Fix T80165: Separate by loose parts breaks custom normals

- Add NULL check for BKE_lnor_spacearr_clear
- Remove unnecessary 'use_toolflags' with BMesh creation.

2 files changed, 25 insertions, 15 deletions

diff --git a/source/blender/blenkernel/intern/mesh_evaluate.c b/source/blender/blenkernel/intern/mesh_evaluate.c
index 6b3a85cc364..eee1b763be5 100644
--- a/source/blender/blenkernel/intern/mesh_evaluate.c
+++ b/source/blender/blenkernel/intern/mesh_evaluate.c
@@ -541,7 +541,9 @@ void BKE_lnor_spacearr_clear(MLoopNorSpaceArray *lnors_spacearr)
   lnors_spacearr->num_spaces = 0;
   lnors_spacearr->lspacearr = NULL;
   lnors_spacearr->loops_pool = NULL;
-  BLI_memarena_clear(lnors_spacearr->mem);
+  if (lnors_spacearr->mem != NULL) {
+    BLI_memarena_clear(lnors_spacearr->mem);
+  }
 }
 
 void BKE_lnor_spacearr_free(MLoopNorSpaceArray *lnors_spacearr)
diff --git a/source/blender/editors/mesh/editmesh_tools.c b/source/blender/editors/mesh/editmesh_tools.c
index 1ceeb3d1fed..47836d2e529 100644
--- a/source/blender/editors/mesh/editmesh_tools.c
+++ b/source/blender/editors/mesh/editmesh_tools.c
@@ -4233,24 +4233,26 @@ static Base *mesh_separate_arrays(Main *bmain,
                                   BMFace **faces,
                                   uint faces_len)
 {
+  const BMAllocTemplate bm_new_allocsize = {
+      .totvert = verts_len,
+      .totedge = edges_len,
+      .totloop = faces_len * 3,
+      .totface = faces_len,
+  };
+  const bool use_custom_normals = (bm_old->lnor_spacearr != NULL);
+
   Base *base_new;
   Object *obedit = base_old->object;
-  BMesh *bm_new;
 
-  bm_new = BM_mesh_create(&bm_mesh_allocsize_default,
-                          &((struct BMeshCreateParams){
-                              .use_toolflags = true,
-                          }));
-
-  CustomData_copy(&bm_old->vdata, &bm_new->vdata, CD_MASK_BMESH.vmask, CD_CALLOC, 0);
-  CustomData_copy(&bm_old->edata, &bm_new->edata, CD_MASK_BMESH.emask, CD_CALLOC, 0);
-  CustomData_copy(&bm_old->ldata, &bm_new->ldata, CD_MASK_BMESH.lmask, CD_CALLOC, 0);
-  CustomData_copy(&bm_old->pdata, &bm_new->pdata, CD_MASK_BMESH.pmask, CD_CALLOC, 0);
+  BMesh *bm_new = BM_mesh_create(&bm_new_allocsize, &((struct BMeshCreateParams){0}));
 
-  CustomData_bmesh_init_pool(&bm_new->vdata, verts_len, BM_VERT);
-  CustomData_bmesh_init_pool(&bm_new->edata, edges_len, BM_EDGE);
-  CustomData_bmesh_init_pool(&bm_new->ldata, faces_len * 3, BM_LOOP);
-  CustomData_bmesh_init_pool(&bm_new->pdata, faces_len, BM_FACE);
+  if (use_custom_normals) {
+    /* Needed so the temporary normal layer is copied too. */
+    BM_mesh_copy_init_customdata_all_layers(bm_new, bm_old, BM_ALL, &bm_new_allocsize);
+  }
+  else {
+    BM_mesh_copy_init_customdata(bm_new, bm_old, &bm_new_allocsize);
+  }
 
   /* Take into account user preferences for duplicating actions. */
   const eDupli_ID_Flags dupflag = USER_DUP_MESH | (U.dupflag & USER_DUP_ACT);
@@ -4270,6 +4272,10 @@ static Base *mesh_separate_arrays(Main *bmain,
 
   BM_mesh_copy_arrays(bm_old, bm_new, verts, verts_len, edges, edges_len, faces, faces_len);
 
+  if (use_custom_normals) {
+    BM_custom_loop_normals_from_vector_layer(bm_new, false);
+  }
+
   for (uint i = 0; i < verts_len; i++) {
     BM_vert_kill(bm_old, verts[i]);
   }
@@ -4432,6 +4438,8 @@ static bool mesh_separate_loose(
     ED_mesh_geometry_clear(base_old->object->data);
   }
 
+  BM_custom_loop_normals_to_vector_layer(bm_old);
+
   /* Separate out all groups except the first. */
   uint group_ofs[3] = {UNPACK3(groups[0])};
   for (int i = 1; i < groups_len; i++) {