tornavis/source/blender/bmesh/operators/bmo_connect_concave.cc

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

/** \file
 * \ingroup bmesh
 *
 * Connect vertices so all resulting faces are convex.
 *
 * Implementation:
 *
 * - triangulate all concave face (tagging convex verts),
 * - rotate edges (beautify) so edges will connect nearby verts.
 * - sort long edges (longest first),
 *   put any edges between 2 convex verts last since they often split convex regions.
 * - merge the sorted edges as long as they don't create convex ngons.
 */

#include "MEM_guardedalloc.h"

#include "BLI_alloca.h"
#include "BLI_heap.h"
#include "BLI_linklist.h"
#include "BLI_math_geom.h"
#include "BLI_math_vector.h"
#include "BLI_memarena.h"
#include "BLI_polyfill_2d.h"
#include "BLI_polyfill_2d_beautify.h"
#include "BLI_utildefines.h"

#include "bmesh.hh"

#include "intern/bmesh_operators_private.hh" /* own include */

#define EDGE_OUT (1 << 0)
#define FACE_OUT (1 << 1)

static int bm_edge_length_cmp(const void *a_, const void *b_)
{
  const BMEdge *e_a = static_cast<const BMEdge *>(*(const void **)a_);
  const BMEdge *e_b = static_cast<const BMEdge *>(*(const void **)b_);

  int e_a_concave = (BM_elem_flag_test(e_a->v1, BM_ELEM_TAG) &&
                     BM_elem_flag_test(e_a->v2, BM_ELEM_TAG));
  int e_b_concave = (BM_elem_flag_test(e_b->v1, BM_ELEM_TAG) &&
                     BM_elem_flag_test(e_b->v2, BM_ELEM_TAG));

  /* merge edges between concave edges last since these
   * are most likely to remain and be the main dividers */
  if (e_a_concave < e_b_concave) {
    return -1;
  }
  if (e_a_concave > e_b_concave) {
    return 1;
  }

  /* otherwise shortest edges last */
  const float e_a_len = BM_edge_calc_length_squared(e_a);
  const float e_b_len = BM_edge_calc_length_squared(e_b);
  if (e_a_len < e_b_len) {
    return 1;
  }
  if (e_a_len > e_b_len) {
    return -1;
  }
  return 0;
}

static bool bm_face_split_by_concave(BMesh *bm,
                                     BMFace *f_base,
                                     const float eps,

                                     MemArena *pf_arena,
                                     Heap *pf_heap)
{
  const int f_base_len = f_base->len;
  int faces_array_tot = f_base_len - 3;
  int edges_array_tot = f_base_len - 3;
  BMFace **faces_array = BLI_array_alloca(faces_array, faces_array_tot);
  BMEdge **edges_array = BLI_array_alloca(edges_array, edges_array_tot);
  const int quad_method = 0, ngon_method = 0; /* beauty */
  LinkNode *faces_double = nullptr;

  float normal[3];
  BLI_assert(f_base->len > 3);

  copy_v3_v3(normal, f_base->no);

  BM_face_triangulate(bm,
                      f_base,
                      faces_array,
                      &faces_array_tot,
                      edges_array,
                      &edges_array_tot,
                      &faces_double,
                      quad_method,
                      ngon_method,
                      false,
                      pf_arena,
                      pf_heap);

  BLI_assert(edges_array_tot <= f_base_len - 3);

  if (faces_array_tot) {
    int i;
    for (i = 0; i < faces_array_tot; i++) {
      BMFace *f = faces_array[i];
      BMO_face_flag_enable(bm, f, FACE_OUT);
    }
  }
  BMO_face_flag_enable(bm, f_base, FACE_OUT);

  if (edges_array_tot) {
    int i;

    qsort(edges_array, edges_array_tot, sizeof(*edges_array), bm_edge_length_cmp);

    for (i = 0; i < edges_array_tot; i++) {
      BMLoop *l_pair[2];
      BMEdge *e = edges_array[i];
      BMO_edge_flag_enable(bm, e, EDGE_OUT);

      if (BM_edge_is_contiguous(e) && BM_edge_loop_pair(e, &l_pair[0], &l_pair[1])) {
        bool ok = true;
        int j;
        for (j = 0; j < 2; j++) {
          BMLoop *l = l_pair[j];

          /* check that merging the edge (on this side)
           * wouldn't result in a convex face-loop.
           *
           * This is the (l->next, l->prev) we would have once joined.
           */
          float cross[3];
          cross_tri_v3(cross, l->v->co, l->radial_next->next->next->v->co, l->prev->v->co);

          if (dot_v3v3(cross, normal) <= eps) {
            ok = false;
            break;
          }
        }

        if (ok) {
          BMFace *f_new, *f_pair[2] = {l_pair[0]->f, l_pair[1]->f};
          f_new = BM_faces_join(bm, f_pair, 2, true);
          if (f_new) {
            BMO_face_flag_enable(bm, f_new, FACE_OUT);
          }
        }
      }
    }
  }

  BLI_heap_clear(pf_heap, nullptr);

  while (faces_double) {
    LinkNode *next = faces_double->next;
    BM_face_kill(bm, static_cast<BMFace *>(faces_double->link));
    MEM_freeN(faces_double);
    faces_double = next;
  }

  return true;
}

static bool bm_face_convex_tag_verts(BMFace *f)
{
  bool is_concave = false;
  if (f->len > 3) {
    const BMLoop *l_iter, *l_first;

    l_iter = l_first = BM_FACE_FIRST_LOOP(f);
    do {
      if (BM_loop_is_convex(l_iter) == false) {
        is_concave = true;
        BM_elem_flag_enable(l_iter->v, BM_ELEM_TAG);
      }
      else {
        BM_elem_flag_disable(l_iter->v, BM_ELEM_TAG);
      }
    } while ((l_iter = l_iter->next) != l_first);
  }
  return is_concave;
}

void bmo_connect_verts_concave_exec(BMesh *bm, BMOperator *op)
{
  BMOIter siter;
  BMFace *f;
  bool changed = false;

  MemArena *pf_arena;
  Heap *pf_heap;

  pf_arena = BLI_memarena_new(BLI_POLYFILL_ARENA_SIZE, __func__);
  pf_heap = BLI_heap_new_ex(BLI_POLYFILL_ALLOC_NGON_RESERVE);

  BMO_ITER (f, &siter, op->slots_in, "faces", BM_FACE) {
    if (f->len > 3 && bm_face_convex_tag_verts(f)) {
      if (bm_face_split_by_concave(bm, f, FLT_EPSILON, pf_arena, pf_heap)) {
        changed = true;
      }
    }
  }

  if (changed) {
    BMO_slot_buffer_from_enabled_flag(bm, op, op->slots_out, "edges.out", BM_EDGE, EDGE_OUT);
    BMO_slot_buffer_from_enabled_flag(bm, op, op->slots_out, "faces.out", BM_FACE, FACE_OUT);
  }

  BLI_memarena_free(pf_arena);
  BLI_heap_free(pf_heap, nullptr);
}