModifierData *md, Object *ob,
 	 * could be disabled.
 	 */
 	if (md->next == NULL && allow_gpu && do_cddm_convert == false) {
-		subsurf_flags |= SUBSURF_USE_GPU_BACKEND;
+		if ((DAG_get_eval_flags_for_object(md->scene, ob) & DAG_EVAL_NEED_CPU) == 0) {
+			subsurf_flags |= SUBSURF_USE_GPU_BACKEND;
+		}
 	}
 #endif