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.
   */
  
  /** \file
   * \ingroup edmesh
   */
  
  #include "MEM_guardedalloc.h"
  
  #include "CLG_log.h"
  
  #include "DNA_mesh_types.h"
  #include "DNA_meshdata_types.h"
  #include "DNA_object_types.h"
  #include "DNA_key_types.h"
  #include "DNA_layer_types.h"
  
  #include "BLI_listbase.h"
  #include "BLI_array_utils.h"
  
  #include "BKE_context.h"
  #include "BKE_key.h"
  #include "BKE_layer.h"
  #include "BKE_main.h"
  #include "BKE_mesh.h"
  #include "BKE_editmesh.h"
  #include "BKE_undo_system.h"
  
  #include "DEG_depsgraph.h"
  
  #include "ED_object.h"
  #include "ED_mesh.h"
  #include "ED_util.h"
  #include "ED_undo.h"
  
  #include "WM_types.h"
  #include "WM_api.h"
  
  #define USE_ARRAY_STORE
  
  #ifdef USE_ARRAY_STORE
  // #  define DEBUG_PRINT
  // #  define DEBUG_TIME
  #  ifdef DEBUG_TIME
  #    include "PIL_time_utildefines.h"
  #  endif
  
  #  include "BLI_array_store.h"
  #  include "BLI_array_store_utils.h"
  /* check on best size later... */
  #  define ARRAY_CHUNK_SIZE 256
  
  #  define USE_ARRAY_STORE_THREAD
  #endif
  
  #ifdef USE_ARRAY_STORE_THREAD
  #  include "BLI_task.h"
  #endif
  
  /** We only need this locally. */
  static CLG_LogRef LOG = {"ed.undo.mesh"};
  
  /* -------------------------------------------------------------------- */
  /** \name Undo Conversion
   * \{ */
  
  #ifdef USE_ARRAY_STORE
  
  /* Single linked list of layers stored per type */
  typedef struct BArrayCustomData {
    struct BArrayCustomData *next;
    CustomDataType type;
    int states_len; /* number of layers for each type */
    BArrayState *states[0];
  } BArrayCustomData;
  
  #endif
  
  typedef struct UndoMesh {
    Mesh me;
    int selectmode;
  
    /** \note
     * this isn't a prefect solution, if you edit keys and change shapes this works well
     * (fixing T32442), but editing shape keys, going into object mode, removing or changing their
     * order, then go back into editmode and undo will give issues - where the old index will be
     * out of sync with the new object index.
     *
     * There are a few ways this could be made to work but for now its a known limitation with mixing
     * object and editmode operations - Campbell. */
    int shapenr;
  
  #ifdef USE_ARRAY_STORE
    /* NULL arrays are considered empty */
    struct { /* most data is stored as 'custom' data */
      BArrayCustomData *vdata, *edata, *ldata, *pdata;
      BArrayState **keyblocks;
      BArrayState *mselect;
    } store;
  #endif /* USE_ARRAY_STORE */
  
    size_t undo_size;
  } UndoMesh;
  
  #ifdef USE_ARRAY_STORE
  
  /** \name Array Store
   * \{ */
  
  static struct {
    struct BArrayStore_AtSize bs_stride;
    int users;
  
    /* We could have the undo API pass in the previous state, for now store a local list */
    ListBase local_links;
  
  #  ifdef USE_ARRAY_STORE_THREAD
    TaskPool *task_pool;
  #  endif
  
  } um_arraystore = {{NULL}};
  
  static void um_arraystore_cd_compact(struct CustomData *cdata,
                                       const size_t data_len,
                                       bool create,
                                       const BArrayCustomData *bcd_reference,
                                       BArrayCustomData **r_bcd_first)
  {
    if (data_len == 0) {
      if (create) {
        *r_bcd_first = NULL;
      }
    }
  
    const BArrayCustomData *bcd_reference_current = bcd_reference;
    BArrayCustomData *bcd = NULL, *bcd_first = NULL, *bcd_prev = NULL;
    for (int layer_start = 0, layer_end; layer_start < cdata->totlayer; layer_start = layer_end) {
      const CustomDataType type = cdata->layers[layer_start].type;
  
      layer_end = layer_start + 1;
      while ((layer_end < cdata->totlayer) && (type == cdata->layers[layer_end].type)) {
        layer_end++;
      }
  
      const int stride = CustomData_sizeof(type);
      BArrayStore *bs = create ? BLI_array_store_at_size_ensure(
                                     &um_arraystore.bs_stride, stride, ARRAY_CHUNK_SIZE) :
                                 NULL;
      const int layer_len = layer_end - layer_start;
  
      if (create) {
        if (bcd_reference_current && (bcd_reference_current->type == type)) {
          /* common case, the reference is aligned */
        }
        else {
          bcd_reference_current = NULL;
  
          /* do a full lookup when un-alligned */
          if (bcd_reference) {
            const BArrayCustomData *bcd_iter = bcd_reference;
            while (bcd_iter) {
              if (bcd_iter->type == type) {
                bcd_reference_current = bcd_iter;
                break;
              }
              bcd_iter = bcd_iter->next;
            }
          }
        }
      }
  
      if (create) {
        bcd = MEM_callocN(sizeof(BArrayCustomData) + (layer_len * sizeof(BArrayState *)), __func__);
        bcd->next = NULL;
        bcd->type = type;
        bcd->states_len = layer_end - layer_start;
  
        if (bcd_prev) {
          bcd_prev->next = bcd;
          bcd_prev = bcd;
        }
        else {
          bcd_first = bcd;
          bcd_prev = bcd;
        }
      }
  
      CustomDataLayer *layer = &cdata->layers[layer_start];
      for (int i = 0; i < layer_len; i++, layer++) {
        if (create) {
          if (layer->data) {
            BArrayState *state_reference = (bcd_reference_current &&
                                            i < bcd_reference_current->states_len) ?
                                               bcd_reference_current->states[i] :
                                               NULL;
            bcd->states[i] = BLI_array_store_state_add(
                bs, layer->data, (size_t)data_len * stride, state_reference);
          }
          else {
            bcd->states[i] = NULL;
          }
        }
  
        if (layer->data) {
          MEM_freeN(layer->data);
          layer->data = NULL;
        }
      }
  
      if (create) {
        if (bcd_reference_current) {
          bcd_reference_current = bcd_reference_current->next;
        }
      }
    }
  
    if (create) {
      *r_bcd_first = bcd_first;
    }
  }
  
  /**
   * \note There is no room for data going out of sync here.
   * The layers and the states are stored together so this can be kept working.
   */
  static void um_arraystore_cd_expand(const BArrayCustomData *bcd,
                                      struct CustomData *cdata,
                                      const size_t data_len)
  {
    CustomDataLayer *layer = cdata->layers;
    while (bcd) {
      const int stride = CustomData_sizeof(bcd->type);
      for (int i = 0; i < bcd->states_len; i++) {
        BLI_assert(bcd->type == layer->type);
        if (bcd->states[i]) {
          size_t state_len;
          layer->data = BLI_array_store_state_data_get_alloc(bcd->states[i], &state_len);
          BLI_assert(stride * data_len == state_len);
          UNUSED_VARS_NDEBUG(stride, data_len);
        }
        else {
          layer->data = NULL;
        }
        layer++;
      }
      bcd = bcd->next;
    }
  }
  
  static void um_arraystore_cd_free(BArrayCustomData *bcd)
  {
    while (bcd) {
      BArrayCustomData *bcd_next = bcd->next;
      const int stride = CustomData_sizeof(bcd->type);
      BArrayStore *bs = BLI_array_store_at_size_get(&um_arraystore.bs_stride, stride);
      for (int i = 0; i < bcd->states_len; i++) {
        if (bcd->states[i]) {
          BLI_array_store_state_remove(bs, bcd->states[i]);
        }
      }
      MEM_freeN(bcd);
      bcd = bcd_next;
    }
  }
  
  /**
   * \param create: When false, only free the arrays.
   * This is done since when reading from an undo state, they must be temporarily expanded.
   * then discarded afterwards, having this argument avoids having 2x code paths.
   */
  static void um_arraystore_compact_ex(UndoMesh *um, const UndoMesh *um_ref, bool create)
  {
    Mesh *me = &um->me;
  
    um_arraystore_cd_compact(
        &me->vdata, me->totvert, create, um_ref ? um_ref->store.vdata : NULL, &um->store.vdata);
    um_arraystore_cd_compact(
        &me->edata, me->totedge, create, um_ref ? um_ref->store.edata : NULL, &um->store.edata);
    um_arraystore_cd_compact(
        &me->ldata, me->totloop, create, um_ref ? um_ref->store.ldata : NULL, &um->store.ldata);
    um_arraystore_cd_compact(
        &me->pdata, me->totpoly, create, um_ref ? um_ref->store.pdata : NULL, &um->store.pdata);
  
    if (me->key && me->key->totkey) {
      const size_t stride = me->key->elemsize;
      BArrayStore *bs = create ? BLI_array_store_at_size_ensure(
                                     &um_arraystore.bs_stride, stride, ARRAY_CHUNK_SIZE) :
                                 NULL;
      if (create) {
        um->store.keyblocks = MEM_mallocN(me->key->totkey * sizeof(*um->store.keyblocks), __func__);
      }
      KeyBlock *keyblock = me->key->block.first;
      for (int i = 0; i < me->key->totkey; i++, keyblock = keyblock->next) {
        if (create) {
          BArrayState *state_reference = (um_ref && um_ref->me.key && (i < um_ref->me.key->totkey)) ?
                                             um_ref->store.keyblocks[i] :
                                             NULL;
          um->store.keyblocks[i] = BLI_array_store_state_add(
              bs, keyblock->data, (size_t)keyblock->totelem * stride, state_reference);
        }
  
        if (keyblock->data) {
          MEM_freeN(keyblock->data);
          keyblock->data = NULL;
        }
      }
    }
  
    if (me->mselect && me->totselect) {
      BLI_assert(create == (um->store.mselect == NULL));
      if (create) {
        BArrayState *state_reference = um_ref ? um_ref->store.mselect : NULL;
        const size_t stride = sizeof(*me->mselect);
        BArrayStore *bs = BLI_array_store_at_size_ensure(
            &um_arraystore.bs_stride, stride, ARRAY_CHUNK_SIZE);
        um->store.mselect = BLI_array_store_state_add(
            bs, me->mselect, (size_t)me->totselect * stride, state_reference);
      }
  
      /* keep me->totselect for validation */
      MEM_freeN(me->mselect);
      me->mselect = NULL;
    }
  
    if (create) {
      um_arraystore.users += 1;
    }
  
    BKE_mesh_update_customdata_pointers(me, false);
  }
  
  /**
   * Move data from allocated arrays to de-duplicated states and clear arrays.
   */
  static void um_arraystore_compact(UndoMesh *um, const UndoMesh *um_ref)
  {
    um_arraystore_compact_ex(um, um_ref, true);
  }
  
  static void um_arraystore_compact_with_info(UndoMesh *um, const UndoMesh *um_ref)
  {
  #  ifdef DEBUG_PRINT
    size_t size_expanded_prev, size_compacted_prev;
    BLI_array_store_at_size_calc_memory_usage(
        &um_arraystore.bs_stride, &size_expanded_prev, &size_compacted_prev);
  #  endif
  
  #  ifdef DEBUG_TIME
    TIMEIT_START(mesh_undo_compact);
  #  endif
  
    um_arraystore_compact(um, um_ref);
  
  #  ifdef DEBUG_TIME
    TIMEIT_END(mesh_undo_compact);
  #  endif
  
  #  ifdef DEBUG_PRINT
    {
      size_t size_expanded, size_compacted;
      BLI_array_store_at_size_calc_memory_usage(
          &um_arraystore.bs_stride, &size_expanded, &size_compacted);
  
      const double percent_total = size_expanded ?
                                       (((double)size_compacted / (double)size_expanded) * 100.0) :
                                       -1.0;
  
      size_t size_expanded_step = size_expanded - size_expanded_prev;
      size_t size_compacted_step = size_compacted - size_compacted_prev;
      const double percent_step = size_expanded_step ?
                                      (((double)size_compacted_step / (double)size_expanded_step) *
                                       100.0) :
                                      -1.0;
  
      printf("overall memory use: %.8f%% of expanded size\n", percent_total);
      printf("step memory use:    %.8f%% of expanded size\n", percent_step);
    }
  #  endif
  }
  
  #  ifdef USE_ARRAY_STORE_THREAD
  
  struct UMArrayData {
    UndoMesh *um;
    const UndoMesh *um_ref; /* can be NULL */
  };
  static void um_arraystore_compact_cb(TaskPool *__restrict UNUSED(pool),
                                       void *taskdata,
                                       int UNUSED(threadid))
  {
    struct UMArrayData *um_data = taskdata;
    um_arraystore_compact_with_info(um_data->um, um_data->um_ref);
  }
  
  #  endif /* USE_ARRAY_STORE_THREAD */
  
  /**
   * Remove data we only expanded for temporary use.
   */
  static void um_arraystore_expand_clear(UndoMesh *um)
  {
    um_arraystore_compact_ex(um, NULL, false);
  }
  
  static void um_arraystore_expand(UndoMesh *um)
  {
    Mesh *me = &um->me;
  
    um_arraystore_cd_expand(um->store.vdata, &me->vdata, me->totvert);
    um_arraystore_cd_expand(um->store.edata, &me->edata, me->totedge);
    um_arraystore_cd_expand(um->store.ldata, &me->ldata, me->totloop);
    um_arraystore_cd_expand(um->store.pdata, &me->pdata, me->totpoly);
  
    if (um->store.keyblocks) {
      const size_t stride = me->key->elemsize;
      KeyBlock *keyblock = me->key->block.first;
      for (int i = 0; i < me->key->totkey; i++, keyblock = keyblock->next) {
        BArrayState *state = um->store.keyblocks[i];
        size_t state_len;
        keyblock->data = BLI_array_store_state_data_get_alloc(state, &state_len);
        BLI_assert(keyblock->totelem == (state_len / stride));
        UNUSED_VARS_NDEBUG(stride);
      }
    }
  
    if (um->store.mselect) {
      const size_t stride = sizeof(*me->mselect);
      BArrayState *state = um->store.mselect;
      size_t state_len;
      me->mselect = BLI_array_store_state_data_get_alloc(state, &state_len);
      BLI_assert(me->totselect == (state_len / stride));
      UNUSED_VARS_NDEBUG(stride);
    }
  
    /* not essential, but prevents accidental dangling pointer access */
    BKE_mesh_update_customdata_pointers(me, false);
  }
  
  static void um_arraystore_free(UndoMesh *um)
  {
    Mesh *me = &um->me;
  
    um_arraystore_cd_free(um->store.vdata);
    um_arraystore_cd_free(um->store.edata);
    um_arraystore_cd_free(um->store.ldata);
    um_arraystore_cd_free(um->store.pdata);
  
    if (um->store.keyblocks) {
      const size_t stride = me->key->elemsize;
      BArrayStore *bs = BLI_array_store_at_size_get(&um_arraystore.bs_stride, stride);
      for (int i = 0; i < me->key->totkey; i++) {
        BArrayState *state = um->store.keyblocks[i];
        BLI_array_store_state_remove(bs, state);
      }
      MEM_freeN(um->store.keyblocks);
      um->store.keyblocks = NULL;
    }
  
    if (um->store.mselect) {
      const size_t stride = sizeof(*me->mselect);
      BArrayStore *bs = BLI_array_store_at_size_get(&um_arraystore.bs_stride, stride);
      BArrayState *state = um->store.mselect;
      BLI_array_store_state_remove(bs, state);
      um->store.mselect = NULL;
    }
  
    um_arraystore.users -= 1;
  
    BLI_assert(um_arraystore.users >= 0);
  
    if (um_arraystore.users == 0) {
  #  ifdef DEBUG_PRINT
      printf("mesh undo store: freeing all data!\n");
  #  endif
      BLI_array_store_at_size_clear(&um_arraystore.bs_stride);
  
  #  ifdef USE_ARRAY_STORE_THREAD
      BLI_task_pool_free(um_arraystore.task_pool);
      um_arraystore.task_pool = NULL;
  #  endif
    }
  }
  
  /** \} */
  
  #endif /* USE_ARRAY_STORE */
  
  /* for callbacks */
  /* undo simply makes copies of a bmesh */
  static void *undomesh_from_editmesh(UndoMesh *um, BMEditMesh *em, Key *key)
  {
    BLI_assert(BLI_array_is_zeroed(um, 1));
  #ifdef USE_ARRAY_STORE_THREAD
    /* changes this waits is low, but must have finished */
    if (um_arraystore.task_pool) {
      BLI_task_pool_work_and_wait(um_arraystore.task_pool);
    }
  #endif
    /* make sure shape keys work */
    um->me.key = key ? BKE_key_copy_nolib(key) : NULL;
  
    /* BM_mesh_validate(em->bm); */ /* for troubleshooting */
  
    BM_mesh_bm_to_me(
        NULL,
        em->bm,
        &um->me,
        (&(struct BMeshToMeshParams){
            /* Undo code should not be manipulating 'G_MAIN->object' hooks/vertex-parent. */
            .calc_object_remap = false,
            .cd_mask_extra = {.vmask = CD_MASK_SHAPE_KEYINDEX},
        }));
  
    um->selectmode = em->selectmode;
    um->shapenr = em->bm->shapenr;
  
  #ifdef USE_ARRAY_STORE
    {
      /* We could be more clever here,
       * the previous undo state may be from a separate mesh. */
      const UndoMesh *um_ref = um_arraystore.local_links.last ?
                                   ((LinkData *)um_arraystore.local_links.last)->data :
                                   NULL;
  
      /* add oursrlves */
      BLI_addtail(&um_arraystore.local_links, BLI_genericNodeN(um));
  
  #  ifdef USE_ARRAY_STORE_THREAD
      if (um_arraystore.task_pool == NULL) {
        TaskScheduler *scheduler = BLI_task_scheduler_get();
        um_arraystore.task_pool = BLI_task_pool_create_background(scheduler, NULL);
      }
  
      struct UMArrayData *um_data = MEM_mallocN(sizeof(*um_data), __func__);
      um_data->um = um;
      um_data->um_ref = um_ref;
  
      BLI_task_pool_push(
          um_arraystore.task_pool, um_arraystore_compact_cb, um_data, true, TASK_PRIORITY_LOW);
  #  else
      um_arraystore_compact_with_info(um, um_ref);
  #  endif
    }
  #endif
  
    return um;
  }
  
  static void undomesh_to_editmesh(UndoMesh *um, BMEditMesh *em, Mesh *obmesh)
  {
    BMEditMesh *em_tmp;
    Object *ob = em->ob;
    BMesh *bm;
    Key *key = obmesh->key;
  
  #ifdef USE_ARRAY_STORE
  #  ifdef USE_ARRAY_STORE_THREAD
    /* changes this waits is low, but must have finished */
    BLI_task_pool_work_and_wait(um_arraystore.task_pool);
  #  endif
  
  #  ifdef DEBUG_TIME
    TIMEIT_START(mesh_undo_expand);
  #  endif
  
    um_arraystore_expand(um);
  
  #  ifdef DEBUG_TIME
    TIMEIT_END(mesh_undo_expand);
  #  endif
  #endif /* USE_ARRAY_STORE */
  
    const BMAllocTemplate allocsize = BMALLOC_TEMPLATE_FROM_ME(&um->me);
  
    em->bm->shapenr = um->shapenr;
  
    EDBM_mesh_free(em);
  
    bm = BM_mesh_create(&allocsize,
                        &((struct BMeshCreateParams){
                            .use_toolflags = true,
                        }));
  
    BM_mesh_bm_from_me(bm,
                       &um->me,
                       (&(struct BMeshFromMeshParams){
                           .calc_face_normal = true,
                           .active_shapekey = um->shapenr,
                       }));
  
    em_tmp = BKE_editmesh_create(bm, true);
    *em = *em_tmp;
  
    em->selectmode = um->selectmode;
    bm->selectmode = um->selectmode;
    em->ob = ob;
  
    bm->spacearr_dirty = BM_SPACEARR_DIRTY_ALL;
  
    /* T35170: Restore the active key on the RealMesh. Otherwise 'fake' offset propagation happens
     *         if the active is a basis for any other. */
    if (key && (key->type == KEY_RELATIVE)) {
      /* Since we can't add, remove or reorder keyblocks in editmode, it's safe to assume
       * shapenr from restored bmesh and keyblock indices are in sync. */
      const int kb_act_idx = ob->shapenr - 1;
  
      /* If it is, let's patch the current mesh key block to its restored value.
       * Else, the offsets won't be computed and it won't matter. */
      if (BKE_keyblock_is_basis(key, kb_act_idx)) {
        KeyBlock *kb_act = BLI_findlink(&key->block, kb_act_idx);
  
        if (kb_act->totelem != um->me.totvert) {
          /* The current mesh has some extra/missing verts compared to the undo, adjust. */
          MEM_SAFE_FREE(kb_act->data);
          kb_act->data = MEM_mallocN((size_t)(key->elemsize * bm->totvert), __func__);
          kb_act->totelem = um->me.totvert;
        }
  
        BKE_keyblock_update_from_mesh(&um->me, kb_act);
      }
    }
  
    ob->shapenr = um->shapenr;
  
    MEM_freeN(em_tmp);
  
  #ifdef USE_ARRAY_STORE
    um_arraystore_expand_clear(um);
  #endif
  }
  
  static void undomesh_free_data(UndoMesh *um)
  {
    Mesh *me = &um->me;
  
  #ifdef USE_ARRAY_STORE
  
  #  ifdef USE_ARRAY_STORE_THREAD
    /* changes this waits is low, but must have finished */
    BLI_task_pool_work_and_wait(um_arraystore.task_pool);
  #  endif
  
    /* we need to expand so any allocations in custom-data are freed with the mesh */
    um_arraystore_expand(um);
  
    {
      LinkData *link = BLI_findptr(&um_arraystore.local_links, um, offsetof(LinkData, data));
      BLI_remlink(&um_arraystore.local_links, link);
      MEM_freeN(link);
    }
    um_arraystore_free(um);
  #endif
  
    if (me->key) {
      BKE_key_free(me->key);
      MEM_freeN(me->key);
    }
  
    BKE_mesh_free(me);
  }
  
  static Object *editmesh_object_from_context(bContext *C)
  {
    Object *obedit = CTX_data_edit_object(C);
    if (obedit && obedit->type == OB_MESH) {
      Mesh *me = obedit->data;
      if (me->edit_mesh != NULL) {
        return obedit;
      }
    }
    return NULL;
  }
  
  /** \} */
  
  /* -------------------------------------------------------------------- */
  /** \name Implements ED Undo System
   *
   * \note This is similar for all edit-mode types.
   * \{ */
  
  typedef struct MeshUndoStep_Elem {
    struct MeshUndoStep_Elem *next, *prev;
    UndoRefID_Object obedit_ref;
    UndoMesh data;
  } MeshUndoStep_Elem;
  
  typedef struct MeshUndoStep {
    UndoStep step;
    MeshUndoStep_Elem *elems;
    uint elems_len;
  } MeshUndoStep;
  
  static bool mesh_undosys_poll(bContext *C)
  {
    return editmesh_object_from_context(C) != NULL;
  }
  
  static bool mesh_undosys_step_encode(struct bContext *C, struct Main *bmain, UndoStep *us_p)
  {
    MeshUndoStep *us = (MeshUndoStep *)us_p;
  
    /* Important not to use the 3D view when getting objects because all objects
     * outside of this list will be moved out of edit-mode when reading back undo steps. */
    ViewLayer *view_layer = CTX_data_view_layer(C);
    uint objects_len = 0;
    Object **objects = BKE_view_layer_array_from_objects_in_edit_mode_unique_data(
        view_layer, NULL, &objects_len);
  
    us->elems = MEM_callocN(sizeof(*us->elems) * objects_len, __func__);
    us->elems_len = objects_len;
  
    for (uint i = 0; i < objects_len; i++) {
      Object *ob = objects[i];
      MeshUndoStep_Elem *elem = &us->elems[i];
  
      elem->obedit_ref.ptr = ob;
      Mesh *me = elem->obedit_ref.ptr->data;
      BMEditMesh *em = me->edit_mesh;
      undomesh_from_editmesh(&elem->data, me->edit_mesh, me->key);
      em->needs_flush_to_id = 1;
      us->step.data_size += elem->data.undo_size;
    }
    MEM_freeN(objects);
  
    bmain->is_memfile_undo_flush_needed = true;
  
    return true;
  }
  
  static void mesh_undosys_step_decode(
      struct bContext *C, struct Main *bmain, UndoStep *us_p, int UNUSED(dir), bool UNUSED(is_final))
  {
    MeshUndoStep *us = (MeshUndoStep *)us_p;
  
    /* Load all our objects  into edit-mode, clear everything else. */
    ED_undo_object_editmode_restore_helper(
        C, &us->elems[0].obedit_ref.ptr, us->elems_len, sizeof(*us->elems));
  
    BLI_assert(mesh_undosys_poll(C));
  
    for (uint i = 0; i < us->elems_len; i++) {
      MeshUndoStep_Elem *elem = &us->elems[i];
      Object *obedit = elem->obedit_ref.ptr;
      Mesh *me = obedit->data;
      if (me->edit_mesh == NULL) {
        /* Should never fail, may not crash but can give odd behavior. */
        CLOG_ERROR(&LOG,
                   "name='%s', failed to enter edit-mode for object '%s', undo state invalid",
                   us_p->name,
                   obedit->id.name);
        continue;
      }
      BMEditMesh *em = me->edit_mesh;
      undomesh_to_editmesh(&elem->data, em, obedit->data);
      em->needs_flush_to_id = 1;
      DEG_id_tag_update(&obedit->id, ID_RECALC_GEOMETRY);
    }
  
    /* The first element is always active */
    ED_undo_object_set_active_or_warn(
        CTX_data_view_layer(C), us->elems[0].obedit_ref.ptr, us_p->name, &LOG);
  
    Scene *scene = CTX_data_scene(C);
    scene->toolsettings->selectmode = us->elems[0].data.selectmode;
  
    bmain->is_memfile_undo_flush_needed = true;
  
    WM_event_add_notifier(C, NC_GEOM | ND_DATA, NULL);
  }
  
  static void mesh_undosys_step_free(UndoStep *us_p)
  {
    MeshUndoStep *us = (MeshUndoStep *)us_p;
  
    for (uint i = 0; i < us->elems_len; i++) {
      MeshUndoStep_Elem *elem = &us->elems[i];
      undomesh_free_data(&elem->data);
    }
    MEM_freeN(us->elems);
  }
  
  static void mesh_undosys_foreach_ID_ref(UndoStep *us_p,
                                          UndoTypeForEachIDRefFn foreach_ID_ref_fn,
                                          void *user_data)
  {
    MeshUndoStep *us = (MeshUndoStep *)us_p;
  
    for (uint i = 0; i < us->elems_len; i++) {
      MeshUndoStep_Elem *elem = &us->elems[i];
      foreach_ID_ref_fn(user_data, ((UndoRefID *)&elem->obedit_ref));
    }
  }
  
  /* Export for ED_undo_sys. */
  void ED_mesh_undosys_type(UndoType *ut)
  {
    ut->name = "Edit Mesh";
    ut->poll = mesh_undosys_poll;
    ut->step_encode = mesh_undosys_step_encode;
    ut->step_decode = mesh_undosys_step_decode;
    ut->step_free = mesh_undosys_step_free;
  
    ut->step_foreach_ID_ref = mesh_undosys_foreach_ID_ref;
  
    ut->use_context = true;
  
    ut->step_size = sizeof(MeshUndoStep);
  }
  
  /** \} */
  