text: /*
   * This program is free software; you can redistribute it and/or
   * modify it under the terms of the GNU General Public License
   * as published by the Free Software Foundation; either version 2
   * of the License, or (at your option) any later version.
   *
   * This program is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   * GNU General Public License for more details.
   *
   * You should have received a copy of the GNU General Public License
   * along with this program; if not, write to the Free Software  Foundation,
   * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
   *
   * The Original Code is Copyright (C) 2006 by Nicholas Bishop
   * All rights reserved.
   * Implements the Sculpt Mode tools
   */
  
  /** \file
   * \ingroup edsculpt
   */
  
  #include <stddef.h>
  
  #include "MEM_guardedalloc.h"
  
  #include "BLI_math.h"
  #include "BLI_utildefines.h"
  #include "BLI_string.h"
  #include "BLI_listbase.h"
  #include "BLI_ghash.h"
  #include "BLI_task.h"
  #include "BLI_threads.h"
  
  #include "DNA_meshdata_types.h"
  #include "DNA_object_types.h"
  #include "DNA_scene_types.h"
  #include "DNA_mesh_types.h"
  #include "DNA_screen_types.h"
  
  #include "BKE_ccg.h"
  #include "BKE_context.h"
  #include "BKE_customdata.h"
  #include "BKE_multires.h"
  #include "BKE_paint.h"
  #include "BKE_key.h"
  #include "BKE_mesh.h"
  #include "BKE_scene.h"
  #include "BKE_subsurf.h"
  #include "BKE_subdiv_ccg.h"
  #include "BKE_undo_system.h"
  #include "BKE_global.h"
  #include "BKE_main.h"
  
  #include "DEG_depsgraph.h"
  
  #include "WM_api.h"
  #include "WM_types.h"
  
  #include "ED_object.h"
  #include "ED_sculpt.h"
  #include "ED_undo.h"
  
  #include "bmesh.h"
  #include "sculpt_intern.h"
  
  typedef struct UndoSculpt {
    ListBase nodes;
  
    size_t undo_size;
  } UndoSculpt;
  
  static UndoSculpt *sculpt_undo_get_nodes(void);
  
  static void update_cb(PBVHNode *node, void *rebuild)
  {
    BKE_pbvh_node_mark_update(node);
    BKE_pbvh_node_mark_update_mask(node);
    if (*((bool *)rebuild)) {
      BKE_pbvh_node_mark_update_visibility(node);
    }
    BKE_pbvh_node_fully_hidden_set(node, 0);
  }
  
  struct PartialUpdateData {
    PBVH *pbvh;
    bool rebuild;
    char *modified_grids;
  };
  
  /**
   * A version of #update_cb that tests for 'ME_VERT_PBVH_UPDATE'
   */
  static void update_cb_partial(PBVHNode *node, void *userdata)
  {
    struct PartialUpdateData *data = userdata;
    if (BKE_pbvh_type(data->pbvh) == PBVH_GRIDS) {
      int *node_grid_indices;
      int totgrid;
      bool update = false;
      BKE_pbvh_node_get_grids(data->pbvh, node, &node_grid_indices, &totgrid, NULL, NULL, NULL);
      for (int i = 0; i < totgrid; i++) {
        if (data->modified_grids[node_grid_indices[i]] == 1) {
          update = true;
        }
      }
      if (update) {
        update_cb(node, &(data->rebuild));
      }
    }
    else {
      if (BKE_pbvh_node_vert_update_check_any(data->pbvh, node)) {
        update_cb(node, &(data->rebuild));
      }
    }
  }
  
  static bool test_swap_v3_v3(float a[3], float b[3])
  {
    /* No need for float comparison here (memory is exactly equal or not). */
    if (memcmp(a, b, sizeof(float[3])) != 0) {
      swap_v3_v3(a, b);
      return true;
    }
    else {
      return false;
    }
  }
  
  static bool sculpt_undo_restore_deformed(
      const SculptSession *ss, SculptUndoNode *unode, int uindex, int oindex, float coord[3])
  {
    if (test_swap_v3_v3(coord, unode->orig_co[uindex])) {
      copy_v3_v3(unode->co[uindex], ss->deform_cos[oindex]);
      return true;
    }
    else {
      return false;
    }
  }
  
  static bool sculpt_undo_restore_coords(bContext *C, Depsgraph *depsgraph, SculptUndoNode *unode)
  {
    ViewLayer *view_layer = CTX_data_view_layer(C);
    Object *ob = OBACT(view_layer);
    SculptSession *ss = ob->sculpt;
    SubdivCCG *subdiv_ccg = ss->subdiv_ccg;
    MVert *mvert;
    int *index;
  
    if (unode->maxvert) {
      /* Regular mesh restore. */
  
      if (ss->shapekey_active && !STREQ(ss->shapekey_active->name, unode->shapeName)) {
        /* Shape key has been changed before calling undo operator. */
  
        Key *key = BKE_key_from_object(ob);
        KeyBlock *kb = key ? BKE_keyblock_find_name(key, unode->shapeName) : NULL;
  
        if (kb) {
          ob->shapenr = BLI_findindex(&key->block, kb) + 1;
  
          BKE_sculpt_update_object_for_edit(depsgraph, ob, false, false);
          WM_event_add_notifier(C, NC_OBJECT | ND_DATA, ob);
        }
        else {
          /* Key has been removed -- skip this undo node. */
          return false;
        }
      }
  
      /* No need for float comparison here (memory is exactly equal or not). */
      index = unode->index;
      mvert = ss->mvert;
  
      if (ss->shapekey_active) {
        float(*vertCos)[3];
        vertCos = BKE_keyblock_convert_to_vertcos(ob, ss->shapekey_active);
  
        if (unode->orig_co) {
          if (ss->deform_modifiers_active) {
            for (int i = 0; i < unode->totvert; i++) {
              sculpt_undo_restore_deformed(ss, unode, i, index[i], vertCos[index[i]]);
            }
          }
          else {
            for (int i = 0; i < unode->totvert; i++) {
              swap_v3_v3(vertCos[index[i]], unode->orig_co[i]);
            }
          }
        }
        else {
          for (int i = 0; i < unode->totvert; i++) {
            swap_v3_v3(vertCos[index[i]], unode->co[i]);
          }
        }
  
        /* Propagate new coords to keyblock. */
        sculpt_vertcos_to_key(ob, ss->shapekey_active, vertCos);
  
        /* PBVH uses it's own mvert array, so coords should be */
        /* propagated to PBVH here. */
        BKE_pbvh_vert_coords_apply(ss->pbvh, vertCos, ss->shapekey_active->totelem);
  
        MEM_freeN(vertCos);
      }
      else {
        if (unode->orig_co) {
          if (ss->deform_modifiers_active) {
            for (int i = 0; i < unode->totvert; i++) {
              sculpt_undo_restore_deformed(ss, unode, i, index[i], mvert[index[i]].co);
              mvert[index[i]].flag |= ME_VERT_PBVH_UPDATE;
            }
          }
          else {
            for (int i = 0; i < unode->totvert; i++) {
              swap_v3_v3(mvert[index[i]].co, unode->orig_co[i]);
              mvert[index[i]].flag |= ME_VERT_PBVH_UPDATE;
            }
          }
        }
        else {
          for (int i = 0; i < unode->totvert; i++) {
            swap_v3_v3(mvert[index[i]].co, unode->co[i]);
            mvert[index[i]].flag |= ME_VERT_PBVH_UPDATE;
          }
        }
      }
    }
    else if (unode->maxgrid && subdiv_ccg != NULL) {
      /* Multires restore. */
      CCGElem **grids, *grid;
      CCGKey key;
      float(*co)[3];
      int gridsize;
  
      grids = subdiv_ccg->grids;
      gridsize = subdiv_ccg->grid_size;
      BKE_subdiv_ccg_key_top_level(&key, subdiv_ccg);
  
      co = unode->co;
      for (int j = 0; j < unode->totgrid; j++) {
        grid = grids[unode->grids[j]];
  
        for (int i = 0; i < gridsize * gridsize; i++, co++) {
          swap_v3_v3(CCG_elem_offset_co(&key, grid, i), co[0]);
        }
      }
    }
  
    return true;
  }
  
  static bool sculpt_undo_restore_hidden(bContext *C, SculptUndoNode *unode)
  {
    ViewLayer *view_layer = CTX_data_view_layer(C);
    Object *ob = OBACT(view_layer);
    SculptSession *ss = ob->sculpt;
    SubdivCCG *subdiv_ccg = ss->subdiv_ccg;
  
    if (unode->maxvert) {
      MVert *mvert = ss->mvert;
  
      for (int i = 0; i < unode->totvert; i++) {
        MVert *v = &mvert[unode->index[i]];
        if ((BLI_BITMAP_TEST(unode->vert_hidden, i) != 0) != ((v->flag & ME_HIDE) != 0)) {
          BLI_BITMAP_FLIP(unode->vert_hidden, i);
          v->flag ^= ME_HIDE;
          v->flag |= ME_VERT_PBVH_UPDATE;
        }
      }
    }
    else if (unode->maxgrid && subdiv_ccg != NULL) {
      BLI_bitmap **grid_hidden = subdiv_ccg->grid_hidden;
  
      for (int i = 0; i < unode->totgrid; i++) {
        SWAP(BLI_bitmap *, unode->grid_hidden[i], grid_hidden[unode->grids[i]]);
      }
    }
  
    return true;
  }
  
  static bool sculpt_undo_restore_mask(bContext *C, SculptUndoNode *unode)
  {
    ViewLayer *view_layer = CTX_data_view_layer(C);
    Object *ob = OBACT(view_layer);
    SculptSession *ss = ob->sculpt;
    SubdivCCG *subdiv_ccg = ss->subdiv_ccg;
    MVert *mvert;
    float *vmask;
    int *index;
  
    if (unode->maxvert) {
      /* Regular mesh restore. */
  
      index = unode->index;
      mvert = ss->mvert;
      vmask = ss->vmask;
  
      for (int i = 0; i < unode->totvert; i++) {
        if (vmask[index[i]] != unode->mask[i]) {
          SWAP(float, vmask[index[i]], unode->mask[i]);
          mvert[index[i]].flag |= ME_VERT_PBVH_UPDATE;
        }
      }
    }
    else if (unode->maxgrid && subdiv_ccg != NULL) {
      /* Multires restore. */
      CCGElem **grids, *grid;
      CCGKey key;
      float *mask;
      int gridsize;
  
      grids = subdiv_ccg->grids;
      gridsize = subdiv_ccg->grid_size;
      BKE_subdiv_ccg_key_top_level(&key, subdiv_ccg);
  
      mask = unode->mask;
      for (int j = 0; j < unode->totgrid; j++) {
        grid = grids[unode->grids[j]];
  
        for (int i = 0; i < gridsize * gridsize; i++, mask++) {
          SWAP(float, *CCG_elem_offset_mask(&key, grid, i), *mask);
        }
      }
    }
  
    return true;
  }
  
  static bool sculpt_undo_restore_face_sets(bContext *C, SculptUndoNode *unode)
  {
    ViewLayer *view_layer = CTX_data_view_layer(C);
    Object *ob = OBACT(view_layer);
    SculptSession *ss = ob->sculpt;
    memcpy(ss->face_sets, unode->face_sets, ss->totpoly * sizeof(int));
    return false;
  }
  
  static void sculpt_undo_bmesh_restore_generic_task_cb(
      void *__restrict userdata, const int n, const TaskParallelTLS *__restrict UNUSED(tls))
  {
    PBVHNode **nodes = userdata;
  
    BKE_pbvh_node_mark_redraw(nodes[n]);
  }
  
  static void sculpt_undo_bmesh_restore_generic(bContext *C,
                                                SculptUndoNode *unode,
                                                Object *ob,
                                                SculptSession *ss)
  {
    if (unode->applied) {
      BM_log_undo(ss->bm, ss->bm_log);
      unode->applied = false;
    }
    else {
      BM_log_redo(ss->bm, ss->bm_log);
      unode->applied = true;
    }
  
    if (unode->type == SCULPT_UNDO_MASK) {
      int totnode;
      PBVHNode **nodes;
      Sculpt *sd = CTX_data_tool_settings(C)->sculpt;
  
      BKE_pbvh_search_gather(ss->pbvh, NULL, NULL, &nodes, &totnode);
  
      PBVHParallelSettings settings;
      BKE_pbvh_parallel_range_settings(&settings, (sd->flags & SCULPT_USE_OPENMP), totnode);
      BKE_pbvh_parallel_range(
          0, totnode, nodes, sculpt_undo_bmesh_restore_generic_task_cb, &settings);
  
      if (nodes) {
        MEM_freeN(nodes);
      }
    }
    else {
      sculpt_pbvh_clear(ob);
    }
  }
  
  /* Create empty sculpt BMesh and enable logging. */
  static void sculpt_undo_bmesh_enable(Object *ob, SculptUndoNode *unode)
  {
    SculptSession *ss = ob->sculpt;
    Mesh *me = ob->data;
  
    sculpt_pbvh_clear(ob);
  
    /* Create empty BMesh and enable logging. */
    ss->bm = BM_mesh_create(&bm_mesh_allocsize_default,
                            &((struct BMeshCreateParams){
                                .use_toolflags = false,
                            }));
    BM_data_layer_add(ss->bm, &ss->bm->vdata, CD_PAINT_MASK);
    sculpt_dyntopo_node_layers_add(ss);
    me->flag |= ME_SCULPT_DYNAMIC_TOPOLOGY;
  
    /* Restore the BMLog using saved entries. */
    ss->bm_log = BM_log_from_existing_entries_create(ss->bm, unode->bm_entry);
  }
  
  static void sculpt_undo_bmesh_restore_begin(bContext *C,
                                              SculptUndoNode *unode,
                                              Object *ob,
                                              SculptSession *ss)
  {
    if (unode->applied) {
      sculpt_dynamic_topology_disable(C, unode);
      unode->applied = false;
    }
    else {
      sculpt_undo_bmesh_enable(ob, unode);
  
      /* Restore the mesh from the first log entry. */
      BM_log_redo(ss->bm, ss->bm_log);
  
      unode->applied = true;
    }
  }
  
  static void sculpt_undo_bmesh_restore_end(bContext *C,
                                            SculptUndoNode *unode,
                                            Object *ob,
                                            SculptSession *ss)
  {
    if (unode->applied) {
      sculpt_undo_bmesh_enable(ob, unode);
  
      /* Restore the mesh from the last log entry. */
      BM_log_undo(ss->bm, ss->bm_log);
  
      unode->applied = false;
    }
    else {
      /* Disable dynamic topology sculpting. */
      sculpt_dynamic_topology_disable(C, NULL);
      unode->applied = true;
    }
  }
  
  static void sculpt_undo_geometry_restore(SculptUndoNode *unode, Object *ob)
  {
    Mesh *me;
    sculpt_pbvh_clear(ob);
    me = ob->data;
    CustomData_free(&me->vdata, me->totvert);
    CustomData_free(&me->edata, me->totedge);
    CustomData_free(&me->fdata, me->totface);
    CustomData_free(&me->ldata, me->totloop);
    CustomData_free(&me->pdata, me->totpoly);
    me->totvert = unode->geom_totvert;
    me->totedge = unode->geom_totedge;
    me->totloop = unode->geom_totloop;
    me->totpoly = unode->geom_totpoly;
    me->totface = 0;
    CustomData_copy(
        &unode->geom_vdata, &me->vdata, CD_MASK_MESH.vmask, CD_DUPLICATE, unode->geom_totvert);
    CustomData_copy(
        &unode->geom_edata, &me->edata, CD_MASK_MESH.emask, CD_DUPLICATE, unode->geom_totedge);
    CustomData_copy(
        &unode->geom_ldata, &me->ldata, CD_MASK_MESH.lmask, CD_DUPLICATE, unode->geom_totloop);
    CustomData_copy(
        &unode->geom_pdata, &me->pdata, CD_MASK_MESH.pmask, CD_DUPLICATE, unode->geom_totpoly);
    BKE_mesh_update_customdata_pointers(me, false);
  }
  
  /* Handle all dynamic-topology updates
   *
   * Returns true if this was a dynamic-topology undo step, otherwise
   * returns false to indicate the non-dyntopo code should run. */
  static int sculpt_undo_bmesh_restore(bContext *C,
                                       SculptUndoNode *unode,
                                       Object *ob,
                                       SculptSession *ss)
  {
    switch (unode->type) {
      case SCULPT_UNDO_DYNTOPO_BEGIN:
        sculpt_undo_bmesh_restore_begin(C, unode, ob, ss);
        return true;
  
      case SCULPT_UNDO_DYNTOPO_END:
        sculpt_undo_bmesh_restore_end(C, unode, ob, ss);
        return true;
      default:
        if (ss->bm_log) {
          sculpt_undo_bmesh_restore_generic(C, unode, ob, ss);
          return true;
        }
        break;
    }
  
    return false;
  }
  
  static void sculpt_undo_restore_list(bContext *C, Depsgraph *depsgraph, ListBase *lb)
  {
    Scene *scene = CTX_data_scene(C);
    ViewLayer *view_layer = CTX_data_view_layer(C);
    View3D *v3d = CTX_wm_view3d(C);
    Object *ob = OBACT(view_layer);
    SculptSession *ss = ob->sculpt;
    SubdivCCG *subdiv_ccg = ss->subdiv_ccg;
    SculptUndoNode *unode;
    bool update = false, rebuild = false, update_mask = false, update_visibility = false;
    bool need_mask = false;
  
    for (unode = lb->first; unode; unode = unode->next) {
      /* Restore pivot. */
      copy_v3_v3(ss->pivot_pos, unode->pivot_pos);
      copy_v3_v3(ss->pivot_rot, unode->pivot_rot);
      if (STREQ(unode->idname, ob->id.name)) {
        if (unode->type == SCULPT_UNDO_MASK) {
          /* Is possible that we can't do the mask undo (below)
           * because of the vertex count. */
          need_mask = true;
          break;
        }
      }
    }
  
    DEG_id_tag_update(&ob->id, ID_RECALC_SHADING);
  
    if (lb->first) {
      unode = lb->first;
      if (unode->type == SCULPT_UNDO_GEOMETRY) {
        if (unode->applied) {
          sculpt_undo_geometry_restore(unode->next, ob);
          unode->next->applied = true;
          unode->applied = false;
        }
        else {
          sculpt_undo_geometry_restore(unode, ob);
          unode->next->applied = false;
          unode->applied = true;
        }
        BKE_sculpt_update_object_for_edit(depsgraph, ob, false, need_mask);
        return;
      }
      else if (unode->type == SCULPT_UNDO_FACE_SETS) {
  
        sculpt_undo_restore_face_sets(C, unode);
  
        rebuild = true;
        BKE_pbvh_search_callback(ss->pbvh, NULL, NULL, update_cb, &rebuild);
  
        BKE_sculpt_update_object_for_edit(depsgraph, ob, true, need_mask);
  
        sculpt_visibility_sync_all_face_sets_to_vertices(ss);
        BKE_pbvh_update_vertex_data(ss->pbvh, PBVH_UpdateVisibility);
  
        if (BKE_pbvh_type(ss->pbvh) == PBVH_FACES) {
          BKE_mesh_flush_hidden_from_verts(ob->data);
        }
  
        if (!BKE_sculptsession_use_pbvh_draw(ob, v3d)) {
          DEG_id_tag_update(&ob->id, ID_RECALC_SHADING);
          DEG_id_tag_update(&ob->id, ID_RECALC_GEOMETRY);
        }
  
        unode->applied = true;
        return;
      }
    }
  
    BKE_sculpt_update_object_for_edit(depsgraph, ob, false, need_mask);
  
    if (lb->first && sculpt_undo_bmesh_restore(C, lb->first, ob, ss)) {
      return;
    }
  
    char *undo_modified_grids = NULL;
    bool use_multires_undo = false;
  
    for (unode = lb->first; unode; unode = unode->next) {
  
      if (!STREQ(unode->idname, ob->id.name)) {
        continue;
      }
  
      /* Check if undo data matches current data well enough to
       * continue. */
      if (unode->maxvert) {
        if (ss->totvert != unode->maxvert) {
          continue;
        }
      }
      else if (unode->maxgrid && subdiv_ccg != NULL) {
        if ((subdiv_ccg->num_grids != unode->maxgrid) ||
            (subdiv_ccg->grid_size != unode->gridsize)) {
          continue;
        }
  
        use_multires_undo = true;
      }
  
      switch (unode->type) {
        case SCULPT_UNDO_COORDS:
          if (sculpt_undo_restore_coords(C, depsgraph, unode)) {
            update = true;
          }
          break;
        case SCULPT_UNDO_HIDDEN:
          if (sculpt_undo_restore_hidden(C, unode)) {
            rebuild = true;
            update_visibility = true;
          }
          break;
        case SCULPT_UNDO_MASK:
          if (sculpt_undo_restore_mask(C, unode)) {
            update = true;
            update_mask = true;
          }
          break;
        case SCULPT_UNDO_FACE_SETS:
          break;
  
        case SCULPT_UNDO_DYNTOPO_BEGIN:
        case SCULPT_UNDO_DYNTOPO_END:
        case SCULPT_UNDO_DYNTOPO_SYMMETRIZE:
          BLI_assert(!"Dynamic topology should've already been handled");
          break;
        case SCULPT_UNDO_GEOMETRY:
          break;
      }
    }
  
    if (use_multires_undo) {
      int max_grid;
      unode = lb->first;
      max_grid = unode->maxgrid;
      undo_modified_grids = MEM_callocN(sizeof(char) * max_grid, "undo_grids");
      for (unode = lb->first; unode; unode = unode->next) {
        for (int i = 0; i < unode->totgrid; i++) {
          undo_modified_grids[unode->grids[i]] = 1;
        }
      }
    }
  
    if (update || rebuild) {
      bool tag_update = false;
      /* We update all nodes still, should be more clever, but also
       * needs to work correct when exiting/entering sculpt mode and
       * the nodes get recreated, though in that case it could do all. */
      struct PartialUpdateData data = {
          .rebuild = rebuild,
          .pbvh = ss->pbvh,
          .modified_grids = undo_modified_grids,
      };
      BKE_pbvh_search_callback(ss->pbvh, NULL, NULL, update_cb_partial, &data);
      BKE_pbvh_update_bounds(ss->pbvh, PBVH_UpdateBB | PBVH_UpdateOriginalBB | PBVH_UpdateRedraw);
  
      if (update_mask) {
        BKE_pbvh_update_vertex_data(ss->pbvh, PBVH_UpdateMask);
      }
  
      if (update_visibility) {
        sculpt_visibility_sync_all_vertex_to_face_sets(ss);
        BKE_pbvh_update_visibility(ss->pbvh);
      }
  
      if (BKE_sculpt_multires_active(scene, ob)) {
        if (rebuild) {
          multires_mark_as_modified(depsgraph, ob, MULTIRES_HIDDEN_MODIFIED);
        }
        else {
          multires_mark_as_modified(depsgraph, ob, MULTIRES_COORDS_MODIFIED);
        }
      }
  
      tag_update |= ID_REAL_USERS(ob->data) > 1 || !BKE_sculptsession_use_pbvh_draw(ob, v3d) ||
                    ss->shapekey_active || ss->deform_modifiers_active;
  
      if (tag_update) {
        Mesh *mesh = ob->data;
        BKE_mesh_calc_normals(mesh);
  
        BKE_sculptsession_free_deformMats(ss);
      }
  
      if (BKE_pbvh_type(ss->pbvh) == PBVH_FACES && update_visibility) {
        Mesh *mesh = ob->data;
        BKE_mesh_flush_hidden_from_verts(mesh);
      }
  
      if (tag_update) {
        DEG_id_tag_update(&ob->id, ID_RECALC_GEOMETRY);
      }
      else {
        sculpt_update_object_bounding_box(ob);
      }
    }
  
    MEM_SAFE_FREE(undo_modified_grids);
  }
  
  static void sculpt_undo_free_list(ListBase *lb)
  {
    SculptUndoNode *unode = lb->first;
    while (unode != NULL) {
      SculptUndoNode *unode_next = unode->next;
      if (unode->co) {
        MEM_freeN(unode->co);
      }
      if (unode->no) {
        MEM_freeN(unode->no);
      }
      if (unode->index) {
        MEM_freeN(unode->index);
      }
      if (unode->grids) {
        MEM_freeN(unode->grids);
      }
      if (unode->orig_co) {
        MEM_freeN(unode->orig_co);
      }
      if (unode->vert_hidden) {
        MEM_freeN(unode->vert_hidden);
      }
      if (unode->grid_hidden) {
        for (int i = 0; i < unode->totgrid; i++) {
          if (unode->grid_hidden[i]) {
            MEM_freeN(unode->grid_hidden[i]);
          }
        }
        MEM_freeN(unode->grid_hidden);
      }
      if (unode->mask) {
        MEM_freeN(unode->mask);
      }
  
      if (unode->bm_entry) {
        BM_log_entry_drop(unode->bm_entry);
      }
  
      if (unode->geom_totvert) {
        CustomData_free(&unode->geom_vdata, unode->geom_totvert);
      }
      if (unode->geom_totedge) {
        CustomData_free(&unode->geom_edata, unode->geom_totedge);
      }
      if (unode->geom_totloop) {
        CustomData_free(&unode->geom_ldata, unode->geom_totloop);
      }
      if (unode->geom_totpoly) {
        CustomData_free(&unode->geom_pdata, unode->geom_totpoly);
      }
  
      if (unode->face_sets) {
        MEM_freeN(unode->face_sets);
      }
  
      MEM_freeN(unode);
  
      unode = unode_next;
    }
  }
  
  /* Most likely we don't need this. */
  #if 0
  static bool sculpt_undo_cleanup(bContext *C, ListBase *lb)
  {
    Scene *scene = CTX_data_scene(C);
    ViewLayer *view_layer = CTX_data_view_layer(C);
    Object *ob = OBACT(view_layer);
    SculptUndoNode *unode;
  
    unode = lb->first;
  
    if (unode && !STREQ(unode->idname, ob->id.name)) {
      if (unode->bm_entry) {
        BM_log_cleanup_entry(unode->bm_entry);
      }
  
      return true;
    }
  
    return false;
  }
  #endif
  
  SculptUndoNode *sculpt_undo_get_node(PBVHNode *node)
  {
    UndoSculpt *usculpt = sculpt_undo_get_nodes();
  
    if (usculpt == NULL) {
      return NULL;
    }
  
    return BLI_findptr(&usculpt->nodes, node, offsetof(SculptUndoNode, node));
  }
  
  static void sculpt_undo_alloc_and_store_hidden(PBVH *pbvh, SculptUndoNode *unode)
  {
    PBVHNode *node = unode->node;
    BLI_bitmap **grid_hidden;
    int i, *grid_indices, totgrid;
  
    grid_hidden = BKE_pbvh_grid_hidden(pbvh);
  
    BKE_pbvh_node_get_grids(pbvh, node, &grid_indices, &totgrid, NULL, NULL, NULL);
  
    unode->grid_hidden = MEM_mapallocN(sizeof(*unode->grid_hidden) * totgrid, "unode->grid_hidden");
  
    for (i = 0; i < totgrid; i++) {
      if (grid_hidden[grid_indices[i]]) {
        unode->grid_hidden[i] = MEM_dupallocN(grid_hidden[grid_indices[i]]);
      }
      else {
        unode->grid_hidden[i] = NULL;
      }
    }
  }
  
  static SculptUndoNode *sculpt_undo_alloc_node(Object *ob, PBVHNode *node, SculptUndoType type)
  {
    UndoSculpt *usculpt = sculpt_undo_get_nodes();
    SculptUndoNode *unode;
    SculptSession *ss = ob->sculpt;
    int totvert, allvert, totgrid, maxgrid, gridsize, *grids;
  
    unode = MEM_callocN(sizeof(SculptUndoNode), "SculptUndoNode");
    BLI_strncpy(unode->idname, ob->id.name, sizeof(unode->idname));
    unode->type = type;
    unode->node = node;
  
    if (node) {
      BKE_pbvh_node_num_verts(ss->pbvh, node, &totvert, &allvert);
      BKE_pbvh_node_get_grids(ss->pbvh, node, &grids, &totgrid, &maxgrid, &gridsize, NULL);
  
      unode->totvert = totvert;
    }
    else {
      maxgrid = 0;
    }
  
    /* We will use this while sculpting, is mapalloc slow to access then? */
  
    /* General TODO, fix count_alloc. */
    switch (type) {
      case SCULPT_UNDO_COORDS:
        unode->co = MEM_mapallocN(sizeof(float[3]) * allvert, "SculptUndoNode.co");
        unode->no = MEM_mapallocN(sizeof(short[3]) * allvert, "SculptUndoNode.no");
  
        usculpt->undo_size = (sizeof(float[3]) + sizeof(short[3]) + sizeof(int)) * allvert;
        break;
      case SCULPT_UNDO_HIDDEN:
        if (maxgrid) {
          sculpt_undo_alloc_and_store_hidden(ss->pbvh, unode);
        }
        else {
          unode->vert_hidden = BLI_BITMAP_NEW(allvert, "SculptUndoNode.vert_hidden");
        }
  
        break;
      case SCULPT_UNDO_MASK:
        unode->mask = MEM_mapallocN(sizeof(float) * allvert, "SculptUndoNode.mask");
  
        usculpt->undo_size += (sizeof(float) * sizeof(int)) * allvert;
  
        break;
      case SCULPT_UNDO_DYNTOPO_BEGIN:
      case SCULPT_UNDO_DYNTOPO_END:
      case SCULPT_UNDO_DYNTOPO_SYMMETRIZE:
        BLI_assert(!"Dynamic topology should've already been handled");
      case SCULPT_UNDO_GEOMETRY:
      case SCULPT_UNDO_FACE_SETS:
        break;
    }
  
    BLI_addtail(&usculpt->nodes, unode);
  
    if (maxgrid) {
      /* Multires. */
      unode->maxgrid = maxgrid;
      unode->totgrid = totgrid;
      unode->gridsize = gridsize;
      unode->grids = MEM_mapallocN(sizeof(int) * totgrid, "SculptUndoNode.grids");
    }
    else {
      /* Regular mesh. */
      unode->maxvert = ss->totvert;
      unode->index = MEM_mapallocN(sizeof(int) * allvert, "SculptUndoNode.index");
    }
  
    if (ss->deform_modifiers_active) {
      unode->orig_co = MEM_callocN(allvert * sizeof(*unode->orig_co), "undoSculpt orig_cos");
    }
  
    return unode;
  }
  
  static void sculpt_undo_store_coords(Object *ob, SculptUndoNode *unode)
  {
    SculptSession *ss = ob->sculpt;
    PBVHVertexIter vd;
  
    BKE_pbvh_vertex_iter_begin(ss->pbvh, unode->node, vd, PBVH_ITER_ALL)
    {
      copy_v3_v3(unode->co[vd.i], vd.co);
      if (vd.no) {
        copy_v3_v3_short(unode->no[vd.i], vd.no);
      }
      else {
        normal_float_to_short_v3(unode->no[vd.i], vd.fno);
      }
  
      if (ss->deform_modifiers_active) {
        copy_v3_v3(unode->orig_co[vd.i], ss->orig_cos[unode->index[vd.i]]);
      }
    }
    BKE_pbvh_vertex_iter_end;
  }
  
  static void sculpt_undo_store_hidden(Object *ob, SculptUndoNode *unode)
  {
    PBVH *pbvh = ob->sculpt->pbvh;
    PBVHNode *node = unode->node;
  
    if (unode->grids) {
      /* Already stored during allocation. */
    }
    else {
      MVert *mvert;
      const int *vert_indices;
      int allvert;
      int i;
  
      BKE_pbvh_node_num_verts(pbvh, node, NULL, &allvert);
      BKE_pbvh_node_get_verts(pbvh, node, &vert_indices, &mvert);
      for (i = 0; i < allvert; i++) {
        BLI_BITMAP_SET(unode->vert_hidden, i, mvert[vert_indices[i]].flag & ME_HIDE);
      }
    }
  }
  
  static void sculpt_undo_store_mask(Object *ob, SculptUndoNode *unode)
  {
    SculptSession *ss = ob->sculpt;
    PBVHVertexIter vd;
  
    BKE_pbvh_vertex_iter_begin(ss->pbvh, unode->node, vd, PBVH_ITER_ALL)
    {
      unode->mask[vd.i] = *vd.mask;
    }
    BKE_pbvh_vertex_iter_end;
  }
  
  static SculptUndoNode *sculpt_undo_geometry_push(Object *ob, SculptUndoType type)
  {
    UndoSculpt *usculpt = sculpt_undo_get_nodes();
    Mesh *me = ob->data;
    bool applied;
  
    SculptUndoNode *unode = usculpt->nodes.first;
    /* Store the original mesh in the first node, modifications in the second. */
    applied = unode != NULL;
  
    unode = MEM_callocN(sizeof(*unode), __func__);
  
    BLI_strncpy(unode->idname, ob->id.name, sizeof(unode->idname));
    unode->type = type;
    unode->applied = applied;
  
    CustomData_copy(&me->vdata, &unode->geom_vdata, CD_MASK_MESH.vmask, CD_DUPLICATE, me->totvert);
    CustomData_copy(&me->edata, &unode->geom_edata, CD_MASK_MESH.emask, CD_DUPLICATE, me->totedge);
    CustomData_copy(&me->ldata, &unode->geom_ldata, CD_MASK_MESH.lmask, CD_DUPLICATE, me->totloop);
    CustomData_copy(&me->pdata, &unode->geom_pdata, CD_MASK_MESH.pmask, CD_DUPLICATE, me->totpoly);
    unode->geom_totvert = me->totvert;
    unode->geom_totedge = me->totedge;
    unode->geom_totloop = me->totloop;
    unode->geom_totpoly = me->totpoly;
  
    BLI_addtail(&usculpt->nodes, unode);
  
    return unode;
  }
  
  static SculptUndoNode *sculpt_undo_face_sets_push(Object *ob, SculptUndoType type)
  {
    UndoSculpt *usculpt = sculpt_undo_get_nodes();
    SculptSession *ss = ob->sculpt;
  
    SculptUndoNode *unode = usculpt->nodes.first;
  
    unode = MEM_callocN(sizeof(*unode), __func__);
  
    BLI_strncpy(unode->idname, ob->id.name, sizeof(unode->idname));
    unode->type = type;
    unode->applied = true;
  
    unode->face_sets = MEM_callocN(ss->totpoly * sizeof(int), "sculpt face sets");
    memcpy(unode->face_sets, ss->face_sets, ss->totpoly * sizeof(int));
  
    BLI_addtail(&usculpt->nodes, unode);
  
    return unode;
  }
  
  static SculptUndoNode *sculpt_undo_bmesh_push(Object *ob, PBVHNode *node, SculptUndoType type)
  {
    UndoSculpt *usculpt = sculpt_undo_get_nodes();
    SculptSession *ss = ob->sculpt;
    PBVHVertexIter vd;
  
    SculptUndoNode *unode = usculpt->nodes.first;
  
    if (unode == NULL) {
      unode = MEM_callocN(sizeof(*unode), __func__);
  
      BLI_strncpy(unode->idname, ob->id.name, sizeof(unode->idname));
      unode->type = type;
      unode->applied = true;
  
      if (type == SCULPT_UNDO_DYNTOPO_END) {
        unode->bm_entry = BM_log_entry_add(ss->bm_log);
        BM_log_before_all_removed(ss->bm, ss->bm_log);
      }
      else if (type == SCULPT_UNDO_DYNTOPO_BEGIN) {
        Mesh *me = ob->data;
  
        /* Store a copy of the mesh's current vertices, loops, and
         * polys. A full copy like this is needed because entering
         * dynamic-topology immediately does topological edits
         * (converting polys to triangles) that the BMLog can't
         * fully restore from. */
        CustomData_copy(
            &me->vdata, &unode->geom_vdata, CD_MASK_MESH.vmask, CD_DUPLICATE, me->totvert);
        CustomData_copy(
            &me->edata, &unode->geom_edata, CD_MASK_MESH.emask, CD_DUPLICATE, me->totedge);
        CustomData_copy(
            &me->ldata, &unode->geom_ldata, CD_MASK_MESH.lmask, CD_DUPLICATE, me->totloop);
        CustomData_copy(
            &me->pdata, &unode->geom_pdata, CD_MASK_MESH.pmask, CD_DUPLICATE, me->totpoly);
        unode->geom_totvert = me->totvert;
        unode->geom_totedge = me->totedge;
        unode->geom_totloop = me->totloop;
        unode->geom_totpoly = me->totpoly;
  
        unode->bm_entry = BM_log_entry_add(ss->bm_log);
        BM_log_all_added(ss->bm, ss->bm_log);
      }
      else {
        unode->bm_entry = BM_log_entry_add(ss->bm_log);
      }
  
      BLI_addtail(&usculpt->nodes, unode);
    }
  
    if (node) {
      switch (type) {
        case SCULPT_UNDO_COORDS:
        case SCULPT_UNDO_MASK:
          /* Before any vertex values get modified, ensure their
           * original positions are logged. */
          BKE_pbvh_vertex_iter_begin(ss->pbvh, node, vd, PBVH_ITER_ALL)
          {
            BM_log_vert_before_modified(ss->bm_log, vd.bm_vert, vd.cd_vert_mask_offset);
          }
          BKE_pbvh_vertex_iter_end;
          break;
  
        case SCULPT_UNDO_HIDDEN: {
          GSetIterator gs_iter;
          GSet *faces = BKE_pbvh_bmesh_node_faces(node);
          BKE_pbvh_vertex_iter_begin(ss->pbvh, node, vd, PBVH_ITER_ALL)
          {
            BM_log_vert_before_modified(ss->bm_log, vd.bm_vert, vd.cd_vert_mask_offset);
          }
          BKE_pbvh_vertex_iter_end;
  
          GSET_ITER (gs_iter, faces) {
            BMFace *f = BLI_gsetIterator_getKey(&gs_iter);
            BM_log_face_modified(ss->bm_log, f);
          }
          break;
        }
  
        case SCULPT_UNDO_DYNTOPO_BEGIN:
        case SCULPT_UNDO_DYNTOPO_END:
        case SCULPT_UNDO_DYNTOPO_SYMMETRIZE:
        case SCULPT_UNDO_GEOMETRY:
        case SCULPT_UNDO_FACE_SETS:
          break;
      }
    }
  
    return unode;
  }
  
  SculptUndoNode *sculpt_undo_push_node(Object *ob, PBVHNode *node, SculptUndoType type)
  {
    SculptSession *ss = ob->sculpt;
    SculptUndoNode *unode;
  
    /* List is manipulated by multiple threads, so we lock. */
    BLI_thread_lock(LOCK_CUSTOM1);
  
    ss->needs_flush_to_id = 1;
  
    if (ss->bm || ELEM(type, SCULPT_UNDO_DYNTOPO_BEGIN, SCULPT_UNDO_DYNTOPO_END)) {
      /* Dynamic topology stores only one undo node per stroke,
       * regardless of the number of PBVH nodes modified. */
      unode = sculpt_undo_bmesh_push(ob, node, type);
      BLI_thread_unlock(LOCK_CUSTOM1);
      return unode;
    }
    else if (type == SCULPT_UNDO_GEOMETRY) {
      unode = sculpt_undo_geometry_push(ob, type);
      BLI_thread_unlock(LOCK_CUSTOM1);
      return unode;
    }
    else if (type == SCULPT_UNDO_FACE_SETS) {
      unode = sculpt_undo_face_sets_push(ob, type);
      BLI_thread_unlock(LOCK_CUSTOM1);
      return unode;
    }
    else if ((unode = sculpt_undo_get_node(node))) {
      BLI_thread_unlock(LOCK_CUSTOM1);
      return unode;
    }
  
    unode = sculpt_undo_alloc_node(ob, node, type);
  
    /* NOTE: If this ever becomes a bottleneck, make a lock inside of the node.
     * so we release global lock sooner, but keep data locked for until it is
     * fully initialized.
     */
  
    if (unode->grids) {
      int totgrid, *grids;
      BKE_pbvh_node_get_grids(ss->pbvh, node, &grids, &totgrid, NULL, NULL, NULL);
      memcpy(unode->grids, grids, sizeof(int) * totgrid);
    }
    else {
      const int *vert_indices;
      int allvert;
      BKE_pbvh_node_num_verts(ss->pbvh, node, NULL, &allvert);
      BKE_pbvh_node_get_verts(ss->pbvh, node, &vert_indices, NULL);
      memcpy(unode->index, vert_indices, sizeof(int) * unode->totvert);
    }
  
    switch (type) {
      case SCULPT_UNDO_COORDS:
        sculpt_undo_store_coords(ob, unode);
        break;
      case SCULPT_UNDO_HIDDEN:
        sculpt_undo_store_hidden(ob, unode);
        break;
      case SCULPT_UNDO_MASK:
        sculpt_undo_store_mask(ob, unode);
        break;
      case SCULPT_UNDO_DYNTOPO_BEGIN:
      case SCULPT_UNDO_DYNTOPO_END:
      case SCULPT_UNDO_DYNTOPO_SYMMETRIZE:
        BLI_assert(!"Dynamic topology should've already been handled");
      case SCULPT_UNDO_GEOMETRY:
      case SCULPT_UNDO_FACE_SETS:
        break;
    }
  
    /* Store sculpt pivot. */
    copy_v3_v3(unode->pivot_pos, ss->pivot_pos);
    copy_v3_v3(unode->pivot_rot, ss->pivot_rot);
  
    /* Store active shape key. */
    if (ss->shapekey_active) {
      BLI_strncpy(unode->shapeName, ss->shapekey_active->name, sizeof(ss->shapekey_active->name));
    }
    else {
      unode->shapeName[0] = '\0';
    }
  
    BLI_thread_unlock(LOCK_CUSTOM1);
  
    return unode;
  }
  
  void sculpt_undo_push_begin(const char *name)
  {
    UndoStack *ustack = ED_undo_stack_get();
  
    /* Special case, we never read from this. */
    bContext *C = NULL;
  
    BKE_undosys_step_push_init_with_type(ustack, C, name, BKE_UNDOSYS_TYPE_SCULPT);
  }
  
  void sculpt_undo_push_end(void)
  {
    UndoSculpt *usculpt = sculpt_undo_get_nodes();
    SculptUndoNode *unode;
  
    /* We don't need normals in the undo stack. */
    for (unode = usculpt->nodes.first; unode; unode = unode->next) {
      if (unode->no) {
        MEM_freeN(unode->no);
        unode->no = NULL;
      }
  
      if (unode->node) {
        BKE_pbvh_node_layer_disp_free(unode->node);
      }
    }
  
    /* We could remove this and enforce all callers run in an operator using 'OPTYPE_UNDO'. */
    wmWindowManager *wm = G_MAIN->wm.first;
    if (wm->op_undo_depth == 0) {
      UndoStack *ustack = ED_undo_stack_get();
      BKE_undosys_step_push(ustack, NULL, NULL);
      WM_file_tag_modified();
    }
  }
  
  /* -------------------------------------------------------------------- */
  /** \name Implements ED Undo System
   * \{ */
  
  typedef struct SculptUndoStep {
    UndoStep step;
    /* Note: will split out into list for multi-object-sculpt-mode. */
    UndoSculpt data;
  } SculptUndoStep;
  
  static void sculpt_undosys_step_encode_init(struct bContext *UNUSED(C), UndoStep *us_p)
  {
    SculptUndoStep *us = (SculptUndoStep *)us_p;
    /* Dummy, memory is cleared anyway. */
    BLI_listbase_clear(&us->data.nodes);
  }
  
  static bool sculpt_undosys_step_encode(struct bContext *UNUSED(C),
                                         struct Main *bmain,
                                         UndoStep *us_p)
  {
    /* Dummy, encoding is done along the way by adding tiles
     * to the current 'SculptUndoStep' added by encode_init. */
    SculptUndoStep *us = (SculptUndoStep *)us_p;
    us->step.data_size = us->data.undo_size;
  
    SculptUndoNode *unode = us->data.nodes.last;
    if (unode && unode->type == SCULPT_UNDO_DYNTOPO_END) {
      us->step.use_memfile_step = true;
    }
    us->step.is_applied = true;
  
    if (!BLI_listbase_is_empty(&us->data.nodes)) {
      bmain->is_memfile_undo_flush_needed = true;
    }
  
    return true;
  }
  
  static void sculpt_undosys_step_decode_undo_impl(struct bContext *C,
                                                   Depsgraph *depsgraph,
                                                   SculptUndoStep *us)
  {
    BLI_assert(us->step.is_applied == true);
    sculpt_undo_restore_list(C, depsgraph, &us->data.nodes);
    us->step.is_applied = false;
  }
  
  static void sculpt_undosys_step_decode_redo_impl(struct bContext *C,
                                                   Depsgraph *depsgraph,
                                                   SculptUndoStep *us)
  {
    BLI_assert(us->step.is_applied == false);
    sculpt_undo_restore_list(C, depsgraph, &us->data.nodes);
    us->step.is_applied = true;
  }
  
  static void sculpt_undosys_step_decode_undo(struct bContext *C,
                                              Depsgraph *depsgraph,
                                              SculptUndoStep *us)
  {
    SculptUndoStep *us_iter = us;
    while (us_iter->step.next && (us_iter->step.next->type == us_iter->step.type)) {
      if (us_iter->step.next->is_applied == false) {
        break;
      }
      us_iter = (SculptUndoStep *)us_iter->step.next;
    }
    while (us_iter != us) {
      sculpt_undosys_step_decode_undo_impl(C, depsgraph, us_iter);
      us_iter = (SculptUndoStep *)us_iter->step.prev;
    }
  }
  
  static void sculpt_undosys_step_decode_redo(struct bContext *C,
                                              Depsgraph *depsgraph,
                                              SculptUndoStep *us)
  {
    SculptUndoStep *us_iter = us;
    while (us_iter->step.prev && (us_iter->step.prev->type == us_iter->step.type)) {
      if (us_iter->step.prev->is_applied == true) {
        break;
      }
      us_iter = (SculptUndoStep *)us_iter->step.prev;
    }
    while (us_iter && (us_iter->step.is_applied == false)) {
      sculpt_undosys_step_decode_redo_impl(C, depsgraph, us_iter);
      if (us_iter == us) {
        break;
      }
      us_iter = (SculptUndoStep *)us_iter->step.next;
    }
  }
  
  static void sculpt_undosys_step_decode(
      struct bContext *C, struct Main *bmain, UndoStep *us_p, int dir, bool UNUSED(is_final))
  {
    Depsgraph *depsgraph = CTX_data_ensure_evaluated_depsgraph(C);
  
    /* Ensure sculpt mode. */
    {
      Scene *scene = CTX_data_scene(C);
      ViewLayer *view_layer = CTX_data_view_layer(C);
      /* Sculpt needs evaluated state. */
      BKE_scene_view_layer_graph_evaluated_ensure(bmain, scene, view_layer);
      Object *ob = OBACT(view_layer);
      if (ob && (ob->type == OB_MESH)) {
        if (ob->mode & OB_MODE_SCULPT) {
          /* Pass. */
        }
        else {
          ED_object_mode_generic_exit(bmain, depsgraph, scene, ob);
          Mesh *me = ob->data;
          /* Don't add sculpt topology undo steps when reading back undo state.
           * The undo steps must enter/exit for us. */
          me->flag &= ~ME_SCULPT_DYNAMIC_TOPOLOGY;
          ED_object_sculptmode_enter_ex(bmain, depsgraph, scene, ob, true, NULL);
        }
  
        if (ob->sculpt) {
          ob->sculpt->needs_flush_to_id = 1;
        }
        bmain->is_memfile_undo_flush_needed = true;
      }
      else {
        BLI_assert(0);
        return;
      }
    }
  
    SculptUndoStep *us = (SculptUndoStep *)us_p;
    if (dir < 0) {
      sculpt_undosys_step_decode_undo(C, depsgraph, us);
    }
    else {
      sculpt_undosys_step_decode_redo(C, depsgraph, us);
    }
  }
  
  static void sculpt_undosys_step_free(UndoStep *us_p)
  {
    SculptUndoStep *us = (SculptUndoStep *)us_p;
    sculpt_undo_free_list(&us->data.nodes);
  }
  
  void ED_sculpt_undo_geometry_begin(struct Object *ob, const char *name)
  {
    sculpt_undo_push_begin(name);
    sculpt_undo_push_node(ob, NULL, SCULPT_UNDO_GEOMETRY);
  }
  
  void ED_sculpt_undo_geometry_end(struct Object *ob)
  {
    sculpt_undo_push_node(ob, NULL, SCULPT_UNDO_GEOMETRY);
    sculpt_undo_push_end();
  }
  
  /* Export for ED_undo_sys. */
  void ED_sculpt_undosys_type(UndoType *ut)
  {
    ut->name = "Sculpt";
    ut->step_encode_init = sculpt_undosys_step_encode_init;
    ut->step_encode = sculpt_undosys_step_encode;
    ut->step_decode = sculpt_undosys_step_decode;
    ut->step_free = sculpt_undosys_step_free;
  
    ut->use_context = true;
  
    ut->step_size = sizeof(SculptUndoStep);
  }
  
  /** \} */
  
  /* -------------------------------------------------------------------- */
  /** \name Utilities
   * \{ */
  
  static UndoSculpt *sculpt_undosys_step_get_nodes(UndoStep *us_p)
  {
    SculptUndoStep *us = (SculptUndoStep *)us_p;
    return &us->data;
  }
  
  static UndoSculpt *sculpt_undo_get_nodes(void)
  {
    UndoStack *ustack = ED_undo_stack_get();
    UndoStep *us = BKE_undosys_stack_init_or_active_with_type(ustack, BKE_UNDOSYS_TYPE_SCULPT);
    return sculpt_undosys_step_get_nodes(us);
  }
  
  /** \} */
  