Refactor: Move vertex group names to object data

This commit moves the storage of `bDeformGroup` and the active index
to `Mesh`, `Lattice`, and `bGPdata` instead of `Object`. Utility
functions are added to allow easy access to the vertex groups given
an object or an ID.

As explained in T88951, the list of vertex group names is currently
stored separately per object, even though vertex group data is stored
on the geometry. This tends to complicate code and cause bugs,
especially as geometry is created procedurally and tied less closely
to an object.

The "Copy Vertex Groups to Linked" operator is removed, since they
are stored on the geometry anyway.

This patch leaves the object-level python API for vertex groups in
place. Creating a geometry-level RNA API can be a separate step;
the changes in this commit are invasive enough as it is.

Note that opening a file saved in 3.0 in an earlier version means
the vertex groups will not be available.

Differential Revision: https://developer.blender.org/D11689

17 files changed, 288 insertions, 173 deletions

diff --git a/source/blender/blenkernel/BKE_blender_version.h b/source/blender/blenkernel/BKE_blender_version.h
index e5217c6692b..dffd70c077f 100644
--- a/source/blender/blenkernel/BKE_blender_version.h
+++ b/source/blender/blenkernel/BKE_blender_version.h
@@ -39,7 +39,7 @@ extern "C" {
 
 /* Blender file format version. */
 #define BLENDER_FILE_VERSION BLENDER_VERSION
-#define BLENDER_FILE_SUBVERSION 10
+#define BLENDER_FILE_SUBVERSION 11
 
 /* Minimum Blender version that supports reading file written with the current
  * version. Older Blender versions will test this and show a warning if the file
diff --git a/source/blender/blenkernel/BKE_deform.h b/source/blender/blenkernel/BKE_deform.h
index 8b5fdf69bb0..0ab126a70ae 100644
--- a/source/blender/blenkernel/BKE_deform.h
+++ b/source/blender/blenkernel/BKE_deform.h
@@ -37,6 +37,19 @@ struct MLoop;
 struct MPoly;
 struct Object;
 struct bDeformGroup;
+struct ID;
+
+bool BKE_object_supports_vertex_groups(const struct Object *ob);
+const struct ListBase *BKE_object_defgroup_list(const struct Object *ob);
+struct ListBase *BKE_object_defgroup_list_mutable(struct Object *ob);
+
+int BKE_object_defgroup_count(const struct Object *ob);
+int BKE_object_defgroup_active_index_get(const struct Object *ob);
+void BKE_object_defgroup_active_index_set(struct Object *ob, const int new_index);
+
+const struct ListBase *BKE_id_defgroup_list_get(const struct ID *id);
+struct ListBase *BKE_id_defgroup_list_get_mutable(struct ID *id);
+int BKE_id_defgroup_name_index(const struct ID *id, const char *name);
 
 struct bDeformGroup *BKE_object_defgroup_new(struct Object *ob, const char *name);
 void BKE_defgroup_copy_list(struct ListBase *outbase, const struct ListBase *inbase);
@@ -171,6 +184,7 @@ void BKE_defvert_blend_write(struct BlendWriter *writer, int count, struct MDefo
 void BKE_defvert_blend_read(struct BlendDataReader *reader,
                             int count,
                             struct MDeformVert *mdverts);
+void BKE_defbase_blend_write(struct BlendWriter *writer, const ListBase *defbase);
 
 #ifdef __cplusplus
 }
diff --git a/source/blender/blenkernel/BKE_geometry_set.hh b/source/blender/blenkernel/BKE_geometry_set.hh
index 82c9a31dfce..77e827bf6f2 100644
--- a/source/blender/blenkernel/BKE_geometry_set.hh
+++ b/source/blender/blenkernel/BKE_geometry_set.hh
@@ -325,10 +325,6 @@ class MeshComponent : public GeometryComponent {
  private:
   Mesh *mesh_ = nullptr;
   GeometryOwnershipType ownership_ = GeometryOwnershipType::Owned;
-  /* Due to historical design choices, vertex group data is stored in the mesh, but the vertex
-   * group names are stored on an object. Since we don't have an object here, we copy over the
-   * names into this map. */
-  blender::Map<std::string, int> vertex_group_names_;
 
  public:
   MeshComponent();
@@ -338,14 +334,8 @@ class MeshComponent : public GeometryComponent {
   void clear();
   bool has_mesh() const;
   void replace(Mesh *mesh, GeometryOwnershipType ownership = GeometryOwnershipType::Owned);
-  void replace_mesh_but_keep_vertex_group_names(
-      Mesh *mesh, GeometryOwnershipType ownership = GeometryOwnershipType::Owned);
   Mesh *release();
 
-  void copy_vertex_group_names_from_object(const struct Object &object);
-  const blender::Map<std::string, int> &vertex_group_names() const;
-  blender::Map<std::string, int> &vertex_group_names();
-
   const Mesh *get_for_read() const;
   Mesh *get_for_write();
 
diff --git a/source/blender/blenkernel/intern/DerivedMesh.cc b/source/blender/blenkernel/intern/DerivedMesh.cc
index ecbb3d1cfab..ba8cf8debe9 100644
--- a/source/blender/blenkernel/intern/DerivedMesh.cc
+++ b/source/blender/blenkernel/intern/DerivedMesh.cc
@@ -900,7 +900,7 @@ static Mesh *prepare_geometry_set_for_mesh_modifier(Mesh *mesh, GeometrySet &r_g
   {
     /* Add the mesh to the geometry set. */
     MeshComponent &mesh_component = r_geometry_set.get_component_for_write<MeshComponent>();
-    mesh_component.replace_mesh_but_keep_vertex_group_names(mesh, GeometryOwnershipType::Editable);
+    mesh_component.replace(mesh, GeometryOwnershipType::Editable);
   }
   {
     /* Combine mesh and all instances into a single mesh that can be passed to the modifier. */
@@ -948,8 +948,7 @@ static Mesh *modifier_modify_mesh_and_geometry_set(ModifierData *md,
     /* Replace only the mesh rather than the whole component, because the entire #MeshComponent
      * might have been replaced by data from a different object in the node tree, which means the
      * component contains vertex group name data for that object that should not be removed. */
-    mesh_component.replace_mesh_but_keep_vertex_group_names(input_mesh,
-                                                            GeometryOwnershipType::Editable);
+    mesh_component.replace(input_mesh, GeometryOwnershipType::Editable);
 
     /* Let the modifier change the geometry set. */
     mti->modifyGeometrySet(md, &mectx, &geometry_set);
@@ -993,12 +992,6 @@ static void mesh_calc_modifiers(struct Depsgraph *depsgraph,
   /* This geometry set contains the non-mesh data that might be generated by modifiers. */
   GeometrySet geometry_set_final;
 
-  /* Add the initial mesh component, with a copy of the vertex group names from the object,
-   * since they need to be stored in the geometry set for evaluation. */
-  MeshComponent &initial_mesh_component =
-      geometry_set_final.get_component_for_write<MeshComponent>();
-  initial_mesh_component.copy_vertex_group_names_from_object(*ob);
-
   BLI_assert((mesh_input->id.tag & LIB_TAG_COPIED_ON_WRITE_EVAL_RESULT) == 0);
 
   /* Deformed vertex locations array. Deform only modifier need this type of
@@ -1602,12 +1595,6 @@ static void editbmesh_calc_modifiers(struct Depsgraph *depsgraph,
   /* This geometry set contains the non-mesh data that might be generated by modifiers. */
   GeometrySet geometry_set_final;
 
-  /* Add the initial mesh component, with a copy of the vertex group names from the object,
-   * since they need to be stored in the geometry set for evaluation. */
-  MeshComponent &initial_mesh_component =
-      geometry_set_final.get_component_for_write<MeshComponent>();
-  initial_mesh_component.copy_vertex_group_names_from_object(*ob);
-
   /* Deformed vertex locations array. Deform only modifier need this type of
    * float array rather than MVert*. Tracked along with mesh_final as an
    * optimization to avoid copying coordinates back and forth if there are
@@ -1951,8 +1938,7 @@ static void mesh_build_data(struct Depsgraph *depsgraph,
 
   /* Add the final mesh as read-only non-owning component to the geometry set. */
   MeshComponent &mesh_component = geometry_set_eval->get_component_for_write<MeshComponent>();
-  mesh_component.replace_mesh_but_keep_vertex_group_names(mesh_eval,
-                                                          GeometryOwnershipType::ReadOnly);
+  mesh_component.replace(mesh_eval, GeometryOwnershipType::ReadOnly);
   ob->runtime.geometry_set_eval = geometry_set_eval;
 
   ob->runtime.mesh_deform_eval = mesh_deform_eval;
diff --git a/source/blender/blenkernel/intern/armature_deform.c b/source/blender/blenkernel/intern/armature_deform.c
index 0b7ca93a824..5e9259f05bb 100644
--- a/source/blender/blenkernel/intern/armature_deform.c
+++ b/source/blender/blenkernel/intern/armature_deform.c
@@ -486,7 +486,7 @@ static void armature_deform_coords_impl(const Object *ob_arm,
   int defbase_len = 0;   /* safety for vertexgroup index overflow */
   int i, dverts_len = 0; /* safety for vertexgroup overflow */
   bool use_dverts = false;
-  int armature_def_nr;
+  int armature_def_nr = -1;
   int cd_dvert_offset = -1;
 
   /* in editmode, or not an armature */
@@ -501,11 +501,11 @@ static void armature_deform_coords_impl(const Object *ob_arm,
     BLI_assert(0);
   }
 
-  /* get the def_nr for the overall armature vertex group if present */
-  armature_def_nr = BKE_object_defgroup_name_index(ob_target, defgrp_name);
-
   if (ELEM(ob_target->type, OB_MESH, OB_LATTICE, OB_GPENCIL)) {
-    defbase_len = BLI_listbase_count(&ob_target->defbase);
+    /* get the def_nr for the overall armature vertex group if present */
+    armature_def_nr = BKE_object_defgroup_name_index(ob_target, defgrp_name);
+
+    defbase_len = BKE_object_defgroup_count(ob_target);
 
     if (ob_target->type == OB_MESH) {
       if (em_target == NULL) {
@@ -552,7 +552,8 @@ static void armature_deform_coords_impl(const Object *ob_arm,
          *
          * - Check whether keeping this consistent across frames gives speedup.
          */
-        for (i = 0, dg = ob_target->defbase.first; dg; i++, dg = dg->next) {
+        const ListBase *defbase = BKE_object_defgroup_list(ob_target);
+        for (i = 0, dg = defbase->first; dg; i++, dg = dg->next) {
           pchan_from_defbase[i] = BKE_pose_channel_find_name(ob_arm->pose, dg->name);
           /* exclude non-deforming bones */
           if (pchan_from_defbase[i]) {
diff --git a/source/blender/blenkernel/intern/data_transfer.c b/source/blender/blenkernel/intern/data_transfer.c
index aec849ebf59..605061570b8 100644
--- a/source/blender/blenkernel/intern/data_transfer.c
+++ b/source/blender/blenkernel/intern/data_transfer.c
@@ -1437,7 +1437,7 @@ bool BKE_object_data_transfer_ex(struct Depsgraph *depsgraph,
   if (vgroup_name) {
     mdef = CustomData_get_layer(&me_dst->vdata, CD_MDEFORMVERT);
     if (mdef) {
-      vg_idx = BKE_object_defgroup_name_index(ob_dst, vgroup_name);
+      vg_idx = BKE_id_defgroup_name_index(&me_dst->id, vgroup_name);
     }
   }
 
diff --git a/source/blender/blenkernel/intern/deform.c b/source/blender/blenkernel/intern/deform.c
index 19840a70bf0..f7ef84728b6 100644
--- a/source/blender/blenkernel/intern/deform.c
+++ b/source/blender/blenkernel/intern/deform.c
@@ -29,6 +29,8 @@
 
 #include "MEM_guardedalloc.h"
 
+#include "DNA_gpencil_types.h"
+#include "DNA_lattice_types.h"
 #include "DNA_mesh_types.h"
 #include "DNA_meshdata_types.h"
 #include "DNA_object_types.h"
@@ -64,7 +66,9 @@ bDeformGroup *BKE_object_defgroup_new(Object *ob, const char *name)
 
   BLI_strncpy(defgroup->name, name, sizeof(defgroup->name));
 
-  BLI_addtail(&ob->defbase, defgroup);
+  ListBase *defbase = BKE_object_defgroup_list_mutable(ob);
+
+  BLI_addtail(defbase, defgroup);
   BKE_object_defgroup_unique_name(defgroup, ob);
 
   BKE_object_batch_cache_dirty_tag(ob);
@@ -484,18 +488,120 @@ void BKE_defvert_flip_merged(MDeformVert *dvert, const int *flip_map, const int
   }
 }
 
+bool BKE_object_supports_vertex_groups(const Object *ob)
+{
+  const ID *id = (const ID *)ob->data;
+  if (id == NULL) {
+    return false;
+  }
+
+  return ELEM(GS(id->name), ID_ME, ID_LT, ID_GD);
+}
+
+const ListBase *BKE_id_defgroup_list_get(const ID *id)
+{
+  switch (GS(id->name)) {
+    case ID_ME: {
+      const Mesh *me = (const Mesh *)id;
+      return &me->vertex_group_names;
+    }
+    case ID_LT: {
+      const Lattice *lt = (const Lattice *)id;
+      return &lt->vertex_group_names;
+    }
+    case ID_GD: {
+      const bGPdata *gpd = (const bGPdata *)id;
+      return &gpd->vertex_group_names;
+    }
+    default: {
+      BLI_assert_unreachable();
+    }
+  }
+  return NULL;
+}
+
+static const int *object_defgroup_active_index_get_p(const Object *ob)
+{
+  BLI_assert(BKE_object_supports_vertex_groups(ob));
+  switch (ob->type) {
+    case OB_MESH: {
+      const Mesh *mesh = (const Mesh *)ob->data;
+      return &mesh->vertex_group_active_index;
+    }
+    case OB_LATTICE: {
+      const Lattice *lattice = (const Lattice *)ob->data;
+      return &lattice->vertex_group_active_index;
+    }
+    case OB_GPENCIL: {
+      const bGPdata *gpd = (const bGPdata *)ob->data;
+      return &gpd->vertex_group_active_index;
+    }
+  }
+  return NULL;
+}
+
+ListBase *BKE_id_defgroup_list_get_mutable(ID *id)
+{
+  /* Cast away const just for the accessor. */
+  return (ListBase *)BKE_id_defgroup_list_get(id);
+}
+
 bDeformGroup *BKE_object_defgroup_find_name(const Object *ob, const char *name)
 {
-  return (name && name[0] != '\0') ?
-             BLI_findstring(&ob->defbase, name, offsetof(bDeformGroup, name)) :
-             NULL;
+  if (name == NULL || name[0] == '\0') {
+    return NULL;
+  }
+  const ListBase *defbase = BKE_object_defgroup_list(ob);
+  return BLI_findstring(defbase, name, offsetof(bDeformGroup, name));
+}
+
+int BKE_id_defgroup_name_index(const ID *id, const char *name)
+{
+  if (name == NULL || name[0] == '\0') {
+    return -1;
+  }
+  const ListBase *defbase = BKE_id_defgroup_list_get(id);
+  return BLI_findstringindex(defbase, name, offsetof(bDeformGroup, name));
+}
+
+const ListBase *BKE_object_defgroup_list(const Object *ob)
+{
+  BLI_assert(BKE_object_supports_vertex_groups(ob));
+  return BKE_id_defgroup_list_get((const ID *)ob->data);
 }
 
 int BKE_object_defgroup_name_index(const Object *ob, const char *name)
 {
-  return (name && name[0] != '\0') ?
-             BLI_findstringindex(&ob->defbase, name, offsetof(bDeformGroup, name)) :
-             -1;
+  return BKE_id_defgroup_name_index((ID *)ob->data, name);
+}
+
+ListBase *BKE_object_defgroup_list_mutable(Object *ob)
+{
+  BLI_assert(BKE_object_supports_vertex_groups(ob));
+  return BKE_id_defgroup_list_get_mutable((ID *)ob->data);
+}
+
+int BKE_object_defgroup_count(const Object *ob)
+{
+  return BLI_listbase_count(BKE_object_defgroup_list(ob));
+}
+
+/**
+ * \note For historical reasons, the index starts at 1 rather than 0.
+ */
+int BKE_object_defgroup_active_index_get(const Object *ob)
+{
+  return *object_defgroup_active_index_get_p(ob);
+}
+
+/**
+ * \note For historical reasons, the index starts at 1 rather than 0.
+ */
+void BKE_object_defgroup_active_index_set(Object *ob, const int new_index)
+{
+  /* Cast away const just for the accessor. */
+  int *index = (int *)object_defgroup_active_index_get_p(ob);
+  *index = new_index;
 }
 
 /**
@@ -503,7 +609,8 @@ int BKE_object_defgroup_name_index(const Object *ob, const char *name)
  */
 int *BKE_object_defgroup_flip_map(const Object *ob, int *flip_map_len, const bool use_default)
 {
-  int defbase_tot = *flip_map_len = BLI_listbase_count(&ob->defbase);
+  const ListBase *defbase = BKE_object_defgroup_list(ob);
+  int defbase_tot = *flip_map_len = BLI_listbase_count(defbase);
 
   if (defbase_tot == 0) {
     return NULL;
@@ -517,7 +624,7 @@ int *BKE_object_defgroup_flip_map(const Object *ob, int *flip_map_len, const boo
     map[i] = -1;
   }
 
-  for (dg = ob->defbase.first, i = 0; dg; dg = dg->next, i++) {
+  for (dg = defbase->first, i = 0; dg; dg = dg->next, i++) {
     if (map[i] == -1) { /* may be calculated previously */
 
       /* in case no valid value is found, use this */
@@ -547,7 +654,8 @@ int *BKE_object_defgroup_flip_map_single(const Object *ob,
                                          const bool use_default,
                                          int defgroup)
 {
-  int defbase_tot = *flip_map_len = BLI_listbase_count(&ob->defbase);
+  const ListBase *defbase = BKE_object_defgroup_list(ob);
+  int defbase_tot = *flip_map_len = BLI_listbase_count(defbase);
 
   if (defbase_tot == 0) {
     return NULL;
@@ -561,7 +669,7 @@ int *BKE_object_defgroup_flip_map_single(const Object *ob,
     map[i] = use_default ? i : -1;
   }
 
-  dg = BLI_findlink(&ob->defbase, defgroup);
+  dg = BLI_findlink(defbase, defgroup);
 
   BLI_string_flip_side_name(name_flip, dg->name, false, sizeof(name_flip));
   if (!STREQ(name_flip, dg->name)) {
@@ -578,7 +686,8 @@ int *BKE_object_defgroup_flip_map_single(const Object *ob,
 
 int BKE_object_defgroup_flip_index(const Object *ob, int index, const bool use_default)
 {
-  bDeformGroup *dg = BLI_findlink(&ob->defbase, index);
+  const ListBase *defbase = BKE_object_defgroup_list(ob);
+  bDeformGroup *dg = BLI_findlink(defbase, index);
   int flip_index = -1;
 
   if (dg) {
@@ -595,9 +704,10 @@ int BKE_object_defgroup_flip_index(const Object *ob, int index, const bool use_d
 
 static bool defgroup_find_name_dupe(const char *name, bDeformGroup *dg, Object *ob)
 {
+  const ListBase *defbase = BKE_object_defgroup_list(ob);
   bDeformGroup *curdef;
 
-  for (curdef = ob->defbase.first; curdef; curdef = curdef->next) {
+  for (curdef = defbase->first; curdef; curdef = curdef->next) {
     if (dg != curdef) {
       if (STREQ(curdef->name, name)) {
         return true;
@@ -1189,7 +1299,10 @@ static bool data_transfer_layersmapping_vgroups_multisrc_to_dst(ListBase *r_map,
 {
   int idx_src;
   int idx_dst;
-  int tot_dst = BLI_listbase_count(&ob_dst->defbase);
+  const ListBase *src_list = BKE_object_defgroup_list(ob_src);
+  ListBase *dst_defbase = BKE_object_defgroup_list_mutable(ob_dst);
+
+  int tot_dst = BLI_listbase_count(dst_defbase);
 
   const size_t elem_size = sizeof(*((MDeformVert *)NULL));
 
@@ -1218,7 +1331,7 @@ static bool data_transfer_layersmapping_vgroups_multisrc_to_dst(ListBase *r_map,
       }
       else if (use_delete && idx_dst > idx_src) {
         while (idx_dst-- > idx_src) {
-          BKE_object_defgroup_remove(ob_dst, ob_dst->defbase.last);
+          BKE_object_defgroup_remove(ob_dst, dst_defbase->last);
         }
       }
       if (r_map) {
@@ -1255,7 +1368,7 @@ static bool data_transfer_layersmapping_vgroups_multisrc_to_dst(ListBase *r_map,
 
       if (use_delete) {
         /* Remove all unused dst vgroups first, simpler in this case. */
-        for (dg_dst = ob_dst->defbase.first; dg_dst;) {
+        for (dg_dst = dst_defbase->first; dg_dst;) {
           bDeformGroup *dg_dst_next = dg_dst->next;
 
           if (BKE_object_defgroup_name_index(ob_src, dg_dst->name) == -1) {
@@ -1265,7 +1378,7 @@ static bool data_transfer_layersmapping_vgroups_multisrc_to_dst(ListBase *r_map,
         }
       }
 
-      for (idx_src = 0, dg_src = ob_src->defbase.first; idx_src < num_layers_src;
+      for (idx_src = 0, dg_src = src_list->first; idx_src < num_layers_src;
            idx_src++, dg_src = dg_src->next) {
         if (!use_layers_src[idx_src]) {
           continue;
@@ -1274,7 +1387,7 @@ static bool data_transfer_layersmapping_vgroups_multisrc_to_dst(ListBase *r_map,
         if ((idx_dst = BKE_object_defgroup_name_index(ob_dst, dg_src->name)) == -1) {
           if (use_create) {
             BKE_object_defgroup_add_name(ob_dst, dg_src->name);
-            idx_dst = ob_dst->actdef - 1;
+            idx_dst = BKE_object_defgroup_active_index_get(ob_dst) - 1;
           }
           else {
             /* If we are not allowed to create missing dst vgroups, just skip matching src one. */
@@ -1340,8 +1453,12 @@ bool data_transfer_layersmapping_vgroups(ListBase *r_map,
    * This implies we may have to handle data layout itself while having NULL data itself,
    * and even have to support NULL data_src in transfer data code
    * (we always create a data_dst, though).
+   *
+   * Note: Above comment is outdated, but this function was written when that was true.
    */
-  if (BLI_listbase_is_empty(&ob_src->defbase)) {
+
+  const ListBase *src_defbase = BKE_object_defgroup_list(ob_src);
+  if (BLI_listbase_is_empty(src_defbase)) {
     if (use_delete) {
       BKE_object_defgroup_remove_all(ob_dst);
     }
@@ -1361,35 +1478,37 @@ bool data_transfer_layersmapping_vgroups(ListBase *r_map,
 
     if (fromlayers >= 0) {
       idx_src = fromlayers;
-      if (idx_src >= BLI_listbase_count(&ob_src->defbase)) {
+      if (idx_src >= BLI_listbase_count(src_defbase)) {
         /* This can happen when vgroups are removed from source object...
          * Remapping would be really tricky here, we'd need to go over all objects in
          * Main every time we delete a vgroup... for now, simpler and safer to abort. */
         return false;
       }
     }
-    else if ((idx_src = ob_src->actdef - 1) == -1) {
+    else if ((idx_src = BKE_object_defgroup_active_index_get(ob_src) - 1) == -1) {
       return false;
     }
 
     if (tolayers >= 0) {
       /* NOTE: in this case we assume layer exists! */
       idx_dst = tolayers;
-      BLI_assert(idx_dst < BLI_listbase_count(&ob_dst->defbase));
+      const ListBase *dst_defbase = BKE_object_defgroup_list(ob_dst);
+      BLI_assert(idx_dst < BLI_listbase_count(dst_defbase));
+      UNUSED_VARS_NDEBUG(dst_defbase);
     }
     else if (tolayers == DT_LAYERS_ACTIVE_DST) {
-      if ((idx_dst = ob_dst->actdef - 1) == -1) {
+      if ((idx_dst = BKE_object_defgroup_active_index_get(ob_dst) - 1) == -1) {
         bDeformGroup *dg_src;
         if (!use_create) {
           return true;
         }
-        dg_src = BLI_findlink(&ob_src->defbase, idx_src);
+        dg_src = BLI_findlink(src_defbase, idx_src);
         BKE_object_defgroup_add_name(ob_dst, dg_src->name);
-        idx_dst = ob_dst->actdef - 1;
+        idx_dst = BKE_object_defgroup_active_index_get(ob_dst) - 1;
       }
     }
     else if (tolayers == DT_LAYERS_INDEX_DST) {
-      int num = BLI_listbase_count(&ob_src->defbase);
+      int num = BLI_listbase_count(src_defbase);
       idx_dst = idx_src;
       if (num <= idx_dst) {
         if (!use_create) {
@@ -1402,13 +1521,13 @@ bool data_transfer_layersmapping_vgroups(ListBase *r_map,
       }
     }
     else if (tolayers == DT_LAYERS_NAME_DST) {
-      bDeformGroup *dg_src = BLI_findlink(&ob_src->defbase, idx_src);
+      bDeformGroup *dg_src = BLI_findlink(src_defbase, idx_src);
       if ((idx_dst = BKE_object_defgroup_name_index(ob_dst, dg_src->name)) == -1) {
         if (!use_create) {
           return true;
         }
         BKE_object_defgroup_add_name(ob_dst, dg_src->name);
-        idx_dst = ob_dst->actdef - 1;
+        idx_dst = BKE_object_defgroup_active_index_get(ob_dst) - 1;
       }
     }
     else {
@@ -1531,6 +1650,13 @@ void BKE_defvert_weight_to_rgb(float r_rgb[3], const float weight)
 /** \name .blend file I/O
  * \{ */
 
+void BKE_defbase_blend_write(BlendWriter *writer, const ListBase *defbase)
+{
+  LISTBASE_FOREACH (bDeformGroup *, defgroup, defbase) {
+    BLO_write_struct(writer, bDeformGroup, defgroup);
+  }
+}
+
 void BKE_defvert_blend_write(BlendWriter *writer, int count, MDeformVert *dvlist)
 {
   if (dvlist == NULL) {
diff --git a/source/blender/blenkernel/intern/geometry_component_mesh.cc b/source/blender/blenkernel/intern/geometry_component_mesh.cc
index 28e46aab732..af500ab3427 100644
--- a/source/blender/blenkernel/intern/geometry_component_mesh.cc
+++ b/source/blender/blenkernel/intern/geometry_component_mesh.cc
@@ -53,7 +53,6 @@ GeometryComponent *MeshComponent::copy() const
   if (mesh_ != nullptr) {
     new_component->mesh_ = BKE_mesh_copy_for_eval(mesh_, false);
     new_component->ownership_ = GeometryOwnershipType::Owned;
-    new_component->vertex_group_names_ = blender::Map(vertex_group_names_);
   }
   return new_component;
 }
@@ -67,7 +66,6 @@ void MeshComponent::clear()
     }
     mesh_ = nullptr;
   }
-  vertex_group_names_.clear();
 }
 
 bool MeshComponent::has_mesh() const
@@ -84,23 +82,6 @@ void MeshComponent::replace(Mesh *mesh, GeometryOwnershipType ownership)
   ownership_ = ownership;
 }
 
-/* This function exists for the same reason as #vertex_group_names_. Non-nodes modifiers need to
- * be able to replace the mesh data without losing the vertex group names, which may have come
- * from another object. */
-void MeshComponent::replace_mesh_but_keep_vertex_group_names(Mesh *mesh,
-                                                             GeometryOwnershipType ownership)
-{
-  BLI_assert(this->is_mutable());
-  if (mesh_ != nullptr) {
-    if (ownership_ == GeometryOwnershipType::Owned) {
-      BKE_id_free(nullptr, mesh_);
-    }
-    mesh_ = nullptr;
-  }
-  mesh_ = mesh;
-  ownership_ = ownership;
-}
-
 /* Return the mesh and clear the component. The caller takes over responsibility for freeing the
  * mesh (if the component was responsible before). */
 Mesh *MeshComponent::release()
@@ -111,28 +92,6 @@ Mesh *MeshComponent::release()
   return mesh;
 }
 
-void MeshComponent::copy_vertex_group_names_from_object(const Object &object)
-{
-  BLI_assert(this->is_mutable());
-  vertex_group_names_.clear();
-  int index = 0;
-  LISTBASE_FOREACH (const bDeformGroup *, group, &object.defbase) {
-    vertex_group_names_.add(group->name, index);
-    index++;
-  }
-}
-
-const blender::Map<std::string, int> &MeshComponent::vertex_group_names() const
-{
-  return vertex_group_names_;
-}
-
-/* This is only exposed for the internal attribute API. */
-blender::Map<std::string, int> &MeshComponent::vertex_group_names()
-{
-  return vertex_group_names_;
-}
-
 /* Get the mesh from this component. This method can be used by multiple threads at the same
  * time. Therefore, the returned mesh should not be modified. No ownership is transferred. */
 const Mesh *MeshComponent::get_for_read() const
@@ -864,8 +823,8 @@ class VertexGroupsAttributeProvider final : public DynamicAttributesProvider {
     BLI_assert(component.type() == GEO_COMPONENT_TYPE_MESH);
     const MeshComponent &mesh_component = static_cast<const MeshComponent &>(component);
     const Mesh *mesh = mesh_component.get_for_read();
-    const int vertex_group_index = mesh_component.vertex_group_names().lookup_default_as(
-        attribute_name, -1);
+    const int vertex_group_index = BLI_findstringindex(
+        &mesh->vertex_group_names, attribute_name.data(), offsetof(bDeformGroup, name));
     if (vertex_group_index < 0) {
       return {};
     }
@@ -889,8 +848,9 @@ class VertexGroupsAttributeProvider final : public DynamicAttributesProvider {
     if (mesh == nullptr) {
       return {};
     }
-    const int vertex_group_index = mesh_component.vertex_group_names().lookup_default_as(
-        attribute_name, -1);
+
+    const int vertex_group_index = BLI_findstringindex(
+        &mesh->vertex_group_names, attribute_name.data(), offsetof(bDeformGroup, name));
     if (vertex_group_index < 0) {
       return {};
     }
@@ -913,13 +873,13 @@ class VertexGroupsAttributeProvider final : public DynamicAttributesProvider {
   {
     BLI_assert(component.type() == GEO_COMPONENT_TYPE_MESH);
     MeshComponent &mesh_component = static_cast<MeshComponent &>(component);
+    Mesh *mesh = mesh_component.get_for_write();
 
-    const int vertex_group_index = mesh_component.vertex_group_names().pop_default_as(
-        attribute_name, -1);
+    const int vertex_group_index = BLI_findstringindex(
+        &mesh->vertex_group_names, attribute_name.data(), offsetof(bDeformGroup, name));
     if (vertex_group_index < 0) {
       return false;
     }
-    Mesh *mesh = mesh_component.get_for_write();
     if (mesh == nullptr) {
       return true;
     }
@@ -938,14 +898,14 @@ class VertexGroupsAttributeProvider final : public DynamicAttributesProvider {
   {
     BLI_assert(component.type() == GEO_COMPONENT_TYPE_MESH);
     const MeshComponent &mesh_component = static_cast<const MeshComponent &>(component);
-    for (const auto item : mesh_component.vertex_group_names().items()) {
-      const StringRefNull name = item.key;
-      const int vertex_group_index = item.value;
-      if (vertex_group_index >= 0) {
-        AttributeMetaData meta_data{ATTR_DOMAIN_POINT, CD_PROP_FLOAT};
-        if (!callback(name, meta_data)) {
-          return false;
-        }
+    const Mesh *mesh = mesh_component.get_for_read();
+    if (mesh == nullptr) {
+      return true;
+    }
+
+    LISTBASE_FOREACH (const bDeformGroup *, group, &mesh->vertex_group_names) {
+      if (!callback(group->name, {ATTR_DOMAIN_POINT, CD_PROP_FLOAT})) {
+        return false;
       }
     }
     return true;
diff --git a/source/blender/blenkernel/intern/geometry_set_instances.cc b/source/blender/blenkernel/intern/geometry_set_instances.cc
index 01b51d552a9..47c8df03375 100644
--- a/source/blender/blenkernel/intern/geometry_set_instances.cc
+++ b/source/blender/blenkernel/intern/geometry_set_instances.cc
@@ -48,7 +48,6 @@ static void add_final_mesh_as_geometry_component(const Object &object, GeometryS
 
     MeshComponent &mesh_component = geometry_set.get_component_for_write<MeshComponent>();
     mesh_component.replace(mesh, GeometryOwnershipType::ReadOnly);
-    mesh_component.copy_vertex_group_names_from_object(object);
   }
 }
 
diff --git a/source/blender/blenkernel/intern/gpencil.c b/source/blender/blenkernel/intern/gpencil.c
index 647db970d09..529096b8523 100644
--- a/source/blender/blenkernel/intern/gpencil.c
+++ b/source/blender/blenkernel/intern/gpencil.c
@@ -87,6 +87,8 @@ static void greasepencil_copy_data(Main *UNUSED(bmain),
     gpd_dst->mat = MEM_dupallocN(gpd_src->mat);
   }
 
+  BKE_defgroup_copy_list(&gpd_dst->vertex_group_names, &gpd_src->vertex_group_names);
+
   /* copy layers */
   BLI_listbase_clear(&gpd_dst->layers);
   LISTBASE_FOREACH (bGPDlayer *, gpl_src, &gpd_src->layers) {
@@ -165,6 +167,8 @@ static void greasepencil_blend_write(BlendWriter *writer, ID *id, const void *id
       BKE_animdata_blend_write(writer, gpd->adt);
     }
 
+    BKE_defbase_blend_write(writer, &gpd->vertex_group_names);
+
     BLO_write_pointer_array(writer, gpd->totcol, gpd->mat);
 
     /* write grease-pencil layers to file */
@@ -227,6 +231,8 @@ void BKE_gpencil_blend_read_data(BlendDataReader *reader, bGPdata *gpd)
     }
   }
 
+  BLO_read_list(reader, &gpd->vertex_group_names);
+
   /* Materials. */
   BLO_read_pointer_array(reader, (void **)&gpd->mat);
 
@@ -498,6 +504,8 @@ void BKE_gpencil_free(bGPdata *gpd, bool free_all)
   /* materials */
   MEM_SAFE_FREE(gpd->mat);
 
+  BLI_freelistN(&gpd->vertex_group_names);
+
   /* free all data */
   if (free_all) {
     /* clear cache */
@@ -2087,8 +2095,9 @@ void BKE_gpencil_vgroup_remove(Object *ob, bDeformGroup *defgroup)
 {
   bGPdata *gpd = ob->data;
   MDeformVert *dvert = NULL;
-  const int def_nr = BLI_findindex(&ob->defbase, defgroup);
-  const int totgrp = BLI_listbase_count(&ob->defbase);
+
+  const int def_nr = BLI_findindex(&gpd->vertex_group_names, defgroup);
+  const int totgrp = BLI_listbase_count(&gpd->vertex_group_names);
 
   /* Remove points data */
   if (gpd) {
@@ -2117,7 +2126,7 @@ void BKE_gpencil_vgroup_remove(Object *ob, bDeformGroup *defgroup)
   }
 
   /* Remove the group */
-  BLI_freelinkN(&ob->defbase, defgroup);
+  BLI_freelinkN(&gpd->vertex_group_names, defgroup);
   DEG_id_tag_update(&gpd->id, ID_RECALC_TRANSFORM | ID_RECALC_GEOMETRY);
 }
 
diff --git a/source/blender/blenkernel/intern/key.c b/source/blender/blenkernel/intern/key.c
index 6cc90f86b4a..52f888d9543 100644
--- a/source/blender/blenkernel/intern/key.c
+++ b/source/blender/blenkernel/intern/key.c
@@ -1317,7 +1317,7 @@ static float *get_weights_array(Object *ob, char *vgroup, WeightsArrayCache *cac
 
     if (cache) {
       if (cache->defgroup_weights == NULL) {
-        int num_defgroup = BLI_listbase_count(&ob->defbase);
+        int num_defgroup = BKE_object_defgroup_count(ob);
         cache->defgroup_weights = MEM_callocN(sizeof(*cache->defgroup_weights) * num_defgroup,
                                               "cached defgroup weights");
         cache->num_defgroup_weights = num_defgroup;
diff --git a/source/blender/blenkernel/intern/lattice.c b/source/blender/blenkernel/intern/lattice.c
index 1357424d5ff..9875d776d33 100644
--- a/source/blender/blenkernel/intern/lattice.c
+++ b/source/blender/blenkernel/intern/lattice.c
@@ -87,6 +87,8 @@ static void lattice_copy_data(Main *bmain, ID *id_dst, const ID *id_src, const i
     lattice_dst->key->from = &lattice_dst->id;
   }
 
+  BKE_defgroup_copy_list(&lattice_dst->vertex_group_names, &lattice_src->vertex_group_names);
+
   if (lattice_src->dvert) {
     int tot = lattice_src->pntsu * lattice_src->pntsv * lattice_src->pntsw;
     lattice_dst->dvert = MEM_mallocN(sizeof(MDeformVert) * tot, "Lattice MDeformVert");
@@ -103,6 +105,8 @@ static void lattice_free_data(ID *id)
 
   BKE_lattice_batch_cache_free(lattice);
 
+  BLI_freelistN(&lattice->vertex_group_names);
+
   MEM_SAFE_FREE(lattice->def);
   if (lattice->dvert) {
     BKE_defvert_array_free(lattice->dvert, lattice->pntsu * lattice->pntsv * lattice->pntsw);
@@ -150,6 +154,7 @@ static void lattice_blend_write(BlendWriter *writer, ID *id, const void *id_addr
     /* direct data */
     BLO_write_struct_array(writer, BPoint, lt->pntsu * lt->pntsv * lt->pntsw, lt->def);
 
+    BKE_defbase_blend_write(writer, &lt->vertex_group_names);
     BKE_defvert_blend_write(writer, lt->pntsu * lt->pntsv * lt->pntsw, lt->dvert);
   }
 }
@@ -161,6 +166,7 @@ static void lattice_blend_read_data(BlendDataReader *reader, ID *id)
 
   BLO_read_data_address(reader, &lt->dvert);
   BKE_defvert_blend_read(reader, lt->pntsu * lt->pntsv * lt->pntsw, lt->dvert);
+  BLO_read_list(reader, &lt->vertex_group_names);
 
   lt->editlatt = NULL;
   lt->batch_cache = NULL;
diff --git a/source/blender/blenkernel/intern/lattice_deform.c b/source/blender/blenkernel/intern/lattice_deform.c
index bd1972e9f1f..f9437eeaffa 100644
--- a/source/blender/blenkernel/intern/lattice_deform.c
+++ b/source/blender/blenkernel/intern/lattice_deform.c
@@ -112,7 +112,7 @@ LatticeDeformData *BKE_lattice_deform_data_create(const Object *oblatt, const Ob
   int defgrp_index = -1;
   const MDeformVert *dvert = BKE_lattice_deform_verts_get(oblatt);
   if (lt->vgroup[0] && dvert) {
-    defgrp_index = BKE_object_defgroup_name_index(oblatt, lt->vgroup);
+    defgrp_index = BKE_id_defgroup_name_index(&lt->id, lt->vgroup);
 
     if (defgrp_index != -1) {
       lattice_weights = MEM_malloc_arrayN(sizeof(float), num_points, "lattice_weights");
@@ -364,7 +364,7 @@ static void lattice_deform_coords_impl(const Object *ob_lattice,
    * We want either a Mesh/Lattice with no derived data, or derived data with deformverts.
    */
   if (defgrp_name && defgrp_name[0] && ob_target && ELEM(ob_target->type, OB_MESH, OB_LATTICE)) {
-    defgrp_index = BKE_object_defgroup_name_index(ob_target, defgrp_name);
+    defgrp_index = BKE_id_defgroup_name_index((ID *)ob_target->data, defgrp_name);
 
     if (defgrp_index != -1) {
       /* if there's derived data without deformverts, don't use vgroups */
diff --git a/source/blender/blenkernel/intern/mesh.c b/source/blender/blenkernel/intern/mesh.c
index a92401d3ba0..c4186ad3180 100644
--- a/source/blender/blenkernel/intern/mesh.c
+++ b/source/blender/blenkernel/intern/mesh.c
@@ -39,6 +39,7 @@
 #include "BLI_ghash.h"
 #include "BLI_hash.h"
 #include "BLI_linklist.h"
+#include "BLI_listbase.h"
 #include "BLI_math.h"
 #include "BLI_memarena.h"
 #include "BLI_string.h"
@@ -125,6 +126,8 @@ static void mesh_copy_data(Main *bmain, ID *id_dst, const ID *id_src, const int
 
   mesh_dst->mat = MEM_dupallocN(mesh_src->mat);
 
+  BKE_defgroup_copy_list(&mesh_dst->vertex_group_names, &mesh_src->vertex_group_names);
+
   const eCDAllocType alloc_type = (flag & LIB_ID_COPY_CD_REFERENCE) ? CD_REFERENCE : CD_DUPLICATE;
   CustomData_copy(&mesh_src->vdata, &mesh_dst->vdata, mask.vmask, alloc_type, mesh_dst->totvert);
   CustomData_copy(&mesh_src->edata, &mesh_dst->edata, mask.emask, alloc_type, mesh_dst->totedge);
@@ -155,6 +158,8 @@ static void mesh_free_data(ID *id)
 {
   Mesh *mesh = (Mesh *)id;
 
+  BLI_freelistN(&mesh->vertex_group_names);
+
   BKE_mesh_runtime_clear_cache(mesh);
   mesh_clear_geometry(mesh);
   MEM_SAFE_FREE(mesh->mat);
@@ -229,6 +234,8 @@ static void mesh_blend_write(BlendWriter *writer, ID *id, const void *id_address
       BKE_animdata_blend_write(writer, mesh->adt);
     }
 
+    BKE_defbase_blend_write(writer, &mesh->vertex_group_names);
+
     BLO_write_pointer_array(writer, mesh->totcol, mesh->mat);
     BLO_write_raw(writer, sizeof(MSelect) * mesh->totselect, mesh->mselect);
 
@@ -288,6 +295,7 @@ static void mesh_blend_read_data(BlendDataReader *reader, ID *id)
   /* Normally BKE_defvert_blend_read should be called in CustomData_blend_read,
    * but for backwards compatibility in do_versions to work we do it here. */
   BKE_defvert_blend_read(reader, mesh->totvert, mesh->dvert);
+  BLO_read_list(reader, &mesh->vertex_group_names);
 
   CustomData_blend_read(reader, &mesh->vdata, mesh->totvert);
   CustomData_blend_read(reader, &mesh->edata, mesh->totedge);
@@ -923,6 +931,12 @@ void BKE_mesh_copy_parameters(Mesh *me_dst, const Mesh *me_src)
   me_dst->texflag = me_src->texflag;
   copy_v3_v3(me_dst->loc, me_src->loc);
   copy_v3_v3(me_dst->size, me_src->size);
+
+  /* Some callers call this on existing meshes, so free the existing vertex groups first. */
+  BLI_freelistN(&me_dst->vertex_group_names);
+  BKE_defgroup_copy_list(&me_dst->vertex_group_names, &me_src->vertex_group_names);
+
+  me_dst->vertex_group_active_index = me_src->vertex_group_active_index;
 }
 
 /**
diff --git a/source/blender/blenkernel/intern/object.c b/source/blender/blenkernel/intern/object.c
index d8b9b851865..912b5e0a0dd 100644
--- a/source/blender/blenkernel/intern/object.c
+++ b/source/blender/blenkernel/intern/object.c
@@ -234,7 +234,7 @@ static void object_copy_data(Main *bmain, ID *id_dst, const ID *id_src, const in
       BKE_pose_rebuild(bmain, ob_dst, ob_dst->data, do_pose_id_user);
     }
   }
-  BKE_defgroup_copy_list(&ob_dst->defbase, &ob_src->defbase);
+
   BKE_object_facemap_copy_list(&ob_dst->fmaps, &ob_src->fmaps);
   BKE_constraints_copy_ex(&ob_dst->constraints, &ob_src->constraints, flag_subdata, true);
 
@@ -285,7 +285,6 @@ static void object_free_data(ID *id)
   MEM_SAFE_FREE(ob->iuser);
   MEM_SAFE_FREE(ob->runtime.bb);
 
-  BLI_freelistN(&ob->defbase);
   BLI_freelistN(&ob->fmaps);
   if (ob->pose) {
     BKE_pose_free_ex(ob->pose, false);
@@ -510,13 +509,6 @@ static void object_foreach_id(ID *id, LibraryForeachIDData *data)
   }
 }
 
-static void write_defgroups(BlendWriter *writer, ListBase *defbase)
-{
-  LISTBASE_FOREACH (bDeformGroup *, defgroup, defbase) {
-    BLO_write_struct(writer, bDeformGroup, defgroup);
-  }
-}
-
 static void write_fmaps(BlendWriter *writer, ListBase *fbase)
 {
   LISTBASE_FOREACH (bFaceMap *, fmap, fbase) {
@@ -561,7 +553,6 @@ static void object_blend_write(BlendWriter *writer, ID *id, const void *id_addre
     }
 
     BKE_pose_blend_write(writer, ob->pose, arm);
-    write_defgroups(writer, &ob->defbase);
     write_fmaps(writer, &ob->fmaps);
     BKE_constraint_blend_write(writer, &ob->constraints);
     animviz_motionpath_blend_write(writer, ob->mpath);
@@ -644,7 +635,9 @@ static void object_blend_read_data(BlendDataReader *reader, ID *id)
     animviz_motionpath_blend_read_data(reader, ob->mpath);
   }
 
+  /* Only for versioning, vertex group names are now stored on object data. */
   BLO_read_list(reader, &ob->defbase);
+
   BLO_read_list(reader, &ob->fmaps);
   /* XXX deprecated - old animation system <<< */
   direct_link_nlastrips(reader, &ob->nlastrips);
@@ -2901,9 +2894,6 @@ void BKE_object_make_proxy(Main *bmain, Object *ob, Object *target, Object *cob)
   ob->data = target->data;
   id_us_plus((ID *)ob->data); /* ensures lib data becomes LIB_TAG_EXTERN */
 
-  /* copy vertex groups */
-  BKE_defgroup_copy_list(&ob->defbase, &target->defbase);
-
   /* copy material and index information */
   ob->actcol = ob->totcol = 0;
   if (ob->mat) {
diff --git a/source/blender/blenkernel/intern/object_deform.c b/source/blender/blenkernel/intern/object_deform.c
index 1e7624d0d7d..c69326a23c6 100644
--- a/source/blender/blenkernel/intern/object_deform.c
+++ b/source/blender/blenkernel/intern/object_deform.c
@@ -33,6 +33,7 @@
 #include "DNA_armature_types.h"
 #include "DNA_cloth_types.h"
 #include "DNA_curve_types.h"
+#include "DNA_gpencil_types.h"
 #include "DNA_lattice_types.h"
 #include "DNA_mesh_types.h"
 #include "DNA_meshdata_types.h"
@@ -123,8 +124,7 @@ bDeformGroup *BKE_object_defgroup_add_name(Object *ob, const char *name)
   }
 
   defgroup = BKE_object_defgroup_new(ob, name);
-
-  ob->actdef = BLI_listbase_count(&ob->defbase);
+  BKE_object_defgroup_active_index_set(ob, BKE_object_defgroup_count(ob));
 
   return defgroup;
 }
@@ -171,7 +171,8 @@ MDeformVert *BKE_object_defgroup_data_create(ID *id)
 bool BKE_object_defgroup_clear(Object *ob, bDeformGroup *dg, const bool use_selection)
 {
   MDeformVert *dv;
-  const int def_nr = BLI_findindex(&ob->defbase, dg);
+  const ListBase *defbase = BKE_object_defgroup_list(ob);
+  const int def_nr = BLI_findindex(defbase, dg);
   bool changed = false;
 
   if (ob->type == OB_MESH) {
@@ -249,7 +250,9 @@ bool BKE_object_defgroup_clear_all(Object *ob, const bool use_selection)
   bDeformGroup *dg;
   bool changed = false;
 
-  for (dg = ob->defbase.first; dg; dg = dg->next) {
+  const ListBase *defbase = BKE_object_defgroup_list(ob);
+
+  for (dg = defbase->first; dg; dg = dg->next) {
     if (BKE_object_defgroup_clear(ob, dg, use_selection)) {
       changed = true;
     }
@@ -265,7 +268,7 @@ bool BKE_object_defgroup_clear_all(Object *ob, const bool use_selection)
 
 static void object_defgroup_remove_update_users(Object *ob, const int idx)
 {
-  int i, defbase_tot = BLI_listbase_count(&ob->defbase) + 1;
+  int i, defbase_tot = BKE_object_defgroup_count(ob) + 1;
   int *map = MEM_mallocN(sizeof(int) * defbase_tot, "vgroup del");
 
   map[idx] = map[0] = 0;
@@ -285,15 +288,18 @@ static void object_defgroup_remove_common(Object *ob, bDeformGroup *dg, const in
   object_defgroup_remove_update_users(ob, def_nr + 1);
 
   /* Remove the group */
-  BLI_freelinkN(&ob->defbase, dg);
+  ListBase *defbase = BKE_object_defgroup_list_mutable(ob);
+
+  BLI_freelinkN(defbase, dg);
 
   /* Update the active deform index if necessary */
-  if (ob->actdef > def_nr) {
-    ob->actdef--;
+  const int active_index = BKE_object_defgroup_active_index_get(ob);
+  if (active_index > def_nr) {
+    BKE_object_defgroup_active_index_set(ob, active_index - 1);
   }
 
   /* remove all dverts */
-  if (BLI_listbase_is_empty(&ob->defbase)) {
+  if (BLI_listbase_is_empty(defbase)) {
     if (ob->type == OB_MESH) {
       Mesh *me = ob->data;
       CustomData_free_layer_active(&me->vdata, CD_MDEFORMVERT, me->totvert);
@@ -307,8 +313,9 @@ static void object_defgroup_remove_common(Object *ob, bDeformGroup *dg, const in
       }
     }
   }
-  else if (ob->actdef < 1) { /* Keep a valid active index if we still have some vgroups. */
-    ob->actdef = 1;
+  else if (BKE_object_defgroup_active_index_get(ob) < 1) {
+    /* Keep a valid active index if we still have some vgroups. */
+    BKE_object_defgroup_active_index_set(ob, 1);
   }
 }
 
@@ -316,7 +323,9 @@ static void object_defgroup_remove_object_mode(Object *ob, bDeformGroup *dg)
 {
   MDeformVert *dvert_array = NULL;
   int dvert_tot = 0;
-  const int def_nr = BLI_findindex(&ob->defbase, dg);
+  const ListBase *defbase = BKE_object_defgroup_list(ob);
+
+  const int def_nr = BLI_findindex(defbase, dg);
 
   BLI_assert(def_nr != -1);
 
@@ -347,7 +356,8 @@ static void object_defgroup_remove_object_mode(Object *ob, bDeformGroup *dg)
 static void object_defgroup_remove_edit_mode(Object *ob, bDeformGroup *dg)
 {
   int i;
-  const int def_nr = BLI_findindex(&ob->defbase, dg);
+  const ListBase *defbase = BKE_object_defgroup_list(ob);
+  const int def_nr = BLI_findindex(defbase, dg);
 
   BLI_assert(def_nr != -1);
 
@@ -425,7 +435,9 @@ void BKE_object_defgroup_remove(Object *ob, bDeformGroup *defgroup)
  */
 void BKE_object_defgroup_remove_all_ex(struct Object *ob, bool only_unlocked)
 {
-  bDeformGroup *dg = (bDeformGroup *)ob->defbase.first;
+  ListBase *defbase = BKE_object_defgroup_list_mutable(ob);
+
+  bDeformGroup *dg = (bDeformGroup *)defbase->first;
   const bool edit_mode = BKE_object_is_in_editmode_vgroup(ob);
 
   if (dg) {
@@ -444,7 +456,7 @@ void BKE_object_defgroup_remove_all_ex(struct Object *ob, bool only_unlocked)
       dg = next_dg;
     }
   }
-  else { /* ob->defbase is empty... */
+  else { /* defbase is empty... */
     /* remove all dverts */
     if (ob->type == OB_MESH) {
       Mesh *me = ob->data;
@@ -459,7 +471,7 @@ void BKE_object_defgroup_remove_all_ex(struct Object *ob, bool only_unlocked)
       }
     }
     /* Fix counters/indices */
-    ob->actdef = 0;
+    BKE_object_defgroup_active_index_set(ob, 0);
   }
 }
 
@@ -478,20 +490,23 @@ void BKE_object_defgroup_remove_all(struct Object *ob)
  */
 int *BKE_object_defgroup_index_map_create(Object *ob_src, Object *ob_dst, int *r_map_len)
 {
+  const ListBase *src_defbase = BKE_object_defgroup_list(ob_src);
+  const ListBase *dst_defbase = BKE_object_defgroup_list(ob_dst);
+
   /* Build src to merged mapping of vgroup indices. */
-  if (BLI_listbase_is_empty(&ob_src->defbase) || BLI_listbase_is_empty(&ob_dst->defbase)) {
+  if (BLI_listbase_is_empty(src_defbase) || BLI_listbase_is_empty(dst_defbase)) {
     *r_map_len = 0;
     return NULL;
   }
 
   bDeformGroup *dg_src;
-  *r_map_len = BLI_listbase_count(&ob_src->defbase);
+  *r_map_len = BLI_listbase_count(src_defbase);
   int *vgroup_index_map = MEM_malloc_arrayN(
       *r_map_len, sizeof(*vgroup_index_map), "defgroup index map create");
   bool is_vgroup_remap_needed = false;
   int i;
 
-  for (dg_src = ob_src->defbase.first, i = 0; dg_src; dg_src = dg_src->next, i++) {
+  for (dg_src = src_defbase->first, i = 0; dg_src; dg_src = dg_src->next, i++) {
     vgroup_index_map[i] = BKE_object_defgroup_name_index(ob_dst, dg_src->name);
     is_vgroup_remap_needed = is_vgroup_remap_needed || (vgroup_index_map[i] != i);
   }
@@ -576,17 +591,17 @@ bool BKE_object_defgroup_array_get(ID *id, MDeformVert **dvert_arr, int *dvert_t
 
 /**
  * gets the status of "flag" for each bDeformGroup
- * in ob->defbase and returns an array containing them
+ * in the object data's vertex group list and returns an array containing them
  */
 bool *BKE_object_defgroup_lock_flags_get(Object *ob, const int defbase_tot)
 {
   bool is_locked = false;
   int i;
-  // int defbase_tot = BLI_listbase_count(&ob->defbase);
+  ListBase *defbase = BKE_object_defgroup_list_mutable(ob);
   bool *lock_flags = MEM_mallocN(defbase_tot * sizeof(bool), "defflags");
   bDeformGroup *defgroup;
 
-  for (i = 0, defgroup = ob->defbase.first; i < defbase_tot && defgroup;
+  for (i = 0, defgroup = defbase->first; i < defbase_tot && defgroup;
        defgroup = defgroup->next, i++) {
     lock_flags[i] = ((defgroup->flag & DG_LOCK_WEIGHT) != 0);
     is_locked |= lock_flags[i];
@@ -606,17 +621,17 @@ bool *BKE_object_defgroup_validmap_get(Object *ob, const int defbase_tot)
   bool *defgroup_validmap;
   GHash *gh;
   int i, step1 = 1;
-  // int defbase_tot = BLI_listbase_count(&ob->defbase);
+  const ListBase *defbase = BKE_object_defgroup_list(ob);
   VirtualModifierData virtualModifierData;
 
-  if (BLI_listbase_is_empty(&ob->defbase)) {
+  if (BLI_listbase_is_empty(defbase)) {
     return NULL;
   }
 
   gh = BLI_ghash_str_new_ex(__func__, defbase_tot);
 
   /* add all names to a hash table */
-  for (dg = ob->defbase.first; dg; dg = dg->next) {
+  for (dg = defbase->first; dg; dg = dg->next) {
     BLI_ghash_insert(gh, dg->name, NULL);
   }
 
@@ -655,7 +670,7 @@ bool *BKE_object_defgroup_validmap_get(Object *ob, const int defbase_tot)
   defgroup_validmap = MEM_mallocN(sizeof(*defgroup_validmap) * defbase_tot, "wpaint valid map");
 
   /* add all names to a hash table */
-  for (dg = ob->defbase.first, i = 0; dg; dg = dg->next, i++) {
+  for (dg = defbase->first, i = 0; dg; dg = dg->next, i++) {
     defgroup_validmap[i] = (BLI_ghash_lookup(gh, dg->name) != NULL);
   }
 
@@ -676,9 +691,11 @@ bool *BKE_object_defgroup_selected_get(Object *ob, int defbase_tot, int *r_dg_fl
   Object *armob = BKE_object_pose_armature_get(ob);
   (*r_dg_flags_sel_tot) = 0;
 
+  const ListBase *defbase = BKE_object_defgroup_list(ob);
+
   if (armob) {
     bPose *pose = armob->pose;
-    for (i = 0, defgroup = ob->defbase.first; i < defbase_tot && defgroup;
+    for (i = 0, defgroup = defbase->first; i < defbase_tot && defgroup;
          defgroup = defgroup->next, i++) {
       bPoseChannel *pchan = BKE_pose_channel_find_name(pose, defgroup->name);
       if (pchan && (pchan->bone->flag & BONE_SELECTED)) {
@@ -774,11 +791,13 @@ void BKE_object_defgroup_mirror_selection(struct Object *ob,
                                           bool *dg_flags_sel,
                                           int *r_dg_flags_sel_tot)
 {
+  const ListBase *defbase = BKE_object_defgroup_list(ob);
+
   bDeformGroup *defgroup;
   unsigned int i;
   int i_mirr;
 
-  for (i = 0, defgroup = ob->defbase.first; i < defbase_tot && defgroup;
+  for (i = 0, defgroup = defbase->first; i < defbase_tot && defgroup;
        defgroup = defgroup->next, i++) {
     if (dg_selection[i]) {
       char name_flip[MAXBONENAME];
@@ -804,11 +823,12 @@ bool *BKE_object_defgroup_subset_from_select_type(Object *ob,
                                                   int *r_subset_count)
 {
   bool *defgroup_validmap = NULL;
-  *r_defgroup_tot = BLI_listbase_count(&ob->defbase);
+
+  *r_defgroup_tot = BKE_object_defgroup_count(ob);
 
   switch (subset_type) {
     case WT_VGROUP_ACTIVE: {
-      const int def_nr_active = ob->actdef - 1;
+      const int def_nr_active = BKE_object_defgroup_active_index_get(ob) - 1;
       defgroup_validmap = MEM_mallocN(*r_defgroup_tot * sizeof(*defgroup_validmap), __func__);
       memset(defgroup_validmap, false, *r_defgroup_tot * sizeof(*defgroup_validmap));
       if ((def_nr_active >= 0) && (def_nr_active < *r_defgroup_tot)) {
diff --git a/source/blender/blenkernel/intern/softbody.c b/source/blender/blenkernel/intern/softbody.c
index c01ca0c617c..e4e2ed94b41 100644
--- a/source/blender/blenkernel/intern/softbody.c
+++ b/source/blender/blenkernel/intern/softbody.c
@@ -2704,8 +2704,8 @@ static void mesh_to_softbody(Object *ob)
   bp = sb->bpoint;
 
   defgroup_index = me->dvert ? (sb->vertgroup - 1) : -1;
-  defgroup_index_mass = me->dvert ? BKE_object_defgroup_name_index(ob, sb->namedVG_Mass) : -1;
-  defgroup_index_spring = me->dvert ? BKE_object_defgroup_name_index(ob, sb->namedVG_Spring_K) :
+  defgroup_index_mass = me->dvert ? BKE_id_defgroup_name_index(&me->id, sb->namedVG_Mass) : -1;
+  defgroup_index_spring = me->dvert ? BKE_id_defgroup_name_index(&me->id, sb->namedVG_Spring_K) :
                                       -1;
 
   for (a = 0; a < me->totvert; a++, bp++) {
@@ -2934,8 +2934,8 @@ static void lattice_to_softbody(Object *ob)
   bp = sb->bpoint;
 
   defgroup_index = lt->dvert ? (sb->vertgroup - 1) : -1;
-  defgroup_index_mass = lt->dvert ? BKE_object_defgroup_name_index(ob, sb->namedVG_Mass) : -1;
-  defgroup_index_spring = lt->dvert ? BKE_object_defgroup_name_index(ob, sb->namedVG_Spring_K) :
+  defgroup_index_mass = lt->dvert ? BKE_id_defgroup_name_index(&lt->id, sb->namedVG_Mass) : -1;
+  defgroup_index_spring = lt->dvert ? BKE_id_defgroup_name_index(&lt->id, sb->namedVG_Spring_K) :
                                       -1;
 
   /* same code used as for mesh vertices */