Depsgraph API: Allow preserving custom data layers

This commit extends dependency graph API with an argument which
denotes that all custom data layers are to be preserved. This
forces modifier stack re-evaluation with more inclusive mask.

Far from ideal, since this might fail in certain configurations
with indirectly used objects which might be missing layers needed
for the current object evaluation. But this is how it worked for
a long time, so should be good enough for until more sophisticated
solution is found.

In order to use this new behavior two things are to be passed:

- Pass keep_all_data_layers=True
- Pass a valid dependency graph.

The dependency graph is only needed if keep_all_data_layers=True
and is NOT to be passed if keep_all_data_layers=False.

If keep_all_data_layers=True the dependency graph MUST be passed.

Reviewers: mont29, brecht

Reviewed By: mont29

Maniphest Tasks: T64994, T64794

Differential Revision: https://developer.blender.org/D4940

1 files changed, 10 insertions, 2 deletions

diff --git a/source/blender/blenkernel/BKE_object.h b/source/blender/blenkernel/BKE_object.h
index aa4d9696527..df1ac0e4081 100644
--- a/source/blender/blenkernel/BKE_object.h
+++ b/source/blender/blenkernel/BKE_object.h
@@ -400,8 +400,16 @@ bool BKE_object_empty_image_data_is_visible_in_view3d(const struct Object *ob,
  * The result is owned by the object.
  *
  * The mesh will be freed when object is re-evaluated or is destroyed. It is possible to force to
- * clear memory sued by this mesh by calling BKE_object_to_mesh_clear(). */
-struct Mesh *BKE_object_to_mesh(struct Object *object);
+ * clear memory sued by this mesh by calling BKE_object_to_mesh_clear().
+ *
+ * If preserve_all_data_layers is truth then the modifier stack is re-evaluated to ensure it
+ * preserves all possible custom data layers.
+ *
+ * NOTE: Dependency graph argument is required when preserve_all_data_layers is truth, and is
+ * ignored otherwise. */
+struct Mesh *BKE_object_to_mesh(struct Depsgraph *depsgraph,
+                                struct Object *object,
+                                bool preserve_all_data_layers);
 
 void BKE_object_to_mesh_clear(struct Object *object);