Animation: correct active track/strip pointers after copying NLA tracks

After copying NLA tracks from one `AnimData` to another, also ensure
that the `AnimData::act_track` and `AnimData::actstrip` pointers are
pointing to the copy rather than the original.

This is a necessary step to allow library overrides on NLA modifiers
without crashing Blender.

The remapping of the pointers is done by looping over the tracks/strips
and comparing pointers. Alternatively, I could update the copy functions
themselves to keep track of those pointers and return them, but IMO that
would produce more spaghetti (they're also used in cases where this
pointer-remapping is not desired).

1 files changed, 8 insertions, 1 deletions

diff --git a/source/blender/blenkernel/BKE_nla.h b/source/blender/blenkernel/BKE_nla.h
index 16d48024d07..af238fda659 100644
--- a/source/blender/blenkernel/BKE_nla.h
+++ b/source/blender/blenkernel/BKE_nla.h
@@ -58,7 +58,14 @@ struct NlaTrack *BKE_nlatrack_copy(struct Main *bmain,
                                    struct NlaTrack *nlt,
                                    const bool use_same_actions,
                                    const int flag);
-void BKE_nla_tracks_copy(struct Main *bmain, ListBase *dst, ListBase *src, const int flag);
+void BKE_nla_tracks_copy(struct Main *bmain, ListBase *dst, const ListBase *src, const int flag);
+
+/* Copy NLA tracks from #adt_source to #adt_dest, and update the active track/strip pointers to
+ * point at those copies. */
+void BKE_nla_tracks_copy_from_adt(struct Main *bmain,
+                                  struct AnimData *adt_dest,
+                                  const struct AnimData *adt_source,
+                                  int flag);
 
 struct NlaTrack *BKE_nlatrack_add(struct AnimData *adt,
                                   struct NlaTrack *prev,