/*
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software  Foundation,
 * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 *
 * Copyright 2017, Blender Foundation.
 */

/** \file
 * \ingroup modifiers
 */

#include "BLI_math.h"
#include "BLI_math_geom.h"
#include "BLI_task.h"

#include "DNA_mesh_types.h"
#include "DNA_meshdata_types.h"
#include "DNA_object_types.h"
#include "DNA_scene_types.h"

#include "BKE_bvhutils.h"
#include "BKE_mesh_runtime.h"
#include "BKE_editmesh.h"
#include "BKE_library.h"
#include "BKE_library_query.h"
#include "BKE_modifier.h"

#include "DEG_depsgraph.h"
#include "DEG_depsgraph_query.h"

#include "MEM_guardedalloc.h"

#include "MOD_util.h"

typedef struct SDefAdjacency {
  struct SDefAdjacency *next;
  unsigned int index;
} SDefAdjacency;

typedef struct SDefAdjacencyArray {
  SDefAdjacency *first;
  unsigned int num; /* Careful, this is twice the number of polygons (avoids an extra loop) */
} SDefAdjacencyArray;

typedef struct SDefEdgePolys {
  unsigned int polys[2], num;
} SDefEdgePolys;

typedef struct SDefBindCalcData {
  BVHTreeFromMesh *const treeData;
  const SDefAdjacencyArray *const vert_edges;
  const SDefEdgePolys *const edge_polys;
  SDefVert *const bind_verts;
  const MLoopTri *const looptri;
  const MPoly *const mpoly;
  const MEdge *const medge;
  const MLoop *const mloop;
  float (*const targetCos)[3];
  float (*const vertexCos)[3];
  float imat[4][4];
  const float falloff;
  int success;
} SDefBindCalcData;

typedef struct SDefBindPoly {
  float (*coords)[3];
  float (*coords_v2)[2];
  float point_v2[2];
  float weight_angular;
  float weight_dist_proj;
  float weight_dist;
  float weight;
  float scales[2];
  float centroid[3];
  float centroid_v2[2];
  float normal[3];
  float cent_edgemid_vecs_v2[2][2];
  float edgemid_angle;
  float point_edgemid_angles[2];
  float corner_edgemid_angles[2];
  float dominant_angle_weight;
  unsigned int index;
  unsigned int numverts;
  unsigned int loopstart;
  unsigned int edge_inds[2];
  unsigned int edge_vert_inds[2];
  unsigned int corner_ind;
  unsigned int dominant_edge;
  bool inside;
} SDefBindPoly;

typedef struct SDefBindWeightData {
  SDefBindPoly *bind_polys;
  unsigned int numpoly;
  unsigned int numbinds;
} SDefBindWeightData;

typedef struct SDefDeformData {
  const SDefVert *const bind_verts;
  float (*const targetCos)[3];
  float (*const vertexCos)[3];
} SDefDeformData;

/* Bind result values */
enum {
  MOD_SDEF_BIND_RESULT_SUCCESS = 1,
  MOD_SDEF_BIND_RESULT_GENERIC_ERR = 0,
  MOD_SDEF_BIND_RESULT_MEM_ERR = -1,
  MOD_SDEF_BIND_RESULT_NONMANY_ERR = -2,
  MOD_SDEF_BIND_RESULT_CONCAVE_ERR = -3,
  MOD_SDEF_BIND_RESULT_OVERLAP_ERR = -4,
};

/* Infinite weight flags */
enum {
  MOD_SDEF_INFINITE_WEIGHT_ANGULAR = (1 << 0),
  MOD_SDEF_INFINITE_WEIGHT_DIST_PROJ = (1 << 1),
  MOD_SDEF_INFINITE_WEIGHT_DIST = (1 << 2),
};

static void initData(ModifierData *md)
{
  SurfaceDeformModifierData *smd = (SurfaceDeformModifierData *)md;
  smd->target = NULL;
  smd->verts = NULL;
  smd->flags = 0;
  smd->falloff = 4.0f;
}

static void freeData(ModifierData *md)
{
  SurfaceDeformModifierData *smd = (SurfaceDeformModifierData *)md;

  if (smd->verts) {
    for (int i = 0; i < smd->numverts; i++) {
      if (smd->verts[i].binds) {
        for (int j = 0; j < smd->verts[i].numbinds; j++) {
          MEM_SAFE_FREE(smd->verts[i].binds[j].vert_inds);
          MEM_SAFE_FREE(smd->verts[i].binds[j].vert_weights);
        }

        MEM_SAFE_FREE(smd->verts[i].binds);
      }
    }

    MEM_SAFE_FREE(smd->verts);
  }
}

static void copyData(const ModifierData *md, ModifierData *target, const int flag)
{
  const SurfaceDeformModifierData *smd = (const SurfaceDeformModifierData *)md;
  SurfaceDeformModifierData *tsmd = (SurfaceDeformModifierData *)target;

  modifier_copyData_generic(md, target, flag);

  if (smd->verts) {
    tsmd->verts = MEM_dupallocN(smd->verts);

    for (int i = 0; i < smd->numverts; i++) {
      if (smd->verts[i].binds) {
        tsmd->verts[i].binds = MEM_dupallocN(smd->verts[i].binds);

        for (int j = 0; j < smd->verts[i].numbinds; j++) {
          if (smd->verts[i].binds[j].vert_inds) {
            tsmd->verts[i].binds[j].vert_inds = MEM_dupallocN(smd->verts[i].binds[j].vert_inds);
          }

          if (smd->verts[i].binds[j].vert_weights) {
            tsmd->verts[i].binds[j].vert_weights = MEM_dupallocN(
                smd->verts[i].binds[j].vert_weights);
          }
        }
      }
    }
  }
}

static void foreachObjectLink(ModifierData *md, Object *ob, ObjectWalkFunc walk, void *userData)
{
  SurfaceDeformModifierData *smd = (SurfaceDeformModifierData *)md;

  walk(userData, ob, &smd->target, IDWALK_NOP);
}

static void updateDepsgraph(ModifierData *md, const ModifierUpdateDepsgraphContext *ctx)
{
  SurfaceDeformModifierData *smd = (SurfaceDeformModifierData *)md;
  if (smd->target != NULL) {
    DEG_add_object_relation(
        ctx->node, smd->target, DEG_OB_COMP_GEOMETRY, "Surface Deform Modifier");
  }
}

static void freeAdjacencyMap(SDefAdjacencyArray *const vert_edges,
                             SDefAdjacency *const adj_ref,
                             SDefEdgePolys *const edge_polys)
{
  MEM_freeN(edge_polys);

  MEM_freeN(adj_ref);

  MEM_freeN(vert_edges);
}

static int buildAdjacencyMap(const MPoly *poly,
                             const MEdge *edge,
                             const MLoop *const mloop,
                             const unsigned int numpoly,
                             const unsigned int numedges,
                             SDefAdjacencyArray *const vert_edges,
                             SDefAdjacency *adj,
                             SDefEdgePolys *const edge_polys)
{
  const MLoop *loop;

  /* Fing polygons adjacent to edges */
  for (int i = 0; i < numpoly; i++, poly++) {
    loop = &mloop[poly->loopstart];

    for (int j = 0; j < poly->totloop; j++, loop++) {
      if (edge_polys[loop->e].num == 0) {
        edge_polys[loop->e].polys[0] = i;
        edge_polys[loop->e].polys[1] = -1;
        edge_polys[loop->e].num++;
      }
      else if (edge_polys[loop->e].num == 1) {
        edge_polys[loop->e].polys[1] = i;
        edge_polys[loop->e].num++;
      }
      else {
        return MOD_SDEF_BIND_RESULT_NONMANY_ERR;
      }
    }
  }

  /* Find edges adjacent to vertices */
  for (int i = 0; i < numedges; i++, edge++) {
    adj->next = vert_edges[edge->v1].first;
    adj->index = i;
    vert_edges[edge->v1].first = adj;
    vert_edges[edge->v1].num += edge_polys[i].num;
    adj++;

    adj->next = vert_edges[edge->v2].first;
    adj->index = i;
    vert_edges[edge->v2].first = adj;
    vert_edges[edge->v2].num += edge_polys[i].num;
    adj++;
  }

  return MOD_SDEF_BIND_RESULT_SUCCESS;
}

BLI_INLINE void sortPolyVertsEdge(unsigned int *indices,
                                  const MLoop *const mloop,
                                  const unsigned int edge,
                                  const unsigned int num)
{
  bool found = false;

  for (int i = 0; i < num; i++) {
    if (mloop[i].e == edge) {
      found = true;
    }
    if (found) {
      *indices = mloop[i].v;
      indices++;
    }
  }

  /* Fill in remaining vertex indices that occur before the edge */
  for (int i = 0; mloop[i].e != edge; i++) {
    *indices = mloop[i].v;
    indices++;
  }
}

BLI_INLINE void sortPolyVertsTri(unsigned int *indices,
                                 const MLoop *const mloop,
                                 const unsigned int loopstart,
                                 const unsigned int num)
{
  for (int i = loopstart; i < num; i++) {
    *indices = mloop[i].v;
    indices++;
  }

  for (int i = 0; i < loopstart; i++) {
    *indices = mloop[i].v;
    indices++;
  }
}

BLI_INLINE unsigned int nearestVert(SDefBindCalcData *const data, const float point_co[3])
{
  BVHTreeNearest nearest = {
      .dist_sq = FLT_MAX,
      .index = -1,
  };
  const MPoly *poly;
  const MEdge *edge;
  const MLoop *loop;
  float t_point[3];
  float max_dist = FLT_MAX;
  float dist;
  unsigned int index = 0;

  mul_v3_m4v3(t_point, data->imat, point_co);

  BLI_bvhtree_find_nearest(
      data->treeData->tree, t_point, &nearest, data->treeData->nearest_callback, data->treeData);

  poly = &data->mpoly[data->looptri[nearest.index].poly];
  loop = &data->mloop[poly->loopstart];

  for (int i = 0; i < poly->totloop; i++, loop++) {
    edge = &data->medge[loop->e];
    dist = dist_squared_to_line_segment_v3(
        point_co, data->targetCos[edge->v1], data->targetCos[edge->v2]);

    if (dist < max_dist) {
      max_dist = dist;
      index = loop->e;
    }
  }

  edge = &data->medge[index];
  if (len_squared_v3v3(point_co, data->targetCos[edge->v1]) <
      len_squared_v3v3(point_co, data->targetCos[edge->v2])) {
    return edge->v1;
  }
  else {
    return edge->v2;
  }
}

BLI_INLINE int isPolyValid(const float coords[][2], const unsigned int nr)
{
  float prev_co[2];
  float curr_vec[2], prev_vec[2];

  if (!is_poly_convex_v2(coords, nr)) {
    return MOD_SDEF_BIND_RESULT_CONCAVE_ERR;
  }

  copy_v2_v2(prev_co, coords[nr - 1]);
  sub_v2_v2v2(prev_vec, prev_co, coords[nr - 2]);
  normalize_v2(prev_vec);

  for (int i = 0; i < nr; i++) {
    sub_v2_v2v2(curr_vec, coords[i], prev_co);

    const float curr_len = normalize_v2(curr_vec);
    if (curr_len < FLT_EPSILON) {
      return MOD_SDEF_BIND_RESULT_OVERLAP_ERR;
    }

    if (1.0f - dot_v2v2(prev_vec, curr_vec) < FLT_EPSILON) {
      return MOD_SDEF_BIND_RESULT_CONCAVE_ERR;
    }

    copy_v2_v2(prev_co, coords[i]);
    copy_v2_v2(prev_vec, curr_vec);
  }

  return MOD_SDEF_BIND_RESULT_SUCCESS;
}

static void freeBindData(SDefBindWeightData *const bwdata)
{
  SDefBindPoly *bpoly = bwdata->bind_polys;

  if (bwdata->bind_polys) {
    for (int i = 0; i < bwdata->numpoly; bpoly++, i++) {
      MEM_SAFE_FREE(bpoly->coords);
      MEM_SAFE_FREE(bpoly->coords_v2);
    }

    MEM_freeN(bwdata->bind_polys);
  }

  MEM_freeN(bwdata);
}

BLI_INLINE float computeAngularWeight(const float point_angle, const float edgemid_angle)
{
  float weight;

  weight = point_angle;
  weight /= edgemid_angle;
  weight *= M_PI_2;

  return sinf(weight);
}

BLI_INLINE SDefBindWeightData *computeBindWeights(SDefBindCalcData *const data,
                                                  const float point_co[3])
{
  const unsigned int nearest = nearestVert(data, point_co);
  const SDefAdjacency *const vert_edges = data->vert_edges[nearest].first;
  const SDefEdgePolys *const edge_polys = data->edge_polys;

  const SDefAdjacency *vedge;
  const MPoly *poly;
  const MLoop *loop;

  SDefBindWeightData *bwdata;
  SDefBindPoly *bpoly;

  float world[3] = {0.0f, 0.0f, 1.0f};
  float avg_point_dist = 0.0f;
  float tot_weight = 0.0f;
  int inf_weight_flags = 0;

  bwdata = MEM_callocN(sizeof(*bwdata), "SDefBindWeightData");
  if (bwdata == NULL) {
    data->success = MOD_SDEF_BIND_RESULT_MEM_ERR;
    return NULL;
  }

  bwdata->numpoly = data->vert_edges[nearest].num / 2;

  bpoly = MEM_calloc_arrayN(bwdata->numpoly, sizeof(*bpoly), "SDefBindPoly");
  if (bpoly == NULL) {
    freeBindData(bwdata);
    data->success = MOD_SDEF_BIND_RESULT_MEM_ERR;
    return NULL;
  }

  bwdata->bind_polys = bpoly;

  /* Loop over all adjacent edges,
   * and build the SDefBindPoly data for each poly adjacent to those. */
  for (vedge = vert_edges; vedge; vedge = vedge->next) {
    unsigned int edge_ind = vedge->index;

    for (int i = 0; i < edge_polys[edge_ind].num; i++) {
      {
        bpoly = bwdata->bind_polys;

        for (int j = 0; j < bwdata->numpoly; bpoly++, j++) {
          /* If coords isn't allocated, we have reached the first uninitialized bpoly */
          if ((bpoly->index == edge_polys[edge_ind].polys[i]) || (!bpoly->coords)) {
            break;
          }
        }
      }

      /* Check if poly was already created by another edge or still has to be initialized */
      if (!bpoly->coords) {
        float angle;
        float axis[3];
        float tmp_vec_v2[2];
        int is_poly_valid;

        bpoly->index = edge_polys[edge_ind].polys[i];
        bpoly->coords = NULL;
        bpoly->coords_v2 = NULL;

        /* Copy poly data */
        poly = &data->mpoly[bpoly->index];
        loop = &data->mloop[poly->loopstart];

        bpoly->numverts = poly->totloop;
        bpoly->loopstart = poly->loopstart;

        bpoly->coords = MEM_malloc_arrayN(
            poly->totloop, sizeof(*bpoly->coords), "SDefBindPolyCoords");
        if (bpoly->coords == NULL) {
          freeBindData(bwdata);
          data->success = MOD_SDEF_BIND_RESULT_MEM_ERR;
          return NULL;
        }

        bpoly->coords_v2 = MEM_malloc_arrayN(
            poly->totloop, sizeof(*bpoly->coords_v2), "SDefBindPolyCoords_v2");
        if (bpoly->coords_v2 == NULL) {
          freeBindData(bwdata);
          data->success = MOD_SDEF_BIND_RESULT_MEM_ERR;
          return NULL;
        }

        for (int j = 0; j < poly->totloop; j++, loop++) {
          copy_v3_v3(bpoly->coords[j], data->targetCos[loop->v]);

          /* Find corner and edge indices within poly loop array */
          if (loop->v == nearest) {
            bpoly->corner_ind = j;
            bpoly->edge_vert_inds[0] = (j == 0) ? (poly->totloop - 1) : (j - 1);
            bpoly->edge_vert_inds[1] = (j == poly->totloop - 1) ? (0) : (j + 1);

            bpoly->edge_inds[0] = data->mloop[poly->loopstart + bpoly->edge_vert_inds[0]].e;
            bpoly->edge_inds[1] = loop->e;
          }
        }

        /* Compute poly's parametric data */
        mid_v3_v3_array(bpoly->centroid, bpoly->coords, poly->totloop);
        normal_poly_v3(bpoly->normal, bpoly->coords, poly->totloop);

        /* Compute poly skew angle and axis */
        angle = angle_normalized_v3v3(bpoly->normal, world);

        cross_v3_v3v3(axis, bpoly->normal, world);
        normalize_v3(axis);

        /* Map coords onto 2d normal plane */
        map_to_plane_axis_angle_v2_v3v3fl(bpoly->point_v2, point_co, axis, angle);

        zero_v2(bpoly->centroid_v2);
        for (int j = 0; j < poly->totloop; j++) {
          map_to_plane_axis_angle_v2_v3v3fl(bpoly->coords_v2[j], bpoly->coords[j], axis, angle);
          madd_v2_v2fl(bpoly->centroid_v2, bpoly->coords_v2[j], 1.0f / poly->totloop);
        }

        is_poly_valid = isPolyValid(bpoly->coords_v2, poly->totloop);

        if (is_poly_valid != MOD_SDEF_BIND_RESULT_SUCCESS) {
          freeBindData(bwdata);
          data->success = is_poly_valid;
          return NULL;
        }

        bpoly->inside = isect_point_poly_v2(
            bpoly->point_v2, bpoly->coords_v2, poly->totloop, false);

        /* Initialize weight components */
        bpoly->weight_angular = 1.0f;
        bpoly->weight_dist_proj = len_v2v2(bpoly->centroid_v2, bpoly->point_v2);
        bpoly->weight_dist = len_v3v3(bpoly->centroid, point_co);

        avg_point_dist += bpoly->weight_dist;

        /* Compute centroid to mid-edge vectors */
        mid_v2_v2v2(bpoly->cent_edgemid_vecs_v2[0],
                    bpoly->coords_v2[bpoly->edge_vert_inds[0]],
                    bpoly->coords_v2[bpoly->corner_ind]);

        mid_v2_v2v2(bpoly->cent_edgemid_vecs_v2[1],
                    bpoly->coords_v2[bpoly->edge_vert_inds[1]],
                    bpoly->coords_v2[bpoly->corner_ind]);

        sub_v2_v2(bpoly->cent_edgemid_vecs_v2[0], bpoly->centroid_v2);
        sub_v2_v2(bpoly->cent_edgemid_vecs_v2[1], bpoly->centroid_v2);

        /* Compute poly scales with respect to mid-edges, and normalize the vectors */
        bpoly->scales[0] = normalize_v2(bpoly->cent_edgemid_vecs_v2[0]);
        bpoly->scales[1] = normalize_v2(bpoly->cent_edgemid_vecs_v2[1]);

        /* Compute the required polygon angles */
        bpoly->edgemid_angle = angle_normalized_v2v2(bpoly->cent_edgemid_vecs_v2[0],
                                                     bpoly->cent_edgemid_vecs_v2[1]);

        sub_v2_v2v2(tmp_vec_v2, bpoly->coords_v2[bpoly->corner_ind], bpoly->centroid_v2);
        normalize_v2(tmp_vec_v2);

        bpoly->corner_edgemid_angles[0] = angle_normalized_v2v2(tmp_vec_v2,
                                                                bpoly->cent_edgemid_vecs_v2[0]);
        bpoly->corner_edgemid_angles[1] = angle_normalized_v2v2(tmp_vec_v2,
                                                                bpoly->cent_edgemid_vecs_v2[1]);

        /* Check for inifnite weights, and compute angular data otherwise */
        if (bpoly->weight_dist < FLT_EPSILON) {
          inf_weight_flags |= MOD_SDEF_INFINITE_WEIGHT_DIST_PROJ;
          inf_weight_flags |= MOD_SDEF_INFINITE_WEIGHT_DIST;
        }
        else if (bpoly->weight_dist_proj < FLT_EPSILON) {
          inf_weight_flags |= MOD_SDEF_INFINITE_WEIGHT_DIST_PROJ;
        }
        else {
          float cent_point_vec[2];

          sub_v2_v2v2(cent_point_vec, bpoly->point_v2, bpoly->centroid_v2);
          normalize_v2(cent_point_vec);

          bpoly->point_edgemid_angles[0] = angle_normalized_v2v2(cent_point_vec,
                                                                 bpoly->cent_edgemid_vecs_v2[0]);
          bpoly->point_edgemid_angles[1] = angle_normalized_v2v2(cent_point_vec,
                                                                 bpoly->cent_edgemid_vecs_v2[1]);
        }
      }
    }
  }

  avg_point_dist /= bwdata->numpoly;

  /* If weights 1 and 2 are not infinite, loop over all adjacent edges again,
   * and build adjacency dependent angle data (depends on all polygons having been computed) */
  if (!inf_weight_flags) {
    for (vedge = vert_edges; vedge; vedge = vedge->next) {
      SDefBindPoly *bpolys[2];
      const SDefEdgePolys *epolys;
      float ang_weights[2];
      unsigned int edge_ind = vedge->index;
      unsigned int edge_on_poly[2];

      epolys = &edge_polys[edge_ind];

      /* Find bind polys corresponding to the edge's adjacent polys */
      bpoly = bwdata->bind_polys;

      for (int i = 0, j = 0; (i < bwdata->numpoly) && (j < epolys->num); bpoly++, i++) {
        if (ELEM(bpoly->index, epolys->polys[0], epolys->polys[1])) {
          bpolys[j] = bpoly;

          if (bpoly->edge_inds[0] == edge_ind) {
            edge_on_poly[j] = 0;
          }
          else {
            edge_on_poly[j] = 1;
          }

          j++;
        }
      }

      /* Compute angular weight component */
      if (epolys->num == 1) {
        ang_weights[0] = computeAngularWeight(bpolys[0]->point_edgemid_angles[edge_on_poly[0]],
                                              bpolys[0]->edgemid_angle);
        bpolys[0]->weight_angular *= ang_weights[0] * ang_weights[0];
      }
      else if (epolys->num == 2) {
        ang_weights[0] = computeAngularWeight(bpolys[0]->point_edgemid_angles[edge_on_poly[0]],
                                              bpolys[0]->edgemid_angle);
        ang_weights[1] = computeAngularWeight(bpolys[1]->point_edgemid_angles[edge_on_poly[1]],
                                              bpolys[1]->edgemid_angle);

        bpolys[0]->weight_angular *= ang_weights[0] * ang_weights[1];
        bpolys[1]->weight_angular *= ang_weights[0] * ang_weights[1];
      }
    }
  }

  /* Compute scalings and falloff.
   * Scale all weights if no infinite weight is found,
   * scale only unprojected weight if projected weight is infinite,
   * scale none if both are infinite. */
  if (!inf_weight_flags) {
    bpoly = bwdata->bind_polys;

    for (int i = 0; i < bwdata->numpoly; bpoly++, i++) {
      float corner_angle_weights[2];
      float scale_weight, sqr, inv_sqr;

      corner_angle_weights[0] = bpoly->point_edgemid_angles[0] / bpoly->corner_edgemid_angles[0];
      corner_angle_weights[1] = bpoly->point_edgemid_angles[1] / bpoly->corner_edgemid_angles[1];

      if (isnan(corner_angle_weights[0]) || isnan(corner_angle_weights[1])) {
        freeBindData(bwdata);
        data->success = MOD_SDEF_BIND_RESULT_GENERIC_ERR;
        return NULL;
      }

      /* Find which edge the point is closer to */
      if (corner_angle_weights[0] < corner_angle_weights[1]) {
        bpoly->dominant_edge = 0;
        bpoly->dominant_angle_weight = corner_angle_weights[0];
      }
      else {
        bpoly->dominant_edge = 1;
        bpoly->dominant_angle_weight = corner_angle_weights[1];
      }

      bpoly->dominant_angle_weight = sinf(bpoly->dominant_angle_weight * M_PI_2);

      /* Compute quadratic angular scale interpolation weight */
      scale_weight = bpoly->point_edgemid_angles[bpoly->dominant_edge] / bpoly->edgemid_angle;
      scale_weight /= scale_weight +
                      (bpoly->point_edgemid_angles[!bpoly->dominant_edge] / bpoly->edgemid_angle);

      sqr = scale_weight * scale_weight;
      inv_sqr = 1.0f - scale_weight;
      inv_sqr *= inv_sqr;
      scale_weight = sqr / (sqr + inv_sqr);

      /* Compute interpolated scale (no longer need the individual scales,
       * so simply storing the result over the scale in index zero) */
      bpoly->scales[0] = bpoly->scales[bpoly->dominant_edge] * (1.0f - scale_weight) +
                         bpoly->scales[!bpoly->dominant_edge] * scale_weight;

      /* Scale the point distance weights, and introduce falloff */
      bpoly->weight_dist_proj /= bpoly->scales[0];
      bpoly->weight_dist_proj = powf(bpoly->weight_dist_proj, data->falloff);

      bpoly->weight_dist /= avg_point_dist;
      bpoly->weight_dist = powf(bpoly->weight_dist, data->falloff);

      /* Re-check for infinite weights, now that all scalings and interpolations are computed */
      if (bpoly->weight_dist < FLT_EPSILON) {
        inf_weight_flags |= MOD_SDEF_INFINITE_WEIGHT_DIST_PROJ;
        inf_weight_flags |= MOD_SDEF_INFINITE_WEIGHT_DIST;
      }
      else if (bpoly->weight_dist_proj < FLT_EPSILON) {
        inf_weight_flags |= MOD_SDEF_INFINITE_WEIGHT_DIST_PROJ;
      }
      else if (bpoly->weight_angular < FLT_EPSILON) {
        inf_weight_flags |= MOD_SDEF_INFINITE_WEIGHT_ANGULAR;
      }
    }
  }
  else if (!(inf_weight_flags & MOD_SDEF_INFINITE_WEIGHT_DIST)) {
    bpoly = bwdata->bind_polys;

    for (int i = 0; i < bwdata->numpoly; bpoly++, i++) {
      /* Scale the point distance weight by average point distance, and introduce falloff */
      bpoly->weight_dist /= avg_point_dist;
      bpoly->weight_dist = powf(bpoly->weight_dist, data->falloff);

      /* Re-check for infinite weights, now that all scalings and interpolations are computed */
      if (bpoly->weight_dist < FLT_EPSILON) {
        inf_weight_flags |= MOD_SDEF_INFINITE_WEIGHT_DIST;
      }
    }
  }

  /* Final loop, to compute actual weights */
  bpoly = bwdata->bind_polys;

  for (int i = 0; i < bwdata->numpoly; bpoly++, i++) {
    /* Weight computation from components */
    if (inf_weight_flags & MOD_SDEF_INFINITE_WEIGHT_DIST) {
      bpoly->weight = bpoly->weight_dist < FLT_EPSILON ? 1.0f : 0.0f;
    }
    else if (inf_weight_flags & MOD_SDEF_INFINITE_WEIGHT_DIST_PROJ) {
      bpoly->weight = bpoly->weight_dist_proj < FLT_EPSILON ? 1.0f / bpoly->weight_dist : 0.0f;
    }
    else if (inf_weight_flags & MOD_SDEF_INFINITE_WEIGHT_ANGULAR) {
      bpoly->weight = bpoly->weight_angular < FLT_EPSILON ?
                          1.0f / bpoly->weight_dist_proj / bpoly->weight_dist :
                          0.0f;
    }
    else {
      bpoly->weight = 1.0f / bpoly->weight_angular / bpoly->weight_dist_proj / bpoly->weight_dist;
    }

    tot_weight += bpoly->weight;
  }

  bpoly = bwdata->bind_polys;

  for (int i = 0; i < bwdata->numpoly; bpoly++, i++) {
    bpoly->weight /= tot_weight;

    /* Evaluate if this poly is relevant to bind */
    /* Even though the weights should add up to 1.0,
     * the losses of weights smaller than epsilon here
     * should be negligible... */
    if (bpoly->weight >= FLT_EPSILON) {
      if (bpoly->inside) {
        bwdata->numbinds += 1;
      }
      else {
        if (bpoly->dominant_angle_weight < FLT_EPSILON ||
            1.0f - bpoly->dominant_angle_weight < FLT_EPSILON) {
          bwdata->numbinds += 1;
        }
        else {
          bwdata->numbinds += 2;
        }
      }
    }
  }

  return bwdata;
}

BLI_INLINE float computeNormalDisplacement(const float point_co[3],
                                           const float point_co_proj[3],
                                           const float normal[3])
{
  float disp_vec[3];
  float normal_dist;

  sub_v3_v3v3(disp_vec, point_co, point_co_proj);
  normal_dist = len_v3(disp_vec);

  if (dot_v3v3(disp_vec, normal) < 0) {
    normal_dist *= -1;
  }

  return normal_dist;
}

static void bindVert(void *__restrict userdata,
                     const int index,
                     const ParallelRangeTLS *__restrict UNUSED(tls))
{
  SDefBindCalcData *const data = (SDefBindCalcData *)userdata;
  float point_co[3];
  float point_co_proj[3];

  SDefBindWeightData *bwdata;
  SDefVert *sdvert = data->bind_verts + index;
  SDefBindPoly *bpoly;
  SDefBind *sdbind;

  if (data->success != MOD_SDEF_BIND_RESULT_SUCCESS) {
    sdvert->binds = NULL;
    sdvert->numbinds = 0;
    return;
  }

  copy_v3_v3(point_co, data->vertexCos[index]);
  bwdata = computeBindWeights(data, point_co);

  if (bwdata == NULL) {
    sdvert->binds = NULL;
    sdvert->numbinds = 0;
    return;
  }

  sdvert->binds = MEM_calloc_arrayN(bwdata->numbinds, sizeof(*sdvert->binds), "SDefVertBindData");
  if (sdvert->binds == NULL) {
    data->success = MOD_SDEF_BIND_RESULT_MEM_ERR;
    sdvert->numbinds = 0;
    return;
  }

  sdvert->numbinds = bwdata->numbinds;

  sdbind = sdvert->binds;

  bpoly = bwdata->bind_polys;

  for (int i = 0; i < bwdata->numbinds; bpoly++) {
    if (bpoly->weight >= FLT_EPSILON) {
      if (bpoly->inside) {
        const MLoop *loop = &data->mloop[bpoly->loopstart];

        sdbind->influence = bpoly->weight;
        sdbind->numverts = bpoly->numverts;

        sdbind->mode = MOD_SDEF_MODE_NGON;
        sdbind->vert_weights = MEM_malloc_arrayN(
            bpoly->numverts, sizeof(*sdbind->vert_weights), "SDefNgonVertWeights");
        if (sdbind->vert_weights == NULL) {
          data->success = MOD_SDEF_BIND_RESULT_MEM_ERR;
          return;
        }

        sdbind->vert_inds = MEM_malloc_arrayN(
            bpoly->numverts, sizeof(*sdbind->vert_inds), "SDefNgonVertInds");
        if (sdbind->vert_inds == NULL) {
          data->success = MOD_SDEF_BIND_RESULT_MEM_ERR;
          return;
        }

        interp_weights_poly_v2(
            sdbind->vert_weights, bpoly->coords_v2, bpoly->numverts, bpoly->point_v2);

        /* Reproject vert based on weights and original poly verts,
         * to reintroduce poly non-planarity */
        zero_v3(point_co_proj);
        for (int j = 0; j < bpoly->numverts; j++, loop++) {
          madd_v3_v3fl(point_co_proj, bpoly->coords[j], sdbind->vert_weights[j]);
          sdbind->vert_inds[j] = loop->v;
        }

        sdbind->normal_dist = computeNormalDisplacement(point_co, point_co_proj, bpoly->normal);

        sdbind++;
        i++;
      }
      else {
        float tmp_vec[3];
        float cent[3], norm[3];
        float v1[3], v2[3], v3[3];

        if (1.0f - bpoly->dominant_angle_weight >= FLT_EPSILON) {
          sdbind->influence = bpoly->weight * (1.0f - bpoly->dominant_angle_weight);
          sdbind->numverts = bpoly->numverts;

          sdbind->mode = MOD_SDEF_MODE_CENTROID;
          sdbind->vert_weights = MEM_malloc_arrayN(
              3, sizeof(*sdbind->vert_weights), "SDefCentVertWeights");
          if (sdbind->vert_weights == NULL) {
            data->success = MOD_SDEF_BIND_RESULT_MEM_ERR;
            return;
          }

          sdbind->vert_inds = MEM_malloc_arrayN(
              bpoly->numverts, sizeof(*sdbind->vert_inds), "SDefCentVertInds");
          if (sdbind->vert_inds == NULL) {
            data->success = MOD_SDEF_BIND_RESULT_MEM_ERR;
            return;
          }

          sortPolyVertsEdge(sdbind->vert_inds,
                            &data->mloop[bpoly->loopstart],
                            bpoly->edge_inds[bpoly->dominant_edge],
                            bpoly->numverts);

          copy_v3_v3(v1, data->targetCos[sdbind->vert_inds[0]]);
          copy_v3_v3(v2, data->targetCos[sdbind->vert_inds[1]]);
          copy_v3_v3(v3, bpoly->centroid);

          mid_v3_v3v3v3(cent, v1, v2, v3);
          normal_tri_v3(norm, v1, v2, v3);

          add_v3_v3v3(tmp_vec, point_co, bpoly->normal);

          /* We are sure the line is not parallel to the plane.
           * Checking return value just to avoid warning... */
          if (!isect_line_plane_v3(point_co_proj, point_co, tmp_vec, cent, norm)) {
            BLI_assert(false);
          }

          interp_weights_tri_v3(sdbind->vert_weights, v1, v2, v3, point_co_proj);

          sdbind->normal_dist = computeNormalDisplacement(point_co, point_co_proj, bpoly->normal);

          sdbind++;
          i++;
        }

        if (bpoly->dominant_angle_weight >= FLT_EPSILON) {
          sdbind->influence = bpoly->weight * bpoly->dominant_angle_weight;
          sdbind->numverts = bpoly->numverts;

          sdbind->mode = MOD_SDEF_MODE_LOOPTRI;
          sdbind->vert_weights = MEM_malloc_arrayN(
              3, sizeof(*sdbind->vert_weights), "SDefTriVertWeights");
          if (sdbind->vert_weights == NULL) {
            data->success = MOD_SDEF_BIND_RESULT_MEM_ERR;
            return;
          }

          sdbind->vert_inds = MEM_malloc_arrayN(
              bpoly->numverts, sizeof(*sdbind->vert_inds), "SDefTriVertInds");
          if (sdbind->vert_inds == NULL) {
            data->success = MOD_SDEF_BIND_RESULT_MEM_ERR;
            return;
          }

          sortPolyVertsTri(sdbind->vert_inds,
                           &data->mloop[bpoly->loopstart],
                           bpoly->edge_vert_inds[0],
                           bpoly->numverts);

          copy_v3_v3(v1, data->targetCos[sdbind->vert_inds[0]]);
          copy_v3_v3(v2, data->targetCos[sdbind->vert_inds[1]]);
          copy_v3_v3(v3, data->targetCos[sdbind->vert_inds[2]]);

          mid_v3_v3v3v3(cent, v1, v2, v3);
          normal_tri_v3(norm, v1, v2, v3);

          add_v3_v3v3(tmp_vec, point_co, bpoly->normal);

          /* We are sure the line is not parallel to the plane.
           * Checking return value just to avoid warning... */
          if (!isect_line_plane_v3(point_co_proj, point_co, tmp_vec, cent, norm)) {
            BLI_assert(false);
          }

          interp_weights_tri_v3(sdbind->vert_weights, v1, v2, v3, point_co_proj);

          sdbind->normal_dist = computeNormalDisplacement(point_co, point_co_proj, bpoly->normal);

          sdbind++;
          i++;
        }
      }
    }
  }

  freeBindData(bwdata);
}

static bool surfacedeformBind(SurfaceDeformModifierData *smd,
                              float (*vertexCos)[3],
                              unsigned int numverts,
                              unsigned int tnumpoly,
                              unsigned int tnumverts,
                              Mesh *target)
{
  BVHTreeFromMesh treeData = {NULL};
  const MVert *mvert = target->mvert;
  const MPoly *mpoly = target->mpoly;
  const MEdge *medge = target->medge;
  const MLoop *mloop = target->mloop;
  unsigned int tnumedges = target->totedge;
  int adj_result;
  SDefAdjacencyArray *vert_edges;
  SDefAdjacency *adj_array;
  SDefEdgePolys *edge_polys;

  vert_edges = MEM_calloc_arrayN(tnumverts, sizeof(*vert_edges), "SDefVertEdgeMap");
  if (vert_edges == NULL) {
    modifier_setError((ModifierData *)smd, "Out of memory");
    return false;
  }

  adj_array = MEM_malloc_arrayN(tnumedges, 2 * sizeof(*adj_array), "SDefVertEdge");
  if (adj_array == NULL) {
    modifier_setError((ModifierData *)smd, "Out of memory");
    MEM_freeN(vert_edges);
    return false;
  }

  edge_polys = MEM_calloc_arrayN(tnumedges, sizeof(*edge_polys), "SDefEdgeFaceMap");
  if (edge_polys == NULL) {
    modifier_setError((ModifierData *)smd, "Out of memory");
    MEM_freeN(vert_edges);
    MEM_freeN(adj_array);
    return false;
  }

  smd->verts = MEM_malloc_arrayN(numverts, sizeof(*smd->verts), "SDefBindVerts");
  if (smd->verts == NULL) {
    modifier_setError((ModifierData *)smd, "Out of memory");
    freeAdjacencyMap(vert_edges, adj_array, edge_polys);
    return false;
  }

  BKE_bvhtree_from_mesh_get(&treeData, target, BVHTREE_FROM_LOOPTRI, 2);
  if (treeData.tree == NULL) {
    modifier_setError((ModifierData *)smd, "Out of memory");
    freeAdjacencyMap(vert_edges, adj_array, edge_polys);
    MEM_freeN(smd->verts);
    smd->verts = NULL;
    return false;
  }

  adj_result = buildAdjacencyMap(
      mpoly, medge, mloop, tnumpoly, tnumedges, vert_edges, adj_array, edge_polys);

  if (adj_result == MOD_SDEF_BIND_RESULT_NONMANY_ERR) {
    modifier_setError((ModifierData *)smd, "Target has edges with more than two polygons");
    freeAdjacencyMap(vert_edges, adj_array, edge_polys);
    free_bvhtree_from_mesh(&treeData);
    MEM_freeN(smd->verts);
    smd->verts = NULL;
    return false;
  }

  smd->numverts = numverts;
  smd->numpoly = tnumpoly;

  SDefBindCalcData data = {
      .treeData = &treeData,
      .vert_edges = vert_edges,
      .edge_polys = edge_polys,
      .mpoly = mpoly,
      .medge = medge,
      .mloop = mloop,
      .looptri = BKE_mesh_runtime_looptri_ensure(target),
      .targetCos = MEM_malloc_arrayN(tnumverts, sizeof(float[3]), "SDefTargetBindVertArray"),
      .bind_verts = smd->verts,
      .vertexCos = vertexCos,
      .falloff = smd->falloff,
      .success = MOD_SDEF_BIND_RESULT_SUCCESS,
  };

  if (data.targetCos == NULL) {
    modifier_setError((ModifierData *)smd, "Out of memory");
    freeData((ModifierData *)smd);
    return false;
  }

  invert_m4_m4(data.imat, smd->mat);

  for (int i = 0; i < tnumverts; i++) {
    mul_v3_m4v3(data.targetCos[i], smd->mat, mvert[i].co);
  }

  ParallelRangeSettings settings;
  BLI_parallel_range_settings_defaults(&settings);
  settings.use_threading = (numverts > 10000);
  BLI_task_parallel_range(0, numverts, &data, bindVert, &settings);

  MEM_freeN(data.targetCos);

  if (data.success == MOD_SDEF_BIND_RESULT_MEM_ERR) {
    modifier_setError((ModifierData *)smd, "Out of memory");
    freeData((ModifierData *)smd);
  }
  else if (data.success == MOD_SDEF_BIND_RESULT_NONMANY_ERR) {
    modifier_setError((ModifierData *)smd, "Target has edges with more than two polygons");
    freeData((ModifierData *)smd);
  }
  else if (data.success == MOD_SDEF_BIND_RESULT_CONCAVE_ERR) {
    modifier_setError((ModifierData *)smd, "Target contains concave polygons");
    freeData((ModifierData *)smd);
  }
  else if (data.success == MOD_SDEF_BIND_RESULT_OVERLAP_ERR) {
    modifier_setError((ModifierData *)smd, "Target contains overlapping verts");
    freeData((ModifierData *)smd);
  }
  else if (data.success == MOD_SDEF_BIND_RESULT_GENERIC_ERR) {
    /* I know this message is vague, but I could not think of a way
     * to explain this with a reasonably sized message.
     * Though it shouldn't really matter all that much,
     * because this is very unlikely to occur */
    modifier_setError((ModifierData *)smd, "Target contains invalid polygons");
    freeData((ModifierData *)smd);
  }

  freeAdjacencyMap(vert_edges, adj_array, edge_polys);
  free_bvhtree_from_mesh(&treeData);

  return data.success == 1;
}

static void deformVert(void *__restrict userdata,
                       const int index,
                       const ParallelRangeTLS *__restrict UNUSED(tls))
{
  const SDefDeformData *const data = (SDefDeformData *)userdata;
  const SDefBind *sdbind = data->bind_verts[index].binds;
  float *const vertexCos = data->vertexCos[index];
  float norm[3], temp[3];

  zero_v3(vertexCos);

  for (int j = 0; j < data->bind_verts[index].numbinds; j++, sdbind++) {
    /* Mode-generic operations (allocate poly coordinates) */
    float(*coords)[3] = MEM_malloc_arrayN(sdbind->numverts, sizeof(*coords), "SDefDoPolyCoords");

    for (int k = 0; k < sdbind->numverts; k++) {
      copy_v3_v3(coords[k], data->targetCos[sdbind->vert_inds[k]]);
    }

    normal_poly_v3(norm, coords, sdbind->numverts);
    zero_v3(temp);

    /* ---------- looptri mode ---------- */
    if (sdbind->mode == MOD_SDEF_MODE_LOOPTRI) {
      madd_v3_v3fl(temp, data->targetCos[sdbind->vert_inds[0]], sdbind->vert_weights[0]);
      madd_v3_v3fl(temp, data->targetCos[sdbind->vert_inds[1]], sdbind->vert_weights[1]);
      madd_v3_v3fl(temp, data->targetCos[sdbind->vert_inds[2]], sdbind->vert_weights[2]);
    }
    else {
      /* ---------- ngon mode ---------- */
      if (sdbind->mode == MOD_SDEF_MODE_NGON) {
        for (int k = 0; k < sdbind->numverts; k++) {
          madd_v3_v3fl(temp, coords[k], sdbind->vert_weights[k]);
        }
      }

      /* ---------- centroid mode ---------- */
      else if (sdbind->mode == MOD_SDEF_MODE_CENTROID) {
        float cent[3];
        mid_v3_v3_array(cent, coords, sdbind->numverts);

        madd_v3_v3fl(temp, data->targetCos[sdbind->vert_inds[0]], sdbind->vert_weights[0]);
        madd_v3_v3fl(temp, data->targetCos[sdbind->vert_inds[1]], sdbind->vert_weights[1]);
        madd_v3_v3fl(temp, cent, sdbind->vert_weights[2]);
      }
    }

    MEM_freeN(coords);

    /* Apply normal offset (generic for all modes) */
    madd_v3_v3fl(temp, norm, sdbind->normal_dist);

    madd_v3_v3fl(vertexCos, temp, sdbind->influence);
  }
}

static void surfacedeformModifier_do(ModifierData *md,
                                     const ModifierEvalContext *ctx,
                                     float (*vertexCos)[3],
                                     unsigned int numverts,
                                     Object *ob)
{
  SurfaceDeformModifierData *smd = (SurfaceDeformModifierData *)md;
  Mesh *target;
  unsigned int tnumverts, tnumpoly;

  /* Exit function if bind flag is not set (free bind data if any). */
  if (!(smd->flags & MOD_SDEF_BIND)) {
    if (smd->verts != NULL) {
      if (!DEG_is_active(ctx->depsgraph)) {
        modifier_setError(md, "Attempt to bind from inactive dependency graph");
        return;
      }
      ModifierData *md_orig = modifier_get_original(md);
      freeData(md_orig);
    }
    return;
  }

  Object *ob_target = smd->target;
  target = BKE_modifier_get_evaluated_mesh_from_evaluated_object(ob_target, false);
  if (!target) {
    modifier_setError(md, "No valid target mesh");
    return;
  }

  tnumverts = target->totvert;
  tnumpoly = target->totpoly;

  /* If not bound, execute bind. */
  if (smd->verts == NULL) {
    if (!DEG_is_active(ctx->depsgraph)) {
      modifier_setError(md, "Attempt to unbind from inactive dependency graph");
      return;
    }

    SurfaceDeformModifierData *smd_orig = (SurfaceDeformModifierData *)modifier_get_original(md);
    float tmp_mat[4][4];

    invert_m4_m4(tmp_mat, ob->obmat);
    mul_m4_m4m4(smd_orig->mat, tmp_mat, ob_target->obmat);

    if (!surfacedeformBind(smd_orig, vertexCos, numverts, tnumpoly, tnumverts, target)) {
      smd->flags &= ~MOD_SDEF_BIND;
    }
    /* Early abort, this is binding 'call', no need to perform whole evaluation. */
    return;
  }

  /* Poly count checks */
  if (smd->numverts != numverts) {
    modifier_setError(md, "Verts changed from %u to %u", smd->numverts, numverts);
    return;
  }
  else if (smd->numpoly != tnumpoly) {
    modifier_setError(md, "Target polygons changed from %u to %u", smd->numpoly, tnumpoly);
    return;
  }

  /* Actual vertex location update starts here */
  SDefDeformData data = {
      .bind_verts = smd->verts,
      .targetCos = MEM_malloc_arrayN(tnumverts, sizeof(float[3]), "SDefTargetVertArray"),
      .vertexCos = vertexCos,
  };

  if (data.targetCos != NULL) {
    const MVert *const mvert = target->mvert;

    for (int i = 0; i < tnumverts; i++) {
      mul_v3_m4v3(data.targetCos[i], smd->mat, mvert[i].co);
    }

    ParallelRangeSettings settings;
    BLI_parallel_range_settings_defaults(&settings);
    settings.use_threading = (numverts > 10000);
    BLI_task_parallel_range(0, numverts, &data, deformVert, &settings);

    MEM_freeN(data.targetCos);
  }
}

static void deformVerts(ModifierData *md,
                        const ModifierEvalContext *ctx,
                        Mesh *UNUSED(mesh),
                        float (*vertexCos)[3],
                        int numVerts)
{
  surfacedeformModifier_do(md, ctx, vertexCos, numVerts, ctx->object);
}

static void deformVertsEM(ModifierData *md,
                          const ModifierEvalContext *ctx,
                          struct BMEditMesh *UNUSED(editData),
                          Mesh *UNUSED(mesh),
                          float (*vertexCos)[3],
                          int numVerts)
{
  surfacedeformModifier_do(md, ctx, vertexCos, numVerts, ctx->object);
}

static bool isDisabled(const Scene *UNUSED(scene), ModifierData *md, bool UNUSED(useRenderParams))
{
  SurfaceDeformModifierData *smd = (SurfaceDeformModifierData *)md;

  return smd->target == NULL && !(smd->verts != NULL && !(smd->flags & MOD_SDEF_BIND));
}

ModifierTypeInfo modifierType_SurfaceDeform = {
    /* name */ "Surface Deform",
    /* structName */ "SurfaceDeformModifierData",
    /* structSize */ sizeof(SurfaceDeformModifierData),
    /* type */ eModifierTypeType_OnlyDeform,
    /* flags */ eModifierTypeFlag_AcceptsMesh | eModifierTypeFlag_SupportsEditmode,

    /* copyData */ copyData,

    /* deformVerts */ deformVerts,
    /* deformMatrices */ NULL,
    /* deformVertsEM */ deformVertsEM,
    /* deformMatricesEM */ NULL,
    /* applyModifier */ NULL,

    /* initData */ initData,
    /* requiredDataMask */ NULL,
    /* freeData */ freeData,
    /* isDisabled */ isDisabled,
    /* updateDepsgraph */ updateDepsgraph,
    /* dependsOnTime */ NULL,
    /* dependsOnNormals */ NULL,
    /* foreachObjectLink */ foreachObjectLink,
    /* foreachIDLink */ NULL,
    /* foreachTexLink */ NULL,
    /* freeRuntimeData */ NULL,
};
