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, 1 insertions, 0 deletions

diff --git a/source/blender/blenkernel/BKE_depsgraph.h b/source/blender/blenkernel/BKE_depsgraph.h
index 4fedf373a22..df7e9561c46 100644
--- a/source/blender/blenkernel/BKE_depsgraph.h
+++ b/source/blender/blenkernel/BKE_depsgraph.h
@@ -159,6 +159,7 @@ void DAG_print_dependencies(struct Main *bmain, struct Scene *scene, struct Obje
 struct Object *DAG_get_node_object(void *node_v);
 const char *DAG_get_node_name(void *node_v);
 short DAG_get_eval_flags_for_object(struct Scene *scene, void *object);
+bool DAG_is_acyclic(struct Scene *scene);
 
 #ifdef __cplusplus
 }