subdiv_mesh.cc

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/* SPDX-FileCopyrightText: 2018 Blender Authors
 *
 * SPDX-License-Identifier: GPL-2.0-or-later */

 
#include "DNA_key_types.h"
#include "DNA_mesh_types.h"
 
#include "BLI_array.hh"
#include "BLI_math_vector.h"
#include "BLI_math_vector.hh"
#include "BLI_math_vector_types.hh"
 
#include "BKE_attribute_math.hh"
#include "BKE_customdata.hh"
#include "BKE_key.hh"
#include "BKE_mesh.hh"
#include "BKE_mesh_mapping.hh"
#include "BKE_subdiv.hh"
#include "BKE_subdiv_eval.hh"
#include "BKE_subdiv_foreach.hh"
#include "BKE_subdiv_mesh.hh"
 
#include "MEM_guardedalloc.h"
 
namespace blender::bke::subdiv {
 
/* -------------------------------------------------------------------- */
 
struct SubdivMeshContext {
  const ToMeshSettings *settings;
  const Mesh *coarse_mesh;
  Span<float3> coarse_positions;
  Span<int2> coarse_edges;
  OffsetIndices<int> coarse_faces;
  Span<int> coarse_corner_verts;

  CustomData coarse_corner_data_interp;
 
  Subdiv *subdiv;
  Mesh *subdiv_mesh;
  MutableSpan<float3> subdiv_positions;
  MutableSpan<int2> subdiv_edges;
  MutableSpan<int> subdiv_face_offsets;

  int *subdiv_corner_verts;
  int *subdiv_corner_edges;
 
  /* Cached custom data arrays for faster access. */
  int *vert_origindex;
  int *edge_origindex;
  int *loop_origindex;
  int *face_origindex;
  /* UV layers interpolation. */
  int num_uv_layers;
  float2 *uv_layers[MAX_MTFACE];
 
  /* Original coordinates (ORCO) interpolation. */
  float (*orco)[3];
  float (*cloth_orco)[3];
  /* Per-subdivided vertex counter of averaged values. */
  int *accumulated_counters;
  bool have_displacement;
 
  /* Write optimal display edge tags into a boolean array rather than the final bit vector
   * to avoid race conditions when setting bits. */
  Array<bool> subdiv_display_edges;
 
  /* Lazily initialize a map from vertices to connected edges. */
  Array<int> vert_to_edge_offsets;
  Array<int> vert_to_edge_indices;
  GroupedSpan<int> vert_to_edge_map;
};
 
static void subdiv_mesh_ctx_cache_uv_layers(SubdivMeshContext *ctx)
{
  Mesh *subdiv_mesh = ctx->subdiv_mesh;
  ctx->num_uv_layers = std::min(
      CustomData_number_of_layers(&subdiv_mesh->corner_data, CD_PROP_FLOAT2), MAX_MTFACE);
  for (int layer_index = 0; layer_index < ctx->num_uv_layers; layer_index++) {
    ctx->uv_layers[layer_index] = static_cast<float2 *>(CustomData_get_layer_n_for_write(
        &subdiv_mesh->corner_data, CD_PROP_FLOAT2, layer_index, subdiv_mesh->corners_num));
  }
}
 
static void subdiv_mesh_ctx_cache_custom_data_layers(SubdivMeshContext *ctx)
{
  Mesh *subdiv_mesh = ctx->subdiv_mesh;
  ctx->subdiv_positions = subdiv_mesh->vert_positions_for_write();
  ctx->subdiv_edges = subdiv_mesh->edges_for_write();
  ctx->subdiv_face_offsets = subdiv_mesh->face_offsets_for_write();
  /* Pointers to original indices layers. */
  ctx->vert_origindex = static_cast<int *>(CustomData_get_layer_for_write(
      &subdiv_mesh->vert_data, CD_ORIGINDEX, subdiv_mesh->verts_num));
  ctx->edge_origindex = static_cast<int *>(CustomData_get_layer_for_write(
      &subdiv_mesh->edge_data, CD_ORIGINDEX, subdiv_mesh->edges_num));
  ctx->loop_origindex = static_cast<int *>(CustomData_get_layer_for_write(
      &subdiv_mesh->corner_data, CD_ORIGINDEX, subdiv_mesh->corners_num));
  ctx->face_origindex = static_cast<int *>(CustomData_get_layer_for_write(
      &subdiv_mesh->face_data, CD_ORIGINDEX, subdiv_mesh->faces_num));
  /* UV layers interpolation. */
  subdiv_mesh_ctx_cache_uv_layers(ctx);
  /* Orco interpolation. */
  ctx->orco = static_cast<float(*)[3]>(
      CustomData_get_layer_for_write(&subdiv_mesh->vert_data, CD_ORCO, subdiv_mesh->verts_num));
  ctx->cloth_orco = static_cast<float(*)[3]>(CustomData_get_layer_for_write(
      &subdiv_mesh->vert_data, CD_CLOTH_ORCO, subdiv_mesh->verts_num));
}
 
static void subdiv_mesh_prepare_accumulator(SubdivMeshContext *ctx, int num_vertices)
{
  if (!ctx->have_displacement) {
    return;
  }
  ctx->accumulated_counters = MEM_calloc_arrayN<int>(num_vertices, __func__);
}
 
static void subdiv_mesh_context_free(SubdivMeshContext *ctx)
{
  MEM_SAFE_FREE(ctx->accumulated_counters);
  MEM_SAFE_FREE(ctx->subdiv_corner_verts);
  MEM_SAFE_FREE(ctx->subdiv_corner_edges);
  CustomData_free(&ctx->coarse_corner_data_interp);
}

 
/* -------------------------------------------------------------------- */
 
struct LoopsOfPtex {
  /* First loop of the ptex, starts at ptex (0, 0) and goes in u direction. */
  int first_loop;
  /* Last loop of the ptex, starts at ptex (0, 0) and goes in v direction. */
  int last_loop;
  /* For quad coarse faces only. */
  int second_loop;
  int third_loop;
};
 
static void loops_of_ptex_get(LoopsOfPtex *loops_of_ptex,
                              const IndexRange coarse_face,
                              const int ptex_of_face_index)
{
  const int first_ptex_loop_index = coarse_face.start() + ptex_of_face_index;
  /* Loop which look in the (opposite) V direction of the current
   * ptex face.
   *
   * TODO(sergey): Get rid of using module on every iteration. */
  const int last_ptex_loop_index = coarse_face.start() +
                                   (ptex_of_face_index + coarse_face.size() - 1) %
                                       coarse_face.size();
  loops_of_ptex->first_loop = first_ptex_loop_index;
  loops_of_ptex->last_loop = last_ptex_loop_index;
  if (coarse_face.size() == 4) {
    loops_of_ptex->second_loop = loops_of_ptex->first_loop + 1;
    loops_of_ptex->third_loop = loops_of_ptex->first_loop + 2;
  }
  else {
    loops_of_ptex->second_loop = -1;
    loops_of_ptex->third_loop = -1;
  }
}

 
/* -------------------------------------------------------------------- */
 
/* TODO(sergey): Somehow de-duplicate with loops storage, without too much
 * exception cases all over the code. */
 
struct VerticesForInterpolation {
  /* This field points to a vertex data which is to be used for interpolation.
   * The idea is to avoid unnecessary allocations for regular faces, where
   * we can simply use corner vertices. */
  const CustomData *vertex_data;
  /* Vertices data calculated for ptex corners. There are always 4 elements
   * in this custom data, aligned the following way:
   *
   *   index 0 -> uv (0, 0)
   *   index 1 -> uv (0, 1)
   *   index 2 -> uv (1, 1)
   *   index 3 -> uv (1, 0)
   *
   * Is allocated for non-regular faces (triangles and n-gons). */
  CustomData vertex_data_storage;
  bool vertex_data_storage_allocated;
  /* Indices within vertex_data to interpolate for. The indices are aligned
   * with uv coordinates in a similar way as indices in corner_data_storage. */
  int vertex_indices[4];
};
 
static void vertex_interpolation_init(const SubdivMeshContext *ctx,
                                      VerticesForInterpolation *vertex_interpolation,
                                      const IndexRange coarse_face)
{
  const Mesh *coarse_mesh = ctx->coarse_mesh;
  if (coarse_face.size() == 4) {
    vertex_interpolation->vertex_data = &coarse_mesh->vert_data;
    vertex_interpolation->vertex_indices[0] = ctx->coarse_corner_verts[coarse_face.start() + 0];
    vertex_interpolation->vertex_indices[1] = ctx->coarse_corner_verts[coarse_face.start() + 1];
    vertex_interpolation->vertex_indices[2] = ctx->coarse_corner_verts[coarse_face.start() + 2];
    vertex_interpolation->vertex_indices[3] = ctx->coarse_corner_verts[coarse_face.start() + 3];
    vertex_interpolation->vertex_data_storage_allocated = false;
  }
  else {
    vertex_interpolation->vertex_data = &vertex_interpolation->vertex_data_storage;
    /* Allocate storage for loops corresponding to ptex corners. */
    CustomData_init_layout_from(&ctx->coarse_mesh->vert_data,
                                &vertex_interpolation->vertex_data_storage,
                                CD_MASK_EVERYTHING.vmask,
                                CD_SET_DEFAULT,
                                4);
    /* Initialize indices. */
    vertex_interpolation->vertex_indices[0] = 0;
    vertex_interpolation->vertex_indices[1] = 1;
    vertex_interpolation->vertex_indices[2] = 2;
    vertex_interpolation->vertex_indices[3] = 3;
    vertex_interpolation->vertex_data_storage_allocated = true;
    /* Interpolate center of face right away, it stays unchanged for all
     * ptex faces. */
    const float weight = 1.0f / float(coarse_face.size());
    Array<float, 32> weights(coarse_face.size());
    Array<int, 32> indices(coarse_face.size());
    for (int i = 0; i < coarse_face.size(); i++) {
      weights[i] = weight;
      indices[i] = ctx->coarse_corner_verts[coarse_face.start() + i];
    }
    CustomData_interp(&coarse_mesh->vert_data,
                      &vertex_interpolation->vertex_data_storage,
                      indices.data(),
                      weights.data(),
                      nullptr,
                      coarse_face.size(),
                      2);
  }
}
 
static void vertex_interpolation_from_corner(const SubdivMeshContext *ctx,
                                             VerticesForInterpolation *vertex_interpolation,
                                             const IndexRange coarse_face,
                                             const int corner)
{
  if (coarse_face.size() == 4) {
    /* Nothing to do, all indices and data is already assigned. */
  }
  else {
    const CustomData *vertex_data = &ctx->coarse_mesh->vert_data;
    LoopsOfPtex loops_of_ptex;
    loops_of_ptex_get(&loops_of_ptex, coarse_face, corner);
    /* PTEX face corner corresponds to a face loop with same index. */
    CustomData_copy_data(vertex_data,
                         &vertex_interpolation->vertex_data_storage,
                         ctx->coarse_corner_verts[coarse_face.start() + corner],
                         0,
                         1);
    /* Interpolate remaining ptex face corners, which hits loops
     * middle points.
     *
     * TODO(sergey): Re-use one of interpolation results from previous
     * iteration. */
    const float weights[2] = {0.5f, 0.5f};
    const int first_loop_index = loops_of_ptex.first_loop;
    const int last_loop_index = loops_of_ptex.last_loop;
    const int first_indices[2] = {
        ctx->coarse_corner_verts[first_loop_index],
        ctx->coarse_corner_verts[coarse_face.start() +
                                 (first_loop_index - coarse_face.start() + 1) %
                                     coarse_face.size()]};
    const int last_indices[2] = {ctx->coarse_corner_verts[first_loop_index],
                                 ctx->coarse_corner_verts[last_loop_index]};
    CustomData_interp(vertex_data,
                      &vertex_interpolation->vertex_data_storage,
                      first_indices,
                      weights,
                      nullptr,
                      2,
                      1);
    CustomData_interp(vertex_data,
                      &vertex_interpolation->vertex_data_storage,
                      last_indices,
                      weights,
                      nullptr,
                      2,
                      3);
  }
}
 
static void vertex_interpolation_end(VerticesForInterpolation *vertex_interpolation)
{
  if (vertex_interpolation->vertex_data_storage_allocated) {
    CustomData_free(&vertex_interpolation->vertex_data_storage);
  }
}

 
/* -------------------------------------------------------------------- */
 
struct LoopsForInterpolation {
  /* This field points to a loop data which is to be used for interpolation.
   * The idea is to avoid unnecessary allocations for regular faces, where
   * we can simply interpolate corner vertices. */
  const CustomData *corner_data;
  /* Loops data calculated for ptex corners. There are always 4 elements
   * in this custom data, aligned the following way:
   *
   *   index 0 -> uv (0, 0)
   *   index 1 -> uv (0, 1)
   *   index 2 -> uv (1, 1)
   *   index 3 -> uv (1, 0)
   *
   * Is allocated for non-regular faces (triangles and n-gons). */
  CustomData corner_data_storage;
  bool corner_data_storage_allocated;
  /* Indices within corner_data to interpolate for. The indices are aligned with
   * uv coordinates in a similar way as indices in corner_data_storage. */
  int loop_indices[4];
};
 
static void loop_interpolation_init(const SubdivMeshContext *ctx,
                                    LoopsForInterpolation *loop_interpolation,
                                    const IndexRange coarse_face)
{
  if (coarse_face.size() == 4) {
    loop_interpolation->corner_data = &ctx->coarse_corner_data_interp;
    loop_interpolation->loop_indices[0] = coarse_face.start() + 0;
    loop_interpolation->loop_indices[1] = coarse_face.start() + 1;
    loop_interpolation->loop_indices[2] = coarse_face.start() + 2;
    loop_interpolation->loop_indices[3] = coarse_face.start() + 3;
    loop_interpolation->corner_data_storage_allocated = false;
  }
  else {
    loop_interpolation->corner_data = &loop_interpolation->corner_data_storage;
    /* Allocate storage for loops corresponding to ptex corners. */
    CustomData_init_layout_from(&ctx->coarse_corner_data_interp,
                                &loop_interpolation->corner_data_storage,
                                CD_MASK_EVERYTHING.lmask,
                                CD_SET_DEFAULT,
                                4);
    /* Initialize indices. */
    loop_interpolation->loop_indices[0] = 0;
    loop_interpolation->loop_indices[1] = 1;
    loop_interpolation->loop_indices[2] = 2;
    loop_interpolation->loop_indices[3] = 3;
    loop_interpolation->corner_data_storage_allocated = true;
    /* Interpolate center of face right away, it stays unchanged for all
     * ptex faces. */
    const float weight = 1.0f / float(coarse_face.size());
    Array<float, 32> weights(coarse_face.size());
    Array<int, 32> indices(coarse_face.size());
    for (int i = 0; i < coarse_face.size(); i++) {
      weights[i] = weight;
      indices[i] = coarse_face.start() + i;
    }
    CustomData_interp(&ctx->coarse_corner_data_interp,
                      &loop_interpolation->corner_data_storage,
                      indices.data(),
                      weights.data(),
                      nullptr,
                      coarse_face.size(),
                      2);
  }
}
 
static void loop_interpolation_from_corner(const SubdivMeshContext *ctx,
                                           LoopsForInterpolation *loop_interpolation,
                                           const IndexRange coarse_face,
                                           const int corner)
{
  if (coarse_face.size() == 4) {
    /* Nothing to do, all indices and data is already assigned. */
  }
  else {
    const CustomData *corner_data = &ctx->coarse_corner_data_interp;
    LoopsOfPtex loops_of_ptex;
    loops_of_ptex_get(&loops_of_ptex, coarse_face, corner);
    /* PTEX face corner corresponds to a face loop with same index. */
    CustomData_free_elem(&loop_interpolation->corner_data_storage, 0, 1);
    CustomData_copy_data(
        corner_data, &loop_interpolation->corner_data_storage, coarse_face.start() + corner, 0, 1);
    /* Interpolate remaining ptex face corners, which hits loops
     * middle points.
     *
     * TODO(sergey): Re-use one of interpolation results from previous
     * iteration. */
    const float weights[2] = {0.5f, 0.5f};
    const int base_loop_index = coarse_face.start();
    const int first_loop_index = loops_of_ptex.first_loop;
    const int second_loop_index = base_loop_index +
                                  (first_loop_index - base_loop_index + 1) % coarse_face.size();
    const int first_indices[2] = {first_loop_index, second_loop_index};
    const int last_indices[2] = {loops_of_ptex.last_loop, loops_of_ptex.first_loop};
    CustomData_interp(corner_data,
                      &loop_interpolation->corner_data_storage,
                      first_indices,
                      weights,
                      nullptr,
                      2,
                      1);
    CustomData_interp(corner_data,
                      &loop_interpolation->corner_data_storage,
                      last_indices,
                      weights,
                      nullptr,
                      2,
                      3);
  }
}
 
static void loop_interpolation_end(LoopsForInterpolation *loop_interpolation)
{
  if (loop_interpolation->corner_data_storage_allocated) {
    CustomData_free(&loop_interpolation->corner_data_storage);
  }
}

 
/* -------------------------------------------------------------------- */
 
struct SubdivMeshTLS {
  bool vertex_interpolation_initialized;
  VerticesForInterpolation vertex_interpolation;
  int vertex_interpolation_coarse_face_index;
  int vertex_interpolation_coarse_corner;
 
  bool loop_interpolation_initialized;
  LoopsForInterpolation loop_interpolation;
  int loop_interpolation_coarse_face_index;
  int loop_interpolation_coarse_corner;
};
 
static void subdiv_mesh_tls_free(void *tls_v)
{
  SubdivMeshTLS *tls = static_cast<SubdivMeshTLS *>(tls_v);
  if (tls->vertex_interpolation_initialized) {
    vertex_interpolation_end(&tls->vertex_interpolation);
  }
  if (tls->loop_interpolation_initialized) {
    loop_interpolation_end(&tls->loop_interpolation);
  }
}

 
/* -------------------------------------------------------------------- */
 
static void subdiv_vertex_orco_evaluate(const SubdivMeshContext *ctx,
                                        const int ptex_face_index,
                                        const float u,
                                        const float v,
                                        const int subdiv_vertex_index)
{
  if (ctx->orco || ctx->cloth_orco) {
    float vertex_data[6];
    eval_vertex_data(ctx->subdiv, ptex_face_index, u, v, vertex_data);
 
    if (ctx->orco) {
      copy_v3_v3(ctx->orco[subdiv_vertex_index], vertex_data);
      if (ctx->cloth_orco) {
        copy_v3_v3(ctx->cloth_orco[subdiv_vertex_index], vertex_data + 3);
      }
    }
    else if (ctx->cloth_orco) {
      copy_v3_v3(ctx->cloth_orco[subdiv_vertex_index], vertex_data);
    }
  }
}

 
/* -------------------------------------------------------------------- */
 
static void subdiv_accumulate_vertex_displacement(SubdivMeshContext *ctx,
                                                  const int ptex_face_index,
                                                  const float u,
                                                  const float v,
                                                  const int subdiv_vertex_index)
{
  /* Accumulate displacement. */
  Subdiv *subdiv = ctx->subdiv;
  float dummy_P[3], dPdu[3], dPdv[3], D[3];
  eval_limit_point_and_derivatives(subdiv, ptex_face_index, u, v, dummy_P, dPdu, dPdv);
 
  /* NOTE: The subdivided mesh is allocated in this module, and its vertices are kept at zero
   * locations as a default calloc(). */
  eval_displacement(subdiv, ptex_face_index, u, v, dPdu, dPdv, D);
  ctx->subdiv_positions[subdiv_vertex_index] += D;
 
  if (ctx->accumulated_counters) {
    ++ctx->accumulated_counters[subdiv_vertex_index];
  }
}

 
/* -------------------------------------------------------------------- */
 
static bool subdiv_mesh_topology_info(const ForeachContext *foreach_context,
                                      const int num_vertices,
                                      const int num_edges,
                                      const int num_loops,
                                      const int num_faces,
                                      const int * /*subdiv_face_offset*/)
{
  /* Multi-resolution grid data will be applied or become invalid after subdivision,
   * so don't try to preserve it and use memory. Crease values should also not be interpolated. */
  CustomData_MeshMasks mask = CD_MASK_EVERYTHING;
  mask.lmask &= ~CD_MASK_MULTIRES_GRIDS;
 
  SubdivMeshContext *subdiv_context = static_cast<SubdivMeshContext *>(foreach_context->user_data);
 
  const Mesh &coarse_mesh = *subdiv_context->coarse_mesh;
  subdiv_context->subdiv_mesh = bke::mesh_new_no_attributes(
      num_vertices, num_edges, num_faces, num_loops);
  Mesh &subdiv_mesh = *subdiv_context->subdiv_mesh;
  BKE_mesh_copy_parameters_for_eval(subdiv_context->subdiv_mesh, &coarse_mesh);
 
  CustomData_free(&subdiv_mesh.vert_data);
  CustomData_init_layout_from(
      &coarse_mesh.vert_data, &subdiv_mesh.vert_data, mask.vmask, CD_SET_DEFAULT, num_vertices);
  CustomData_free(&subdiv_mesh.edge_data);
  CustomData_init_layout_from(
      &coarse_mesh.edge_data, &subdiv_mesh.edge_data, mask.emask, CD_SET_DEFAULT, num_edges);
  CustomData_free(&subdiv_mesh.face_data);
  CustomData_init_layout_from(
      &coarse_mesh.face_data, &subdiv_mesh.face_data, mask.pmask, CD_SET_DEFAULT, num_faces);
  if (num_faces != 0) {
    subdiv_mesh.face_offsets_for_write().last() = num_loops;
  }
 
  /* Create corner data for interpolation without topology attributes. */
  CustomData_init_from(&coarse_mesh.corner_data,
                       &subdiv_context->coarse_corner_data_interp,
                       mask.lmask,
                       coarse_mesh.corners_num);
  CustomData_free_layer_named(&subdiv_context->coarse_corner_data_interp, ".corner_vert");
  CustomData_free_layer_named(&subdiv_context->coarse_corner_data_interp, ".corner_edge");
  CustomData_free(&subdiv_mesh.corner_data);
  CustomData_init_layout_from(&subdiv_context->coarse_corner_data_interp,
                              &subdiv_mesh.corner_data,
                              mask.lmask,
                              CD_SET_DEFAULT,
                              num_loops);
 
  /* Allocate corner topology arrays which are added to the result at the end. */
  subdiv_context->subdiv_corner_verts = MEM_malloc_arrayN<int>(size_t(num_loops), __func__);
  subdiv_context->subdiv_corner_edges = MEM_malloc_arrayN<int>(size_t(num_loops), __func__);
 
  subdiv_mesh_ctx_cache_custom_data_layers(subdiv_context);
  subdiv_mesh_prepare_accumulator(subdiv_context, num_vertices);
  subdiv_mesh.runtime->subsurf_face_dot_tags.clear();
  subdiv_mesh.runtime->subsurf_face_dot_tags.resize(num_vertices);
  if (subdiv_context->settings->use_optimal_display) {
    subdiv_context->subdiv_display_edges = Array<bool>(num_edges, false);
  }
  return true;
}

 
/* -------------------------------------------------------------------- */
 
static void subdiv_vertex_data_copy(const SubdivMeshContext *ctx,
                                    const int coarse_vertex_index,
                                    const int subdiv_vertex_index)
{
  const Mesh *coarse_mesh = ctx->coarse_mesh;
  CustomData_copy_data(&coarse_mesh->vert_data,
                       &ctx->subdiv_mesh->vert_data,
                       coarse_vertex_index,
                       subdiv_vertex_index,
                       1);
}
 
static void subdiv_vertex_data_interpolate(const SubdivMeshContext *ctx,
                                           const int subdiv_vertex_index,
                                           const VerticesForInterpolation *vertex_interpolation,
                                           const float u,
                                           const float v)
{
  const float weights[4] = {(1.0f - u) * (1.0f - v), u * (1.0f - v), u * v, (1.0f - u) * v};
  CustomData_interp(vertex_interpolation->vertex_data,
                    &ctx->subdiv_mesh->vert_data,
                    vertex_interpolation->vertex_indices,
                    weights,
                    nullptr,
                    4,
                    subdiv_vertex_index);
  if (ctx->vert_origindex != nullptr) {
    ctx->vert_origindex[subdiv_vertex_index] = ORIGINDEX_NONE;
  }
}
 
static void evaluate_vertex_and_apply_displacement_copy(const SubdivMeshContext *ctx,
                                                        const int ptex_face_index,
                                                        const float u,
                                                        const float v,
                                                        const int coarse_vertex_index,
                                                        const int subdiv_vertex_index)
{
  float3 &subdiv_position = ctx->subdiv_positions[subdiv_vertex_index];
  /* Displacement is accumulated in subdiv vertex position.
   * Needs to be backed up before copying data from original vertex. */
  float D[3] = {0.0f, 0.0f, 0.0f};
  if (ctx->have_displacement) {
    const float inv_num_accumulated = 1.0f / ctx->accumulated_counters[subdiv_vertex_index];
    copy_v3_v3(D, subdiv_position);
    mul_v3_fl(D, inv_num_accumulated);
  }
  /* Copy custom data and evaluate position. */
  subdiv_vertex_data_copy(ctx, coarse_vertex_index, subdiv_vertex_index);
  eval_limit_point(ctx->subdiv, ptex_face_index, u, v, subdiv_position);
  /* Apply displacement. */
  subdiv_position += D;
  /* Evaluate undeformed texture coordinate. */
  subdiv_vertex_orco_evaluate(ctx, ptex_face_index, u, v, subdiv_vertex_index);
  /* Remove face-dot flag. This can happen if there is more than one subsurf modifier. */
  ctx->subdiv_mesh->runtime->subsurf_face_dot_tags[subdiv_vertex_index].reset();
}
 
static void evaluate_vertex_and_apply_displacement_interpolate(
    const SubdivMeshContext *ctx,
    const int ptex_face_index,
    const float u,
    const float v,
    VerticesForInterpolation *vertex_interpolation,
    const int subdiv_vertex_index)
{
  float3 &subdiv_position = ctx->subdiv_positions[subdiv_vertex_index];
  /* Displacement is accumulated in subdiv vertex position.
   * Needs to be backed up before copying data from original vertex. */
  float D[3] = {0.0f, 0.0f, 0.0f};
  if (ctx->have_displacement) {
    const float inv_num_accumulated = 1.0f / ctx->accumulated_counters[subdiv_vertex_index];
    copy_v3_v3(D, subdiv_position);
    mul_v3_fl(D, inv_num_accumulated);
  }
  /* Interpolate custom data and evaluate position. */
  subdiv_vertex_data_interpolate(ctx, subdiv_vertex_index, vertex_interpolation, u, v);
  eval_limit_point(ctx->subdiv, ptex_face_index, u, v, subdiv_position);
  /* Apply displacement. */
  add_v3_v3(subdiv_position, D);
  /* Evaluate undeformed texture coordinate. */
  subdiv_vertex_orco_evaluate(ctx, ptex_face_index, u, v, subdiv_vertex_index);
}
 
static void subdiv_mesh_vertex_displacement_every_corner_or_edge(
    const ForeachContext *foreach_context,
    void * /*tls*/,
    const int ptex_face_index,
    const float u,
    const float v,
    const int subdiv_vertex_index)
{
  SubdivMeshContext *ctx = static_cast<SubdivMeshContext *>(foreach_context->user_data);
  subdiv_accumulate_vertex_displacement(ctx, ptex_face_index, u, v, subdiv_vertex_index);
}
 
static void subdiv_mesh_vertex_displacement_every_corner(const ForeachContext *foreach_context,
                                                         void *tls,
                                                         const int ptex_face_index,
                                                         const float u,
                                                         const float v,
                                                         const int /*coarse_vertex_index*/,
                                                         const int /*coarse_face_index*/,
                                                         const int /*coarse_corner*/,
                                                         const int subdiv_vertex_index)
{
  subdiv_mesh_vertex_displacement_every_corner_or_edge(
      foreach_context, tls, ptex_face_index, u, v, subdiv_vertex_index);
}
 
static void subdiv_mesh_vertex_displacement_every_edge(const ForeachContext *foreach_context,
                                                       void *tls,
                                                       const int ptex_face_index,
                                                       const float u,
                                                       const float v,
                                                       const int /*coarse_edge_index*/,
                                                       const int /*coarse_face_index*/,
                                                       const int /*coarse_corner*/,
                                                       const int subdiv_vertex_index)
{
  subdiv_mesh_vertex_displacement_every_corner_or_edge(
      foreach_context, tls, ptex_face_index, u, v, subdiv_vertex_index);
}
 
static void subdiv_mesh_vertex_corner(const ForeachContext *foreach_context,
                                      void * /*tls*/,
                                      const int ptex_face_index,
                                      const float u,
                                      const float v,
                                      const int coarse_vertex_index,
                                      const int /*coarse_face_index*/,
                                      const int /*coarse_corner*/,
                                      const int subdiv_vertex_index)
{
  BLI_assert(coarse_vertex_index != ORIGINDEX_NONE);
  SubdivMeshContext *ctx = static_cast<SubdivMeshContext *>(foreach_context->user_data);
  evaluate_vertex_and_apply_displacement_copy(
      ctx, ptex_face_index, u, v, coarse_vertex_index, subdiv_vertex_index);
}
 
static void subdiv_mesh_ensure_vertex_interpolation(SubdivMeshContext *ctx,
                                                    SubdivMeshTLS *tls,
                                                    const int coarse_face_index,
                                                    const int coarse_corner)
{
  const IndexRange coarse_face = ctx->coarse_faces[coarse_face_index];
  /* Check whether we've moved to another corner or face. */
  if (tls->vertex_interpolation_initialized) {
    if (tls->vertex_interpolation_coarse_face_index != coarse_face_index ||
        tls->vertex_interpolation_coarse_corner != coarse_corner)
    {
      vertex_interpolation_end(&tls->vertex_interpolation);
      tls->vertex_interpolation_initialized = false;
    }
  }
  /* Initialize the interpolation. */
  if (!tls->vertex_interpolation_initialized) {
    vertex_interpolation_init(ctx, &tls->vertex_interpolation, coarse_face);
  }
  /* Update it for a new corner if needed. */
  if (!tls->vertex_interpolation_initialized ||
      tls->vertex_interpolation_coarse_corner != coarse_corner)
  {
    vertex_interpolation_from_corner(ctx, &tls->vertex_interpolation, coarse_face, coarse_corner);
  }
  /* Store settings used for the current state of interpolator. */
  tls->vertex_interpolation_initialized = true;
  tls->vertex_interpolation_coarse_face_index = coarse_face_index;
  tls->vertex_interpolation_coarse_corner = coarse_corner;
}
 
static void subdiv_mesh_vertex_edge(const ForeachContext *foreach_context,
                                    void *tls_v,
                                    const int ptex_face_index,
                                    const float u,
                                    const float v,
                                    const int /*coarse_edge_index*/,
                                    const int coarse_face_index,
                                    const int coarse_corner,
                                    const int subdiv_vertex_index)
{
  SubdivMeshContext *ctx = static_cast<SubdivMeshContext *>(foreach_context->user_data);
  SubdivMeshTLS *tls = static_cast<SubdivMeshTLS *>(tls_v);
  subdiv_mesh_ensure_vertex_interpolation(ctx, tls, coarse_face_index, coarse_corner);
  evaluate_vertex_and_apply_displacement_interpolate(
      ctx, ptex_face_index, u, v, &tls->vertex_interpolation, subdiv_vertex_index);
}
 
static bool subdiv_mesh_is_center_vertex(const IndexRange coarse_face,
                                         const float u,
                                         const float v)
{
  if (coarse_face.size() == 4) {
    if (u == 0.5f && v == 0.5f) {
      return true;
    }
  }
  else {
    if (u == 1.0f && v == 1.0f) {
      return true;
    }
  }
  return false;
}
 
static void subdiv_mesh_tag_center_vertex(const IndexRange coarse_face,
                                          const int subdiv_vertex_index,
                                          const float u,
                                          const float v,
                                          Mesh *subdiv_mesh)
{
  if (subdiv_mesh_is_center_vertex(coarse_face, u, v)) {
    subdiv_mesh->runtime->subsurf_face_dot_tags[subdiv_vertex_index].set();
  }
}
 
static void subdiv_mesh_vertex_inner(const ForeachContext *foreach_context,
                                     void *tls_v,
                                     const int ptex_face_index,
                                     const float u,
                                     const float v,
                                     const int coarse_face_index,
                                     const int coarse_corner,
                                     const int subdiv_vertex_index)
{
  SubdivMeshContext *ctx = static_cast<SubdivMeshContext *>(foreach_context->user_data);
  SubdivMeshTLS *tls = static_cast<SubdivMeshTLS *>(tls_v);
  Subdiv *subdiv = ctx->subdiv;
  const IndexRange coarse_face = ctx->coarse_faces[coarse_face_index];
  Mesh *subdiv_mesh = ctx->subdiv_mesh;
  float3 &subdiv_position = ctx->subdiv_positions[subdiv_vertex_index];
  subdiv_mesh_ensure_vertex_interpolation(ctx, tls, coarse_face_index, coarse_corner);
  subdiv_vertex_data_interpolate(ctx, subdiv_vertex_index, &tls->vertex_interpolation, u, v);
  eval_final_point(subdiv, ptex_face_index, u, v, subdiv_position);
  subdiv_mesh_tag_center_vertex(coarse_face, subdiv_vertex_index, u, v, subdiv_mesh);
  subdiv_vertex_orco_evaluate(ctx, ptex_face_index, u, v, subdiv_vertex_index);
}

 
/* -------------------------------------------------------------------- */
 
static void subdiv_copy_edge_data(SubdivMeshContext *ctx,
                                  const int subdiv_edge_index,
                                  const int coarse_edge_index)
{
  if (coarse_edge_index == ORIGINDEX_NONE) {
    if (ctx->edge_origindex != nullptr) {
      ctx->edge_origindex[subdiv_edge_index] = ORIGINDEX_NONE;
    }
    return;
  }
  CustomData_copy_data(&ctx->coarse_mesh->edge_data,
                       &ctx->subdiv_mesh->edge_data,
                       coarse_edge_index,
                       subdiv_edge_index,
                       1);
  if (ctx->settings->use_optimal_display) {
    ctx->subdiv_display_edges[subdiv_edge_index] = true;
  }
}
 
static void subdiv_mesh_edge(const ForeachContext *foreach_context,
                             void * /*tls*/,
                             const int coarse_edge_index,
                             const int subdiv_edge_index,
                             const bool /*is_loose*/,
                             const int subdiv_v1,
                             const int subdiv_v2)
{
  SubdivMeshContext *ctx = static_cast<SubdivMeshContext *>(foreach_context->user_data);
  subdiv_copy_edge_data(ctx, subdiv_edge_index, coarse_edge_index);
  ctx->subdiv_edges[subdiv_edge_index][0] = subdiv_v1;
  ctx->subdiv_edges[subdiv_edge_index][1] = subdiv_v2;
}

 
/* -------------------------------------------------------------------- */
 
static void subdiv_interpolate_corner_data(const SubdivMeshContext *ctx,
                                           const int subdiv_loop_index,
                                           const LoopsForInterpolation *loop_interpolation,
                                           const float u,
                                           const float v)
{
  const float weights[4] = {(1.0f - u) * (1.0f - v), u * (1.0f - v), u * v, (1.0f - u) * v};
  CustomData_interp(loop_interpolation->corner_data,
                    &ctx->subdiv_mesh->corner_data,
                    loop_interpolation->loop_indices,
                    weights,
                    nullptr,
                    4,
                    subdiv_loop_index);
  /* TODO(sergey): Set ORIGINDEX. */
}
 
static void subdiv_eval_uv_layer(SubdivMeshContext *ctx,
                                 const int corner_index,
                                 const int ptex_face_index,
                                 const float u,
                                 const float v)
{
  if (ctx->num_uv_layers == 0) {
    return;
  }
  Subdiv *subdiv = ctx->subdiv;
  for (int layer_index = 0; layer_index < ctx->num_uv_layers; layer_index++) {
    eval_face_varying(
        subdiv, layer_index, ptex_face_index, u, v, ctx->uv_layers[layer_index][corner_index]);
  }
}
 
static void subdiv_mesh_ensure_loop_interpolation(SubdivMeshContext *ctx,
                                                  SubdivMeshTLS *tls,
                                                  const int coarse_face_index,
                                                  const int coarse_corner)
{
  const IndexRange coarse_face = ctx->coarse_faces[coarse_face_index];
  /* Check whether we've moved to another corner or face. */
  if (tls->loop_interpolation_initialized) {
    if (tls->loop_interpolation_coarse_face_index != coarse_face_index ||
        tls->loop_interpolation_coarse_corner != coarse_corner)
    {
      loop_interpolation_end(&tls->loop_interpolation);
      tls->loop_interpolation_initialized = false;
    }
  }
  /* Initialize the interpolation. */
  if (!tls->loop_interpolation_initialized) {
    loop_interpolation_init(ctx, &tls->loop_interpolation, coarse_face);
  }
  /* Update it for a new corner if needed. */
  if (!tls->loop_interpolation_initialized ||
      tls->loop_interpolation_coarse_corner != coarse_corner)
  {
    loop_interpolation_from_corner(ctx, &tls->loop_interpolation, coarse_face, coarse_corner);
  }
  /* Store settings used for the current state of interpolator. */
  tls->loop_interpolation_initialized = true;
  tls->loop_interpolation_coarse_face_index = coarse_face_index;
  tls->loop_interpolation_coarse_corner = coarse_corner;
}
 
static void subdiv_mesh_loop(const ForeachContext *foreach_context,
                             void *tls_v,
                             const int ptex_face_index,
                             const float u,
                             const float v,
                             const int /*coarse_loop_index*/,
                             const int coarse_face_index,
                             const int coarse_corner,
                             const int subdiv_loop_index,
                             const int subdiv_vertex_index,
                             const int subdiv_edge_index)
{
  SubdivMeshContext *ctx = static_cast<SubdivMeshContext *>(foreach_context->user_data);
  SubdivMeshTLS *tls = static_cast<SubdivMeshTLS *>(tls_v);
  subdiv_mesh_ensure_loop_interpolation(ctx, tls, coarse_face_index, coarse_corner);
  subdiv_interpolate_corner_data(ctx, subdiv_loop_index, &tls->loop_interpolation, u, v);
  subdiv_eval_uv_layer(ctx, subdiv_loop_index, ptex_face_index, u, v);
  ctx->subdiv_corner_verts[subdiv_loop_index] = subdiv_vertex_index;
  ctx->subdiv_corner_edges[subdiv_loop_index] = subdiv_edge_index;
}

 
/* -------------------------------------------------------------------- */
 
static void subdiv_mesh_face(const ForeachContext *foreach_context,
                             void * /*tls*/,
                             const int coarse_face_index,
                             const int subdiv_face_index,
                             const int start_loop_index,
                             const int /*num_loops*/)
{
  BLI_assert(coarse_face_index != ORIGINDEX_NONE);
  SubdivMeshContext *ctx = static_cast<SubdivMeshContext *>(foreach_context->user_data);
  CustomData_copy_data(&ctx->coarse_mesh->face_data,
                       &ctx->subdiv_mesh->face_data,
                       coarse_face_index,
                       subdiv_face_index,
                       1);
  ctx->subdiv_face_offsets[subdiv_face_index] = start_loop_index;
}

 
/* -------------------------------------------------------------------- */
 
static void subdiv_mesh_vertex_loose(const ForeachContext *foreach_context,
                                     void * /*tls*/,
                                     const int coarse_vertex_index,
                                     const int subdiv_vertex_index)
{
  SubdivMeshContext *ctx = static_cast<SubdivMeshContext *>(foreach_context->user_data);
  subdiv_vertex_data_copy(ctx, coarse_vertex_index, subdiv_vertex_index);
}
 
/* Get neighbor edges of the given one.
 * - neighbors[0] is an edge adjacent to edge->v1.
 * - neighbors[1] is an edge adjacent to edge->v2. */
static std::array<std::optional<int2>, 2> find_edge_neighbors(
    const Span<int2> coarse_edges, const GroupedSpan<int> vert_to_edge_map, const int edge_index)
{
  /* Vertices which has more than one neighbor are considered infinitely
   * sharp. This is also how topology factory treats vertices of a surface
   * which are adjacent to a loose edge. */
  const auto neighbor_edge_if_single = [&](const int vert) -> std::optional<int2> {
    const Span<int> neighbors = vert_to_edge_map[vert];
    if (neighbors.size() != 2) {
      return std::nullopt;
    }
    return neighbors[0] == edge_index ? coarse_edges[neighbors[1]] : coarse_edges[neighbors[0]];
  };
  const int2 edge = coarse_edges[edge_index];
  return {neighbor_edge_if_single(edge[0]), neighbor_edge_if_single(edge[1])};
}
 
static std::array<float3, 4> find_loose_edge_interpolation_positions(
    const Span<float3> coarse_positions,
    const int2 &coarse_edge,
    const std::array<std::optional<int2>, 2> &neighbors)
{
  std::array<float3, 4> result;
  /* Middle points corresponds to the edge. */
  result[1] = coarse_positions[coarse_edge[0]];
  result[2] = coarse_positions[coarse_edge[1]];
  /* Start point, duplicate from edge start if no neighbor. */
  if (const std::optional<int2> &other = neighbors[0]) {
    result[0] = coarse_positions[mesh::edge_other_vert(*other, coarse_edge[0])];
  }
  else {
    result[0] = result[1] * 2.0f - result[2];
  }
  /* End point, duplicate from edge end if no neighbor. */
  if (const std::optional<int2> &other = neighbors[1]) {
    result[3] = coarse_positions[mesh::edge_other_vert(*other, coarse_edge[1])];
  }
  else {
    result[3] = result[2] * 2.0f - result[1];
  }
  return result;
}
 
float3 mesh_interpolate_position_on_edge(const Span<float3> coarse_positions,
                                         const Span<int2> coarse_edges,
                                         const GroupedSpan<int> vert_to_edge_map,
                                         const int coarse_edge_index,
                                         const bool is_simple,
                                         const float u)
{
  const int2 edge = coarse_edges[coarse_edge_index];
  if (is_simple) {
    return math::interpolate(coarse_positions[edge[0]], coarse_positions[edge[1]], u);
  }
  /* Find neighbors of the coarse edge. */
  const std::array<std::optional<int2>, 2> neighbors = find_edge_neighbors(
      coarse_edges, vert_to_edge_map, coarse_edge_index);
  const std::array<float3, 4> points = find_loose_edge_interpolation_positions(
      coarse_positions, edge, neighbors);
  float4 weights;
  key_curve_position_weights(u, weights, KEY_BSPLINE);
  return bke::attribute_math::mix4(weights, points[0], points[1], points[2], points[3]);
}
 
static void subdiv_mesh_vertex_of_loose_edge_interpolate(SubdivMeshContext *ctx,
                                                         const int2 &coarse_edge,
                                                         const float u,
                                                         const int subdiv_vertex_index)
{
  const Mesh *coarse_mesh = ctx->coarse_mesh;
  Mesh *subdiv_mesh = ctx->subdiv_mesh;
  /* This is never used for end-points (which are copied from the original). */
  BLI_assert(u > 0.0f);
  BLI_assert(u < 1.0f);
  const float interpolation_weights[2] = {1.0f - u, u};
  const int coarse_vertex_indices[2] = {coarse_edge[0], coarse_edge[1]};
  CustomData_interp(&coarse_mesh->vert_data,
                    &subdiv_mesh->vert_data,
                    coarse_vertex_indices,
                    interpolation_weights,
                    nullptr,
                    2,
                    subdiv_vertex_index);
  if (ctx->vert_origindex != nullptr) {
    ctx->vert_origindex[subdiv_vertex_index] = ORIGINDEX_NONE;
  }
}
 
static void subdiv_mesh_vertex_of_loose_edge(const ForeachContext *foreach_context,
                                             void * /*tls*/,
                                             const int coarse_edge_index,
                                             const float u,
                                             const int subdiv_vertex_index)
{
  SubdivMeshContext *ctx = static_cast<SubdivMeshContext *>(foreach_context->user_data);
  const int2 &coarse_edge = ctx->coarse_edges[coarse_edge_index];
  const bool is_simple = ctx->subdiv->settings.is_simple;
 
  /* Interpolate custom data when not an end point.
   * This data has already been copied from the original vertex by #subdiv_mesh_vertex_loose. */
  if (!ELEM(u, 0.0, 1.0)) {
    subdiv_mesh_vertex_of_loose_edge_interpolate(ctx, coarse_edge, u, subdiv_vertex_index);
  }
  /* Interpolate coordinate. */
  ctx->subdiv_positions[subdiv_vertex_index] = mesh_interpolate_position_on_edge(
      ctx->coarse_positions,
      ctx->coarse_edges,
      ctx->vert_to_edge_map,
      coarse_edge_index,
      is_simple,
      u);
}

 
/* -------------------------------------------------------------------- */
 
static void setup_foreach_callbacks(const SubdivMeshContext *subdiv_context,
                                    ForeachContext *foreach_context)
{
  memset(foreach_context, 0, sizeof(*foreach_context));
  /* General information. */
  foreach_context->topology_info = subdiv_mesh_topology_info;
  /* Every boundary geometry. Used for displacement averaging. */
  if (subdiv_context->have_displacement) {
    foreach_context->vertex_every_corner = subdiv_mesh_vertex_displacement_every_corner;
    foreach_context->vertex_every_edge = subdiv_mesh_vertex_displacement_every_edge;
  }
  foreach_context->vertex_corner = subdiv_mesh_vertex_corner;
  foreach_context->vertex_edge = subdiv_mesh_vertex_edge;
  foreach_context->vertex_inner = subdiv_mesh_vertex_inner;
  foreach_context->edge = subdiv_mesh_edge;
  foreach_context->loop = subdiv_mesh_loop;
  foreach_context->poly = subdiv_mesh_face;
  foreach_context->vertex_loose = subdiv_mesh_vertex_loose;
  foreach_context->vertex_of_loose_edge = subdiv_mesh_vertex_of_loose_edge;
  foreach_context->user_data_tls_free = subdiv_mesh_tls_free;
}

 
/* -------------------------------------------------------------------- */
 
Mesh *subdiv_to_mesh(Subdiv *subdiv, const ToMeshSettings *settings, const Mesh *coarse_mesh)
{
 
  stats_begin(&subdiv->stats, SUBDIV_STATS_SUBDIV_TO_MESH);
  /* Make sure evaluator is up to date with possible new topology, and that
   * it is refined for the new positions of coarse vertices. */
  if (!eval_begin_from_mesh(subdiv, coarse_mesh, {}, SUBDIV_EVALUATOR_TYPE_CPU, nullptr)) {
    /* This could happen in two situations:
     * - OpenSubdiv is disabled.
     * - Something totally bad happened, and OpenSubdiv rejected our
     *   topology.
     * In either way, we can't safely continue. */
    if (coarse_mesh->faces_num) {
      stats_end(&subdiv->stats, SUBDIV_STATS_SUBDIV_TO_MESH);
      return nullptr;
    }
  }
  /* Initialize subdivision mesh creation context. */
  SubdivMeshContext subdiv_context{};
  subdiv_context.settings = settings;
 
  subdiv_context.coarse_mesh = coarse_mesh;
  subdiv_context.coarse_positions = coarse_mesh->vert_positions();
  subdiv_context.coarse_edges = coarse_mesh->edges();
  subdiv_context.coarse_faces = coarse_mesh->faces();
  subdiv_context.coarse_corner_verts = coarse_mesh->corner_verts();
  if (coarse_mesh->loose_edges().count > 0) {
    subdiv_context.vert_to_edge_map = mesh::build_vert_to_edge_map(
        subdiv_context.coarse_edges,
        coarse_mesh->verts_num,
        subdiv_context.vert_to_edge_offsets,
        subdiv_context.vert_to_edge_indices);
  }
 
  subdiv_context.subdiv = subdiv;
  subdiv_context.have_displacement = (subdiv->displacement_evaluator != nullptr);
  /* Multi-threaded traversal/evaluation. */
  stats_begin(&subdiv->stats, SUBDIV_STATS_SUBDIV_TO_MESH_GEOMETRY);
  ForeachContext foreach_context;
  setup_foreach_callbacks(&subdiv_context, &foreach_context);
  SubdivMeshTLS tls{};
  foreach_context.user_data = &subdiv_context;
  foreach_context.user_data_tls_size = sizeof(SubdivMeshTLS);
  foreach_context.user_data_tls = &tls;
  foreach_subdiv_geometry(subdiv, &foreach_context, settings, coarse_mesh);
  stats_end(&subdiv->stats, SUBDIV_STATS_SUBDIV_TO_MESH_GEOMETRY);
  Mesh *result = subdiv_context.subdiv_mesh;
 
  CustomData_add_layer_named_with_data(&result->corner_data,
                                       CD_PROP_INT32,
                                       subdiv_context.subdiv_corner_verts,
                                       result->corners_num,
                                       ".corner_vert",
                                       nullptr);
  subdiv_context.subdiv_corner_verts = nullptr;
  CustomData_add_layer_named_with_data(&result->corner_data,
                                       CD_PROP_INT32,
                                       subdiv_context.subdiv_corner_edges,
                                       result->corners_num,
                                       ".corner_edge",
                                       nullptr);
  subdiv_context.subdiv_corner_edges = nullptr;
 
  /* NOTE: Using normals from the limit surface gives different results than Blender's vertex
   * normal calculation. Since vertex normals are supposed to be a consistent cache, don't bother
   * calculating them here. The work may have been pointless anyway if the mesh is deformed or
   * changed afterwards. */
 
  /* Move the optimal display edge array to the final bit vector. */
  if (!subdiv_context.subdiv_display_edges.is_empty()) {
    result->runtime->subsurf_optimal_display_edges = BitVector<>(
        subdiv_context.subdiv_display_edges);
  }
 
  if (coarse_mesh->verts_no_face().count == 0) {
    result->tag_loose_verts_none();
  }
  if (coarse_mesh->loose_edges().count == 0) {
    result->tag_loose_edges_none();
  }
  result->tag_overlapping_none();
 
  if (subdiv->settings.is_simple) {
    /* In simple subdivision, min and max positions are not changed, avoid recomputing bounds. */
    result->runtime->bounds_cache = coarse_mesh->runtime->bounds_cache;
  }
 
  // BKE_mesh_validate(result, true, true);
  stats_end(&subdiv->stats, SUBDIV_STATS_SUBDIV_TO_MESH);
  subdiv_mesh_context_free(&subdiv_context);
  return result;
}

 
}  // namespace blender::bke::subdiv