Fix T38139: Objects which are in cyclic dependency are not updated

Graph traversal which is based on counting parents which are still
to be updated fails in cases there are cycles in the graph.

If there are cyclic dependencies in the scene all the objects from
the cycles will be updated in a single thread now one by one. This
makes blender behave the same way as it was before multi-threaded
DAG landed to master.

This needed to tweak depsgraph a bit so now dag_check_cycle() sets
is_acyclic field of DAG forest if there are cycles in the graph.

TODO: It might be possible to save some time on evaluation when
      all the tagged objects were updated in multi-threaded DAG
      traversal.

1 files changed, 7 insertions, 0 deletions

diff --git a/source/blender/blenkernel/intern/depsgraph.c b/source/blender/blenkernel/intern/depsgraph.c
index 01327452831..ea76ff291e5 100644
--- a/source/blender/blenkernel/intern/depsgraph.c
+++ b/source/blender/blenkernel/intern/depsgraph.c
@@ -1193,6 +1193,8 @@ static void dag_check_cycle(DagForest *dag)
 	DagNode *node;
 	DagAdjList *itA;
 
+	dag->is_acyclic = true;
+
 	/* debugging print */
 	if (dag_print_dependencies)
 		for (node = dag->DagNode.first; node; node = node->next)
@@ -1213,6 +1215,7 @@ static void dag_check_cycle(DagForest *dag)
 		for (itA = node->parent; itA; itA = itA->next) {
 			if (itA->node->ancestor_count > node->ancestor_count) {
 				if (node->ob && itA->node->ob) {
+					dag->is_acyclic = false;
 					printf("Dependency cycle detected:\n");
 					dag_node_print_dependency_cycle(dag, itA->node, node, itA->name);
 				}
@@ -2904,3 +2907,7 @@ short DAG_get_eval_flags_for_object(struct Scene *scene, void *object)
 	return node->eval_flags;
 }
 
+bool DAG_is_acyclic(Scene *scene)
+{
+	return scene->theDag->is_acyclic;
+}