bmesh_polygon_edgenet.cc

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/* SPDX-FileCopyrightText: 2023 Blender Authors
 *
 * SPDX-License-Identifier: GPL-2.0-or-later */
 
// #define DEBUG_PRINT
 
#include "MEM_guardedalloc.h"
 
#include "BLI_alloca.h"
#include "BLI_kdopbvh.h"
#include "BLI_linklist_stack.h"
#include "BLI_math_geom.h"
#include "BLI_math_matrix.h"
#include "BLI_math_vector.h"
#include "BLI_memarena.h"
#include "BLI_sort_utils.h"
#include "BLI_utildefines_stack.h"
#include "BLI_vector.hh"
 
#include "BKE_customdata.hh"
 
#include "bmesh.hh"
#include "intern/bmesh_private.hh"
 
/* -------------------------------------------------------------------- */
/* NOTE: All these flags _must_ be cleared on exit. */
 
/* face is a part of the edge-net (including the original face we're splitting) */
#define FACE_NET _FLAG_WALK
/* edge is a part of the edge-net we're filling */
#define EDGE_NET _FLAG_WALK
/* tag verts we've visit */
#define VERT_VISIT _FLAG_WALK
#define VERT_IN_QUEUE _FLAG_WALK_ALT
 
struct VertOrder {
  float angle;
  BMVert *v;
};
 
static uint bm_edge_flagged_radial_count(BMEdge *e)
{
  uint count = 0;
  BMLoop *l;
 
  if ((l = e->l)) {
    do {
      if (BM_ELEM_API_FLAG_TEST(l->f, FACE_NET)) {
        count++;
      }
    } while ((l = l->radial_next) != e->l);
  }
  return count;
}
 
static BMLoop *bm_edge_flagged_radial_first(BMEdge *e)
{
  BMLoop *l;
 
  if ((l = e->l)) {
    do {
      if (BM_ELEM_API_FLAG_TEST(l->f, FACE_NET)) {
        return l;
      }
    } while ((l = l->radial_next) != e->l);
  }
  return nullptr;
}
 
static void normalize_v2_m3_v3v3(float out[2],
                                 const float axis_mat[3][3],
                                 const float v1[3],
                                 const float v2[3])
{
  float dir[3];
  sub_v3_v3v3(dir, v1, v2);
  mul_v2_m3v3(out, axis_mat, dir);
  normalize_v2(out);
}
 
static bool bm_face_split_edgenet_find_loop_pair(BMVert *v_init,
                                                 const float face_normal[3],
                                                 const float face_normal_matrix[3][3],
                                                 BMEdge *e_pair[2])
{
  /* Always find one boundary edge (to determine winding)
   * and one wire (if available), otherwise another boundary.
   */
 
  /* detect winding */
  BMLoop *l_walk;
  bool swap;
 
  BLI_SMALLSTACK_DECLARE(edges_boundary, BMEdge *);
  BLI_SMALLSTACK_DECLARE(edges_wire, BMEdge *);
  int edges_boundary_len = 0;
  int edges_wire_len = 0;
 
  {
    BMEdge *e, *e_first;
    e = e_first = v_init->e;
    do {
      if (BM_ELEM_API_FLAG_TEST(e, EDGE_NET)) {
        const uint count = bm_edge_flagged_radial_count(e);
        if (count == 1) {
          BLI_SMALLSTACK_PUSH(edges_boundary, e);
          edges_boundary_len++;
        }
        else if (count == 0) {
          BLI_SMALLSTACK_PUSH(edges_wire, e);
          edges_wire_len++;
        }
      }
    } while ((e = BM_DISK_EDGE_NEXT(e, v_init)) != e_first);
  }
 
  /* first edge should always be boundary */
  if (edges_boundary_len == 0) {
    return false;
  }
  e_pair[0] = static_cast<BMEdge *>(BLI_SMALLSTACK_POP(edges_boundary));
 
  /* use to hold boundary OR wire edges */
  BLI_SMALLSTACK_DECLARE(edges_search, BMEdge *);
 
  /* attempt one boundary and one wire, or 2 boundary */
  if (edges_wire_len == 0) {
    if (edges_boundary_len > 1) {
      e_pair[1] = static_cast<BMEdge *>(BLI_SMALLSTACK_POP(edges_boundary));
 
      if (edges_boundary_len > 2) {
        BLI_SMALLSTACK_SWAP(edges_search, edges_boundary);
      }
    }
    else {
      /* one boundary and no wire */
      return false;
    }
  }
  else {
    e_pair[1] = static_cast<BMEdge *>(BLI_SMALLSTACK_POP(edges_wire));
    if (edges_wire_len > 1) {
      BLI_SMALLSTACK_SWAP(edges_search, edges_wire);
    }
  }
 
  /* if we swapped above, search this list for the best edge */
  if (!BLI_SMALLSTACK_IS_EMPTY(edges_search)) {
    /* find the best edge in 'edge_list' to use for 'e_pair[1]' */
    const BMVert *v_prev = BM_edge_other_vert(e_pair[0], v_init);
    const BMVert *v_next = BM_edge_other_vert(e_pair[1], v_init);
 
    float dir_prev[2], dir_next[2];
 
    normalize_v2_m3_v3v3(dir_prev, face_normal_matrix, v_prev->co, v_init->co);
    normalize_v2_m3_v3v3(dir_next, face_normal_matrix, v_next->co, v_init->co);
    float angle_best_cos = dot_v2v2(dir_next, dir_prev);
 
    BMEdge *e;
    while ((e = static_cast<BMEdge *>(BLI_SMALLSTACK_POP(edges_search)))) {
      v_next = BM_edge_other_vert(e, v_init);
      float dir_test[2];
 
      normalize_v2_m3_v3v3(dir_test, face_normal_matrix, v_next->co, v_init->co);
      const float angle_test_cos = dot_v2v2(dir_prev, dir_test);
 
      if (angle_test_cos > angle_best_cos) {
        angle_best_cos = angle_test_cos;
        e_pair[1] = e;
      }
    }
  }
 
  /* flip based on winding */
  l_walk = bm_edge_flagged_radial_first(e_pair[0]);
  swap = false;
  if (face_normal == l_walk->f->no) {
    swap = !swap;
  }
  if (l_walk->v != v_init) {
    swap = !swap;
  }
  if (swap) {
    std::swap(e_pair[0], e_pair[1]);
  }
 
  return true;
}
 
static bool bm_face_split_edgenet_find_loop_pair_exists(BMVert *v_init)
{
  int edges_boundary_len = 0;
  int edges_wire_len = 0;
 
  {
    BMEdge *e, *e_first;
    e = e_first = v_init->e;
    do {
      if (BM_ELEM_API_FLAG_TEST(e, EDGE_NET)) {
        const uint count = bm_edge_flagged_radial_count(e);
        if (count == 1) {
          edges_boundary_len++;
        }
        else if (count == 0) {
          edges_wire_len++;
        }
      }
    } while ((e = BM_DISK_EDGE_NEXT(e, v_init)) != e_first);
  }
 
  /* first edge should always be boundary */
  if (edges_boundary_len == 0) {
    return false;
  }
 
  /* attempt one boundary and one wire, or 2 boundary */
  if (edges_wire_len == 0) {
    if (edges_boundary_len >= 2) {
      /* pass */
    }
    else {
      /* one boundary and no wire */
      return false;
    }
  }
  else {
    /* pass */
  }
 
  return true;
}
 
static bool bm_face_split_edgenet_find_loop_walk(BMVert *v_init,
                                                 const float face_normal[3],
                                                 /* cache to avoid realloc every time */
                                                 VertOrder *edge_order,
                                                 const uint edge_order_len,
                                                 BMEdge *e_pair[2])
{
  UNUSED_VARS_NDEBUG(edge_order_len);
 
/* fast-path for the common case (avoid push-pop).
 * Also avoids tagging as visited since we know we
 * can't reach these verts some other way */
#define USE_FASTPATH_NOFORK
 
  BMVert *v;
  BMVert *v_dst;
  bool found = false;
 
  VertOrder *eo;
  STACK_DECLARE(edge_order);
 
  /* store visited verts so we can clear the visit flag after execution */
  BLI_SMALLSTACK_DECLARE(vert_visit, BMVert *);
 
  /* likely this will stay very small
   * all verts pushed into this stack _must_ have their previous edges set! */
  BLI_SMALLSTACK_DECLARE(vert_stack, BMVert *);
  BLI_SMALLSTACK_DECLARE(vert_stack_next, BMVert *);
 
  STACK_INIT(edge_order, edge_order_len);
 
  /* start stepping */
  v = BM_edge_other_vert(e_pair[0], v_init);
  v->e = e_pair[0];
  BLI_SMALLSTACK_PUSH(vert_stack, v);
 
  v_dst = BM_edge_other_vert(e_pair[1], v_init);
 
#ifdef DEBUG_PRINT
  printf("%s: vert (search) %d\n", __func__, BM_elem_index_get(v_init));
#endif
 
  /* This loop will keep stepping over the best possible edge,
   * in most cases it finds the direct route to close the face.
   *
   * In cases where paths can't be closed,
   * alternatives are stored in the 'vert_stack'.
   */
  while ((v = static_cast<BMVert *>(BLI_SMALLSTACK_POP_EX(vert_stack, vert_stack_next)))) {
#ifdef USE_FASTPATH_NOFORK
  walk_nofork:
#else
    BLI_SMALLSTACK_PUSH(vert_visit, v);
    BM_ELEM_API_FLAG_ENABLE(v, VERT_VISIT);
#endif
 
    BLI_assert(STACK_SIZE(edge_order) == 0);
 
    /* check if we're done! */
    if (v == v_dst) {
      found = true;
      goto finally;
    }
 
    BMEdge *e_next, *e_first;
    e_first = v->e;
    e_next = BM_DISK_EDGE_NEXT(e_first, v); /* always skip this verts edge */
 
    /* in rare cases there may be edges with a single connecting vertex */
    if (e_next != e_first) {
      do {
        if (BM_ELEM_API_FLAG_TEST(e_next, EDGE_NET) && (bm_edge_flagged_radial_count(e_next) < 2))
        {
          BMVert *v_next;
 
          v_next = BM_edge_other_vert(e_next, v);
          BLI_assert(v->e != e_next);
 
#ifdef DEBUG_PRINT
          /* indent and print */
          {
            BMVert *_v = v;
            do {
              printf("  ");
            } while ((_v = BM_edge_other_vert(_v->e, _v)) != v_init);
            printf("vert %d -> %d (add=%d)\n",
                   BM_elem_index_get(v),
                   BM_elem_index_get(v_next),
                   BM_ELEM_API_FLAG_TEST(v_next, VERT_VISIT) == 0);
          }
#endif
 
          if (!BM_ELEM_API_FLAG_TEST(v_next, VERT_VISIT)) {
            eo = STACK_PUSH_RET_PTR(edge_order);
            eo->v = v_next;
 
            v_next->e = e_next;
          }
        }
      } while ((e_next = BM_DISK_EDGE_NEXT(e_next, v)) != e_first);
    }
 
#ifdef USE_FASTPATH_NOFORK
    if (STACK_SIZE(edge_order) == 1) {
      eo = STACK_POP_PTR(edge_order);
      v = eo->v;
 
      goto walk_nofork;
    }
#endif
 
    /* sort by angle if needed */
    if (STACK_SIZE(edge_order) > 1) {
      uint j;
      BMVert *v_prev = BM_edge_other_vert(v->e, v);
 
      for (j = 0; j < STACK_SIZE(edge_order); j++) {
        edge_order[j].angle = angle_signed_on_axis_v3v3v3_v3(
            v_prev->co, v->co, edge_order[j].v->co, face_normal);
      }
      qsort(edge_order, STACK_SIZE(edge_order), sizeof(VertOrder), BLI_sortutil_cmp_float_reverse);
 
#ifdef USE_FASTPATH_NOFORK
      /* only tag forks */
      BLI_SMALLSTACK_PUSH(vert_visit, v);
      BM_ELEM_API_FLAG_ENABLE(v, VERT_VISIT);
#endif
    }
 
    while ((eo = STACK_POP_PTR(edge_order))) {
      BLI_SMALLSTACK_PUSH(vert_stack_next, eo->v);
    }
 
    if (!BLI_SMALLSTACK_IS_EMPTY(vert_stack_next)) {
      BLI_SMALLSTACK_SWAP(vert_stack, vert_stack_next);
    }
  }
 
finally:
  /* clear flag for next execution */
  while ((v = static_cast<BMVert *>(BLI_SMALLSTACK_POP(vert_visit)))) {
    BM_ELEM_API_FLAG_DISABLE(v, VERT_VISIT);
  }
 
  return found;
 
#undef USE_FASTPATH_NOFORK
}
 
static bool bm_face_split_edgenet_find_loop(BMVert *v_init,
                                            const float face_normal[3],
                                            const float face_normal_matrix[3][3],
                                            /* cache to avoid realloc every time */
                                            VertOrder *edge_order,
                                            const uint edge_order_len,
                                            BMVert **r_face_verts,
                                            int *r_face_verts_len)
{
  BMEdge *e_pair[2];
  BMVert *v;
 
  if (!bm_face_split_edgenet_find_loop_pair(v_init, face_normal, face_normal_matrix, e_pair)) {
    return false;
  }
 
  BLI_assert((bm_edge_flagged_radial_count(e_pair[0]) == 1) ||
             (bm_edge_flagged_radial_count(e_pair[1]) == 1));
 
  if (bm_face_split_edgenet_find_loop_walk(
          v_init, face_normal, edge_order, edge_order_len, e_pair))
  {
    uint i = 0;
 
    r_face_verts[i++] = v_init;
    v = BM_edge_other_vert(e_pair[1], v_init);
    do {
      r_face_verts[i++] = v;
    } while ((v = BM_edge_other_vert(v->e, v)) != v_init);
    *r_face_verts_len = i;
    return (i > 2) ? true : false;
  }
  return false;
}
 
bool BM_face_split_edgenet(BMesh *bm,
                           BMFace *f,
                           BMEdge **edge_net,
                           const int edge_net_len,
                           blender::Vector<BMFace *> *r_face_arr)
{
  /* re-use for new face verts */
  BMVert **face_verts;
  int face_verts_len;
 
  BMVert **vert_queue;
  STACK_DECLARE(vert_queue);
  int i;
 
  VertOrder *edge_order;
  const uint edge_order_len = edge_net_len + 2;
 
  BMVert *v;
 
  BMLoop *l_iter, *l_first;
 
  if (!edge_net_len) {
    if (r_face_arr) {
      r_face_arr->clear_and_shrink();
    }
    return false;
  }
 
  /* These arrays used to be stack memory, however they can be
   * large for single faces with complex edge-nets, see: #65980. */
 
  /* over-alloc (probably 2-4 is only used in most cases), for the biggest-fan */
  edge_order = static_cast<VertOrder *>(
      MEM_mallocN(sizeof(*edge_order) * edge_order_len, __func__));
 
  /* use later */
  face_verts = static_cast<BMVert **>(
      MEM_mallocN(sizeof(*face_verts) * (edge_net_len + f->len), __func__));
 
  vert_queue = static_cast<BMVert **>(
      MEM_mallocN(sizeof(vert_queue) * (edge_net_len + f->len), __func__));
  STACK_INIT(vert_queue, f->len + edge_net_len);
 
  BLI_assert(BM_ELEM_API_FLAG_TEST(f, FACE_NET) == 0);
  BM_ELEM_API_FLAG_ENABLE(f, FACE_NET);
 
#ifndef NDEBUG
  for (i = 0; i < edge_net_len; i++) {
    BLI_assert(BM_ELEM_API_FLAG_TEST(edge_net[i], EDGE_NET) == 0);
    BLI_assert(BM_edge_in_face(edge_net[i], f) == false);
  }
  l_iter = l_first = BM_FACE_FIRST_LOOP(f);
  do {
    BLI_assert(BM_ELEM_API_FLAG_TEST(l_iter->e, EDGE_NET) == 0);
  } while ((l_iter = l_iter->next) != l_first);
#endif
 
  /* NOTE: 'VERT_IN_QUEUE' is often not needed at all,
   * however in rare cases verts are added multiple times to the queue,
   * that on its own is harmless but in _very_ rare cases,
   * the queue will overflow its maximum size,
   * so we better be strict about this! see: #51539 */
 
  for (i = 0; i < edge_net_len; i++) {
    BM_ELEM_API_FLAG_ENABLE(edge_net[i], EDGE_NET);
    BM_ELEM_API_FLAG_DISABLE(edge_net[i]->v1, VERT_IN_QUEUE);
    BM_ELEM_API_FLAG_DISABLE(edge_net[i]->v2, VERT_IN_QUEUE);
  }
  l_iter = l_first = BM_FACE_FIRST_LOOP(f);
  do {
    BM_ELEM_API_FLAG_ENABLE(l_iter->e, EDGE_NET);
    BM_ELEM_API_FLAG_DISABLE(l_iter->v, VERT_IN_QUEUE);
  } while ((l_iter = l_iter->next) != l_first);
 
  float face_normal_matrix[3][3];
  axis_dominant_v3_to_m3(face_normal_matrix, f->no);
 
  /* any vert can be used to begin with */
  STACK_PUSH(vert_queue, l_first->v);
  BM_ELEM_API_FLAG_ENABLE(l_first->v, VERT_IN_QUEUE);
 
  blender::Vector<BMFace *> face_arr;
  while ((v = STACK_POP(vert_queue))) {
    BM_ELEM_API_FLAG_DISABLE(v, VERT_IN_QUEUE);
    if (bm_face_split_edgenet_find_loop(
            v, f->no, face_normal_matrix, edge_order, edge_order_len, face_verts, &face_verts_len))
    {
      BMFace *f_new;
 
      f_new = BM_face_create_verts(bm, face_verts, face_verts_len, f, BM_CREATE_NOP, false);
 
      for (i = 0; i < edge_net_len; i++) {
        BLI_assert(BM_ELEM_API_FLAG_TEST(edge_net[i], EDGE_NET));
      }
 
      if (f_new) {
        face_arr.append(f_new);
        copy_v3_v3(f_new->no, f->no);
 
        /* warning, normally don't do this,
         * its needed for mesh intersection - which tracks face-sides based on selection */
        f_new->head.hflag = f->head.hflag;
        if (f->head.hflag & BM_ELEM_SELECT) {
          bm->totfacesel++;
        }
 
        BM_ELEM_API_FLAG_ENABLE(f_new, FACE_NET);
 
        /* add new verts to keep finding loops for
         * (verts between boundary and manifold edges) */
        l_iter = l_first = BM_FACE_FIRST_LOOP(f_new);
        do {
          /* Avoid adding to queue multiple times (not common but happens). */
          if (!BM_ELEM_API_FLAG_TEST(l_iter->v, VERT_IN_QUEUE) &&
              bm_face_split_edgenet_find_loop_pair_exists(l_iter->v))
          {
            STACK_PUSH(vert_queue, l_iter->v);
            BM_ELEM_API_FLAG_ENABLE(l_iter->v, VERT_IN_QUEUE);
          }
        } while ((l_iter = l_iter->next) != l_first);
      }
    }
  }
 
  if (CustomData_has_math(&bm->ldata)) {
    /* reuse VERT_VISIT here to tag vert's already interpolated */
    BMIter iter;
    BMLoop *l_other;
 
    /* See: #BM_loop_interp_from_face for similar logic. */
    void **blocks = BLI_array_alloca(blocks, f->len);
    float(*cos_2d)[2] = BLI_array_alloca(cos_2d, f->len);
    float *w = BLI_array_alloca(w, f->len);
    float axis_mat[3][3];
    float co[2];
 
    /* interior loops */
    axis_dominant_v3_to_m3(axis_mat, f->no);
 
    /* first simply copy from existing face */
    i = 0;
    l_iter = l_first = BM_FACE_FIRST_LOOP(f);
    do {
      BM_ITER_ELEM (l_other, &iter, l_iter->v, BM_LOOPS_OF_VERT) {
        if ((l_other->f != f) && BM_ELEM_API_FLAG_TEST(l_other->f, FACE_NET)) {
          CustomData_bmesh_copy_block(bm->ldata, l_iter->head.data, &l_other->head.data);
        }
      }
      /* tag not to interpolate */
      BM_ELEM_API_FLAG_ENABLE(l_iter->v, VERT_VISIT);
 
      mul_v2_m3v3(cos_2d[i], axis_mat, l_iter->v->co);
      blocks[i] = l_iter->head.data;
 
    } while ((void)i++, (l_iter = l_iter->next) != l_first);
 
    for (i = 0; i < edge_net_len; i++) {
      BM_ITER_ELEM (v, &iter, edge_net[i], BM_VERTS_OF_EDGE) {
        if (!BM_ELEM_API_FLAG_TEST(v, VERT_VISIT)) {
          BMIter liter;
 
          BM_ELEM_API_FLAG_ENABLE(v, VERT_VISIT);
 
          /* interpolate this loop, then copy to the rest */
          l_first = nullptr;
 
          BM_ITER_ELEM (l_iter, &liter, v, BM_LOOPS_OF_VERT) {
            if (BM_ELEM_API_FLAG_TEST(l_iter->f, FACE_NET)) {
              if (l_first == nullptr) {
                mul_v2_m3v3(co, axis_mat, v->co);
                interp_weights_poly_v2(w, cos_2d, f->len, co);
                CustomData_bmesh_interp(
                    &bm->ldata, (const void **)blocks, w, nullptr, f->len, l_iter->head.data);
                l_first = l_iter;
              }
              else {
                CustomData_bmesh_copy_block(bm->ldata, l_first->head.data, &l_iter->head.data);
              }
            }
          }
        }
      }
    }
  }
 
  /* cleanup */
  for (i = 0; i < edge_net_len; i++) {
    BM_ELEM_API_FLAG_DISABLE(edge_net[i], EDGE_NET);
    /* from interp only */
    BM_ELEM_API_FLAG_DISABLE(edge_net[i]->v1, VERT_VISIT);
    BM_ELEM_API_FLAG_DISABLE(edge_net[i]->v2, VERT_VISIT);
  }
  l_iter = l_first = BM_FACE_FIRST_LOOP(f);
  do {
    BM_ELEM_API_FLAG_DISABLE(l_iter->e, EDGE_NET);
    /* from interp only */
    BM_ELEM_API_FLAG_DISABLE(l_iter->v, VERT_VISIT);
  } while ((l_iter = l_iter->next) != l_first);
 
  if (!face_arr.is_empty()) {
    bmesh_face_swap_data(f, face_arr[0]);
    BM_face_kill(bm, face_arr[0]);
    face_arr[0] = f;
  }
  else {
    BM_ELEM_API_FLAG_DISABLE(f, FACE_NET);
  }
 
  for (BMFace *face : face_arr) {
    BM_ELEM_API_FLAG_DISABLE(face, FACE_NET);
  }
 
  if (r_face_arr) {
    *r_face_arr = std::move(face_arr);
  }
 
  MEM_freeN(edge_order);
  MEM_freeN(face_verts);
  MEM_freeN(vert_queue);
 
  return true;
}
 
#undef FACE_NET
#undef VERT_VISIT
#undef EDGE_NET
 
/* -------------------------------------------------------------------- */
#define USE_PARTIAL_CONNECT
 
#define VERT_IS_VALID BM_ELEM_INTERNAL_TAG
 
/* can be X or Y */
#define SORT_AXIS 0
 
BLI_INLINE bool edge_isect_verts_point_2d(const BMEdge *e,
                                          const BMVert *v_a,
                                          const BMVert *v_b,
                                          float r_isect[2])
{
  /* This bias seems like it could be too large,
   * mostly its not needed, see #52329 for example where it is. */
  const float endpoint_bias = 1e-4f;
  return ((isect_seg_seg_v2_point_ex(
               v_a->co, v_b->co, e->v1->co, e->v2->co, endpoint_bias, r_isect) == 1) &&
          ((e->v1 != v_a) && (e->v2 != v_a) && (e->v1 != v_b) && (e->v2 != v_b)));
}
 
BLI_INLINE int axis_pt_cmp(const float pt_a[2], const float pt_b[2])
{
  if (pt_a[0] < pt_b[0]) {
    return -1;
  }
  if (pt_a[0] > pt_b[0]) {
    return 1;
  }
  if (pt_a[1] < pt_b[1]) {
    return -1;
  }
  if (pt_a[1] > pt_b[1]) {
    return 1;
  }
  return 0;
}
 
struct EdgeGroupIsland {
  LinkNode edge_links; /* keep first */
  uint vert_len, edge_len;
 
  /* Set the following vars once we have >1 groups */
 
  /* when an edge in a previous group connects to this one,
   * so there's no need to create one pointing back. */
  uint has_prev_edge : 1;
 
  /* verts in the group which has the lowest & highest values,
   * the lower vertex is connected to the first edge */
  struct {
    BMVert *min, *max;
    /* used for sorting only */
    float min_axis[2];
    float max_axis[2];
  } vert_span;
};
 
static int group_min_cmp_fn(const void *p1, const void *p2)
{
  const EdgeGroupIsland *g1 = *(EdgeGroupIsland **)p1;
  const EdgeGroupIsland *g2 = *(EdgeGroupIsland **)p2;
  /* min->co[SORT_AXIS] hasn't been applied yet */
  int test = axis_pt_cmp(g1->vert_span.min_axis, g2->vert_span.min_axis);
  if (UNLIKELY(test == 0)) {
    test = axis_pt_cmp(g1->vert_span.max_axis, g2->vert_span.max_axis);
  }
  return test;
}
 
struct Edges_VertVert_BVHTreeTest {
  float dist_orig;
  BMEdge **edge_arr;
 
  BMVert *v_origin;
  BMVert *v_other;
 
  const uint *vert_range;
};
 
struct Edges_VertRay_BVHTreeTest {
  BMEdge **edge_arr;
 
  BMVert *v_origin;
 
  const uint *vert_range;
};
 
static void bvhtree_test_edges_isect_2d_vert_cb(void *user_data,
                                                int index,
                                                const BVHTreeRay * /*ray*/,
                                                BVHTreeRayHit *hit)
{
  Edges_VertVert_BVHTreeTest *data = static_cast<Edges_VertVert_BVHTreeTest *>(user_data);
  const BMEdge *e = data->edge_arr[index];
  const int v1_index = BM_elem_index_get(e->v1);
  float co_isect[2];
 
  if (edge_isect_verts_point_2d(e, data->v_origin, data->v_other, co_isect)) {
    const float t = line_point_factor_v2(co_isect, data->v_origin->co, data->v_other->co);
    const float dist_new = data->dist_orig * t;
    /* avoid float precision issues, possible this is greater,
     * check above zero to allow some overlap
     * (and needed for partial-connect which will overlap vertices) */
    if (LIKELY((dist_new < hit->dist) && (dist_new > 0.0f))) {
      /* v1/v2 will both be in the same group */
      if (v1_index < int(data->vert_range[0]) || v1_index >= int(data->vert_range[1])) {
        hit->dist = dist_new;
        hit->index = index;
      }
    }
  }
}
 
static void bvhtree_test_edges_isect_2d_ray_cb(void *user_data,
                                               int index,
                                               const BVHTreeRay *ray,
                                               BVHTreeRayHit *hit)
{
  Edges_VertRay_BVHTreeTest *data = static_cast<Edges_VertRay_BVHTreeTest *>(user_data);
  const BMEdge *e = data->edge_arr[index];
 
  /* direction is normalized, so this will be the distance */
  float dist_new;
  if (isect_ray_seg_v2(
          data->v_origin->co, ray->direction, e->v1->co, e->v2->co, &dist_new, nullptr))
  {
    /* avoid float precision issues, possible this is greater,
     * check above zero to allow some overlap
     * (and needed for partial-connect which will overlap vertices) */
    if (LIKELY(dist_new < hit->dist && (dist_new > 0.0f))) {
      if (e->v1 != data->v_origin && e->v2 != data->v_origin) {
        const int v1_index = BM_elem_index_get(e->v1);
        /* v1/v2 will both be in the same group */
        if (v1_index < int(data->vert_range[0]) || v1_index >= int(data->vert_range[1])) {
          hit->dist = dist_new;
          hit->index = index;
        }
      }
    }
  }
}
 
struct EdgeGroup_FindConnection_Args {
  BVHTree *bvhtree;
  BMEdge **edge_arr;
  uint edge_arr_len;
 
  BMEdge **edge_arr_new;
  uint edge_arr_new_len;
 
  const uint *vert_range;
};
 
static BMEdge *test_edges_isect_2d_vert(const EdgeGroup_FindConnection_Args *args,
                                        BMVert *v_origin,
                                        BMVert *v_other)
{
  int index;
 
  BVHTreeRayHit hit = {0};
  float dir[3];
 
  sub_v2_v2v2(dir, v_other->co, v_origin->co);
  dir[2] = 0.0f;
  hit.index = -1;
  hit.dist = normalize_v2(dir);
 
  Edges_VertVert_BVHTreeTest user_data = {0};
  user_data.dist_orig = hit.dist;
  user_data.edge_arr = args->edge_arr;
  user_data.v_origin = v_origin;
  user_data.v_other = v_other;
  user_data.vert_range = args->vert_range;
 
  index = BLI_bvhtree_ray_cast_ex(args->bvhtree,
                                  v_origin->co,
                                  dir,
                                  0.0f,
                                  &hit,
                                  bvhtree_test_edges_isect_2d_vert_cb,
                                  &user_data,
                                  0);
 
  BMEdge *e_hit = (index != -1) ? args->edge_arr[index] : nullptr;
 
  /* check existing connections (no spatial optimization here since we're continually adding). */
  if (LIKELY(index == -1)) {
    float t_best = 1.0f;
    for (uint i = 0; i < args->edge_arr_new_len; i++) {
      float co_isect[2];
      if (UNLIKELY(edge_isect_verts_point_2d(args->edge_arr_new[i], v_origin, v_other, co_isect)))
      {
        const float t_test = line_point_factor_v2(co_isect, v_origin->co, v_other->co);
        if (t_test < t_best) {
          t_best = t_test;
 
          e_hit = args->edge_arr_new[i];
        }
      }
    }
  }
 
  return e_hit;
}
 
static BMEdge *test_edges_isect_2d_ray(const EdgeGroup_FindConnection_Args *args,
                                       BMVert *v_origin,
                                       const float dir[3])
{
  int index;
  BVHTreeRayHit hit = {0};
 
  BLI_ASSERT_UNIT_V2(dir);
 
  hit.index = -1;
  hit.dist = BVH_RAYCAST_DIST_MAX;
 
  Edges_VertRay_BVHTreeTest user_data = {nullptr};
  user_data.edge_arr = args->edge_arr;
  user_data.v_origin = v_origin;
  user_data.vert_range = args->vert_range;
 
  index = BLI_bvhtree_ray_cast_ex(args->bvhtree,
                                  v_origin->co,
                                  dir,
                                  0.0f,
                                  &hit,
                                  bvhtree_test_edges_isect_2d_ray_cb,
                                  &user_data,
                                  0);
 
  BMEdge *e_hit = (index != -1) ? args->edge_arr[index] : nullptr;
 
  /* check existing connections (no spatial optimization here since we're continually adding). */
  if (LIKELY(index != -1)) {
    for (uint i = 0; i < args->edge_arr_new_len; i++) {
      BMEdge *e = args->edge_arr_new[i];
      float dist_new;
      if (isect_ray_seg_v2(v_origin->co, dir, e->v1->co, e->v2->co, &dist_new, nullptr)) {
        if (e->v1 != v_origin && e->v2 != v_origin) {
          /* avoid float precision issues, possible this is greater */
          if (LIKELY(dist_new < hit.dist)) {
            hit.dist = dist_new;
 
            e_hit = args->edge_arr_new[i];
          }
        }
      }
    }
  }
 
  return e_hit;
}
 
static int bm_face_split_edgenet_find_connection(const EdgeGroup_FindConnection_Args *args,
                                                 BMVert *v_origin,
                                                 /* false = negative, true = positive */
                                                 bool direction_sign)
{
  float dir[3] = {0, 0, 0};
  dir[SORT_AXIS] = direction_sign ? 1.0f : -1.0f;
  BMEdge *e_hit = test_edges_isect_2d_ray(args, v_origin, dir);
  BMVert *v_other = nullptr;
 
  if (e_hit) {
    BMVert *v_other_fallback = nullptr;
 
    BLI_SMALLSTACK_DECLARE(vert_search, BMVert *);
 
    /* ensure we never add verts multiple times (not all that likely - but possible) */
    BLI_SMALLSTACK_DECLARE(vert_blacklist, BMVert *);
 
    do {
      BMVert *v_pair[2];
      /* ensure the closest vertex is popped back off the stack first */
      if (len_squared_v2v2(v_origin->co, e_hit->v1->co) >
          len_squared_v2v2(v_origin->co, e_hit->v2->co))
      {
        ARRAY_SET_ITEMS(v_pair, e_hit->v1, e_hit->v2);
      }
      else {
        ARRAY_SET_ITEMS(v_pair, e_hit->v2, e_hit->v1);
      }
 
      for (int j = 0; j < 2; j++) {
        BMVert *v_iter = v_pair[j];
        if (BM_elem_flag_test(v_iter, VERT_IS_VALID)) {
          if (direction_sign ? (v_iter->co[SORT_AXIS] > v_origin->co[SORT_AXIS]) :
                               (v_iter->co[SORT_AXIS] < v_origin->co[SORT_AXIS]))
          {
            BLI_SMALLSTACK_PUSH(vert_search, v_iter);
            BLI_SMALLSTACK_PUSH(vert_blacklist, v_iter);
            BM_elem_flag_disable(v_iter, VERT_IS_VALID);
          }
        }
      }
      v_other_fallback = v_other;
 
    } while ((v_other = static_cast<BMVert *>(BLI_SMALLSTACK_POP(vert_search))) &&
             (e_hit = test_edges_isect_2d_vert(args, v_origin, v_other)));
 
    if (v_other == nullptr) {
      printf("Using fallback\n");
      v_other = v_other_fallback;
    }
 
    /* reset the blacklist flag, for future use */
    BMVert *v;
    while ((v = static_cast<BMVert *>(BLI_SMALLSTACK_POP(vert_blacklist)))) {
      BM_elem_flag_enable(v, VERT_IS_VALID);
    }
  }
 
  /* if we reach this line, v_other is either the best vertex or its nullptr */
  return v_other ? BM_elem_index_get(v_other) : -1;
}
 
#ifdef USE_PARTIAL_CONNECT
 
static bool test_tagged_and_notface(BMEdge *e, void *fptr)
{
  BMFace *f = (BMFace *)fptr;
  return BM_elem_flag_test(e, BM_ELEM_INTERNAL_TAG) && !BM_edge_in_face(e, f);
}
 
static BMVert *bm_face_split_edgenet_partial_connect(BMesh *bm, BMVert *v_delimit, BMFace *f)
{
  /* -------------------------------------------------------------------- */
  /* Initial check that we may be a delimiting vert (keep this fast) */
 
  /* initial check - see if we have 3+ flagged edges attached to 'v_delimit'
   * if not, we can early exit */
  LinkNode *e_delimit_list = nullptr;
  uint e_delimit_list_len = 0;
 
#  define EDGE_NOT_IN_STACK BM_ELEM_INTERNAL_TAG
#  define VERT_NOT_IN_STACK BM_ELEM_INTERNAL_TAG
 
#  define FOREACH_VERT_EDGE(v_, e_, body_) \
    { \
      BMEdge *e_ = v_->e; \
      do { \
        body_ \
      } while ((e_ = BM_DISK_EDGE_NEXT(e_, v_)) != v_->e); \
    } \
    ((void)0)
 
  /* start with face edges, since we need to split away wire-only edges */
  BMEdge *e_face_init = nullptr;
 
  FOREACH_VERT_EDGE(v_delimit, e_iter, {
    if (BM_elem_flag_test(e_iter, EDGE_NOT_IN_STACK)) {
      BLI_assert(BM_elem_flag_test(BM_edge_other_vert(e_iter, v_delimit), VERT_NOT_IN_STACK));
      BLI_linklist_prepend_alloca(&e_delimit_list, e_iter);
      e_delimit_list_len++;
      if (e_iter->l != nullptr && BM_edge_in_face(e_iter, f)) {
        e_face_init = e_iter;
      }
    }
  });
 
  /* skip typical edge-chain verts */
  if (LIKELY(e_delimit_list_len <= 2)) {
    return nullptr;
  }
 
  /* -------------------------------------------------------------------- */
  /* Complicated stuff starts now! */
 
  /* Store connected vertices for restoring the flag */
  LinkNode *vert_stack = nullptr;
  BLI_linklist_prepend_alloca(&vert_stack, v_delimit);
  BM_elem_flag_disable(v_delimit, VERT_NOT_IN_STACK);
 
  /* Walk the net... */
  {
    BLI_SMALLSTACK_DECLARE(search, BMVert *);
    BMVert *v_other = BM_edge_other_vert(e_face_init ? e_face_init : v_delimit->e, v_delimit);
 
    BLI_SMALLSTACK_PUSH(search, v_other);
    if (BM_elem_flag_test(v_other, VERT_NOT_IN_STACK)) {
      BM_elem_flag_disable(v_other, VERT_NOT_IN_STACK);
      BLI_linklist_prepend_alloca(&vert_stack, v_other);
    }
 
    while ((v_other = static_cast<BMVert *>(BLI_SMALLSTACK_POP(search)))) {
      BLI_assert(BM_elem_flag_test(v_other, VERT_NOT_IN_STACK) == false);
      BMEdge *e_iter = v_other->e;
      do {
        BMVert *v_step = BM_edge_other_vert(e_iter, v_other);
        if (BM_elem_flag_test(e_iter, EDGE_NOT_IN_STACK)) {
          if (BM_elem_flag_test(v_step, VERT_NOT_IN_STACK)) {
            BM_elem_flag_disable(v_step, VERT_NOT_IN_STACK);
            BLI_SMALLSTACK_PUSH(search, v_step);
            BLI_linklist_prepend_alloca(&vert_stack, v_step);
          }
        }
      } while ((e_iter = BM_DISK_EDGE_NEXT(e_iter, v_other)) != v_other->e);
    }
  }
 
  /* Detect if this is a delimiter
   * by checking if we didn't walk any of edges connected to 'v_delimit'. */
  bool is_delimit = false;
  FOREACH_VERT_EDGE(v_delimit, e_iter, {
    BMVert *v_step = BM_edge_other_vert(e_iter, v_delimit);
    if (BM_elem_flag_test(v_step, VERT_NOT_IN_STACK) && !BM_edge_in_face(e_iter, f)) {
      is_delimit = true; /* if one vertex is valid - we have a mix */
    }
    else {
      /* match the vertex flag (only for edges around 'v_delimit') */
      BM_elem_flag_disable(e_iter, EDGE_NOT_IN_STACK);
    }
  });
 
#  undef FOREACH_VERT_EDGE
 
  /* Execute the split */
  BMVert *v_split = nullptr;
  if (is_delimit) {
    v_split = BM_vert_create(bm, v_delimit->co, nullptr, eBMCreateFlag(0));
    BM_vert_separate_tested_edges(bm, v_split, v_delimit, test_tagged_and_notface, f);
    BM_elem_flag_enable(v_split, VERT_NOT_IN_STACK);
 
    BLI_assert(v_delimit->e != nullptr);
 
/* Degenerate, avoid eternal loop, see: #59074. */
#  if 0
    BLI_assert(v_split->e != nullptr);
#  else
    if (UNLIKELY(v_split->e == nullptr)) {
      BM_vert_kill(bm, v_split);
      v_split = nullptr;
    }
#  endif
  }
 
  /* Restore flags */
  do {
    BM_elem_flag_enable((BMVert *)vert_stack->link, VERT_NOT_IN_STACK);
  } while ((vert_stack = vert_stack->next));
 
  do {
    BM_elem_flag_enable((BMEdge *)e_delimit_list->link, EDGE_NOT_IN_STACK);
  } while ((e_delimit_list = e_delimit_list->next));
 
#  undef EDGE_NOT_IN_STACK
#  undef VERT_NOT_IN_STACK
 
  return v_split;
}
 
static bool bm_vert_partial_connect_check_overlap(const int *remap,
                                                  const int v_a_index,
                                                  const int v_b_index)
{
  /* Connected to each other. */
  if (UNLIKELY((remap[v_a_index] == v_b_index) || (remap[v_b_index] == v_a_index))) {
    return true;
  }
  return false;
}
 
#endif /* USE_PARTIAL_CONNECT */
 
bool BM_face_split_edgenet_connect_islands(BMesh *bm,
                                           BMFace *f,
                                           BMEdge **edge_net_init,
                                           const uint edge_net_init_len,
                                           bool use_partial_connect,
                                           MemArena *mem_arena,
                                           BMEdge ***r_edge_net_new,
                                           uint *r_edge_net_new_len)
{
  /* -------------------------------------------------------------------- */
  const uint edge_arr_len = uint(edge_net_init_len) + uint(f->len);
  BMEdge **edge_arr = static_cast<BMEdge **>(
      BLI_memarena_alloc(mem_arena, sizeof(*edge_arr) * edge_arr_len));
  bool ok = false;
  uint edge_net_new_len = uint(edge_net_init_len);
 
  memcpy(edge_arr, edge_net_init, sizeof(*edge_arr) * size_t(edge_net_init_len));
 
/* _must_ clear on exit */
#define EDGE_NOT_IN_STACK BM_ELEM_INTERNAL_TAG
#define VERT_NOT_IN_STACK BM_ELEM_INTERNAL_TAG
 
  {
    uint i = edge_net_init_len;
    BMLoop *l_iter, *l_first;
    l_iter = l_first = BM_FACE_FIRST_LOOP(f);
    do {
      BLI_assert(!BM_elem_flag_test(l_iter->v, VERT_NOT_IN_STACK));
      BLI_assert(!BM_elem_flag_test(l_iter->e, EDGE_NOT_IN_STACK));
      edge_arr[i++] = l_iter->e;
    } while ((l_iter = l_iter->next) != l_first);
    BLI_assert(i == edge_arr_len);
  }
 
  for (uint i = 0; i < edge_arr_len; i++) {
    BM_elem_flag_enable(edge_arr[i], EDGE_NOT_IN_STACK);
    BM_elem_flag_enable(edge_arr[i]->v1, VERT_NOT_IN_STACK);
    BM_elem_flag_enable(edge_arr[i]->v2, VERT_NOT_IN_STACK);
  }
 
#ifdef USE_PARTIAL_CONNECT
  /* Split-out delimiting vertices */
  struct TempVertPair {
    TempVertPair *next;
    BMVert *v_temp;
    BMVert *v_orig;
  };
 
  struct {
    TempVertPair *list;
    uint len;
    int *remap; /* temp -> orig mapping */
  } temp_vert_pairs = {nullptr};
 
  if (use_partial_connect) {
    for (uint i = 0; i < edge_net_init_len; i++) {
      for (uint j = 0; j < 2; j++) {
        BMVert *v_delimit = (&edge_arr[i]->v1)[j];
        BMVert *v_other;
 
        /* NOTE: remapping will _never_ map a vertex to an already mapped vertex. */
        while (UNLIKELY(v_other = bm_face_split_edgenet_partial_connect(bm, v_delimit, f))) {
          TempVertPair *tvp = static_cast<TempVertPair *>(
              BLI_memarena_alloc(mem_arena, sizeof(*tvp)));
          tvp->next = temp_vert_pairs.list;
          tvp->v_orig = v_delimit;
          tvp->v_temp = v_other;
          temp_vert_pairs.list = tvp;
          temp_vert_pairs.len++;
        }
      }
    }
 
    if (temp_vert_pairs.len == 0) {
      use_partial_connect = false;
    }
  }
#endif /* USE_PARTIAL_CONNECT */
 
  uint group_arr_len = 0;
  LinkNode *group_head = nullptr;
  {
    /* scan 'edge_arr' backwards so the outer face boundary is handled first
     * (since its likely to be the largest) */
    uint edge_index = (edge_arr_len - 1);
    uint edge_in_group_tot = 0;
 
    BLI_SMALLSTACK_DECLARE(vstack, BMVert *);
 
    while (true) {
      LinkNode *edge_links = nullptr;
      uint unique_verts_in_group = 0, unique_edges_in_group = 0;
 
      /* list of groups */
      BLI_assert(BM_elem_flag_test(edge_arr[edge_index]->v1, VERT_NOT_IN_STACK));
      BLI_SMALLSTACK_PUSH(vstack, edge_arr[edge_index]->v1);
      BM_elem_flag_disable(edge_arr[edge_index]->v1, VERT_NOT_IN_STACK);
 
      BMVert *v_iter;
      while ((v_iter = static_cast<BMVert *>(BLI_SMALLSTACK_POP(vstack)))) {
        unique_verts_in_group++;
 
        BMEdge *e_iter = v_iter->e;
        do {
          if (BM_elem_flag_test(e_iter, EDGE_NOT_IN_STACK)) {
            BM_elem_flag_disable(e_iter, EDGE_NOT_IN_STACK);
            unique_edges_in_group++;
 
            BLI_linklist_prepend_arena(&edge_links, e_iter, mem_arena);
 
            BMVert *v_other = BM_edge_other_vert(e_iter, v_iter);
            if (BM_elem_flag_test(v_other, VERT_NOT_IN_STACK)) {
              BLI_SMALLSTACK_PUSH(vstack, v_other);
              BM_elem_flag_disable(v_other, VERT_NOT_IN_STACK);
            }
          }
        } while ((e_iter = BM_DISK_EDGE_NEXT(e_iter, v_iter)) != v_iter->e);
      }
 
      EdgeGroupIsland *g = static_cast<EdgeGroupIsland *>(
          BLI_memarena_alloc(mem_arena, sizeof(*g)));
      g->vert_len = unique_verts_in_group;
      g->edge_len = unique_edges_in_group;
      edge_in_group_tot += unique_edges_in_group;
 
      BLI_linklist_prepend_nlink(&group_head, edge_links, (LinkNode *)g);
 
      group_arr_len++;
 
      if (edge_in_group_tot == edge_arr_len) {
        break;
      }
 
      /* skip edges in the stack */
      while (BM_elem_flag_test(edge_arr[edge_index], EDGE_NOT_IN_STACK) == false) {
        BLI_assert(edge_index != 0);
        edge_index--;
      }
    }
  }
 
  /* Declare here because of `goto` below. */
  BMEdge **edge_net_new = nullptr;
  BVHTree *bvhtree = nullptr;
  float(*vert_coords_backup)[3] = nullptr;
  uint *verts_group_table = nullptr;
  BMVert **vert_arr = nullptr;
  uint vert_arr_len = 0;
  EdgeGroupIsland **group_arr = nullptr;
 
  /* single group - no holes */
  if (group_arr_len == 1) {
    goto finally;
  }
 
  /* -------------------------------------------------------------------- */
  /* Previous checks need to be kept fast, since they will run very often,
   * now we know there are holes, so calculate a spatial lookup info and
   * other per-group data.
   */
 
  float axis_mat[3][3];
  axis_dominant_v3_to_m3(axis_mat, f->no);
 
#define VERT_IN_ARRAY BM_ELEM_INTERNAL_TAG
 
  group_arr = static_cast<EdgeGroupIsland **>(
      BLI_memarena_alloc(mem_arena, sizeof(*group_arr) * group_arr_len));
  /* sort groups by lowest value vertex */
  {
    /* fill 'groups_arr' in reverse order so the boundary face is first */
    EdgeGroupIsland **group_arr_p = &group_arr[group_arr_len];
 
    for (EdgeGroupIsland *g = static_cast<EdgeGroupIsland *>((void *)group_head); g;
         g = (EdgeGroupIsland *)g->edge_links.next)
    {
      LinkNode *edge_links = static_cast<LinkNode *>(g->edge_links.link);
 
      /* init with *any* different verts */
      g->vert_span.min = ((BMEdge *)edge_links->link)->v1;
      g->vert_span.max = ((BMEdge *)edge_links->link)->v2;
      float min_axis[2] = {FLT_MAX, FLT_MAX};
      float max_axis[2] = {-FLT_MAX, -FLT_MAX};
 
      do {
        BMEdge *e = static_cast<BMEdge *>(edge_links->link);
        BLI_assert(e->head.htype == BM_EDGE);
 
        for (int j = 0; j < 2; j++) {
          BMVert *v_iter = (&e->v1)[j];
          BLI_assert(v_iter->head.htype == BM_VERT);
          /* ideally we could use 'v_iter->co[SORT_AXIS]' here,
           * but we need to sort the groups before setting the vertex array order */
          const float axis_value[2] = {
#if SORT_AXIS == 0
            dot_m3_v3_row_x(axis_mat, v_iter->co),
            dot_m3_v3_row_y(axis_mat, v_iter->co),
#else
            dot_m3_v3_row_y(axis_mat, v_iter->co),
            dot_m3_v3_row_x(axis_mat, v_iter->co),
#endif
          };
 
          if (axis_pt_cmp(axis_value, min_axis) == -1) {
            g->vert_span.min = v_iter;
            copy_v2_v2(min_axis, axis_value);
          }
          if (axis_pt_cmp(axis_value, max_axis) == 1) {
            g->vert_span.max = v_iter;
            copy_v2_v2(max_axis, axis_value);
          }
        }
      } while ((edge_links = edge_links->next));
 
      copy_v2_v2(g->vert_span.min_axis, min_axis);
      copy_v2_v2(g->vert_span.max_axis, max_axis);
 
      g->has_prev_edge = false;
 
      vert_arr_len += g->vert_len;
 
      *(--group_arr_p) = g;
    }
  }
 
  qsort(group_arr, group_arr_len, sizeof(*group_arr), group_min_cmp_fn);
 
  /* we don't know how many unique verts there are connecting the edges, so over-alloc */
  vert_arr = static_cast<BMVert **>(
      BLI_memarena_alloc(mem_arena, sizeof(*vert_arr) * vert_arr_len));
  /* map vertex -> group index */
  verts_group_table = static_cast<uint *>(
      BLI_memarena_alloc(mem_arena, sizeof(*verts_group_table) * vert_arr_len));
 
  vert_coords_backup = static_cast<float(*)[3]>(
      BLI_memarena_alloc(mem_arena, sizeof(*vert_coords_backup) * vert_arr_len));
 
  {
    /* relative location, for higher precision calculations */
    const float f_co_ref[3] = {UNPACK3(BM_FACE_FIRST_LOOP(f)->v->co)};
 
    int v_index = 0; /* global vert index */
    for (uint g_index = 0; g_index < group_arr_len; g_index++) {
      LinkNode *edge_links = static_cast<LinkNode *>(group_arr[g_index]->edge_links.link);
      do {
        BMEdge *e = static_cast<BMEdge *>(edge_links->link);
        for (int j = 0; j < 2; j++) {
          BMVert *v_iter = (&e->v1)[j];
          if (!BM_elem_flag_test(v_iter, VERT_IN_ARRAY)) {
            BM_elem_flag_enable(v_iter, VERT_IN_ARRAY);
 
            /* not nice, but alternatives aren't much better :S */
            {
              copy_v3_v3(vert_coords_backup[v_index], v_iter->co);
 
              /* for higher precision */
              sub_v3_v3(v_iter->co, f_co_ref);
 
              float co_2d[2];
              mul_v2_m3v3(co_2d, axis_mat, v_iter->co);
              v_iter->co[0] = co_2d[0];
              v_iter->co[1] = co_2d[1];
              v_iter->co[2] = 0.0f;
            }
 
            BM_elem_index_set(v_iter, v_index); /* set_dirty */
 
            vert_arr[v_index] = v_iter;
            verts_group_table[v_index] = g_index;
            v_index++;
          }
        }
      } while ((edge_links = edge_links->next));
    }
  }
 
  bm->elem_index_dirty |= BM_VERT;
 
  /* Now create BVH tree.
   *
   * Note that a large epsilon is used because meshes with dimensions of around 100+ need it.
   * see #52329. */
  bvhtree = BLI_bvhtree_new(edge_arr_len, 1e-4f, 8, 8);
  for (uint i = 0; i < edge_arr_len; i++) {
    const float e_cos[2][3] = {
        {UNPACK2(edge_arr[i]->v1->co), 0.0f},
        {UNPACK2(edge_arr[i]->v2->co), 0.0f},
    };
    BLI_bvhtree_insert(bvhtree, i, (const float *)e_cos, 2);
  }
  BLI_bvhtree_balance(bvhtree);
 
#ifdef USE_PARTIAL_CONNECT
  if (use_partial_connect) {
    /* needs to be done once the vertex indices have been written into */
    temp_vert_pairs.remap = static_cast<int *>(
        BLI_memarena_alloc(mem_arena, sizeof(*temp_vert_pairs.remap) * vert_arr_len));
    copy_vn_i(temp_vert_pairs.remap, vert_arr_len, -1);
 
    TempVertPair *tvp = temp_vert_pairs.list;
    do {
      temp_vert_pairs.remap[BM_elem_index_get(tvp->v_temp)] = BM_elem_index_get(tvp->v_orig);
    } while ((tvp = tvp->next));
  }
#endif /* USE_PARTIAL_CONNECT */
 
  /* Create connections between groups */
 
  /* may be an over-alloc, but not by much */
  edge_net_new_len = uint(edge_net_init_len) + ((group_arr_len - 1) * 2);
  edge_net_new = static_cast<BMEdge **>(
      BLI_memarena_alloc(mem_arena, sizeof(*edge_net_new) * edge_net_new_len));
  memcpy(edge_net_new, edge_net_init, sizeof(*edge_net_new) * size_t(edge_net_init_len));
 
  {
    uint edge_net_new_index = edge_net_init_len;
    /* start-end of the verts in the current group */
 
    uint vert_range[2];
 
    vert_range[0] = 0;
    vert_range[1] = group_arr[0]->vert_len;
 
    EdgeGroup_FindConnection_Args args{};
    args.bvhtree = bvhtree;
 
    /* use the new edge array so we can scan edges which have been added */
    args.edge_arr = edge_arr;
    args.edge_arr_len = edge_arr_len;
 
    /* we only want to check newly created edges */
    args.edge_arr_new = edge_net_new + edge_net_init_len;
    args.edge_arr_new_len = 0;
 
    args.vert_range = vert_range;
 
    for (uint g_index = 1; g_index < group_arr_len; g_index++) {
      EdgeGroupIsland *g = group_arr[g_index];
 
      /* The range of verts this group uses in 'verts_arr' (not including the last index). */
      vert_range[0] = vert_range[1];
      vert_range[1] += g->vert_len;
 
      if (g->has_prev_edge == false) {
        BMVert *v_origin = g->vert_span.min;
        /* Index of BMVert for the edge group connection with `v_origin`. */
        const int index_other = bm_face_split_edgenet_find_connection(&args, v_origin, false);
        // BLI_assert(index_other >= 0 && index_other < int(vert_arr_len));
 
        /* only for degenerate geometry */
        if (index_other != -1) {
#ifdef USE_PARTIAL_CONNECT
          if ((use_partial_connect == false) ||
              (bm_vert_partial_connect_check_overlap(
                   temp_vert_pairs.remap, BM_elem_index_get(v_origin), index_other) == false))
#endif
          {
            BMVert *v_end = vert_arr[index_other];
 
            edge_net_new[edge_net_new_index] = BM_edge_create(
                bm, v_origin, v_end, nullptr, eBMCreateFlag(0));
#ifdef USE_PARTIAL_CONNECT
            BM_elem_index_set(edge_net_new[edge_net_new_index], edge_net_new_index);
#endif
            edge_net_new_index++;
            args.edge_arr_new_len++;
          }
        }
      }
 
      {
        BMVert *v_origin = g->vert_span.max;
        /* Index of BMVert for the edge group connection with `v_origin`. */
        const int index_other = bm_face_split_edgenet_find_connection(&args, v_origin, true);
        // BLI_assert(index_other >= 0 && index_other < int(vert_arr_len));
 
        /* only for degenerate geometry */
        if (index_other != -1) {
#ifdef USE_PARTIAL_CONNECT
          if ((use_partial_connect == false) ||
              (bm_vert_partial_connect_check_overlap(
                   temp_vert_pairs.remap, BM_elem_index_get(v_origin), index_other) == false))
#endif
          {
            BMVert *v_end = vert_arr[index_other];
            edge_net_new[edge_net_new_index] = BM_edge_create(
                bm, v_origin, v_end, nullptr, eBMCreateFlag(0));
#ifdef USE_PARTIAL_CONNECT
            BM_elem_index_set(edge_net_new[edge_net_new_index], edge_net_new_index);
#endif
            edge_net_new_index++;
            args.edge_arr_new_len++;
          }
 
          /* tell the 'next' group it doesn't need to create its own back-link */
          uint g_index_other = verts_group_table[index_other];
          group_arr[g_index_other]->has_prev_edge = true;
        }
      }
    }
    BLI_assert(edge_net_new_len >= edge_net_new_index);
    edge_net_new_len = edge_net_new_index;
  }
 
  BLI_bvhtree_free(bvhtree);
 
  *r_edge_net_new = edge_net_new;
  *r_edge_net_new_len = edge_net_new_len;
  ok = true;
 
  for (uint i = 0; i < vert_arr_len; i++) {
    copy_v3_v3(vert_arr[i]->co, vert_coords_backup[i]);
  }
 
finally:
 
#ifdef USE_PARTIAL_CONNECT
  /* don't free 'vert_temp_pair_list', its part of the arena */
  if (use_partial_connect) {
 
/* Sanity check: ensure we don't have connecting edges before splicing begins. */
#  ifndef NDEBUG
    {
      TempVertPair *tvp = temp_vert_pairs.list;
      do {
        /* We must _never_ create connections here
         * (in case the islands can't have a connection at all). */
        BLI_assert(BM_edge_exists(tvp->v_orig, tvp->v_temp) == nullptr);
      } while ((tvp = tvp->next));
    }
#  endif
 
    TempVertPair *tvp = temp_vert_pairs.list;
    do {
      /* its _very_ unlikely the edge exists,
       * however splicing may cause this. see: #48012 */
      if (!BM_edge_exists(tvp->v_orig, tvp->v_temp)) {
        BM_vert_splice(bm, tvp->v_orig, tvp->v_temp);
      }
    } while ((tvp = tvp->next));
 
    /* Remove edges which have become doubles since splicing vertices together,
     * its less trouble than detecting future-doubles on edge-creation. */
    for (uint i = edge_net_init_len; i < edge_net_new_len; i++) {
      while (BM_edge_find_double(edge_net_new[i])) {
        BM_edge_kill(bm, edge_net_new[i]);
        edge_net_new_len--;
        if (i == edge_net_new_len) {
          break;
        }
        edge_net_new[i] = edge_net_new[edge_net_new_len];
      }
    }
 
    *r_edge_net_new_len = edge_net_new_len;
  }
#endif
 
  for (uint i = 0; i < edge_arr_len; i++) {
    BM_elem_flag_disable(edge_arr[i], EDGE_NOT_IN_STACK);
    BM_elem_flag_disable(edge_arr[i]->v1, VERT_NOT_IN_STACK);
    BM_elem_flag_disable(edge_arr[i]->v2, VERT_NOT_IN_STACK);
  }
 
#undef VERT_IN_ARRAY
#undef VERT_NOT_IN_STACK
#undef EDGE_NOT_IN_STACK
 
  return ok;
}
 
#undef SORT_AXIS