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, 14 insertions, 3 deletions

diff --git a/source/blender/blenkernel/BKE_mesh.h b/source/blender/blenkernel/BKE_mesh.h
index c410946f438..54fbda1fa31 100644
--- a/source/blender/blenkernel/BKE_mesh.h
+++ b/source/blender/blenkernel/BKE_mesh.h
@@ -209,11 +209,22 @@ float (*BKE_mesh_vertexCos_get(const struct Mesh *me, int *r_numVerts))[3];
 void BKE_mesh_split_faces(struct Mesh *mesh, bool free_loop_normals);
 
 /* Create new mesh from the given object at its current state.
- * The owner of this mesh is unknown, it is up to the caller to decide. */
-struct Mesh *BKE_mesh_new_from_object(struct Object *object);
+ * The owner of this mesh is unknown, it is up to the caller to decide.
+ *
+ * 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_mesh_new_from_object(struct Depsgraph *depsgraph,
+                                      struct Object *object,
+                                      bool preserve_all_data_layers);
 
 /* This is a version of BKE_mesh_new_from_object() which stores mesh in the given main database. */
-struct Mesh *BKE_mesh_new_from_object_to_bmain(struct Main *bmain, struct Object *object);
+struct Mesh *BKE_mesh_new_from_object_to_bmain(struct Main *bmain,
+                                               struct Depsgraph *depsgraph,
+                                               struct Object *object,
+                                               bool preserve_all_data_layers);
 
 struct Mesh *BKE_mesh_create_derived_for_modifier(struct Depsgraph *depsgraph,
                                                   struct Scene *scene,