Bugfix [#33970] Background Scene does not show animation of rigid body objects

This was caused by multiple instantiations of the same basic problem. The
rigidbody handling code often assumed that "scene" pointers referred to the
scene where an object participating in the sim resided (and where the rigidbody
world for that sim lived). However, when dealing with background sets, "scene"
often only refers to the active scene, and not the set that the object actually
came from. Hence, the rigidbody code would often (wrongly) conclude that there
was nothing to do.

For example, we may have the following backgound set/scene chaining scenario:
"active"  <-- ... <-- set i (rigidbody objects live here) <-- ... <-- set n

The fix here is a multi-part fix:
1) Moved sim-world calculation from BKE_scene_update_newframe() to
scene_update_tagged_recursive()
    + This is currently the only way that rigidbody sims in background sets will
get calculated, as part of the recursion
     - These checks will get run on each update. <--- FIXME!!!

2) Tweaked depsgraph code so that when checking if there are any time-dependent
features on objects to tag for updating, the checking is done relative to the
scene that the object actually resides in (and not the active scene). Otherwise,
even if we recalculate the sim, the affected objects won't get tagged for
updating. This tagging is needed to actually flush the transforms out of the
RigidBodyObject structs (written by the sim/cache) and into the Object
transforms (obmat's)

3) Removed the requirement for rigidbody world to actually exist before we can
flush rigidbody transforms. In many cases, it should be sufficient to assume
that because the object with rigidbody data attached has been tagged for
updates, it should have updates to perform. Of course, we still check on this
data if we've got it, but that's only if the sim is in the active scene.
   - TODO: if we have further problems, we should investigate passing the
"actual" scene down alongside the "active" scene for BKE_object_handle_update().

1 files changed, 7 insertions, 1 deletions

diff --git a/source/blender/blenkernel/intern/object.c b/source/blender/blenkernel/intern/object.c
index 0140152790c..4b940fa8274 100644
--- a/source/blender/blenkernel/intern/object.c
+++ b/source/blender/blenkernel/intern/object.c
@@ -2141,7 +2141,8 @@ void BKE_object_where_is_calc_time(Scene *scene, Object *ob, float ctime)
 	else {
 		BKE_object_to_mat4(ob, ob->obmat);
 	}
-	
+
+	/* read values pushed into RBO from sim/cache... */
 	BKE_rigidbody_sync_transforms(scene, ob, ctime);
 	
 	/* solve constraints */
@@ -2617,6 +2618,11 @@ int BKE_object_parent_loop_check(const Object *par, const Object *ob)
 
 /* the main object update call, for object matrix, constraints, keys and displist (modifiers) */
 /* requires flags to be set! */
+
+/* WARNING: "scene" here may not be the scene object actually resides in. 
+ * When dealing with background-sets, "scene" is actually the active scene.
+ * e.g. "scene" <-- set 1 <-- set 2 ("ob" lives here) <-- set 3 <-- ... <-- set n
+ */
 void BKE_object_handle_update(Scene *scene, Object *ob)
 {
 	if (ob->recalc & OB_RECALC_ALL) {