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

2 files changed, 65 insertions, 39 deletions

diff --git a/source/blender/bmesh/intern/bmesh_construct.c b/source/blender/bmesh/intern/bmesh_construct.c
index 3ee9fa7aee4..22900ecef85 100644
--- a/source/blender/bmesh/intern/bmesh_construct.c
+++ b/source/blender/bmesh/intern/bmesh_construct.c
@@ -507,26 +507,32 @@ void BM_mesh_copy_init_customdata_from_mesh_array(BMesh *bm_dst,
 
   for (int i = 0; i < me_src_array_len; i++) {
     const Mesh *me_src = me_src_array[i];
+    CustomData mesh_vdata = CustomData_shallow_copy_remove_non_bmesh_attributes(
+        &me_src->vdata, CD_MASK_BMESH.vmask);
+    CustomData mesh_edata = CustomData_shallow_copy_remove_non_bmesh_attributes(
+        &me_src->edata, CD_MASK_BMESH.emask);
+    CustomData mesh_pdata = CustomData_shallow_copy_remove_non_bmesh_attributes(
+        &me_src->pdata, CD_MASK_BMESH.lmask);
+    CustomData mesh_ldata = CustomData_shallow_copy_remove_non_bmesh_attributes(
+        &me_src->ldata, CD_MASK_BMESH.pmask);
+
     if (i == 0) {
-      CustomData_copy_mesh_to_bmesh(
-          &me_src->vdata, &bm_dst->vdata, CD_MASK_BMESH.vmask, CD_SET_DEFAULT, 0);
-      CustomData_copy_mesh_to_bmesh(
-          &me_src->edata, &bm_dst->edata, CD_MASK_BMESH.emask, CD_SET_DEFAULT, 0);
-      CustomData_copy_mesh_to_bmesh(
-          &me_src->ldata, &bm_dst->ldata, CD_MASK_BMESH.lmask, CD_SET_DEFAULT, 0);
-      CustomData_copy_mesh_to_bmesh(
-          &me_src->pdata, &bm_dst->pdata, CD_MASK_BMESH.pmask, CD_SET_DEFAULT, 0);
+      CustomData_copy(&me_src->vdata, &bm_dst->vdata, CD_MASK_BMESH.vmask, CD_SET_DEFAULT, 0);
+      CustomData_copy(&me_src->edata, &bm_dst->edata, CD_MASK_BMESH.emask, CD_SET_DEFAULT, 0);
+      CustomData_copy(&me_src->ldata, &bm_dst->ldata, CD_MASK_BMESH.lmask, CD_SET_DEFAULT, 0);
+      CustomData_copy(&me_src->pdata, &bm_dst->pdata, CD_MASK_BMESH.pmask, CD_SET_DEFAULT, 0);
     }
     else {
-      CustomData_merge_mesh_to_bmesh(
-          &me_src->vdata, &bm_dst->vdata, CD_MASK_BMESH.vmask, CD_SET_DEFAULT, 0);
-      CustomData_merge_mesh_to_bmesh(
-          &me_src->edata, &bm_dst->edata, CD_MASK_BMESH.emask, CD_SET_DEFAULT, 0);
-      CustomData_merge_mesh_to_bmesh(
-          &me_src->ldata, &bm_dst->ldata, CD_MASK_BMESH.lmask, CD_SET_DEFAULT, 0);
-      CustomData_merge_mesh_to_bmesh(
-          &me_src->pdata, &bm_dst->pdata, CD_MASK_BMESH.pmask, CD_SET_DEFAULT, 0);
+      CustomData_merge(&me_src->vdata, &bm_dst->vdata, CD_MASK_BMESH.vmask, CD_SET_DEFAULT, 0);
+      CustomData_merge(&me_src->edata, &bm_dst->edata, CD_MASK_BMESH.emask, CD_SET_DEFAULT, 0);
+      CustomData_merge(&me_src->ldata, &bm_dst->ldata, CD_MASK_BMESH.lmask, CD_SET_DEFAULT, 0);
+      CustomData_merge(&me_src->pdata, &bm_dst->pdata, CD_MASK_BMESH.pmask, CD_SET_DEFAULT, 0);
     }
+
+    MEM_SAFE_FREE(mesh_vdata.layers);
+    MEM_SAFE_FREE(mesh_edata.layers);
+    MEM_SAFE_FREE(mesh_pdata.layers);
+    MEM_SAFE_FREE(mesh_ldata.layers);
   }
 
   CustomData_bmesh_init_pool(&bm_dst->vdata, allocsize->totvert, BM_VERT);
diff --git a/source/blender/bmesh/intern/bmesh_mesh_convert.cc b/source/blender/bmesh/intern/bmesh_mesh_convert.cc
index 82d707c7e54..d65cac08db8 100644
--- a/source/blender/bmesh/intern/bmesh_mesh_convert.cc
+++ b/source/blender/bmesh/intern/bmesh_mesh_convert.cc
@@ -129,6 +129,10 @@ static BMFace *bm_face_create_from_mpoly(BMesh &bm,
 
 void BM_mesh_bm_from_me(BMesh *bm, const Mesh *me, const struct BMeshFromMeshParams *params)
 {
+  if (!me) {
+    /* Sanity check. */
+    return;
+  }
   const bool is_new = !(bm->totvert || (bm->vdata.totlayer || bm->edata.totlayer ||
                                         bm->pdata.totlayer || bm->ldata.totlayer));
   KeyBlock *actkey;
@@ -136,19 +140,35 @@ void BM_mesh_bm_from_me(BMesh *bm, const Mesh *me, const struct BMeshFromMeshPar
   CustomData_MeshMasks mask = CD_MASK_BMESH;
   CustomData_MeshMasks_update(&mask, &params->cd_mask_extra);
 
-  if (!me || !me->totvert) {
-    if (me && is_new) { /* No verts? still copy custom-data layout. */
-      CustomData_copy_mesh_to_bmesh(&me->vdata, &bm->vdata, mask.vmask, CD_CONSTRUCT, 0);
-      CustomData_copy_mesh_to_bmesh(&me->edata, &bm->edata, mask.emask, CD_CONSTRUCT, 0);
-      CustomData_copy_mesh_to_bmesh(&me->ldata, &bm->ldata, mask.lmask, CD_CONSTRUCT, 0);
-      CustomData_copy_mesh_to_bmesh(&me->pdata, &bm->pdata, mask.pmask, CD_CONSTRUCT, 0);
+  CustomData mesh_vdata = CustomData_shallow_copy_remove_non_bmesh_attributes(&me->vdata,
+                                                                              mask.vmask);
+  CustomData mesh_edata = CustomData_shallow_copy_remove_non_bmesh_attributes(&me->edata,
+                                                                              mask.emask);
+  CustomData mesh_pdata = CustomData_shallow_copy_remove_non_bmesh_attributes(&me->pdata,
+                                                                              mask.pmask);
+  CustomData mesh_ldata = CustomData_shallow_copy_remove_non_bmesh_attributes(&me->ldata,
+                                                                              mask.lmask);
+  BLI_SCOPED_DEFER([&]() {
+    MEM_SAFE_FREE(mesh_vdata.layers);
+    MEM_SAFE_FREE(mesh_edata.layers);
+    MEM_SAFE_FREE(mesh_pdata.layers);
+    MEM_SAFE_FREE(mesh_ldata.layers);
+  });
+
+  if (me->totvert == 0) {
+    if (is_new) {
+      /* No verts? still copy custom-data layout. */
+      CustomData_copy(&mesh_vdata, &bm->vdata, mask.vmask, CD_CONSTRUCT, 0);
+      CustomData_copy(&mesh_edata, &bm->edata, mask.emask, CD_CONSTRUCT, 0);
+      CustomData_copy(&mesh_pdata, &bm->pdata, mask.pmask, CD_CONSTRUCT, 0);
+      CustomData_copy(&mesh_ldata, &bm->ldata, mask.lmask, CD_CONSTRUCT, 0);
 
       CustomData_bmesh_init_pool(&bm->vdata, me->totvert, BM_VERT);
       CustomData_bmesh_init_pool(&bm->edata, me->totedge, BM_EDGE);
       CustomData_bmesh_init_pool(&bm->ldata, me->totloop, BM_LOOP);
       CustomData_bmesh_init_pool(&bm->pdata, me->totpoly, BM_FACE);
     }
-    return; /* Sanity check. */
+    return;
   }
 
   const float(*vert_normals)[3] = nullptr;
@@ -157,16 +177,16 @@ void BM_mesh_bm_from_me(BMesh *bm, const Mesh *me, const struct BMeshFromMeshPar
   }
 
   if (is_new) {
-    CustomData_copy_mesh_to_bmesh(&me->vdata, &bm->vdata, mask.vmask, CD_SET_DEFAULT, 0);
-    CustomData_copy_mesh_to_bmesh(&me->edata, &bm->edata, mask.emask, CD_SET_DEFAULT, 0);
-    CustomData_copy_mesh_to_bmesh(&me->ldata, &bm->ldata, mask.lmask, CD_SET_DEFAULT, 0);
-    CustomData_copy_mesh_to_bmesh(&me->pdata, &bm->pdata, mask.pmask, CD_SET_DEFAULT, 0);
+    CustomData_copy(&mesh_vdata, &bm->vdata, mask.vmask, CD_SET_DEFAULT, 0);
+    CustomData_copy(&mesh_edata, &bm->edata, mask.emask, CD_SET_DEFAULT, 0);
+    CustomData_copy(&mesh_pdata, &bm->pdata, mask.pmask, CD_SET_DEFAULT, 0);
+    CustomData_copy(&mesh_ldata, &bm->ldata, mask.lmask, CD_SET_DEFAULT, 0);
   }
   else {
-    CustomData_bmesh_merge(&me->vdata, &bm->vdata, mask.vmask, CD_SET_DEFAULT, bm, BM_VERT);
-    CustomData_bmesh_merge(&me->edata, &bm->edata, mask.emask, CD_SET_DEFAULT, bm, BM_EDGE);
-    CustomData_bmesh_merge(&me->ldata, &bm->ldata, mask.lmask, CD_SET_DEFAULT, bm, BM_LOOP);
-    CustomData_bmesh_merge(&me->pdata, &bm->pdata, mask.pmask, CD_SET_DEFAULT, bm, BM_FACE);
+    CustomData_bmesh_merge(&mesh_vdata, &bm->vdata, mask.vmask, CD_SET_DEFAULT, bm, BM_VERT);
+    CustomData_bmesh_merge(&mesh_edata, &bm->edata, mask.emask, CD_SET_DEFAULT, bm, BM_EDGE);
+    CustomData_bmesh_merge(&mesh_pdata, &bm->pdata, mask.pmask, CD_SET_DEFAULT, bm, BM_FACE);
+    CustomData_bmesh_merge(&mesh_ldata, &bm->ldata, mask.lmask, CD_SET_DEFAULT, bm, BM_LOOP);
   }
 
   /* -------------------------------------------------------------------- */
@@ -302,7 +322,7 @@ void BM_mesh_bm_from_me(BMesh *bm, const Mesh *me, const struct BMeshFromMeshPar
     }
 
     /* Copy Custom Data */
-    CustomData_to_bmesh_block(&me->vdata, &bm->vdata, i, &v->head.data, true);
+    CustomData_to_bmesh_block(&mesh_vdata, &bm->vdata, i, &v->head.data, true);
 
     /* Set shape key original index. */
     if (cd_shape_keyindex_offset != -1) {
@@ -338,7 +358,7 @@ void BM_mesh_bm_from_me(BMesh *bm, const Mesh *me, const struct BMeshFromMeshPar
     }
 
     /* Copy Custom Data */
-    CustomData_to_bmesh_block(&me->edata, &bm->edata, i, &e->head.data, true);
+    CustomData_to_bmesh_block(&mesh_edata, &bm->edata, i, &e->head.data, true);
   }
   if (is_new) {
     bm->elem_index_dirty &= ~BM_EDGE; /* Added in order, clear dirty flag. */
@@ -397,11 +417,11 @@ void BM_mesh_bm_from_me(BMesh *bm, const Mesh *me, const struct BMeshFromMeshPar
       BM_elem_index_set(l_iter, totloops++); /* set_ok */
 
       /* Save index of corresponding #MLoop. */
-      CustomData_to_bmesh_block(&me->ldata, &bm->ldata, j++, &l_iter->head.data, true);
+      CustomData_to_bmesh_block(&mesh_ldata, &bm->ldata, j++, &l_iter->head.data, true);
     } while ((l_iter = l_iter->next) != l_first);
 
     /* Copy Custom Data */
-    CustomData_to_bmesh_block(&me->pdata, &bm->pdata, i, &f->head.data, true);
+    CustomData_to_bmesh_block(&mesh_pdata, &bm->pdata, i, &f->head.data, true);
 
     if (params->calc_face_normal) {
       BM_face_normal_update(f);
@@ -951,10 +971,10 @@ void BM_mesh_bm_to_me(Main *bmain, BMesh *bm, Mesh *me, const struct BMeshToMesh
   {
     CustomData_MeshMasks mask = CD_MASK_MESH;
     CustomData_MeshMasks_update(&mask, &params->cd_mask_extra);
-    CustomData_copy_mesh_to_bmesh(&bm->vdata, &me->vdata, mask.vmask, CD_SET_DEFAULT, me->totvert);
-    CustomData_copy_mesh_to_bmesh(&bm->edata, &me->edata, mask.emask, CD_SET_DEFAULT, me->totedge);
-    CustomData_copy_mesh_to_bmesh(&bm->ldata, &me->ldata, mask.lmask, CD_SET_DEFAULT, me->totloop);
-    CustomData_copy_mesh_to_bmesh(&bm->pdata, &me->pdata, mask.pmask, CD_SET_DEFAULT, me->totpoly);
+    CustomData_copy(&bm->vdata, &me->vdata, mask.vmask, CD_SET_DEFAULT, me->totvert);
+    CustomData_copy(&bm->edata, &me->edata, mask.emask, CD_SET_DEFAULT, me->totedge);
+    CustomData_copy(&bm->ldata, &me->ldata, mask.lmask, CD_SET_DEFAULT, me->totloop);
+    CustomData_copy(&bm->pdata, &me->pdata, mask.pmask, CD_SET_DEFAULT, me->totpoly);
   }
 
   CustomData_add_layer(&me->vdata, CD_MVERT, CD_SET_DEFAULT, nullptr, me->totvert);