Fix: Attribute layers can be skipped in Mesh to BMesh conversion

In some situations, layers were filled with their default value
when converting from Mesh to BMesh (entering edit mode, for example).
This was caused by the recently added "copy mesh to bmesh" or "merge
mesh to bmesh" custom data functions creating a difference custom
data format than was used for the copying functions used later.

`CustomData_to_bmesh_block` is not robust enough to handle simple
differences in layout between the layout of the source and result
CustomData layers, because it relies on the order of the types and
the number of layers within each type.

As a fix, make the "mesh to bmesh" special case more explicit in
the conversion functions. This makes the difference in the API
smaller, which is a nice improvement anwyay.

Fixes T101796

1 files changed, 8 insertions, 18 deletions

diff --git a/source/blender/blenkernel/BKE_customdata.h b/source/blender/blenkernel/BKE_customdata.h
index 61f3a0e1d5e..f761e28cbb4 100644
--- a/source/blender/blenkernel/BKE_customdata.h
+++ b/source/blender/blenkernel/BKE_customdata.h
@@ -146,15 +146,6 @@ void CustomData_copy(const struct CustomData *source,
                      eCDAllocType alloctype,
                      int totelem);
 
-/**
- * Like #CustomData_copy but skips copying layers that are stored as flags on #BMesh.
- */
-void CustomData_copy_mesh_to_bmesh(const struct CustomData *source,
-                                   struct CustomData *dest,
-                                   eCustomDataMask mask,
-                                   eCDAllocType alloctype,
-                                   int totelem);
-
 /* BMESH_TODO, not really a public function but readfile.c needs it */
 void CustomData_update_typemap(struct CustomData *data);
 
@@ -169,15 +160,6 @@ bool CustomData_merge(const struct CustomData *source,
                       int totelem);
 
 /**
- * Like #CustomData_copy but skips copying layers that are stored as flags on #BMesh.
- */
-bool CustomData_merge_mesh_to_bmesh(const struct CustomData *source,
-                                    struct CustomData *dest,
-                                    eCustomDataMask mask,
-                                    eCDAllocType alloctype,
-                                    int totelem);
-
-/**
  * Reallocate custom data to a new element count. If the new size is larger, the new values use
  * the #CD_CONSTRUCT behavior, so trivial types must be initialized by the caller. After being
  * resized, the #CustomData does not contain any referenced layers.
@@ -197,6 +179,14 @@ bool CustomData_bmesh_merge(const struct CustomData *source,
                             char htype);
 
 /**
+ * Remove layers that aren't stored in BMesh or are stored as flags on BMesh.
+ * The `layers` array of the returned #CustomData must be freed, but may be null.
+ * Used during conversion of #Mesh data to #BMesh storage format.
+ */
+CustomData CustomData_shallow_copy_remove_non_bmesh_attributes(const CustomData *src,
+                                                               eCustomDataMask mask);
+
+/**
  * NULL's all members and resets the #CustomData.typemap.
  */
 void CustomData_reset(struct CustomData *data);