test/source/blender/bmesh/intern/bmesh_log.cc

/* SPDX-FileCopyrightText: 2023 Blender Authors
 *
 * SPDX-License-Identifier: GPL-2.0-or-later */

/** \file
 * \ingroup bmesh
 *
 * The BMLog is an interface for storing undo/redo steps as a BMesh is
 * modified. It only stores changes to the BMesh, not full copies.
 *
 * Currently it supports the following types of changes:
 *
 * - Adding and removing vertices
 * - Adding and removing faces
 * - Moving vertices
 * - Setting vertex paint-mask values
 * - Setting vertex hflags
 */

#include "MEM_guardedalloc.h"

#include "BLI_ghash.h"
#include "BLI_listbase.h"
#include "BLI_math_vector.h"
#include "BLI_mempool.h"
#include "BLI_utildefines.h"

#include "BKE_customdata.h"

#include "bmesh.h"
#include "bmesh_log.h"
#include "range_tree.h"

#include "BLI_strict_flags.h"

struct BMLogEntry {
  BMLogEntry *next, *prev;

  /* The following #GHash members map from an element ID to one of the log types above. */

  /** Elements that were in the previous entry, but have been deleted. */
  GHash *deleted_verts;
  GHash *deleted_faces;
  /** Elements that were not in the previous entry, but are in the result of this entry. */
  GHash *added_verts;
  GHash *added_faces;

  /** Vertices whose coordinates, mask value, or hflag have changed. */
  GHash *modified_verts;
  GHash *modified_faces;

  BLI_mempool *pool_verts;
  BLI_mempool *pool_faces;

  /**
   * This is only needed for dropping BMLogEntries while still in
   * dynamic-topology mode, as that should release vert/face IDs
   * back to the BMLog but no BMLog pointer is available at that time.
   *
   * This field is not guaranteed to be valid, any use of it should
   * check for nullptr.
   */
  BMLog *log;
};

struct BMLog {
  /** Tree of free IDs */
  RangeTreeUInt *unused_ids;

  /**
   * Mapping from unique IDs to vertices and faces
   *
   * Each vertex and face in the log gets a unique `uint`
   * assigned. That ID is taken from the set managed by the
   * unused_ids range tree.
   *
   * The ID is needed because element pointers will change as they
   * are created and deleted.
   */
  GHash *id_to_elem;
  GHash *elem_to_id;

  /** All #BMLogEntrys, ordered from earliest to most recent. */
  ListBase entries;

  /**
   * The current log entry from entries list
   *
   * If null, then the original mesh from before any of the log
   * entries is current (i.e. there is nothing left to undo.)
   *
   * If equal to the last entry in the entries list, then all log
   * entries have been applied (i.e. there is nothing left to redo.)
   */
  BMLogEntry *current_entry;
};

struct BMLogVert {
  float co[3];
  float no[3];
  char hflag;
  float mask;
};

struct BMLogFace {
  uint v_ids[3];
  char hflag;
};

/************************* Get/set element IDs ************************/

/* bypass actual hashing, the keys don't overlap */
#define logkey_hash BLI_ghashutil_inthash_p_simple
#define logkey_cmp BLI_ghashutil_intcmp

/* Get the vertex's unique ID from the log */
static uint bm_log_vert_id_get(BMLog *log, BMVert *v)
{
  BLI_assert(BLI_ghash_haskey(log->elem_to_id, v));
  return POINTER_AS_UINT(BLI_ghash_lookup(log->elem_to_id, v));
}

/* Set the vertex's unique ID in the log */
static void bm_log_vert_id_set(BMLog *log, BMVert *v, uint id)
{
  void *vid = POINTER_FROM_UINT(id);

  BLI_ghash_reinsert(log->id_to_elem, vid, v, nullptr, nullptr);
  BLI_ghash_reinsert(log->elem_to_id, v, vid, nullptr, nullptr);
}

/* Get a vertex from its unique ID */
static BMVert *bm_log_vert_from_id(BMLog *log, uint id)
{
  void *key = POINTER_FROM_UINT(id);
  BLI_assert(BLI_ghash_haskey(log->id_to_elem, key));
  return static_cast<BMVert *>(BLI_ghash_lookup(log->id_to_elem, key));
}

/* Get the face's unique ID from the log */
static uint bm_log_face_id_get(BMLog *log, BMFace *f)
{
  BLI_assert(BLI_ghash_haskey(log->elem_to_id, f));
  return POINTER_AS_UINT(BLI_ghash_lookup(log->elem_to_id, f));
}

/* Set the face's unique ID in the log */
static void bm_log_face_id_set(BMLog *log, BMFace *f, uint id)
{
  void *fid = POINTER_FROM_UINT(id);

  BLI_ghash_reinsert(log->id_to_elem, fid, f, nullptr, nullptr);
  BLI_ghash_reinsert(log->elem_to_id, f, fid, nullptr, nullptr);
}

/* Get a face from its unique ID */
static BMFace *bm_log_face_from_id(BMLog *log, uint id)
{
  void *key = POINTER_FROM_UINT(id);
  BLI_assert(BLI_ghash_haskey(log->id_to_elem, key));
  return static_cast<BMFace *>(BLI_ghash_lookup(log->id_to_elem, key));
}

/************************ BMLogVert / BMLogFace ***********************/

/* Get a vertex's paint-mask value
 *
 * Returns zero if no paint-mask layer is present */
static float vert_mask_get(BMVert *v, const int cd_vert_mask_offset)
{
  if (cd_vert_mask_offset != -1) {
    return BM_ELEM_CD_GET_FLOAT(v, cd_vert_mask_offset);
  }
  return 0.0f;
}

/* Set a vertex's paint-mask value
 *
 * Has no effect is no paint-mask layer is present */
static void vert_mask_set(BMVert *v, const float new_mask, const int cd_vert_mask_offset)
{
  if (cd_vert_mask_offset != -1) {
    BM_ELEM_CD_SET_FLOAT(v, cd_vert_mask_offset, new_mask);
  }
}

/* Update a BMLogVert with data from a BMVert */
static void bm_log_vert_bmvert_copy(BMLogVert *lv, BMVert *v, const int cd_vert_mask_offset)
{
  copy_v3_v3(lv->co, v->co);
  copy_v3_v3(lv->no, v->no);
  lv->mask = vert_mask_get(v, cd_vert_mask_offset);
  lv->hflag = v->head.hflag;
}

/* Allocate and initialize a BMLogVert */
static BMLogVert *bm_log_vert_alloc(BMLog *log, BMVert *v, const int cd_vert_mask_offset)
{
  BMLogEntry *entry = log->current_entry;
  BMLogVert *lv = static_cast<BMLogVert *>(BLI_mempool_alloc(entry->pool_verts));

  bm_log_vert_bmvert_copy(lv, v, cd_vert_mask_offset);

  return lv;
}

/* Allocate and initialize a BMLogFace */
static BMLogFace *bm_log_face_alloc(BMLog *log, BMFace *f)
{
  BMLogEntry *entry = log->current_entry;
  BMLogFace *lf = static_cast<BMLogFace *>(BLI_mempool_alloc(entry->pool_faces));
  BMVert *v[3];

  BLI_assert(f->len == 3);

  // BM_iter_as_array(nullptr, BM_VERTS_OF_FACE, f, (void **)v, 3);
  BM_face_as_array_vert_tri(f, v);

  lf->v_ids[0] = bm_log_vert_id_get(log, v[0]);
  lf->v_ids[1] = bm_log_vert_id_get(log, v[1]);
  lf->v_ids[2] = bm_log_vert_id_get(log, v[2]);

  lf->hflag = f->head.hflag;
  return lf;
}

/************************ Helpers for undo/redo ***********************/

static void bm_log_verts_unmake(BMesh *bm, BMLog *log, GHash *verts)
{
  const int cd_vert_mask_offset = CustomData_get_offset(&bm->vdata, CD_PAINT_MASK);

  GHashIterator gh_iter;
  GHASH_ITER (gh_iter, verts) {
    void *key = BLI_ghashIterator_getKey(&gh_iter);
    BMLogVert *lv = static_cast<BMLogVert *>(BLI_ghashIterator_getValue(&gh_iter));
    uint id = POINTER_AS_UINT(key);
    BMVert *v = bm_log_vert_from_id(log, id);

    /* Ensure the log has the final values of the vertex before
     * deleting it */
    bm_log_vert_bmvert_copy(lv, v, cd_vert_mask_offset);

    BM_vert_kill(bm, v);
  }
}

static void bm_log_faces_unmake(BMesh *bm, BMLog *log, GHash *faces)
{
  GHashIterator gh_iter;
  GHASH_ITER (gh_iter, faces) {
    void *key = BLI_ghashIterator_getKey(&gh_iter);
    uint id = POINTER_AS_UINT(key);
    BMFace *f = bm_log_face_from_id(log, id);
    BMEdge *e_tri[3];
    BMLoop *l_iter;
    int i;

    l_iter = BM_FACE_FIRST_LOOP(f);
    for (i = 0; i < 3; i++, l_iter = l_iter->next) {
      e_tri[i] = l_iter->e;
    }

    /* Remove any unused edges */
    BM_face_kill(bm, f);
    for (i = 0; i < 3; i++) {
      if (BM_edge_is_wire(e_tri[i])) {
        BM_edge_kill(bm, e_tri[i]);
      }
    }
  }
}

static void bm_log_verts_restore(BMesh *bm, BMLog *log, GHash *verts)
{
  const int cd_vert_mask_offset = CustomData_get_offset(&bm->vdata, CD_PAINT_MASK);

  GHashIterator gh_iter;
  GHASH_ITER (gh_iter, verts) {
    void *key = BLI_ghashIterator_getKey(&gh_iter);
    BMLogVert *lv = static_cast<BMLogVert *>(BLI_ghashIterator_getValue(&gh_iter));
    BMVert *v = BM_vert_create(bm, lv->co, nullptr, BM_CREATE_NOP);
    vert_mask_set(v, lv->mask, cd_vert_mask_offset);
    v->head.hflag = lv->hflag;
    copy_v3_v3(v->no, lv->no);
    bm_log_vert_id_set(log, v, POINTER_AS_UINT(key));
  }
}

static void bm_log_faces_restore(BMesh *bm, BMLog *log, GHash *faces)
{
  GHashIterator gh_iter;
  const int cd_face_sets = CustomData_get_offset_named(
      &bm->pdata, CD_PROP_INT32, ".sculpt_face_set");

  GHASH_ITER (gh_iter, faces) {
    void *key = BLI_ghashIterator_getKey(&gh_iter);
    BMLogFace *lf = static_cast<BMLogFace *>(BLI_ghashIterator_getValue(&gh_iter));
    BMVert *v[3] = {
        bm_log_vert_from_id(log, lf->v_ids[0]),
        bm_log_vert_from_id(log, lf->v_ids[1]),
        bm_log_vert_from_id(log, lf->v_ids[2]),
    };
    BMFace *f;

    f = BM_face_create_verts(bm, v, 3, nullptr, BM_CREATE_NOP, true);
    f->head.hflag = lf->hflag;
    bm_log_face_id_set(log, f, POINTER_AS_UINT(key));

    /* Ensure face sets have valid values.  Fixes #80174. */
    if (cd_face_sets != -1) {
      BM_ELEM_CD_SET_INT(f, cd_face_sets, 1);
    }
  }
}

static void bm_log_vert_values_swap(BMesh *bm, BMLog *log, GHash *verts)
{
  const int cd_vert_mask_offset = CustomData_get_offset(&bm->vdata, CD_PAINT_MASK);

  GHashIterator gh_iter;
  GHASH_ITER (gh_iter, verts) {
    void *key = BLI_ghashIterator_getKey(&gh_iter);
    BMLogVert *lv = static_cast<BMLogVert *>(BLI_ghashIterator_getValue(&gh_iter));
    uint id = POINTER_AS_UINT(key);
    BMVert *v = bm_log_vert_from_id(log, id);
    float mask;

    swap_v3_v3(v->co, lv->co);
    swap_v3_v3(v->no, lv->no);
    SWAP(char, v->head.hflag, lv->hflag);
    mask = lv->mask;
    lv->mask = vert_mask_get(v, cd_vert_mask_offset);
    vert_mask_set(v, mask, cd_vert_mask_offset);
  }
}

static void bm_log_face_values_swap(BMLog *log, GHash *faces)
{
  GHashIterator gh_iter;
  GHASH_ITER (gh_iter, faces) {
    void *key = BLI_ghashIterator_getKey(&gh_iter);
    BMLogFace *lf = static_cast<BMLogFace *>(BLI_ghashIterator_getValue(&gh_iter));
    uint id = POINTER_AS_UINT(key);
    BMFace *f = bm_log_face_from_id(log, id);

    SWAP(char, f->head.hflag, lf->hflag);
  }
}

/**********************************************************************/

/* Assign unique IDs to all vertices and faces already in the BMesh */
static void bm_log_assign_ids(BMesh *bm, BMLog *log)
{
  BMIter iter;
  BMVert *v;
  BMFace *f;

  /* Generate vertex IDs */
  BM_ITER_MESH (v, &iter, bm, BM_VERTS_OF_MESH) {
    uint id = range_tree_uint_take_any(log->unused_ids);
    bm_log_vert_id_set(log, v, id);
  }

  /* Generate face IDs */
  BM_ITER_MESH (f, &iter, bm, BM_FACES_OF_MESH) {
    uint id = range_tree_uint_take_any(log->unused_ids);
    bm_log_face_id_set(log, f, id);
  }
}

/* Allocate an empty log entry */
static BMLogEntry *bm_log_entry_create()
{
  BMLogEntry *entry = static_cast<BMLogEntry *>(MEM_callocN(sizeof(BMLogEntry), __func__));

  entry->deleted_verts = BLI_ghash_new(logkey_hash, logkey_cmp, __func__);
  entry->deleted_faces = BLI_ghash_new(logkey_hash, logkey_cmp, __func__);
  entry->added_verts = BLI_ghash_new(logkey_hash, logkey_cmp, __func__);
  entry->added_faces = BLI_ghash_new(logkey_hash, logkey_cmp, __func__);
  entry->modified_verts = BLI_ghash_new(logkey_hash, logkey_cmp, __func__);
  entry->modified_faces = BLI_ghash_new(logkey_hash, logkey_cmp, __func__);

  entry->pool_verts = BLI_mempool_create(sizeof(BMLogVert), 0, 64, BLI_MEMPOOL_NOP);
  entry->pool_faces = BLI_mempool_create(sizeof(BMLogFace), 0, 64, BLI_MEMPOOL_NOP);

  return entry;
}

/* Free the data in a log entry
 *
 * NOTE: does not free the log entry itself. */
static void bm_log_entry_free(BMLogEntry *entry)
{
  BLI_ghash_free(entry->deleted_verts, nullptr, nullptr);
  BLI_ghash_free(entry->deleted_faces, nullptr, nullptr);
  BLI_ghash_free(entry->added_verts, nullptr, nullptr);
  BLI_ghash_free(entry->added_faces, nullptr, nullptr);
  BLI_ghash_free(entry->modified_verts, nullptr, nullptr);
  BLI_ghash_free(entry->modified_faces, nullptr, nullptr);

  BLI_mempool_destroy(entry->pool_verts);
  BLI_mempool_destroy(entry->pool_faces);
}

static void bm_log_id_ghash_retake(RangeTreeUInt *unused_ids, GHash *id_ghash)
{
  GHashIterator gh_iter;

  GHASH_ITER (gh_iter, id_ghash) {
    void *key = BLI_ghashIterator_getKey(&gh_iter);
    uint id = POINTER_AS_UINT(key);

    range_tree_uint_retake(unused_ids, id);
  }
}

static int uint_compare(const void *a_v, const void *b_v)
{
  const uint *a = static_cast<const uint *>(a_v);
  const uint *b = static_cast<const uint *>(b_v);
  return (*a) < (*b);
}

/* Remap IDs to contiguous indices
 *
 * E.g. if the vertex IDs are (4, 1, 10, 3), the mapping will be:
 *    4 -> 2
 *    1 -> 0
 *   10 -> 3
 *    3 -> 1
 */
static GHash *bm_log_compress_ids_to_indices(uint *ids, uint totid)
{
  GHash *map = BLI_ghash_int_new_ex(__func__, totid);
  uint i;

  qsort(ids, totid, sizeof(*ids), uint_compare);

  for (i = 0; i < totid; i++) {
    void *key = POINTER_FROM_UINT(ids[i]);
    void *val = POINTER_FROM_UINT(i);
    BLI_ghash_insert(map, key, val);
  }

  return map;
}

/* Release all ID keys in id_ghash */
static void bm_log_id_ghash_release(BMLog *log, GHash *id_ghash)
{
  GHashIterator gh_iter;

  GHASH_ITER (gh_iter, id_ghash) {
    void *key = BLI_ghashIterator_getKey(&gh_iter);
    uint id = POINTER_AS_UINT(key);
    range_tree_uint_release(log->unused_ids, id);
  }
}

/***************************** Public API *****************************/

BMLog *BM_log_create(BMesh *bm)
{
  BMLog *log = static_cast<BMLog *>(MEM_callocN(sizeof(*log), __func__));
  const uint reserve_num = uint(bm->totvert + bm->totface);

  log->unused_ids = range_tree_uint_alloc(0, uint(-1));
  log->id_to_elem = BLI_ghash_new_ex(logkey_hash, logkey_cmp, __func__, reserve_num);
  log->elem_to_id = BLI_ghash_ptr_new_ex(__func__, reserve_num);

  /* Assign IDs to all existing vertices and faces */
  bm_log_assign_ids(bm, log);

  return log;
}

void BM_log_cleanup_entry(BMLogEntry *entry)
{
  BMLog *log = entry->log;

  if (log) {
    /* Take all used IDs */
    bm_log_id_ghash_retake(log->unused_ids, entry->deleted_verts);
    bm_log_id_ghash_retake(log->unused_ids, entry->deleted_faces);
    bm_log_id_ghash_retake(log->unused_ids, entry->added_verts);
    bm_log_id_ghash_retake(log->unused_ids, entry->added_faces);
    bm_log_id_ghash_retake(log->unused_ids, entry->modified_verts);
    bm_log_id_ghash_retake(log->unused_ids, entry->modified_faces);

    /* delete entries to avoid releasing ids in node cleanup */
    BLI_ghash_clear(entry->deleted_verts, nullptr, nullptr);
    BLI_ghash_clear(entry->deleted_faces, nullptr, nullptr);
    BLI_ghash_clear(entry->added_verts, nullptr, nullptr);
    BLI_ghash_clear(entry->added_faces, nullptr, nullptr);
    BLI_ghash_clear(entry->modified_verts, nullptr, nullptr);
  }
}

BMLog *BM_log_from_existing_entries_create(BMesh *bm, BMLogEntry *entry)
{
  BMLog *log = BM_log_create(bm);

  if (entry->prev) {
    log->current_entry = entry;
  }
  else {
    log->current_entry = nullptr;
  }

  /* Let BMLog manage the entry list again */
  log->entries.first = log->entries.last = entry;

  {
    while (entry->prev) {
      entry = entry->prev;
      log->entries.first = entry;
    }
    entry = static_cast<BMLogEntry *>(log->entries.last);
    while (entry->next) {
      entry = entry->next;
      log->entries.last = entry;
    }
  }

  for (entry = static_cast<BMLogEntry *>(log->entries.first); entry; entry = entry->next) {
    entry->log = log;

    /* Take all used IDs */
    bm_log_id_ghash_retake(log->unused_ids, entry->deleted_verts);
    bm_log_id_ghash_retake(log->unused_ids, entry->deleted_faces);
    bm_log_id_ghash_retake(log->unused_ids, entry->added_verts);
    bm_log_id_ghash_retake(log->unused_ids, entry->added_faces);
    bm_log_id_ghash_retake(log->unused_ids, entry->modified_verts);
    bm_log_id_ghash_retake(log->unused_ids, entry->modified_faces);
  }

  return log;
}

void BM_log_free(BMLog *log)
{
  if (log->unused_ids) {
    range_tree_uint_free(log->unused_ids);
  }

  if (log->id_to_elem) {
    BLI_ghash_free(log->id_to_elem, nullptr, nullptr);
  }

  if (log->elem_to_id) {
    BLI_ghash_free(log->elem_to_id, nullptr, nullptr);
  }

  /* Clear the BMLog references within each entry, but do not free
   * the entries themselves */
  LISTBASE_FOREACH (BMLogEntry *, entry, &log->entries) {
    entry->log = nullptr;
  }

  MEM_freeN(log);
}

int BM_log_length(const BMLog *log)
{
  return BLI_listbase_count(&log->entries);
}

void BM_log_mesh_elems_reorder(BMesh *bm, BMLog *log)
{
  uint *varr;
  uint *farr;

  GHash *id_to_idx;

  BMIter bm_iter;
  BMVert *v;
  BMFace *f;

  uint i;

  /* Put all vertex IDs into an array */
  varr = static_cast<uint *>(MEM_mallocN(sizeof(int) * size_t(bm->totvert), __func__));
  BM_ITER_MESH_INDEX (v, &bm_iter, bm, BM_VERTS_OF_MESH, i) {
    varr[i] = bm_log_vert_id_get(log, v);
  }

  /* Put all face IDs into an array */
  farr = static_cast<uint *>(MEM_mallocN(sizeof(int) * size_t(bm->totface), __func__));
  BM_ITER_MESH_INDEX (f, &bm_iter, bm, BM_FACES_OF_MESH, i) {
    farr[i] = bm_log_face_id_get(log, f);
  }

  /* Create BMVert index remap array */
  id_to_idx = bm_log_compress_ids_to_indices(varr, uint(bm->totvert));
  BM_ITER_MESH_INDEX (v, &bm_iter, bm, BM_VERTS_OF_MESH, i) {
    const uint id = bm_log_vert_id_get(log, v);
    const void *key = POINTER_FROM_UINT(id);
    const void *val = BLI_ghash_lookup(id_to_idx, key);
    varr[i] = POINTER_AS_UINT(val);
  }
  BLI_ghash_free(id_to_idx, nullptr, nullptr);

  /* Create BMFace index remap array */
  id_to_idx = bm_log_compress_ids_to_indices(farr, uint(bm->totface));
  BM_ITER_MESH_INDEX (f, &bm_iter, bm, BM_FACES_OF_MESH, i) {
    const uint id = bm_log_face_id_get(log, f);
    const void *key = POINTER_FROM_UINT(id);
    const void *val = BLI_ghash_lookup(id_to_idx, key);
    farr[i] = POINTER_AS_UINT(val);
  }
  BLI_ghash_free(id_to_idx, nullptr, nullptr);

  BM_mesh_remap(bm, varr, nullptr, farr);

  MEM_freeN(varr);
  MEM_freeN(farr);
}

BMLogEntry *BM_log_entry_add(BMLog *log)
{
  /* WARNING: this is now handled by the UndoSystem: BKE_UNDOSYS_TYPE_SCULPT
   * freeing here causes unnecessary complications. */
  BMLogEntry *entry;
#if 0
  /* Delete any entries after the current one */
  entry = log->current_entry;
  if (entry) {
    BMLogEntry *next;
    for (entry = entry->next; entry; entry = next) {
      next = entry->next;
      bm_log_entry_free(entry);
      BLI_freelinkN(&log->entries, entry);
    }
  }
#endif

  /* Create and append the new entry */
  entry = bm_log_entry_create();
  BLI_addtail(&log->entries, entry);
  entry->log = log;
  log->current_entry = entry;

  return entry;
}

void BM_log_entry_drop(BMLogEntry *entry)
{
  BMLog *log = entry->log;

  if (!log) {
    /* Unlink */
    BLI_assert(!(entry->prev && entry->next));
    if (entry->prev) {
      entry->prev->next = nullptr;
    }
    else if (entry->next) {
      entry->next->prev = nullptr;
    }

    bm_log_entry_free(entry);
    MEM_freeN(entry);
    return;
  }

  if (!entry->prev) {
    /* Release IDs of elements that are deleted by this
     * entry. Since the entry is at the beginning of the undo
     * stack, and it's being deleted, those elements can never be
     * restored. Their IDs can go back into the pool. */

    /* This would never happen usually since first entry of log is
     * usually dyntopo enable, which, when reverted will free the log
     * completely. However, it is possible have a stroke instead of
     * dyntopo enable as first entry if nodes have been cleaned up
     * after sculpting on a different object than A, B.
     *
     * The steps are:
     * A dyntopo enable - sculpt
     * B dyntopo enable - sculpt - undo (A objects operators get cleaned up)
     * A sculpt (now A's log has a sculpt operator as first entry)
     *
     * Causing a cleanup at this point will call the code below, however
     * this will invalidate the state of the log since the deleted vertices
     * have been reclaimed already on step 2 (see BM_log_cleanup_entry)
     *
     * Also, design wise, a first entry should not have any deleted vertices since it
     * should not have anything to delete them -from-
     */
    // bm_log_id_ghash_release(log, entry->deleted_faces);
    // bm_log_id_ghash_release(log, entry->deleted_verts);
  }
  else if (!entry->next) {
    /* Release IDs of elements that are added by this entry. Since
     * the entry is at the end of the undo stack, and it's being
     * deleted, those elements can never be restored. Their IDs
     * can go back into the pool. */
    bm_log_id_ghash_release(log, entry->added_faces);
    bm_log_id_ghash_release(log, entry->added_verts);
  }
  else {
    BLI_assert_msg(0, "Cannot drop BMLogEntry from middle");
  }

  if (log->current_entry == entry) {
    log->current_entry = entry->prev;
  }

  bm_log_entry_free(entry);
  BLI_freelinkN(&log->entries, entry);
}

void BM_log_undo(BMesh *bm, BMLog *log)
{
  BMLogEntry *entry = log->current_entry;

  if (entry) {
    log->current_entry = entry->prev;

    /* Delete added faces and verts */
    bm_log_faces_unmake(bm, log, entry->added_faces);
    bm_log_verts_unmake(bm, log, entry->added_verts);

    /* Restore deleted verts and faces */
    bm_log_verts_restore(bm, log, entry->deleted_verts);
    bm_log_faces_restore(bm, log, entry->deleted_faces);

    /* Restore vertex coordinates, mask, and hflag */
    bm_log_vert_values_swap(bm, log, entry->modified_verts);
    bm_log_face_values_swap(log, entry->modified_faces);
  }
}

void BM_log_redo(BMesh *bm, BMLog *log)
{
  BMLogEntry *entry = log->current_entry;

  if (!entry) {
    /* Currently at the beginning of the undo stack, move to first entry */
    entry = static_cast<BMLogEntry *>(log->entries.first);
  }
  else if (entry->next) {
    /* Move to next undo entry */
    entry = entry->next;
  }
  else {
    /* Currently at the end of the undo stack, nothing left to redo */
    return;
  }

  log->current_entry = entry;

  if (entry) {
    /* Re-delete previously deleted faces and verts */
    bm_log_faces_unmake(bm, log, entry->deleted_faces);
    bm_log_verts_unmake(bm, log, entry->deleted_verts);

    /* Restore previously added verts and faces */
    bm_log_verts_restore(bm, log, entry->added_verts);
    bm_log_faces_restore(bm, log, entry->added_faces);

    /* Restore vertex coordinates, mask, and hflag */
    bm_log_vert_values_swap(bm, log, entry->modified_verts);
    bm_log_face_values_swap(log, entry->modified_faces);
  }
}

void BM_log_vert_before_modified(BMLog *log, BMVert *v, const int cd_vert_mask_offset)
{
  BMLogEntry *entry = log->current_entry;
  BMLogVert *lv;
  uint v_id = bm_log_vert_id_get(log, v);
  void *key = POINTER_FROM_UINT(v_id);
  void **val_p;

  /* Find or create the BMLogVert entry */
  if ((lv = static_cast<BMLogVert *>(BLI_ghash_lookup(entry->added_verts, key)))) {
    bm_log_vert_bmvert_copy(lv, v, cd_vert_mask_offset);
  }
  else if (!BLI_ghash_ensure_p(entry->modified_verts, key, &val_p)) {
    lv = bm_log_vert_alloc(log, v, cd_vert_mask_offset);
    *val_p = lv;
  }
}

void BM_log_vert_added(BMLog *log, BMVert *v, const int cd_vert_mask_offset)
{
  BMLogVert *lv;
  uint v_id = range_tree_uint_take_any(log->unused_ids);
  void *key = POINTER_FROM_UINT(v_id);

  bm_log_vert_id_set(log, v, v_id);
  lv = bm_log_vert_alloc(log, v, cd_vert_mask_offset);
  BLI_ghash_insert(log->current_entry->added_verts, key, lv);
}

void BM_log_face_modified(BMLog *log, BMFace *f)
{
  BMLogFace *lf;
  uint f_id = bm_log_face_id_get(log, f);
  void *key = POINTER_FROM_UINT(f_id);

  lf = bm_log_face_alloc(log, f);
  BLI_ghash_insert(log->current_entry->modified_faces, key, lf);
}

void BM_log_face_added(BMLog *log, BMFace *f)
{
  BMLogFace *lf;
  uint f_id = range_tree_uint_take_any(log->unused_ids);
  void *key = POINTER_FROM_UINT(f_id);

  /* Only triangles are supported for now */
  BLI_assert(f->len == 3);

  bm_log_face_id_set(log, f, f_id);
  lf = bm_log_face_alloc(log, f);
  BLI_ghash_insert(log->current_entry->added_faces, key, lf);
}

void BM_log_vert_removed(BMLog *log, BMVert *v, const int cd_vert_mask_offset)
{
  BMLogEntry *entry = log->current_entry;
  uint v_id = bm_log_vert_id_get(log, v);
  void *key = POINTER_FROM_UINT(v_id);

  /* if it has a key, it shouldn't be nullptr */
  BLI_assert(!!BLI_ghash_lookup(entry->added_verts, key) ==
             !!BLI_ghash_haskey(entry->added_verts, key));

  if (BLI_ghash_remove(entry->added_verts, key, nullptr, nullptr)) {
    range_tree_uint_release(log->unused_ids, v_id);
  }
  else {
    BMLogVert *lv, *lv_mod;

    lv = bm_log_vert_alloc(log, v, cd_vert_mask_offset);
    BLI_ghash_insert(entry->deleted_verts, key, lv);

    /* If the vertex was modified before deletion, ensure that the
     * original vertex values are stored */
    if ((lv_mod = static_cast<BMLogVert *>(BLI_ghash_lookup(entry->modified_verts, key)))) {
      (*lv) = (*lv_mod);
      BLI_ghash_remove(entry->modified_verts, key, nullptr, nullptr);
    }
  }
}

void BM_log_face_removed(BMLog *log, BMFace *f)
{
  BMLogEntry *entry = log->current_entry;
  uint f_id = bm_log_face_id_get(log, f);
  void *key = POINTER_FROM_UINT(f_id);

  /* if it has a key, it shouldn't be nullptr */
  BLI_assert(!!BLI_ghash_lookup(entry->added_faces, key) ==
             !!BLI_ghash_haskey(entry->added_faces, key));

  if (BLI_ghash_remove(entry->added_faces, key, nullptr, nullptr)) {
    range_tree_uint_release(log->unused_ids, f_id);
  }
  else {
    BMLogFace *lf;

    lf = bm_log_face_alloc(log, f);
    BLI_ghash_insert(entry->deleted_faces, key, lf);
  }
}

void BM_log_all_added(BMesh *bm, BMLog *log)
{
  const int cd_vert_mask_offset = CustomData_get_offset(&bm->vdata, CD_PAINT_MASK);
  BMIter bm_iter;
  BMVert *v;
  BMFace *f;

  /* avoid unnecessary resizing on initialization */
  if (BLI_ghash_len(log->current_entry->added_verts) == 0) {
    BLI_ghash_reserve(log->current_entry->added_verts, uint(bm->totvert));
  }

  if (BLI_ghash_len(log->current_entry->added_faces) == 0) {
    BLI_ghash_reserve(log->current_entry->added_faces, uint(bm->totface));
  }

  /* Log all vertices as newly created */
  BM_ITER_MESH (v, &bm_iter, bm, BM_VERTS_OF_MESH) {
    BM_log_vert_added(log, v, cd_vert_mask_offset);
  }

  /* Log all faces as newly created */
  BM_ITER_MESH (f, &bm_iter, bm, BM_FACES_OF_MESH) {
    BM_log_face_added(log, f);
  }
}

void BM_log_before_all_removed(BMesh *bm, BMLog *log)
{
  const int cd_vert_mask_offset = CustomData_get_offset(&bm->vdata, CD_PAINT_MASK);
  BMIter bm_iter;
  BMVert *v;
  BMFace *f;

  /* Log deletion of all faces */
  BM_ITER_MESH (f, &bm_iter, bm, BM_FACES_OF_MESH) {
    BM_log_face_removed(log, f);
  }

  /* Log deletion of all vertices */
  BM_ITER_MESH (v, &bm_iter, bm, BM_VERTS_OF_MESH) {
    BM_log_vert_removed(log, v, cd_vert_mask_offset);
  }
}

const float *BM_log_original_vert_co(BMLog *log, BMVert *v)
{
  BMLogEntry *entry = log->current_entry;
  const BMLogVert *lv;
  uint v_id = bm_log_vert_id_get(log, v);
  void *key = POINTER_FROM_UINT(v_id);

  BLI_assert(entry);

  BLI_assert(BLI_ghash_haskey(entry->modified_verts, key));

  lv = static_cast<const BMLogVert *>(BLI_ghash_lookup(entry->modified_verts, key));
  return lv->co;
}

const float *BM_log_original_vert_no(BMLog *log, BMVert *v)
{
  BMLogEntry *entry = log->current_entry;
  const BMLogVert *lv;
  uint v_id = bm_log_vert_id_get(log, v);
  void *key = POINTER_FROM_UINT(v_id);

  BLI_assert(entry);

  BLI_assert(BLI_ghash_haskey(entry->modified_verts, key));

  lv = static_cast<const BMLogVert *>(BLI_ghash_lookup(entry->modified_verts, key));
  return lv->no;
}

float BM_log_original_mask(BMLog *log, BMVert *v)
{
  BMLogEntry *entry = log->current_entry;
  const BMLogVert *lv;
  uint v_id = bm_log_vert_id_get(log, v);
  void *key = POINTER_FROM_UINT(v_id);

  BLI_assert(entry);

  BLI_assert(BLI_ghash_haskey(entry->modified_verts, key));

  lv = static_cast<const BMLogVert *>(BLI_ghash_lookup(entry->modified_verts, key));
  return lv->mask;
}

void BM_log_original_vert_data(BMLog *log, BMVert *v, const float **r_co, const float **r_no)
{
  BMLogEntry *entry = log->current_entry;
  const BMLogVert *lv;
  uint v_id = bm_log_vert_id_get(log, v);
  void *key = POINTER_FROM_UINT(v_id);

  BLI_assert(entry);

  BLI_assert(BLI_ghash_haskey(entry->modified_verts, key));

  lv = static_cast<const BMLogVert *>(BLI_ghash_lookup(entry->modified_verts, key));
  *r_co = lv->co;
  *r_no = lv->no;
}

/************************ Debugging and Testing ***********************/

BMLogEntry *BM_log_current_entry(BMLog *log)
{
  return log->current_entry;
}

RangeTreeUInt *BM_log_unused_ids(BMLog *log)
{
  return log->unused_ids;
}

#if 0
/* Print the list of entries, marking the current one
 *
 * Keep around for debugging */
void bm_log_print(const BMLog *log, const char *description)
{
  const BMLogEntry *entry;
  const char *current = " <-- current";
  int i;

  printf("%s:\n", description);
  printf("    % 2d: [ initial ]%s\n", 0, (!log->current_entry) ? current : "");
  for (entry = log->entries.first, i = 1; entry; entry = entry->next, i++) {
    printf("    % 2d: [%p]%s\n", i, entry, (entry == log->current_entry) ? current : "");
  }
}
#endif

void BM_log_print_entry(BMesh *bm, BMLogEntry *entry)
{
  if (bm) {
    printf("BM { totvert=%d totedge=%d totloop=%d faces_num=%d\n",
           bm->totvert,
           bm->totedge,
           bm->totloop,
           bm->totface);

    if (!bm->totvert) {
      printf("%s: Warning: empty bmesh\n", __func__);
    }
  }
  else {
    printf("BM { totvert=unknown totedge=unknown totloop=unknown faces_num=unknown\n");
  }

  printf("v | added: %d, removed: %d, modified: %d\n",
         int(BLI_ghash_len(entry->added_verts)),
         int(BLI_ghash_len(entry->deleted_verts)),
         int(BLI_ghash_len(entry->modified_verts)));
  printf("f | added: %d, removed: %d, modified: %d\n",
         int(BLI_ghash_len(entry->added_faces)),
         int(BLI_ghash_len(entry->deleted_faces)),
         int(BLI_ghash_len(entry->modified_faces)));
  printf("}\n");
}