Commit: 947dc920835bcd9116a9a03e5958526509c58ff4
Author: Campbell Barton
Date: Wed Jan 6 18:03:42 2021 +1100
Branches: master
https://developer.blender.org/rB947dc920835bcd9116a9a03e5958526509c58ff4
BMesh: assert when a mesh has two kinds of shake-key data
Assert with comment to avoid confusion caused by
mixing two kinds of shape-key data.
This problem was exposed when investigating T84364.
===================================================================
M source/blender/bmesh/intern/bmesh_mesh_convert.c
===================================================================
diff --git a/source/blender/bmesh/intern/bmesh_mesh_convert.c
b/source/blender/bmesh/intern/bmesh_mesh_convert.c
index c30f71e029f..ba413c3c547 100644
--- a/source/blender/bmesh/intern/bmesh_mesh_convert.c
+++ b/source/blender/bmesh/intern/bmesh_mesh_convert.c
@@ -239,6 +239,24 @@ void BM_mesh_bm_from_me(BMesh *bm, const Mesh *me, const
struct BMeshFromMeshPar
* Shape keys are also already integrated into the state of the evaluated
* mesh, so considering them here would kind of apply them twice. */
tot_shape_keys = BLI_listbase_count(&me->key->block);
+
+ /* Original meshes must never contain a shape-key custom-data layers.
+ *
+ * This may happen if and object's mesh data is accidentally
+ * set to the output from the modifier stack, causing it to be an
"original" ID,
+ * even though the data isn't fully compatible (hence this assert).
+ *
+ * This results in:
+ * - The newly created #BMesh having twice the number of custom-data
layers.
+ * - When converting the #BMesh back to a regular mesh,
+ * At least one of the extra shape-key blocks will be created in
#Mesh.key
+ * depending on the value of #CustomDataLayer.uid.
+ *
+ * We could support mixing both kinds of data if there is a compelling
use-case for it.
+ * At the moment it's simplest to assume all original meshes use the
key-block and meshes
+ * that are evaluated (through the modifier stack for example) use
custom-data layers.
+ */
+ BLI_assert(!CustomData_has_layer(&me->vdata, CD_SHAPEKEY));
}
if (is_new == false) {
tot_shape_keys = min_ii(tot_shape_keys,
CustomData_number_of_layers(&bm->vdata, CD_SHAPEKEY));
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