Convert rigidbody conversion to looptri.

[blender.git] / source / blender / blenkernel / intern / mesh_evaluate.c

/*
 * ***** BEGIN GPL LICENSE BLOCK *****
 *
 * 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.
 *
 * The Original Code is Copyright (C) 2001-2002 by NaN Holding BV.
 * All rights reserved.
 *
 * Contributor(s): Blender Foundation
 *
 * ***** END GPL LICENSE BLOCK *****
 */

/** \file blender/blenkernel/intern/mesh_evaluate.c
 *  \ingroup bke
 *
 * Functions to evaluate mesh data.
 */

#include <limits.h>

#include "MEM_guardedalloc.h"

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

#include "BLI_utildefines.h"
#include "BLI_memarena.h"
#include "BLI_mempool.h"
#include "BLI_math.h"
#include "BLI_edgehash.h"
#include "BLI_bitmap.h"
#include "BLI_polyfill2d.h"
#include "BLI_linklist.h"
#include "BLI_linklist_stack.h"
#include "BLI_alloca.h"
#include "BLI_stack.h"
#include "BLI_task.h"

#include "BKE_customdata.h"
#include "BKE_mesh.h"
#include "BKE_multires.h"
#include "BKE_report.h"

#include "BLI_strict_flags.h"

#include "mikktspace.h"

// #define DEBUG_TIME

#include "PIL_time.h"
#ifdef DEBUG_TIME
#  include "PIL_time_utildefines.h"
#endif

/* -------------------------------------------------------------------- */

/** \name Mesh Normal Calculation
 * \{ */

/**
 * Call when there are no polygons.
 */
static void mesh_calc_normals_vert_fallback(MVert *mverts, int numVerts)
{
        int i;
        for (i = 0; i < numVerts; i++) {
                MVert *mv = &mverts[i];
                float no[3];

                normalize_v3_v3(no, mv->co);
                normal_float_to_short_v3(mv->no, no);
        }
}

/* Calculate vertex and face normals, face normals are returned in *r_faceNors if non-NULL
 * and vertex normals are stored in actual mverts.
 */
void BKE_mesh_calc_normals_mapping(
        MVert *mverts, int numVerts,
        const MLoop *mloop, const MPoly *mpolys, int numLoops, int numPolys, float (*r_polyNors)[3],
        const MFace *mfaces, int numFaces, const int *origIndexFace, float (*r_faceNors)[3])
{
        BKE_mesh_calc_normals_mapping_ex(
                mverts, numVerts, mloop, mpolys,
                numLoops, numPolys, r_polyNors, mfaces, numFaces,
                origIndexFace, r_faceNors, false);
}
/* extended version of 'BKE_mesh_calc_normals_poly' with option not to calc vertex normals */
void BKE_mesh_calc_normals_mapping_ex(
        MVert *mverts, int numVerts,
        const MLoop *mloop, const MPoly *mpolys,
        int numLoops, int numPolys, float (*r_polyNors)[3],
        const MFace *mfaces, int numFaces, const int *origIndexFace, float (*r_faceNors)[3],
        const bool only_face_normals)
{
        float (*pnors)[3] = r_polyNors, (*fnors)[3] = r_faceNors;
        int i;
        const MFace *mf;
        const MPoly *mp;

        if (numPolys == 0) {
                if (only_face_normals == false) {
                        mesh_calc_normals_vert_fallback(mverts, numVerts);
                }
                return;
        }

        /* if we are not calculating verts and no verts were passes then we have nothing to do */
        if ((only_face_normals == true) && (r_polyNors == NULL) && (r_faceNors == NULL)) {
                printf("%s: called with nothing to do\n", __func__);
                return;
        }

        if (!pnors) pnors = MEM_callocN(sizeof(float[3]) * (size_t)numPolys, __func__);
        /* if (!fnors) fnors = MEM_callocN(sizeof(float[3]) * numFaces, "face nors mesh.c"); */ /* NO NEED TO ALLOC YET */


        if (only_face_normals == false) {
                /* vertex normals are optional, they require some extra calculations,
                 * so make them optional */
                BKE_mesh_calc_normals_poly(mverts, numVerts, mloop, mpolys, numLoops, numPolys, pnors, false);
        }
        else {
                /* only calc poly normals */
                mp = mpolys;
                for (i = 0; i < numPolys; i++, mp++) {
                        BKE_mesh_calc_poly_normal(mp, mloop + mp->loopstart, mverts, pnors[i]);
                }
        }

        if (origIndexFace &&
            /* fnors == r_faceNors */ /* NO NEED TO ALLOC YET */
            fnors != NULL &&
            numFaces)
        {
                mf = mfaces;
                for (i = 0; i < numFaces; i++, mf++, origIndexFace++) {
                        if (*origIndexFace < numPolys) {
                                copy_v3_v3(fnors[i], pnors[*origIndexFace]);
                        }
                        else {
                                /* eek, we're not corresponding to polys */
                                printf("error in %s: tessellation face indices are incorrect.  normals may look bad.\n", __func__);
                        }
                }
        }

        if (pnors != r_polyNors) MEM_freeN(pnors);
        /* if (fnors != r_faceNors) MEM_freeN(fnors); */ /* NO NEED TO ALLOC YET */

        fnors = pnors = NULL;
        
}

static void mesh_calc_normals_poly_accum(
        const MPoly *mp, const MLoop *ml,
        const MVert *mvert,
        float r_polyno[3], float (*r_tnorms)[3])
{
        const int nverts = mp->totloop;
        float (*edgevecbuf)[3] = BLI_array_alloca(edgevecbuf, (size_t)nverts);
        int i;

        /* Polygon Normal and edge-vector */
        /* inline version of #BKE_mesh_calc_poly_normal, also does edge-vectors */
        {
                int i_prev = nverts - 1;
                const float *v_prev = mvert[ml[i_prev].v].co;
                const float *v_curr;

                zero_v3(r_polyno);
                /* Newell's Method */
                for (i = 0; i < nverts; i++) {
                        v_curr = mvert[ml[i].v].co;
                        add_newell_cross_v3_v3v3(r_polyno, v_prev, v_curr);

                        /* Unrelated to normalize, calculate edge-vector */
                        sub_v3_v3v3(edgevecbuf[i_prev], v_prev, v_curr);
                        normalize_v3(edgevecbuf[i_prev]);
                        i_prev = i;

                        v_prev = v_curr;
                }
                if (UNLIKELY(normalize_v3(r_polyno) == 0.0f)) {
                        r_polyno[2] = 1.0f; /* other axis set to 0.0 */
                }
        }

        /* accumulate angle weighted face normal */
        /* inline version of #accumulate_vertex_normals_poly */
        {
                const float *prev_edge = edgevecbuf[nverts - 1];

                for (i = 0; i < nverts; i++) {
                        const float *cur_edge = edgevecbuf[i];

                        /* calculate angle between the two poly edges incident on
                         * this vertex */
                        const float fac = saacos(-dot_v3v3(cur_edge, prev_edge));

                        /* accumulate */
                        madd_v3_v3fl(r_tnorms[ml[i].v], r_polyno, fac);
                        prev_edge = cur_edge;
                }
        }

}

void BKE_mesh_calc_normals_poly(
        MVert *mverts, int numVerts,
        const MLoop *mloop, const MPoly *mpolys,
        int UNUSED(numLoops), int numPolys, float (*r_polynors)[3],
        const bool only_face_normals)
{
        float (*pnors)[3] = r_polynors;
        float (*tnorms)[3];
        int i;
        const MPoly *mp;

        if (only_face_normals) {
                BLI_assert((pnors != NULL) || (numPolys == 0));

#pragma omp parallel for if (numPolys > BKE_MESH_OMP_LIMIT)
                for (i = 0; i < numPolys; i++) {
                        BKE_mesh_calc_poly_normal(&mpolys[i], mloop + mpolys[i].loopstart, mverts, pnors[i]);
                }
                return;
        }

        /* first go through and calculate normals for all the polys */
        tnorms = MEM_callocN(sizeof(*tnorms) * (size_t)numVerts, __func__);

        if (pnors) {
                mp = mpolys;
                for (i = 0; i < numPolys; i++, mp++) {
                        mesh_calc_normals_poly_accum(mp, mloop + mp->loopstart, mverts, pnors[i], tnorms);
                }
        }
        else {
                float tpnor[3];  /* temp poly normal */
                mp = mpolys;
                for (i = 0; i < numPolys; i++, mp++) {
                        mesh_calc_normals_poly_accum(mp, mloop + mp->loopstart, mverts, tpnor, tnorms);
                }
        }

        for (i = 0; i < numVerts; i++) {
                MVert *mv = &mverts[i];
                float *no = tnorms[i];

                if (UNLIKELY(normalize_v3(no) == 0.0f)) {
                        /* following Mesh convention; we use vertex coordinate itself for normal in this case */
                        normalize_v3_v3(no, mv->co);
                }

                normal_float_to_short_v3(mv->no, no);
        }

        MEM_freeN(tnorms);
}

void BKE_mesh_calc_normals(Mesh *mesh)
{
#ifdef DEBUG_TIME
        TIMEIT_START(BKE_mesh_calc_normals);
#endif
        BKE_mesh_calc_normals_poly(mesh->mvert, mesh->totvert,
                                   mesh->mloop, mesh->mpoly, mesh->totloop, mesh->totpoly,
                                   NULL, false);
#ifdef DEBUG_TIME
        TIMEIT_END(BKE_mesh_calc_normals);
#endif
}

void BKE_mesh_calc_normals_tessface(
        MVert *mverts, int numVerts,
        const MFace *mfaces, int numFaces,
        float (*r_faceNors)[3])
{
        float (*tnorms)[3] = MEM_callocN(sizeof(*tnorms) * (size_t)numVerts, "tnorms");
        float (*fnors)[3] = (r_faceNors) ? r_faceNors : MEM_callocN(sizeof(*fnors) * (size_t)numFaces, "meshnormals");
        int i;

        for (i = 0; i < numFaces; i++) {
                const MFace *mf = &mfaces[i];
                float *f_no = fnors[i];
                float *n4 = (mf->v4) ? tnorms[mf->v4] : NULL;
                const float *c4 = (mf->v4) ? mverts[mf->v4].co : NULL;

                if (mf->v4)
                        normal_quad_v3(f_no, mverts[mf->v1].co, mverts[mf->v2].co, mverts[mf->v3].co, mverts[mf->v4].co);
                else
                        normal_tri_v3(f_no, mverts[mf->v1].co, mverts[mf->v2].co, mverts[mf->v3].co);

                accumulate_vertex_normals(tnorms[mf->v1], tnorms[mf->v2], tnorms[mf->v3], n4,
                                          f_no, mverts[mf->v1].co, mverts[mf->v2].co, mverts[mf->v3].co, c4);
        }

        /* following Mesh convention; we use vertex coordinate itself for normal in this case */
        for (i = 0; i < numVerts; i++) {
                MVert *mv = &mverts[i];
                float *no = tnorms[i];
                
                if (UNLIKELY(normalize_v3(no) == 0.0f)) {
                        normalize_v3_v3(no, mv->co);
                }

                normal_float_to_short_v3(mv->no, no);
        }
        
        MEM_freeN(tnorms);

        if (fnors != r_faceNors)
                MEM_freeN(fnors);
}

void BKE_mesh_calc_normals_looptri(
        MVert *mverts, int numVerts,
        const MLoop *mloop,
        const MLoopTri *looptri, int looptri_num,
        float (*r_tri_nors)[3])
{
        float (*tnorms)[3] = MEM_callocN(sizeof(*tnorms) * (size_t)numVerts, "tnorms");
        float (*fnors)[3] = (r_tri_nors) ? r_tri_nors : MEM_callocN(sizeof(*fnors) * (size_t)looptri_num, "meshnormals");
        int i;

        for (i = 0; i < looptri_num; i++) {
                const MLoopTri *lt = &looptri[i];
                float *f_no = fnors[i];
                const unsigned int vtri[3] = {
                    mloop[lt->tri[0]].v,
                    mloop[lt->tri[1]].v,
                    mloop[lt->tri[2]].v,
                };

                normal_tri_v3(
                        f_no,
                        mverts[vtri[0]].co, mverts[vtri[1]].co, mverts[vtri[2]].co);

                accumulate_vertex_normals_tri(
                        tnorms[vtri[0]], tnorms[vtri[1]], tnorms[vtri[2]],
                        f_no, mverts[vtri[0]].co, mverts[vtri[1]].co, mverts[vtri[2]].co);
        }

        /* following Mesh convention; we use vertex coordinate itself for normal in this case */
        for (i = 0; i < numVerts; i++) {
                MVert *mv = &mverts[i];
                float *no = tnorms[i];

                if (UNLIKELY(normalize_v3(no) == 0.0f)) {
                        normalize_v3_v3(no, mv->co);
                }

                normal_float_to_short_v3(mv->no, no);
        }

        MEM_freeN(tnorms);

        if (fnors != r_tri_nors)
                MEM_freeN(fnors);
}

void BKE_lnor_spacearr_init(MLoopNorSpaceArray *lnors_spacearr, const int numLoops)
{
        if (!(lnors_spacearr->lspacearr && lnors_spacearr->loops_pool)) {
                MemArena *mem;

                if (!lnors_spacearr->mem) {
                        lnors_spacearr->mem = BLI_memarena_new(BLI_MEMARENA_STD_BUFSIZE, __func__);
                }
                mem = lnors_spacearr->mem;
                lnors_spacearr->lspacearr = BLI_memarena_calloc(mem, sizeof(MLoopNorSpace *) * (size_t)numLoops);
                lnors_spacearr->loops_pool = BLI_memarena_alloc(mem, sizeof(LinkNode) * (size_t)numLoops);
        }
}

void BKE_lnor_spacearr_clear(MLoopNorSpaceArray *lnors_spacearr)
{
        BLI_memarena_clear(lnors_spacearr->mem);
        lnors_spacearr->lspacearr = NULL;
        lnors_spacearr->loops_pool = NULL;
}

void BKE_lnor_spacearr_free(MLoopNorSpaceArray *lnors_spacearr)
{
        BLI_memarena_free(lnors_spacearr->mem);
        lnors_spacearr->lspacearr = NULL;
        lnors_spacearr->loops_pool = NULL;
        lnors_spacearr->mem = NULL;
}

MLoopNorSpace *BKE_lnor_space_create(MLoopNorSpaceArray *lnors_spacearr)
{
        return BLI_memarena_calloc(lnors_spacearr->mem, sizeof(MLoopNorSpace));
}

/* This threshold is a bit touchy (usual float precision issue), this value seems OK. */
#define LNOR_SPACE_TRIGO_THRESHOLD (1.0f - 1e-6f)

/* Should only be called once.
 * Beware, this modifies ref_vec and other_vec in place!
 * In case no valid space can be generated, ref_alpha and ref_beta are set to zero (which means 'use auto lnors').
 */
void BKE_lnor_space_define(MLoopNorSpace *lnor_space, const float lnor[3],
                           float vec_ref[3], float vec_other[3], BLI_Stack *edge_vectors)
{
        const float pi2 = (float)M_PI * 2.0f;
        float tvec[3], dtp;
        const float dtp_ref = dot_v3v3(vec_ref, lnor);
        const float dtp_other = dot_v3v3(vec_other, lnor);

        if (UNLIKELY(fabsf(dtp_ref) >= LNOR_SPACE_TRIGO_THRESHOLD || fabsf(dtp_other) >= LNOR_SPACE_TRIGO_THRESHOLD)) {
                /* If vec_ref or vec_other are too much aligned with lnor, we can't build lnor space,
                 * tag it as invalid and abort. */
                lnor_space->ref_alpha = lnor_space->ref_beta = 0.0f;

                if (edge_vectors) {
                        BLI_stack_clear(edge_vectors);
                }
                return;
        }

        copy_v3_v3(lnor_space->vec_lnor, lnor);

        /* Compute ref alpha, average angle of all available edge vectors to lnor. */
        if (edge_vectors) {
                float alpha = 0.0f;
                int nbr = 0;
                while (!BLI_stack_is_empty(edge_vectors)) {
                        const float *vec = BLI_stack_peek(edge_vectors);
                        alpha += saacosf(dot_v3v3(vec, lnor));
                        BLI_stack_discard(edge_vectors);
                        nbr++;
                }
                /* Note: In theory, this could be 'nbr > 2', but there is one case where we only have two edges for
                 *       two loops: a smooth vertex with only two edges and two faces (our Monkey's nose has that, e.g.). */
                BLI_assert(nbr >= 2);  /* This piece of code shall only be called for more than one loop... */
                lnor_space->ref_alpha = alpha / (float)nbr;
        }
        else {
                lnor_space->ref_alpha = (saacosf(dot_v3v3(vec_ref, lnor)) + saacosf(dot_v3v3(vec_other, lnor))) / 2.0f;
        }

        /* Project vec_ref on lnor's ortho plane. */
        mul_v3_v3fl(tvec, lnor, dtp_ref);
        sub_v3_v3(vec_ref, tvec);
        normalize_v3_v3(lnor_space->vec_ref, vec_ref);

        cross_v3_v3v3(tvec, lnor, lnor_space->vec_ref);
        normalize_v3_v3(lnor_space->vec_ortho, tvec);

        /* Project vec_other on lnor's ortho plane. */
        mul_v3_v3fl(tvec, lnor, dtp_other);
        sub_v3_v3(vec_other, tvec);
        normalize_v3(vec_other);

        /* Beta is angle between ref_vec and other_vec, around lnor. */
        dtp = dot_v3v3(lnor_space->vec_ref, vec_other);
        if (LIKELY(dtp < LNOR_SPACE_TRIGO_THRESHOLD)) {
                const float beta = saacos(dtp);
                lnor_space->ref_beta = (dot_v3v3(lnor_space->vec_ortho, vec_other) < 0.0f) ? pi2 - beta : beta;
        }
        else {
                lnor_space->ref_beta = pi2;
        }
}

void BKE_lnor_space_add_loop(MLoopNorSpaceArray *lnors_spacearr, MLoopNorSpace *lnor_space, const int ml_index,
                             const bool do_add_loop)
{
        lnors_spacearr->lspacearr[ml_index] = lnor_space;
        if (do_add_loop) {
                BLI_linklist_prepend_nlink(&lnor_space->loops, SET_INT_IN_POINTER(ml_index), &lnors_spacearr->loops_pool[ml_index]);
        }
}

MINLINE float unit_short_to_float(const short val)
{
        return (float)val / (float)SHRT_MAX;
}

MINLINE short unit_float_to_short(const float val)
{
        /* Rounding... */
        return (short)floorf(val * (float)SHRT_MAX + 0.5f);
}

void BKE_lnor_space_custom_data_to_normal(MLoopNorSpace *lnor_space, const short clnor_data[2], float r_custom_lnor[3])
{
        /* NOP custom normal data or invalid lnor space, return. */
        if (clnor_data[0] == 0 || lnor_space->ref_alpha == 0.0f || lnor_space->ref_beta == 0.0f) {
                copy_v3_v3(r_custom_lnor, lnor_space->vec_lnor);
                return;
        }

        {
                /* TODO Check whether using sincosf() gives any noticeable benefit
                 *      (could not even get it working under linux though)! */
                const float pi2 = (float)(M_PI * 2.0);
                const float alphafac = unit_short_to_float(clnor_data[0]);
                const float alpha = (alphafac > 0.0f ? lnor_space->ref_alpha : pi2 - lnor_space->ref_alpha) * alphafac;
                const float betafac = unit_short_to_float(clnor_data[1]);

                mul_v3_v3fl(r_custom_lnor, lnor_space->vec_lnor, cosf(alpha));

                if (betafac == 0.0f) {
                        madd_v3_v3fl(r_custom_lnor, lnor_space->vec_ref, sinf(alpha));
                }
                else {
                        const float sinalpha = sinf(alpha);
                        const float beta = (betafac > 0.0f ? lnor_space->ref_beta : pi2 - lnor_space->ref_beta) * betafac;
                        madd_v3_v3fl(r_custom_lnor, lnor_space->vec_ref, sinalpha * cosf(beta));
                        madd_v3_v3fl(r_custom_lnor, lnor_space->vec_ortho, sinalpha * sinf(beta));
                }
        }
}

void BKE_lnor_space_custom_normal_to_data(MLoopNorSpace *lnor_space, const float custom_lnor[3], short r_clnor_data[2])
{
        /* We use null vector as NOP custom normal (can be simpler than giving autocomputed lnor...). */
        if (is_zero_v3(custom_lnor) || compare_v3v3(lnor_space->vec_lnor, custom_lnor, 1e-4f)) {
                r_clnor_data[0] = r_clnor_data[1] = 0;
                return;
        }

        {
                const float pi2 = (float)(M_PI * 2.0);
                const float cos_alpha = dot_v3v3(lnor_space->vec_lnor, custom_lnor);
                float vec[3], cos_beta;
                float alpha;

                alpha = saacosf(cos_alpha);
                if (alpha > lnor_space->ref_alpha) {
                        /* Note we could stick to [0, pi] range here, but makes decoding more complex, not worth it. */
                        r_clnor_data[0] = unit_float_to_short(-(pi2 - alpha) / (pi2 - lnor_space->ref_alpha));
                }
                else {
                        r_clnor_data[0] = unit_float_to_short(alpha / lnor_space->ref_alpha);
                }

                /* Project custom lnor on (vec_ref, vec_ortho) plane. */
                mul_v3_v3fl(vec, lnor_space->vec_lnor, -cos_alpha);
                add_v3_v3(vec, custom_lnor);
                normalize_v3(vec);

                cos_beta = dot_v3v3(lnor_space->vec_ref, vec);

                if (cos_beta < LNOR_SPACE_TRIGO_THRESHOLD) {
                        float beta = saacosf(cos_beta);
                        if (dot_v3v3(lnor_space->vec_ortho, vec) < 0.0f) {
                                beta = pi2 - beta;
                        }

                        if (beta > lnor_space->ref_beta) {
                                r_clnor_data[1] = unit_float_to_short(-(pi2 - beta) / (pi2 - lnor_space->ref_beta));
                        }
                        else {
                                r_clnor_data[1] = unit_float_to_short(beta / lnor_space->ref_beta);
                        }
                }
                else {
                        r_clnor_data[1] = 0;
                }
        }
}

#define LOOP_SPLIT_TASK_BLOCK_SIZE 1024

typedef struct LoopSplitTaskData {
        /* Specific to each instance (each task). */
        MLoopNorSpace *lnor_space;  /* We have to create those outside of tasks, since afaik memarena is not threadsafe. */
        float (*lnor)[3];
        const MLoop *ml_curr;
        const MLoop *ml_prev;
        int ml_curr_index;
        int ml_prev_index;
        const int *e2l_prev;  /* Also used a flag to switch between single or fan process! */
        int mp_index;

        /* This one is special, it's owned and managed by worker tasks, avoid to have to create it for each fan! */
        BLI_Stack *edge_vectors;

        char pad_c;
} LoopSplitTaskData;

typedef struct LoopSplitTaskDataCommon {
        /* Read/write.
         * Note we do not need to protect it, though, since two different tasks will *always* affect different
         * elements in the arrays. */
        MLoopNorSpaceArray *lnors_spacearr;
        BLI_bitmap *sharp_verts;
        float (*loopnors)[3];
        short (*clnors_data)[2];

        /* Read-only. */
        const MVert *mverts;
        const MEdge *medges;
        const MLoop *mloops;
        const MPoly *mpolys;
        const int (*edge_to_loops)[2];
        const int *loop_to_poly;
        const float (*polynors)[3];

        int numPolys;

        /* ***** Workers communication. ***** */
        ThreadQueue *task_queue;

} LoopSplitTaskDataCommon;

#define INDEX_UNSET INT_MIN
#define INDEX_INVALID -1
/* See comment about edge_to_loops below. */
#define IS_EDGE_SHARP(_e2l) (ELEM((_e2l)[1], INDEX_UNSET, INDEX_INVALID))

static void split_loop_nor_single_do(LoopSplitTaskDataCommon *common_data, LoopSplitTaskData *data)
{
        MLoopNorSpaceArray *lnors_spacearr = common_data->lnors_spacearr;
        short (*clnors_data)[2] = common_data->clnors_data;

        const MVert *mverts = common_data->mverts;
        const MEdge *medges = common_data->medges;
        const float (*polynors)[3] = common_data->polynors;

        MLoopNorSpace *lnor_space = data->lnor_space;
        float (*lnor)[3] = data->lnor;
        const MLoop *ml_curr = data->ml_curr;
        const MLoop *ml_prev = data->ml_prev;
        const int ml_curr_index = data->ml_curr_index;
#if 0  /* Not needed for 'single' loop. */
        const int ml_prev_index = data->ml_prev_index;
        const int *e2l_prev = data->e2l_prev;
#endif
        const int mp_index = data->mp_index;

        /* Simple case (both edges around that vertex are sharp in current polygon),
         * this loop just takes its poly normal.
         */
        copy_v3_v3(*lnor, polynors[mp_index]);

        /* printf("BASIC: handling loop %d / edge %d / vert %d\n", ml_curr_index, ml_curr->e, ml_curr->v); */

        /* If needed, generate this (simple!) lnor space. */
        if (lnors_spacearr) {
                float vec_curr[3], vec_prev[3];

                const unsigned int mv_pivot_index = ml_curr->v;  /* The vertex we are "fanning" around! */
                const MVert *mv_pivot = &mverts[mv_pivot_index];
                const MEdge *me_curr = &medges[ml_curr->e];
                const MVert *mv_2 = (me_curr->v1 == mv_pivot_index) ? &mverts[me_curr->v2] : &mverts[me_curr->v1];
                const MEdge *me_prev = &medges[ml_prev->e];
                const MVert *mv_3 = (me_prev->v1 == mv_pivot_index) ? &mverts[me_prev->v2] : &mverts[me_prev->v1];

                sub_v3_v3v3(vec_curr, mv_2->co, mv_pivot->co);
                normalize_v3(vec_curr);
                sub_v3_v3v3(vec_prev, mv_3->co, mv_pivot->co);
                normalize_v3(vec_prev);

                BKE_lnor_space_define(lnor_space, *lnor, vec_curr, vec_prev, NULL);
                /* We know there is only one loop in this space, no need to create a linklist in this case... */
                BKE_lnor_space_add_loop(lnors_spacearr, lnor_space, ml_curr_index, false);

                if (clnors_data) {
                        BKE_lnor_space_custom_data_to_normal(lnor_space, clnors_data[ml_curr_index], *lnor);
                }
        }
}

static void split_loop_nor_fan_do(LoopSplitTaskDataCommon *common_data, LoopSplitTaskData *data)
{
        MLoopNorSpaceArray *lnors_spacearr = common_data->lnors_spacearr;
        float (*loopnors)[3] = common_data->loopnors;
        short (*clnors_data)[2] = common_data->clnors_data;

        const MVert *mverts = common_data->mverts;
        const MEdge *medges = common_data->medges;
        const MLoop *mloops = common_data->mloops;
        const MPoly *mpolys = common_data->mpolys;
        const int (*edge_to_loops)[2] = common_data->edge_to_loops;
        const int *loop_to_poly = common_data->loop_to_poly;
        const float (*polynors)[3] = common_data->polynors;

        MLoopNorSpace *lnor_space = data->lnor_space;
#if 0  /* Not needed for 'fan' loops. */
        float (*lnor)[3] = data->lnor;
#endif
        const MLoop *ml_curr = data->ml_curr;
        const MLoop *ml_prev = data->ml_prev;
        const int ml_curr_index = data->ml_curr_index;
        const int ml_prev_index = data->ml_prev_index;
        const int mp_index = data->mp_index;
        const int *e2l_prev = data->e2l_prev;

        BLI_Stack *edge_vectors = data->edge_vectors;

        /* Gah... We have to fan around current vertex, until we find the other non-smooth edge,
         * and accumulate face normals into the vertex!
         * Note in case this vertex has only one sharp edges, this is a waste because the normal is the same as
         * the vertex normal, but I do not see any easy way to detect that (would need to count number
         * of sharp edges per vertex, I doubt the additional memory usage would be worth it, especially as
         * it should not be a common case in real-life meshes anyway).
         */
        const unsigned int mv_pivot_index = ml_curr->v;  /* The vertex we are "fanning" around! */
        const MVert *mv_pivot = &mverts[mv_pivot_index];
        const MEdge *me_org = &medges[ml_curr->e];  /* ml_curr would be mlfan_prev if we needed that one */
        const int *e2lfan_curr;
        float vec_curr[3], vec_prev[3], vec_org[3];
        const MLoop *mlfan_curr, *mlfan_next;
        const MPoly *mpfan_next;
        float lnor[3] = {0.0f, 0.0f, 0.0f};
        /* mlfan_vert_index: the loop of our current edge might not be the loop of our current vertex! */
        int mlfan_curr_index, mlfan_vert_index, mpfan_curr_index;

        /* We validate clnors data on the fly - cheapest way to do! */
        int clnors_avg[2] = {0, 0};
        short (*clnor_ref)[2] = NULL;
        int clnors_nbr = 0;
        bool clnors_invalid = false;

        /* Temp loop normal stack. */
        BLI_SMALLSTACK_DECLARE(normal, float *);
        /* Temp clnors stack. */
        BLI_SMALLSTACK_DECLARE(clnors, short *);

        e2lfan_curr = e2l_prev;
        mlfan_curr = ml_prev;
        mlfan_curr_index = ml_prev_index;
        mlfan_vert_index = ml_curr_index;
        mpfan_curr_index = mp_index;

        BLI_assert(mlfan_curr_index >= 0);
        BLI_assert(mlfan_vert_index >= 0);
        BLI_assert(mpfan_curr_index >= 0);

        /* Only need to compute previous edge's vector once, then we can just reuse old current one! */
        {
                const MVert *mv_2 = (me_org->v1 == mv_pivot_index) ? &mverts[me_org->v2] : &mverts[me_org->v1];

                sub_v3_v3v3(vec_org, mv_2->co, mv_pivot->co);
                normalize_v3(vec_org);
                copy_v3_v3(vec_prev, vec_org);

                if (lnors_spacearr) {
                        BLI_stack_push(edge_vectors, vec_org);
                }
        }

        /* printf("FAN: vert %d, start edge %d\n", mv_pivot_index, ml_curr->e); */

        while (true) {
                const MEdge *me_curr = &medges[mlfan_curr->e];
                /* Compute edge vectors.
                 * NOTE: We could pre-compute those into an array, in the first iteration, instead of computing them
                 *       twice (or more) here. However, time gained is not worth memory and time lost,
                 *       given the fact that this code should not be called that much in real-life meshes...
                 */
                {
                        const MVert *mv_2 = (me_curr->v1 == mv_pivot_index) ? &mverts[me_curr->v2] : &mverts[me_curr->v1];

                        sub_v3_v3v3(vec_curr, mv_2->co, mv_pivot->co);
                        normalize_v3(vec_curr);
                }

                /* printf("\thandling edge %d / loop %d\n", mlfan_curr->e, mlfan_curr_index); */

                {
                        /* Code similar to accumulate_vertex_normals_poly. */
                        /* Calculate angle between the two poly edges incident on this vertex. */
                        const float fac = saacos(dot_v3v3(vec_curr, vec_prev));
                        /* Accumulate */
                        madd_v3_v3fl(lnor, polynors[mpfan_curr_index], fac);

                        if (clnors_data) {
                                /* Accumulate all clnors, if they are not all equal we have to fix that! */
                                short (*clnor)[2] = &clnors_data[mlfan_vert_index];
                                if (clnors_nbr) {
                                        clnors_invalid |= ((*clnor_ref)[0] != (*clnor)[0] || (*clnor_ref)[1] != (*clnor)[1]);
                                }
                                else {
                                        clnor_ref = clnor;
                                }
                                clnors_avg[0] += (*clnor)[0];
                                clnors_avg[1] += (*clnor)[1];
                                clnors_nbr++;
                                /* We store here a pointer to all custom lnors processed. */
                                BLI_SMALLSTACK_PUSH(clnors, (short *)*clnor);
                        }
                }

                /* We store here a pointer to all loop-normals processed. */
                BLI_SMALLSTACK_PUSH(normal, (float *)(loopnors[mlfan_vert_index]));

                if (lnors_spacearr) {
                        /* Assign current lnor space to current 'vertex' loop. */
                        BKE_lnor_space_add_loop(lnors_spacearr, lnor_space, mlfan_vert_index, true);
                        if (me_curr != me_org) {
                                /* We store here all edges-normalized vectors processed. */
                                BLI_stack_push(edge_vectors, vec_curr);
                        }
                }

                if (IS_EDGE_SHARP(e2lfan_curr) || (me_curr == me_org)) {
                        /* Current edge is sharp and we have finished with this fan of faces around this vert,
                         * or this vert is smooth, and we have completed a full turn around it.
                         */
                        /* printf("FAN: Finished!\n"); */
                        break;
                }

                copy_v3_v3(vec_prev, vec_curr);

                /* Warning! This is rather complex!
                 * We have to find our next edge around the vertex (fan mode).
                 * First we find the next loop, which is either previous or next to mlfan_curr_index, depending
                 * whether both loops using current edge are in the same direction or not, and whether
                 * mlfan_curr_index actually uses the vertex we are fanning around!
                 * mlfan_curr_index is the index of mlfan_next here, and mlfan_next is not the real next one
                 * (i.e. not the future mlfan_curr)...
                 */
                mlfan_curr_index = (e2lfan_curr[0] == mlfan_curr_index) ? e2lfan_curr[1] : e2lfan_curr[0];
                mpfan_curr_index = loop_to_poly[mlfan_curr_index];

                BLI_assert(mlfan_curr_index >= 0);
                BLI_assert(mpfan_curr_index >= 0);

                mlfan_next = &mloops[mlfan_curr_index];
                mpfan_next = &mpolys[mpfan_curr_index];
                if ((mlfan_curr->v == mlfan_next->v && mlfan_curr->v == mv_pivot_index) ||
                    (mlfan_curr->v != mlfan_next->v && mlfan_curr->v != mv_pivot_index))
                {
                        /* We need the previous loop, but current one is our vertex's loop. */
                        mlfan_vert_index = mlfan_curr_index;
                        if (--mlfan_curr_index < mpfan_next->loopstart) {
                                mlfan_curr_index = mpfan_next->loopstart + mpfan_next->totloop - 1;
                        }
                }
                else {
                        /* We need the next loop, which is also our vertex's loop. */
                        if (++mlfan_curr_index >= mpfan_next->loopstart + mpfan_next->totloop) {
                                mlfan_curr_index = mpfan_next->loopstart;
                        }
                        mlfan_vert_index = mlfan_curr_index;
                }
                mlfan_curr = &mloops[mlfan_curr_index];
                /* And now we are back in sync, mlfan_curr_index is the index of mlfan_curr! Pff! */

                e2lfan_curr = edge_to_loops[mlfan_curr->e];
        }

        {
                float lnor_len = normalize_v3(lnor);

                /* If we are generating lnor spacearr, we can now define the one for this fan,
                 * and optionally compute final lnor from custom data too!
                 */
                if (lnors_spacearr) {
                        if (UNLIKELY(lnor_len == 0.0f)) {
                                /* Use vertex normal as fallback! */
                                copy_v3_v3(lnor, loopnors[mlfan_vert_index]);
                                lnor_len = 1.0f;
                        }

                        BKE_lnor_space_define(lnor_space, lnor, vec_org, vec_curr, edge_vectors);

                        if (clnors_data) {
                                if (clnors_invalid) {
                                        short *clnor;

                                        clnors_avg[0] /= clnors_nbr;
                                        clnors_avg[1] /= clnors_nbr;
                                        /* Fix/update all clnors of this fan with computed average value. */
                                        printf("Invalid clnors in this fan!\n");
                                        while ((clnor = BLI_SMALLSTACK_POP(clnors))) {
                                                //print_v2("org clnor", clnor);
                                                clnor[0] = (short)clnors_avg[0];
                                                clnor[1] = (short)clnors_avg[1];
                                        }
                                        //print_v2("new clnors", clnors_avg);
                                }
                                /* Extra bonus: since smallstack is local to this func, no more need to empty it at all cost! */

                                BKE_lnor_space_custom_data_to_normal(lnor_space, *clnor_ref, lnor);
                        }
                }

                /* In case we get a zero normal here, just use vertex normal already set! */
                if (LIKELY(lnor_len != 0.0f)) {
                        /* Copy back the final computed normal into all related loop-normals. */
                        float *nor;

                        while ((nor = BLI_SMALLSTACK_POP(normal))) {
                                copy_v3_v3(nor, lnor);
                        }
                }
                /* Extra bonus: since smallstack is local to this func, no more need to empty it at all cost! */
        }
}

static void loop_split_worker_do(
        LoopSplitTaskDataCommon *common_data, LoopSplitTaskData *data, BLI_Stack *edge_vectors)
{
        BLI_assert(data->ml_curr);
        if (data->e2l_prev) {
                BLI_assert((edge_vectors == NULL) || BLI_stack_is_empty(edge_vectors));
                data->edge_vectors = edge_vectors;
                split_loop_nor_fan_do(common_data, data);
        }
        else {
                /* No need for edge_vectors for 'single' case! */
                split_loop_nor_single_do(common_data, data);
        }
}

static void loop_split_worker(TaskPool *UNUSED(pool), void *taskdata, int UNUSED(threadid))
{
        LoopSplitTaskDataCommon *common_data = taskdata;
        LoopSplitTaskData *data_buff;

        /* Temp edge vectors stack, only used when computing lnor spacearr. */
        BLI_Stack *edge_vectors = common_data->lnors_spacearr ? BLI_stack_new(sizeof(float[3]), __func__) : NULL;

#ifdef DEBUG_TIME
        TIMEIT_START(loop_split_worker);
#endif

        while ((data_buff = BLI_thread_queue_pop(common_data->task_queue))) {
                LoopSplitTaskData *data = data_buff;
                int i;

                for (i = 0; i < LOOP_SPLIT_TASK_BLOCK_SIZE; i++, data++) {
                        /* A NULL ml_curr is used to tag ended data! */
                        if (data->ml_curr == NULL) {
                                break;
                        }
                        loop_split_worker_do(common_data, data, edge_vectors);
                }

                MEM_freeN(data_buff);
        }

        if (edge_vectors) {
                BLI_stack_free(edge_vectors);
        }

#ifdef DEBUG_TIME
        TIMEIT_END(loop_split_worker);
#endif
}

/* Note we use data_buff to detect whether we are in threaded context or not, in later case it is NULL. */
static void loop_split_generator_do(LoopSplitTaskDataCommon *common_data, const bool threaded)
{
        MLoopNorSpaceArray *lnors_spacearr = common_data->lnors_spacearr;
        BLI_bitmap *sharp_verts = common_data->sharp_verts;
        float (*loopnors)[3] = common_data->loopnors;

        const MLoop *mloops = common_data->mloops;
        const MPoly *mpolys = common_data->mpolys;
        const int (*edge_to_loops)[2] = common_data->edge_to_loops;
        const int numPolys = common_data->numPolys;

        const MPoly *mp;
        int mp_index;

        LoopSplitTaskData *data, *data_buff = NULL, data_mem;
        int data_idx = 0;

        /* Temp edge vectors stack, only used when computing lnor spacearr (and we are not multi-threading). */
        BLI_Stack *edge_vectors = (lnors_spacearr && !data_buff) ? BLI_stack_new(sizeof(float[3]), __func__) : NULL;

#ifdef DEBUG_TIME
        TIMEIT_START(loop_split_generator);
#endif

        if (!threaded) {
                memset(&data_mem, 0, sizeof(data_mem));
                data = &data_mem;
        }

        /* We now know edges that can be smoothed (with their vector, and their two loops), and edges that will be hard!
         * Now, time to generate the normals.
         */
        for (mp = mpolys, mp_index = 0; mp_index < numPolys; mp++, mp_index++) {
                const MLoop *ml_curr, *ml_prev;
                float (*lnors)[3];
                const int ml_last_index = (mp->loopstart + mp->totloop) - 1;
                int ml_curr_index = mp->loopstart;
                int ml_prev_index = ml_last_index;

                ml_curr = &mloops[ml_curr_index];
                ml_prev = &mloops[ml_prev_index];
                lnors = &loopnors[ml_curr_index];

                for (; ml_curr_index <= ml_last_index; ml_curr++, ml_curr_index++, lnors++) {
                        const int *e2l_curr = edge_to_loops[ml_curr->e];
                        const int *e2l_prev = edge_to_loops[ml_prev->e];

                        if (!IS_EDGE_SHARP(e2l_curr) && (!lnors_spacearr || BLI_BITMAP_TEST_BOOL(sharp_verts, ml_curr->v))) {
                                /* A smooth edge, and we are not generating lnor_spacearr, or the related vertex is sharp.
                                 * We skip it because it is either:
                                 * - in the middle of a 'smooth fan' already computed (or that will be as soon as we hit
                                 *   one of its ends, i.e. one of its two sharp edges), or...
                                 * - the related vertex is a "full smooth" one, in which case pre-populated normals from vertex
                                 *   are just fine (or it has already be handled in a previous loop in case of needed lnors spacearr)!
                                 */
                                /* printf("Skipping loop %d / edge %d / vert %d(%d)\n", ml_curr_index, ml_curr->e, ml_curr->v, sharp_verts[ml_curr->v]); */
                        }
                        else {
                                if (threaded) {
                                        if (data_idx == 0) {
                                                data_buff = MEM_callocN(sizeof(*data_buff) * LOOP_SPLIT_TASK_BLOCK_SIZE, __func__);
                                        }
                                        data = &data_buff[data_idx];
                                }

                                if (IS_EDGE_SHARP(e2l_curr) && IS_EDGE_SHARP(e2l_prev)) {
                                        data->lnor = lnors;
                                        data->ml_curr = ml_curr;
                                        data->ml_prev = ml_prev;
                                        data->ml_curr_index = ml_curr_index;
#if 0  /* Not needed for 'single' loop. */
                                        data->ml_prev_index = ml_prev_index;
                                        data->e2l_prev = NULL;  /* Tag as 'single' task. */
#endif
                                        data->mp_index = mp_index;
                                        if (lnors_spacearr) {
                                                data->lnor_space = BKE_lnor_space_create(lnors_spacearr);
                                        }
                                }
                                /* We *do not need* to check/tag loops as already computed!
                                 * Due to the fact a loop only links to one of its two edges, a same fan *will never be walked
                                 * more than once!*
                                 * Since we consider edges having neighbor polys with inverted (flipped) normals as sharp, we are sure
                                 * that no fan will be skipped, even only considering the case (sharp curr_edge, smooth prev_edge),
                                 * and not the alternative (smooth curr_edge, sharp prev_edge).
                                 * All this due/thanks to link between normals and loop ordering (i.e. winding).
                                 */
                                else {
#if 0  /* Not needed for 'fan' loops. */
                                        data->lnor = lnors;
#endif
                                        data->ml_curr = ml_curr;
                                        data->ml_prev = ml_prev;
                                        data->ml_curr_index = ml_curr_index;
                                        data->ml_prev_index = ml_prev_index;
                                        data->e2l_prev = e2l_prev;  /* Also tag as 'fan' task. */
                                        data->mp_index = mp_index;
                                        if (lnors_spacearr) {
                                                data->lnor_space = BKE_lnor_space_create(lnors_spacearr);
                                                /* Tag related vertex as sharp, to avoid fanning around it again (in case it was a smooth one).
                                                 * This *has* to be done outside of workers tasks! */
                                                BLI_BITMAP_ENABLE(sharp_verts, ml_curr->v);
                                        }
                                }

                                if (threaded) {
                                        data_idx++;
                                        if (data_idx == LOOP_SPLIT_TASK_BLOCK_SIZE) {
                                                BLI_thread_queue_push(common_data->task_queue, data_buff);
                                                data_idx = 0;
                                        }
                                }
                                else {
                                        loop_split_worker_do(common_data, data, edge_vectors);
                                        memset(data, 0, sizeof(data_mem));
                                }
                        }

                        ml_prev = ml_curr;
                        ml_prev_index = ml_curr_index;
                }
        }

        if (threaded) {
                /* Last block of data... Since it is calloc'ed and we use first NULL item as stopper, everything is fine. */
                if (LIKELY(data_idx)) {
                        BLI_thread_queue_push(common_data->task_queue, data_buff);
                }

                /* This will signal all other worker threads to wake up and finish! */
                BLI_thread_queue_nowait(common_data->task_queue);
        }

        if (edge_vectors) {
                BLI_stack_free(edge_vectors);
        }

#ifdef DEBUG_TIME
        TIMEIT_END(loop_split_generator);
#endif
}

static void loop_split_generator(TaskPool *UNUSED(pool), void *taskdata, int UNUSED(threadid))
{
        LoopSplitTaskDataCommon *common_data = taskdata;

        loop_split_generator_do(common_data, true);
}

/**
 * Compute split normals, i.e. vertex normals associated with each poly (hence 'loop normals').
 * Useful to materialize sharp edges (or non-smooth faces) without actually modifying the geometry (splitting edges).
 */
void BKE_mesh_normals_loop_split(
        const MVert *mverts, const int numVerts, MEdge *medges, const int numEdges,
        MLoop *mloops, float (*r_loopnors)[3], const int numLoops,
        MPoly *mpolys, const float (*polynors)[3], const int numPolys,
        const bool use_split_normals, float split_angle,
        MLoopNorSpaceArray *r_lnors_spacearr, short (*clnors_data)[2], int *r_loop_to_poly)
{

        /* For now this is not supported. If we do not use split normals, we do not generate anything fancy! */
        BLI_assert(use_split_normals || !(r_lnors_spacearr));

        if (!use_split_normals) {
                /* In this case, we simply fill lnors with vnors (or fnors for flat faces), quite simple!
                 * Note this is done here to keep some logic and consistency in this quite complex code,
                 * since we may want to use lnors even when mesh's 'autosmooth' is disabled (see e.g. mesh mapping code).
                 * As usual, we could handle that on case-by-case basis, but simpler to keep it well confined here.
                 */
                int mp_index;

                for (mp_index = 0; mp_index < numPolys; mp_index++) {
                        MPoly *mp = &mpolys[mp_index];
                        int ml_index = mp->loopstart;
                        const int ml_index_end = ml_index + mp->totloop;
                        const bool is_poly_flat = ((mp->flag & ME_SMOOTH) == 0);

                        for (; ml_index < ml_index_end; ml_index++) {
                                if (r_loop_to_poly) {
                                        r_loop_to_poly[ml_index] = mp_index;
                                }
                                if (is_poly_flat) {
                                        copy_v3_v3(r_loopnors[ml_index], polynors[mp_index]);
                                }
                                else {
                                        normal_short_to_float_v3(r_loopnors[ml_index], mverts[mloops[ml_index].v].no);
                                }
                        }
                }
                return;
        }

        {

        /* Mapping edge -> loops.
         * If that edge is used by more than two loops (polys), it is always sharp (and tagged as such, see below).
         * We also use the second loop index as a kind of flag: smooth edge: > 0,
         *                                                      sharp edge: < 0 (INDEX_INVALID || INDEX_UNSET),
         *                                                      unset: INDEX_UNSET
         * Note that currently we only have two values for second loop of sharp edges. However, if needed, we can
         * store the negated value of loop index instead of INDEX_INVALID to retrieve the real value later in code).
         * Note also that lose edges always have both values set to 0!
         */
        int (*edge_to_loops)[2] = MEM_callocN(sizeof(int[2]) * (size_t)numEdges, __func__);

        /* Simple mapping from a loop to its polygon index. */
        int *loop_to_poly = r_loop_to_poly ? r_loop_to_poly : MEM_mallocN(sizeof(int) * (size_t)numLoops, __func__);

        MPoly *mp;
        int mp_index, me_index;
        bool check_angle = (split_angle < (float)M_PI);
        int i;

        BLI_bitmap *sharp_verts = NULL;
        MLoopNorSpaceArray _lnors_spacearr = {NULL};

        LoopSplitTaskDataCommon common_data = {NULL};

#ifdef DEBUG_TIME
        TIMEIT_START(BKE_mesh_normals_loop_split);
#endif

        if (check_angle) {
                /* When using custom loop normals, disable the angle feature! */
                if (clnors_data) {
                        check_angle = false;
                }
                else {
                        split_angle = cosf(split_angle);
                }
        }

        if (!r_lnors_spacearr && clnors_data) {
                /* We need to compute lnor spacearr if some custom lnor data are given to us! */
                r_lnors_spacearr = &_lnors_spacearr;
        }
        if (r_lnors_spacearr) {
                BKE_lnor_spacearr_init(r_lnors_spacearr, numLoops);
                sharp_verts = BLI_BITMAP_NEW((size_t)numVerts, __func__);
        }

        /* This first loop check which edges are actually smooth, and compute edge vectors. */
        for (mp = mpolys, mp_index = 0; mp_index < numPolys; mp++, mp_index++) {
                MLoop *ml_curr;
                int *e2l;
                int ml_curr_index = mp->loopstart;
                const int ml_last_index = (ml_curr_index + mp->totloop) - 1;

                ml_curr = &mloops[ml_curr_index];

                for (; ml_curr_index <= ml_last_index; ml_curr++, ml_curr_index++) {
                        e2l = edge_to_loops[ml_curr->e];

                        loop_to_poly[ml_curr_index] = mp_index;

                        /* Pre-populate all loop normals as if their verts were all-smooth, this way we don't have to compute
                         * those later!
                         */
                        normal_short_to_float_v3(r_loopnors[ml_curr_index], mverts[ml_curr->v].no);

                        /* Check whether current edge might be smooth or sharp */
                        if ((e2l[0] | e2l[1]) == 0) {
                                /* 'Empty' edge until now, set e2l[0] (and e2l[1] to INDEX_UNSET to tag it as unset). */
                                e2l[0] = ml_curr_index;
                                /* We have to check this here too, else we might miss some flat faces!!! */
                                e2l[1] = (mp->flag & ME_SMOOTH) ? INDEX_UNSET : INDEX_INVALID;
                        }
                        else if (e2l[1] == INDEX_UNSET) {
                                /* Second loop using this edge, time to test its sharpness.
                                 * An edge is sharp if it is tagged as such, or its face is not smooth,
                                 * or both poly have opposed (flipped) normals, i.e. both loops on the same edge share the same vertex,
                                 * or angle between both its polys' normals is above split_angle value.
                                 */
                                if (!(mp->flag & ME_SMOOTH) || (medges[ml_curr->e].flag & ME_SHARP) ||
                                    ml_curr->v == mloops[e2l[0]].v ||
                                    (check_angle && dot_v3v3(polynors[loop_to_poly[e2l[0]]], polynors[mp_index]) < split_angle))
                                {
                                        /* Note: we are sure that loop != 0 here ;) */
                                        e2l[1] = INDEX_INVALID;
                                }
                                else {
                                        e2l[1] = ml_curr_index;
                                }
                        }
                        else if (!IS_EDGE_SHARP(e2l)) {
                                /* More than two loops using this edge, tag as sharp if not yet done. */
                                e2l[1] = INDEX_INVALID;
                        }
                        /* Else, edge is already 'disqualified' (i.e. sharp)! */
                }
        }

        if (r_lnors_spacearr) {
                /* Tag vertices that have at least one sharp edge as 'sharp' (used for the lnor spacearr computation).
                 * XXX This third loop over edges is a bit disappointing, could not find any other way yet.
                 *     Not really performance-critical anyway.
                 */
                for (me_index = 0; me_index < numEdges; me_index++) {
                        const int *e2l = edge_to_loops[me_index];
                        const MEdge *me = &medges[me_index];
                        if (IS_EDGE_SHARP(e2l)) {
                                BLI_BITMAP_ENABLE(sharp_verts, me->v1);
                                BLI_BITMAP_ENABLE(sharp_verts, me->v2);
                        }
                }
        }

        /* Init data common to all tasks. */
        common_data.lnors_spacearr = r_lnors_spacearr;
        common_data.loopnors = r_loopnors;
        common_data.clnors_data = clnors_data;

        common_data.mverts = mverts;
        common_data.medges = medges;
        common_data.mloops = mloops;
        common_data.mpolys = mpolys;
        common_data.sharp_verts = sharp_verts;
        common_data.edge_to_loops = (const int(*)[2])edge_to_loops;
        common_data.loop_to_poly = loop_to_poly;
        common_data.polynors = polynors;
        common_data.numPolys = numPolys;

        if (numLoops < LOOP_SPLIT_TASK_BLOCK_SIZE * 8) {
                /* Not enough loops to be worth the whole threading overhead... */
                loop_split_generator_do(&common_data, false);
        }
        else {
                TaskScheduler *task_scheduler;
                TaskPool *task_pool;
                int nbr_workers;

                common_data.task_queue = BLI_thread_queue_init();

                task_scheduler = BLI_task_scheduler_get();
                task_pool = BLI_task_pool_create(task_scheduler, NULL);

                nbr_workers = max_ii(2, BLI_task_scheduler_num_threads(task_scheduler));
                for (i = 1; i < nbr_workers; i++) {
                        BLI_task_pool_push(task_pool, loop_split_worker, &common_data, false, TASK_PRIORITY_HIGH);
                }
                BLI_task_pool_push(task_pool, loop_split_generator, &common_data, false, TASK_PRIORITY_HIGH);
                BLI_task_pool_work_and_wait(task_pool);

                BLI_task_pool_free(task_pool);

                BLI_thread_queue_free(common_data.task_queue);
        }

        MEM_freeN(edge_to_loops);
        if (!r_loop_to_poly) {
                MEM_freeN(loop_to_poly);
        }

        if (r_lnors_spacearr) {
                MEM_freeN(sharp_verts);
                if (r_lnors_spacearr == &_lnors_spacearr) {
                        BKE_lnor_spacearr_free(r_lnors_spacearr);
                }
        }

#ifdef DEBUG_TIME
        TIMEIT_END(BKE_mesh_normals_loop_split);
#endif

        }
}

#undef INDEX_UNSET
#undef INDEX_INVALID
#undef IS_EDGE_SHARP

/**
 * Compute internal representation of given custom normals (as an array of float[2]).
 * It also makes sure the mesh matches those custom normals, by setting sharp edges flag as needed to get a
 * same custom lnor for all loops sharing a same smooth fan.
 * If use_vertices if true, custom_loopnors is assumed to be per-vertex, not per-loop
 * (this allows to set whole vert's normals at once, useful in some cases).
 */
static void mesh_normals_loop_custom_set(
        const MVert *mverts, const int numVerts, MEdge *medges, const int numEdges,
        MLoop *mloops, float (*custom_loopnors)[3], const int numLoops,
        MPoly *mpolys, const float (*polynors)[3], const int numPolys,
        short (*r_clnors_data)[2], const bool use_vertices)
{
        /* We *may* make that poor BKE_mesh_normals_loop_split() even more complex by making it handling that
         * feature too, would probably be more efficient in absolute.
         * However, this function *is not* performance-critical, since it is mostly expected to be called
         * by io addons when importing custom normals, and modifier (and perhaps from some editing tools later?).
         * So better to keep some simplicity here, and just call BKE_mesh_normals_loop_split() twice!
         */
        MLoopNorSpaceArray lnors_spacearr = {NULL};
        BLI_bitmap *done_loops = BLI_BITMAP_NEW((size_t)numLoops, __func__);
        float (*lnors)[3] = MEM_callocN(sizeof(*lnors) * (size_t)numLoops, __func__);
        int *loop_to_poly = MEM_mallocN(sizeof(int) * (size_t)numLoops, __func__);
        /* In this case we always consider split nors as ON, and do not want to use angle to define smooth fans! */
        const bool use_split_normals = true;
        const float split_angle = (float)M_PI;
        int i;

        BLI_SMALLSTACK_DECLARE(clnors_data, short *);

        /* Compute current lnor spacearr. */
        BKE_mesh_normals_loop_split(mverts, numVerts, medges, numEdges, mloops, lnors, numLoops,
                                    mpolys, polynors, numPolys, use_split_normals, split_angle,
                                    &lnors_spacearr, NULL, loop_to_poly);

        /* Now, check each current smooth fan (one lnor space per smooth fan!), and if all its matching custom lnors
         * are not (enough) equal, add sharp edges as needed.
         * This way, next time we run BKE_mesh_normals_loop_split(), we'll get lnor spacearr/smooth fans matching
         * given custom lnors.
         * Note this code *will never* unsharp edges!
         * And quite obviously, when we set custom normals per vertices, running this is absolutely useless.
         */
        if (!use_vertices) {
                for (i = 0; i < numLoops; i++) {
                        if (!lnors_spacearr.lspacearr[i]) {
                                /* This should not happen in theory, but in some rare case (probably ugly geometry)
                                 * we can get some NULL loopspacearr at this point. :/
                                 * Maybe we should set those loops' edges as sharp?
                                 */
                                BLI_BITMAP_ENABLE(done_loops, i);
                                printf("WARNING! Getting invalid NULL loop space for loop %d!\n", i);
                                continue;
                        }

                        if (!BLI_BITMAP_TEST(done_loops, i)) {
                                /* Notes:
                                 *     * In case of mono-loop smooth fan, loops is NULL, so everything is fine (we have nothing to do).
                                 *     * Loops in this linklist are ordered (in reversed order compared to how they were discovered by
                                 *       BKE_mesh_normals_loop_split(), but this is not a problem). Which means if we find a
                                 *       mismatching clnor, we know all remaining loops will have to be in a new, different smooth fan/
                                 *       lnor space.
                                 *     * In smooth fan case, we compare each clnor against a ref one, to avoid small differences adding
                                 *       up into a real big one in the end!
                                 */
                                LinkNode *loops = lnors_spacearr.lspacearr[i]->loops;
                                MLoop *prev_ml = NULL;
                                const float *org_nor = NULL;

                                while (loops) {
                                        const int lidx = GET_INT_FROM_POINTER(loops->link);
                                        MLoop *ml = &mloops[lidx];
                                        const int nidx = lidx;
                                        float *nor = custom_loopnors[nidx];

                                        if (is_zero_v3(nor)) {
                                                nor = lnors[nidx];
                                        }

                                        if (!org_nor) {
                                                org_nor = nor;
                                        }
                                        else if (dot_v3v3(org_nor, nor) < LNOR_SPACE_TRIGO_THRESHOLD) {
                                                /* Current normal differs too much from org one, we have to tag the edge between
                                                 * previous loop's face and current's one as sharp.
                                                 * We know those two loops do not point to the same edge, since we do not allow reversed winding
                                                 * in a same smooth fan.
                                                 */
                                                const MPoly *mp = &mpolys[loop_to_poly[lidx]];
                                                const MLoop *mlp = &mloops[(lidx == mp->loopstart) ? mp->loopstart + mp->totloop - 1 : lidx - 1];
                                                medges[(prev_ml->e == mlp->e) ? prev_ml->e : ml->e].flag |= ME_SHARP;

                                                org_nor = nor;
                                        }

                                        prev_ml = ml;
                                        loops = loops->next;
                                        BLI_BITMAP_ENABLE(done_loops, lidx);
                                }
                                BLI_BITMAP_ENABLE(done_loops, i);  /* For single loops, where lnors_spacearr.lspacearr[i]->loops is NULL. */
                        }
                }

                /* And now, recompute our new auto lnors and lnor spacearr! */
                BKE_lnor_spacearr_clear(&lnors_spacearr);
                BKE_mesh_normals_loop_split(mverts, numVerts, medges, numEdges, mloops, lnors, numLoops,
                                            mpolys, polynors, numPolys, use_split_normals, split_angle,
                                            &lnors_spacearr, NULL, loop_to_poly);
        }
        else {
                BLI_BITMAP_SET_ALL(done_loops, true, (size_t)numLoops);
        }

        /* And we just have to convert plain object-space custom normals to our lnor space-encoded ones. */
        for (i = 0; i < numLoops; i++) {
                if (!lnors_spacearr.lspacearr[i]) {
                        BLI_BITMAP_DISABLE(done_loops, i);
                        printf("WARNING! Still getting invalid NULL loop space in second loop for loop %d!\n", i);
                        continue;
                }

                if (BLI_BITMAP_TEST_BOOL(done_loops, i)) {
                        /* Note we accumulate and average all custom normals in current smooth fan, to avoid getting different
                         * clnors data (tiny differences in plain custom normals can give rather huge differences in
                         * computed 2D factors).
                         */
                        LinkNode *loops = lnors_spacearr.lspacearr[i]->loops;
                        if (loops) {
                                int nbr_nors = 0;
                                float avg_nor[3];
                                short clnor_data_tmp[2], *clnor_data;

                                zero_v3(avg_nor);
                                while (loops) {
                                        const int lidx = GET_INT_FROM_POINTER(loops->link);
                                        const int nidx = use_vertices ? (int)mloops[lidx].v : lidx;
                                        float *nor = custom_loopnors[nidx];

                                        if (is_zero_v3(nor)) {
                                                nor = lnors[nidx];
                                        }

                                        nbr_nors++;
                                        add_v3_v3(avg_nor, nor);
                                        BLI_SMALLSTACK_PUSH(clnors_data, (short *)r_clnors_data[lidx]);

                                        loops = loops->next;
                                        BLI_BITMAP_DISABLE(done_loops, lidx);
                                }

                                mul_v3_fl(avg_nor, 1.0f / (float)nbr_nors);
                                BKE_lnor_space_custom_normal_to_data(lnors_spacearr.lspacearr[i], avg_nor, clnor_data_tmp);

                                while ((clnor_data = BLI_SMALLSTACK_POP(clnors_data))) {
                                        clnor_data[0] = clnor_data_tmp[0];
                                        clnor_data[1] = clnor_data_tmp[1];
                                }
                        }
                        else {
                                const int nidx = use_vertices ? (int)mloops[i].v : i;
                                float *nor = custom_loopnors[nidx];

                                BKE_lnor_space_custom_normal_to_data(lnors_spacearr.lspacearr[i], nor, r_clnors_data[i]);
                                BLI_BITMAP_DISABLE(done_loops, i);
                        }
                }
        }

        MEM_freeN(lnors);
        MEM_freeN(loop_to_poly);
        MEM_freeN(done_loops);
        BKE_lnor_spacearr_free(&lnors_spacearr);
}

void BKE_mesh_normals_loop_custom_set(
        const MVert *mverts, const int numVerts, MEdge *medges, const int numEdges,
        MLoop *mloops, float (*custom_loopnors)[3], const int numLoops,
        MPoly *mpolys, const float (*polynors)[3], const int numPolys,
        short (*r_clnors_data)[2])
{
        mesh_normals_loop_custom_set(mverts, numVerts, medges, numEdges, mloops, custom_loopnors, numLoops,
                                     mpolys, polynors, numPolys, r_clnors_data, false);
}

void BKE_mesh_normals_loop_custom_from_vertices_set(
        const MVert *mverts, float (*custom_vertnors)[3], const int numVerts,
        MEdge *medges, const int numEdges, MLoop *mloops, const int numLoops,
        MPoly *mpolys, const float (*polynors)[3], const int numPolys,
        short (*r_clnors_data)[2])
{
        mesh_normals_loop_custom_set(mverts, numVerts, medges, numEdges, mloops, custom_vertnors, numLoops,
                                     mpolys, polynors, numPolys, r_clnors_data, true);
}

#undef LNOR_SPACE_TRIGO_THRESHOLD

/** \} */


/* -------------------------------------------------------------------- */

/** \name Mesh Tangent Calculations
 * \{ */

/* Tangent space utils. */

/* User data. */
typedef struct {
        const MPoly *mpolys;   /* faces */
        const MLoop *mloops;   /* faces's vertices */
        const MVert *mverts;   /* vertices */
        const MLoopUV *luvs;   /* texture coordinates */
        float (*lnors)[3];     /* loops' normals */
        float (*tangents)[4];  /* output tangents */
        int num_polys;         /* number of polygons */
} BKEMeshToTangent;

/* Mikktspace's API */
static int get_num_faces(const SMikkTSpaceContext *pContext)
{
        BKEMeshToTangent *p_mesh = (BKEMeshToTangent *)pContext->m_pUserData;
        return p_mesh->num_polys;
}

static int get_num_verts_of_face(const SMikkTSpaceContext *pContext, const int face_idx)
{
        BKEMeshToTangent *p_mesh = (BKEMeshToTangent *)pContext->m_pUserData;
        return p_mesh->mpolys[face_idx].totloop;
}

static void get_position(const SMikkTSpaceContext *pContext, float r_co[3], const int face_idx, const int vert_idx)
{
        BKEMeshToTangent *p_mesh = (BKEMeshToTangent *)pContext->m_pUserData;
        const int loop_idx = p_mesh->mpolys[face_idx].loopstart + vert_idx;
        copy_v3_v3(r_co, p_mesh->mverts[p_mesh->mloops[loop_idx].v].co);
}

static void get_texture_coordinate(const SMikkTSpaceContext *pContext, float r_uv[2], const int face_idx,
                                   const int vert_idx)
{
        BKEMeshToTangent *p_mesh = (BKEMeshToTangent *)pContext->m_pUserData;
        copy_v2_v2(r_uv, p_mesh->luvs[p_mesh->mpolys[face_idx].loopstart + vert_idx].uv);
}

static void get_normal(const SMikkTSpaceContext *pContext, float r_no[3], const int face_idx, const int vert_idx)
{
        BKEMeshToTangent *p_mesh = (BKEMeshToTangent *)pContext->m_pUserData;
        copy_v3_v3(r_no, p_mesh->lnors[p_mesh->mpolys[face_idx].loopstart + vert_idx]);
}

static void set_tspace(const SMikkTSpaceContext *pContext, const float fv_tangent[3], const float face_sign,
                       const int face_idx, const int vert_idx)
{
        BKEMeshToTangent *p_mesh = (BKEMeshToTangent *)pContext->m_pUserData;
        float *p_res = p_mesh->tangents[p_mesh->mpolys[face_idx].loopstart + vert_idx];
        copy_v3_v3(p_res, fv_tangent);
        p_res[3] = face_sign;
}

/**
 * Compute simplified tangent space normals, i.e. tangent vector + sign of bi-tangent one, which combined with
 * split normals can be used to recreate the full tangent space.
 * Note: * The mesh should be made of only tris and quads!
 */
void BKE_mesh_loop_tangents_ex(
        const MVert *mverts, const int UNUSED(numVerts), const MLoop *mloops,
        float (*r_looptangent)[4], float (*loopnors)[3], const MLoopUV *loopuvs,
        const int UNUSED(numLoops), const MPoly *mpolys, const int numPolys,
        ReportList *reports)
{
        BKEMeshToTangent mesh_to_tangent = {NULL};
        SMikkTSpaceContext s_context = {NULL};
        SMikkTSpaceInterface s_interface = {NULL};

        const MPoly *mp;
        int mp_index;

        /* First check we do have a tris/quads only mesh. */
        for (mp = mpolys, mp_index = 0; mp_index < numPolys; mp++, mp_index++) {
                if (mp->totloop > 4) {
                        BKE_report(reports, RPT_ERROR, "Tangent space can only be computed for tris/quads, aborting");
                        return;
                }
        }

        /* Compute Mikktspace's tangent normals. */
        mesh_to_tangent.mpolys = mpolys;
        mesh_to_tangent.mloops = mloops;
        mesh_to_tangent.mverts = mverts;
        mesh_to_tangent.luvs = loopuvs;
        mesh_to_tangent.lnors = loopnors;
        mesh_to_tangent.tangents = r_looptangent;
        mesh_to_tangent.num_polys = numPolys;

        s_context.m_pUserData = &mesh_to_tangent;
        s_context.m_pInterface = &s_interface;
        s_interface.m_getNumFaces = get_num_faces;
        s_interface.m_getNumVerticesOfFace = get_num_verts_of_face;
        s_interface.m_getPosition = get_position;
        s_interface.m_getTexCoord = get_texture_coordinate;
        s_interface.m_getNormal = get_normal;
        s_interface.m_setTSpaceBasic = set_tspace;

        /* 0 if failed */
        if (genTangSpaceDefault(&s_context) == false) {
                BKE_report(reports, RPT_ERROR, "Mikktspace failed to generate tangents for this mesh!");
        }
}

/**
 * Wrapper around BKE_mesh_loop_tangents_ex, which takes care of most boiling code.
 * \note
 * - There must be a valid loop's CD_NORMALS available.
 * - The mesh should be made of only tris and quads!
 */
void BKE_mesh_loop_tangents(Mesh *mesh, const char *uvmap, float (*r_looptangents)[4], ReportList *reports)
{
        MLoopUV *loopuvs;
        float (*loopnors)[3];

        /* Check we have valid texture coordinates first! */
        if (uvmap) {
                loopuvs = CustomData_get_layer_named(&mesh->ldata, CD_MLOOPUV, uvmap);
        }
        else {
                loopuvs = CustomData_get_layer(&mesh->ldata, CD_MLOOPUV);
        }
        if (!loopuvs) {
                BKE_reportf(reports, RPT_ERROR, "Tangent space computation needs an UVMap, \"%s\" not found, aborting", uvmap);
                return;
        }

        loopnors = CustomData_get_layer(&mesh->ldata, CD_NORMAL);
        if (!loopnors) {
                BKE_report(reports, RPT_ERROR, "Tangent space computation needs loop normals, none found, aborting");
                return;
        }

        BKE_mesh_loop_tangents_ex(mesh->mvert, mesh->totvert, mesh->mloop, r_looptangents,
                                  loopnors, loopuvs, mesh->totloop, mesh->mpoly, mesh->totpoly, reports);
}

/** \} */


/* -------------------------------------------------------------------- */

/** \name Polygon Calculations
 * \{ */

/*
 * COMPUTE POLY NORMAL
 *
 * Computes the normal of a planar
 * polygon See Graphics Gems for
 * computing newell normal.
 *
 */
static void mesh_calc_ngon_normal(
        const MPoly *mpoly, const MLoop *loopstart,
        const MVert *mvert, float normal[3])
{
        const int nverts = mpoly->totloop;
        const float *v_prev = mvert[loopstart[nverts - 1].v].co;
        const float *v_curr;
        int i;

        zero_v3(normal);

        /* Newell's Method */
        for (i = 0; i < nverts; i++) {
                v_curr = mvert[loopstart[i].v].co;
                add_newell_cross_v3_v3v3(normal, v_prev, v_curr);
                v_prev = v_curr;
        }

        if (UNLIKELY(normalize_v3(normal) == 0.0f)) {
                normal[2] = 1.0f; /* other axis set to 0.0 */
        }
}

void BKE_mesh_calc_poly_normal(
        const MPoly *mpoly, const MLoop *loopstart,
        const MVert *mvarray, float r_no[3])
{
        if (mpoly->totloop > 4) {
                mesh_calc_ngon_normal(mpoly, loopstart, mvarray, r_no);
        }
        else if (mpoly->totloop == 3) {
                normal_tri_v3(r_no,
                              mvarray[loopstart[0].v].co,
                              mvarray[loopstart[1].v].co,
                              mvarray[loopstart[2].v].co
                              );
        }
        else if (mpoly->totloop == 4) {
                normal_quad_v3(r_no,
                               mvarray[loopstart[0].v].co,
                               mvarray[loopstart[1].v].co,
                               mvarray[loopstart[2].v].co,
                               mvarray[loopstart[3].v].co
                               );
        }
        else { /* horrible, two sided face! */
                r_no[0] = 0.0;
                r_no[1] = 0.0;
                r_no[2] = 1.0;
        }
}
/* duplicate of function above _but_ takes coords rather then mverts */
static void mesh_calc_ngon_normal_coords(
        const MPoly *mpoly, const MLoop *loopstart,
        const float (*vertex_coords)[3], float r_normal[3])
{
        const int nverts = mpoly->totloop;
        const float *v_prev = vertex_coords[loopstart[nverts - 1].v];
        const float *v_curr;
        int i;

        zero_v3(r_normal);

        /* Newell's Method */
        for (i = 0; i < nverts; i++) {
                v_curr = vertex_coords[loopstart[i].v];
                add_newell_cross_v3_v3v3(r_normal, v_prev, v_curr);
                v_prev = v_curr;
        }

        if (UNLIKELY(normalize_v3(r_normal) == 0.0f)) {
                r_normal[2] = 1.0f; /* other axis set to 0.0 */
        }
}

void BKE_mesh_calc_poly_normal_coords(
        const MPoly *mpoly, const MLoop *loopstart,
        const float (*vertex_coords)[3], float r_no[3])
{
        if (mpoly->totloop > 4) {
                mesh_calc_ngon_normal_coords(mpoly, loopstart, vertex_coords, r_no);
        }
        else if (mpoly->totloop == 3) {
                normal_tri_v3(r_no,
                              vertex_coords[loopstart[0].v],
                              vertex_coords[loopstart[1].v],
                              vertex_coords[loopstart[2].v]
                              );
        }
        else if (mpoly->totloop == 4) {
                normal_quad_v3(r_no,
                               vertex_coords[loopstart[0].v],
                               vertex_coords[loopstart[1].v],
                               vertex_coords[loopstart[2].v],
                               vertex_coords[loopstart[3].v]
                               );
        }
        else { /* horrible, two sided face! */
                r_no[0] = 0.0;
                r_no[1] = 0.0;
                r_no[2] = 1.0;
        }
}

static void mesh_calc_ngon_center(
        const MPoly *mpoly, const MLoop *loopstart,
        const MVert *mvert, float cent[3])
{
        const float w = 1.0f / (float)mpoly->totloop;
        int i;

        zero_v3(cent);

        for (i = 0; i < mpoly->totloop; i++) {
                madd_v3_v3fl(cent, mvert[(loopstart++)->v].co, w);
        }
}

void BKE_mesh_calc_poly_center(
        const MPoly *mpoly, const MLoop *loopstart,
        const MVert *mvarray, float r_cent[3])
{
        if (mpoly->totloop == 3) {
                cent_tri_v3(r_cent,
                            mvarray[loopstart[0].v].co,
                            mvarray[loopstart[1].v].co,
                            mvarray[loopstart[2].v].co
                            );
        }
        else if (mpoly->totloop == 4) {
                cent_quad_v3(r_cent,
                             mvarray[loopstart[0].v].co,
                             mvarray[loopstart[1].v].co,
                             mvarray[loopstart[2].v].co,
                             mvarray[loopstart[3].v].co
                             );
        }
        else {
                mesh_calc_ngon_center(mpoly, loopstart, mvarray, r_cent);
        }
}

/* note, passing polynormal is only a speedup so we can skip calculating it */
float BKE_mesh_calc_poly_area(
        const MPoly *mpoly, const MLoop *loopstart,
        const MVert *mvarray)
{
        if (mpoly->totloop == 3) {
                return area_tri_v3(mvarray[loopstart[0].v].co,
                                   mvarray[loopstart[1].v].co,
                                   mvarray[loopstart[2].v].co
                                   );
        }
        else {
                int i;
                const MLoop *l_iter = loopstart;
                float area;
                float (*vertexcos)[3] = BLI_array_alloca(vertexcos, (size_t)mpoly->totloop);

                /* pack vertex cos into an array for area_poly_v3 */
                for (i = 0; i < mpoly->totloop; i++, l_iter++) {
                        copy_v3_v3(vertexcos[i], mvarray[l_iter->v].co);
                }

                /* finally calculate the area */
                area = area_poly_v3((const float (*)[3])vertexcos, (unsigned int)mpoly->totloop);

                return area;
        }
}

/* note, results won't be correct if polygon is non-planar */
static float mesh_calc_poly_planar_area_centroid(
        const MPoly *mpoly, const MLoop *loopstart, const MVert *mvarray,
        float r_cent[3])
{
        int i;
        float tri_area;
        float total_area = 0.0f;
        float v1[3], v2[3], v3[3], normal[3], tri_cent[3];

        BKE_mesh_calc_poly_normal(mpoly, loopstart, mvarray, normal);
        copy_v3_v3(v1, mvarray[loopstart[0].v].co);
        copy_v3_v3(v2, mvarray[loopstart[1].v].co);
        zero_v3(r_cent);

        for (i = 2; i < mpoly->totloop; i++) {
                copy_v3_v3(v3, mvarray[loopstart[i].v].co);

                tri_area = area_tri_signed_v3(v1, v2, v3, normal);
                total_area += tri_area;

                cent_tri_v3(tri_cent, v1, v2, v3);
                madd_v3_v3fl(r_cent, tri_cent, tri_area);

                copy_v3_v3(v2, v3);
        }

        mul_v3_fl(r_cent, 1.0f / total_area);

        return total_area;
}

#if 0 /* slow version of the function below */
void BKE_mesh_calc_poly_angles(MPoly *mpoly, MLoop *loopstart,
                               MVert *mvarray, float angles[])
{
        MLoop *ml;
        MLoop *mloop = &loopstart[-mpoly->loopstart];

        int j;
        for (j = 0, ml = loopstart; j < mpoly->totloop; j++, ml++) {
                MLoop *ml_prev = ME_POLY_LOOP_PREV(mloop, mpoly, j);
                MLoop *ml_next = ME_POLY_LOOP_NEXT(mloop, mpoly, j);

                float e1[3], e2[3];

                sub_v3_v3v3(e1, mvarray[ml_next->v].co, mvarray[ml->v].co);
                sub_v3_v3v3(e2, mvarray[ml_prev->v].co, mvarray[ml->v].co);

                angles[j] = (float)M_PI - angle_v3v3(e1, e2);
        }
}

#else /* equivalent the function above but avoid multiple subtractions + normalize */

void BKE_mesh_calc_poly_angles(
        const MPoly *mpoly, const MLoop *loopstart,
        const MVert *mvarray, float angles[])
{
        float nor_prev[3];
        float nor_next[3];

        int i_this = mpoly->totloop - 1;
        int i_next = 0;

        sub_v3_v3v3(nor_prev, mvarray[loopstart[i_this - 1].v].co, mvarray[loopstart[i_this].v].co);
        normalize_v3(nor_prev);

        while (i_next < mpoly->totloop) {
                sub_v3_v3v3(nor_next, mvarray[loopstart[i_this].v].co, mvarray[loopstart[i_next].v].co);
                normalize_v3(nor_next);
                angles[i_this] = angle_normalized_v3v3(nor_prev, nor_next);

                /* step */
                copy_v3_v3(nor_prev, nor_next);
                i_this = i_next;
                i_next++;
        }
}
#endif

void BKE_mesh_poly_edgehash_insert(EdgeHash *ehash, const MPoly *mp, const MLoop *mloop)
{
        const MLoop *ml, *ml_next;
        int i = mp->totloop;

        ml_next = mloop;       /* first loop */
        ml = &ml_next[i - 1];  /* last loop */

        while (i-- != 0) {
                BLI_edgehash_reinsert(ehash, ml->v, ml_next->v, NULL);

                ml = ml_next;
                ml_next++;
        }
}

void BKE_mesh_poly_edgebitmap_insert(unsigned int *edge_bitmap, const MPoly *mp, const MLoop *mloop)
{
        const MLoop *ml;
        int i = mp->totloop;

        ml = mloop;

        while (i-- != 0) {
                BLI_BITMAP_ENABLE(edge_bitmap, ml->e);
                ml++;
        }
}

/** \} */


/* -------------------------------------------------------------------- */

/** \name Mesh Center Calculation
 * \{ */

bool BKE_mesh_center_median(const Mesh *me, float r_cent[3])
{
        int i = me->totvert;
        const MVert *mvert;
        zero_v3(r_cent);
        for (mvert = me->mvert; i--; mvert++) {
                add_v3_v3(r_cent, mvert->co);
        }
        /* otherwise we get NAN for 0 verts */
        if (me->totvert) {
                mul_v3_fl(r_cent, 1.0f / (float)me->totvert);
        }

        return (me->totvert != 0);
}

bool BKE_mesh_center_bounds(const Mesh *me, float r_cent[3])
{
        float min[3], max[3];
        INIT_MINMAX(min, max);
        if (BKE_mesh_minmax(me, min, max)) {
                mid_v3_v3v3(r_cent, min, max);
                return true;
        }

        return false;
}

bool BKE_mesh_center_centroid(const Mesh *me, float r_cent[3])
{
        int i = me->totpoly;
        MPoly *mpoly;
        float poly_area;
        float total_area = 0.0f;
        float poly_cent[3];

        zero_v3(r_cent);

        /* calculate a weighted average of polygon centroids */
        for (mpoly = me->mpoly; i--; mpoly++) {
                poly_area = mesh_calc_poly_planar_area_centroid(mpoly, me->mloop + mpoly->loopstart, me->mvert, poly_cent);

                madd_v3_v3fl(r_cent, poly_cent, poly_area);
                total_area += poly_area;
        }
        /* otherwise we get NAN for 0 polys */
        if (me->totpoly) {
                mul_v3_fl(r_cent, 1.0f / total_area);
        }

        /* zero area faces cause this, fallback to median */
        if (UNLIKELY(!is_finite_v3(r_cent))) {
                return BKE_mesh_center_median(me, r_cent);
        }

        return (me->totpoly != 0);
}
/** \} */


/* -------------------------------------------------------------------- */

/** \name Mesh Volume Calculation
 * \{ */

static bool mesh_calc_center_centroid_ex(
        const MVert *mverts, int UNUSED(numVerts),
        const MLoopTri *lt, int numTris,
        const MLoop *mloop, float r_center[3])
{
        float totweight;
        int t;
        
        zero_v3(r_center);
        
        if (numTris == 0)
                return false;
        
        totweight = 0.0f;
        for (t = 0; t < numTris; t++, lt++) {
                const MVert *v1 = &mverts[mloop[lt->tri[0]].v];
                const MVert *v2 = &mverts[mloop[lt->tri[1]].v];
                const MVert *v3 = &mverts[mloop[lt->tri[2]].v];
                float area;
                
                area = area_tri_v3(v1->co, v2->co, v3->co);
                madd_v3_v3fl(r_center, v1->co, area);
                madd_v3_v3fl(r_center, v2->co, area);
                madd_v3_v3fl(r_center, v3->co, area);
                totweight += area;
        }
        if (totweight == 0.0f)
                return false;
        
        mul_v3_fl(r_center, 1.0f / (3.0f * totweight));
        
        return true;
}

void BKE_mesh_calc_volume(const MVert *mverts, const int numVerts,
        const MLoopTri *lt, const int numTris,
        const MLoop *mloop, float *r_vol, float *r_com)
{
        float center[3];
        float totvol;
        int f;
        
        if (r_vol) *r_vol = 0.0f;
        if (r_com) zero_v3(r_com);
        
        if (numTris == 0)
                return;
        
        if (!mesh_calc_center_centroid_ex(mverts, numVerts, lt, numTris, mloop, center))
                return;
        
        totvol = 0.0f;
        for (f = 0; f < numTris; f++, lt++) {
                const MVert *v1 = &mverts[mloop[lt->tri[0]].v];
                const MVert *v2 = &mverts[mloop[lt->tri[1]].v];
                const MVert *v3 = &mverts[mloop[lt->tri[2]].v];
                float vol;
                
                vol = volume_tetrahedron_signed_v3(center, v1->co, v2->co, v3->co);
                if (r_vol) {
                        totvol += vol;
                }
                if (r_com) {
                        /* averaging factor 1/4 is applied in the end */
                        madd_v3_v3fl(r_com, center, vol); // XXX could extract this
                        madd_v3_v3fl(r_com, v1->co, vol);
                        madd_v3_v3fl(r_com, v2->co, vol);
                        madd_v3_v3fl(r_com, v3->co, vol);
                }
        }
        
        /* Note: Depending on arbitrary centroid position,
         * totvol can become negative even for a valid mesh.
         * The true value is always the positive value.
         */
        if (r_vol) {
                *r_vol = fabsf(totvol);
        }
        if (r_com) {
                /* Note: Factor 1/4 is applied once for all vertices here.
                 * This also automatically negates the vector if totvol is negative.
                 */
                if (totvol != 0.0f)
                        mul_v3_fl(r_com, 0.25f / totvol);
        }
}


/* -------------------------------------------------------------------- */

/** \name NGon Tessellation (NGon/Tessface Conversion)
 * \{ */

/**
 * Convert a triangle or quadrangle of loop/poly data to tessface data
 */
void BKE_mesh_loops_to_mface_corners(
        CustomData *fdata, CustomData *ldata,
        CustomData *pdata, unsigned int lindex[4], int findex,
        const int polyindex,
        const int mf_len, /* 3 or 4 */

        /* cache values to avoid lookups every time */
        const int numTex, /* CustomData_number_of_layers(pdata, CD_MTEXPOLY) */
        const int numCol, /* CustomData_number_of_layers(ldata, CD_MLOOPCOL) */
        const bool hasPCol, /* CustomData_has_layer(ldata, CD_PREVIEW_MLOOPCOL) */
        const bool hasOrigSpace, /* CustomData_has_layer(ldata, CD_ORIGSPACE_MLOOP) */
        const bool hasLNor /* CustomData_has_layer(ldata, CD_NORMAL) */
)
{
        MTFace *texface;
        MTexPoly *texpoly;
        MCol *mcol;
        MLoopCol *mloopcol;
        MLoopUV *mloopuv;
        int i, j;

        for (i = 0; i < numTex; i++) {
                texface = CustomData_get_n(fdata, CD_MTFACE, findex, i);
                texpoly = CustomData_get_n(pdata, CD_MTEXPOLY, polyindex, i);

                ME_MTEXFACE_CPY(texface, texpoly);

                for (j = 0; j < mf_len; j++) {
                        mloopuv = CustomData_get_n(ldata, CD_MLOOPUV, (int)lindex[j], i);
                        copy_v2_v2(texface->uv[j], mloopuv->uv);
                }
        }

        for (i = 0; i < numCol; i++) {
                mcol = CustomData_get_n(fdata, CD_MCOL, findex, i);

                for (j = 0; j < mf_len; j++) {
                        mloopcol = CustomData_get_n(ldata, CD_MLOOPCOL, (int)lindex[j], i);
                        MESH_MLOOPCOL_TO_MCOL(mloopcol, &mcol[j]);
                }
        }

        if (hasPCol) {
                mcol = CustomData_get(fdata,  findex, CD_PREVIEW_MCOL);

                for (j = 0; j < mf_len; j++) {
                        mloopcol = CustomData_get(ldata, (int)lindex[j], CD_PREVIEW_MLOOPCOL);
                        MESH_MLOOPCOL_TO_MCOL(mloopcol, &mcol[j]);
                }
        }

        if (hasOrigSpace) {
                OrigSpaceFace *of = CustomData_get(fdata, findex, CD_ORIGSPACE);
                OrigSpaceLoop *lof;

                for (j = 0; j < mf_len; j++) {
                        lof = CustomData_get(ldata, (int)lindex[j], CD_ORIGSPACE_MLOOP);
                        copy_v2_v2(of->uv[j], lof->uv);
                }
        }

        if (hasLNor) {
                short (*tlnors)[3] = CustomData_get(fdata, findex, CD_TESSLOOPNORMAL);

                for (j = 0; j < mf_len; j++) {
                        normal_float_to_short_v3(tlnors[j], CustomData_get(ldata, (int)lindex[j], CD_NORMAL));
                }
        }
}

/**
 * Convert all CD layers from loop/poly to tessface data.
 *
 * \param loopindices is an array of an int[4] per tessface, mapping tessface's verts to loops indices.
 *
 * \note when mface is not NULL, mface[face_index].v4 is used to test quads, else, loopindices[face_index][3] is used.
 */
void BKE_mesh_loops_to_tessdata(CustomData *fdata, CustomData *ldata, CustomData *pdata, MFace *mface,
                                int *polyindices, unsigned int (*loopindices)[4], const int num_faces)
{
        /* Note: performances are sub-optimal when we get a NULL mface, we could be ~25% quicker with dedicated code...
         *       Issue is, unless having two different functions with nearly the same code, there's not much ways to solve
         *       this. Better imho to live with it for now. :/ --mont29
         */
        const int numTex = CustomData_number_of_layers(pdata, CD_MTEXPOLY);
        const int numCol = CustomData_number_of_layers(ldata, CD_MLOOPCOL);
        const bool hasPCol = CustomData_has_layer(ldata, CD_PREVIEW_MLOOPCOL);
        const bool hasOrigSpace = CustomData_has_layer(ldata, CD_ORIGSPACE_MLOOP);
        const bool hasLoopNormal = CustomData_has_layer(ldata, CD_NORMAL);
        int findex, i, j;
        const int *pidx;
        unsigned int (*lidx)[4];

        for (i = 0; i < numTex; i++) {
                MTFace *texface = CustomData_get_layer_n(fdata, CD_MTFACE, i);
                MTexPoly *texpoly = CustomData_get_layer_n(pdata, CD_MTEXPOLY, i);
                MLoopUV *mloopuv = CustomData_get_layer_n(ldata, CD_MLOOPUV, i);

                for (findex = 0, pidx = polyindices, lidx = loopindices;
                     findex < num_faces;
                     pidx++, lidx++, findex++, texface++)
                {
                        ME_MTEXFACE_CPY(texface, &texpoly[*pidx]);

                        for (j = (mface ? mface[findex].v4 : (*lidx)[3]) ? 4 : 3; j--;) {
                                copy_v2_v2(texface->uv[j], mloopuv[(*lidx)[j]].uv);
                        }
                }
        }

        for (i = 0; i < numCol; i++) {
                MCol (*mcol)[4] = CustomData_get_layer_n(fdata, CD_MCOL, i);
                MLoopCol *mloopcol = CustomData_get_layer_n(ldata, CD_MLOOPCOL, i);

                for (findex = 0, lidx = loopindices; findex < num_faces; lidx++, findex++, mcol++) {
                        for (j = (mface ? mface[findex].v4 : (*lidx)[3]) ? 4 : 3; j--;) {
                                MESH_MLOOPCOL_TO_MCOL(&mloopcol[(*lidx)[j]], &(*mcol)[j]);
                        }
                }
        }

        if (hasPCol) {
                MCol (*mcol)[4] = CustomData_get_layer(fdata, CD_PREVIEW_MCOL);
                MLoopCol *mloopcol = CustomData_get_layer(ldata, CD_PREVIEW_MLOOPCOL);

                for (findex = 0, lidx = loopindices; findex < num_faces; lidx++, findex++, mcol++) {
                        for (j = (mface ? mface[findex].v4 : (*lidx)[3]) ? 4 : 3; j--;) {
                                MESH_MLOOPCOL_TO_MCOL(&mloopcol[(*lidx)[j]], &(*mcol)[j]);
                        }
                }
        }

        if (hasOrigSpace) {
                OrigSpaceFace *of = CustomData_get_layer(fdata, CD_ORIGSPACE);
                OrigSpaceLoop *lof = CustomData_get_layer(ldata, CD_ORIGSPACE_MLOOP);

                for (findex = 0, lidx = loopindices; findex < num_faces; lidx++, findex++, of++) {
                        for (j = (mface ? mface[findex].v4 : (*lidx)[3]) ? 4 : 3; j--;) {
                                copy_v2_v2(of->uv[j], lof[(*lidx)[j]].uv);
                        }
                }
        }

        if (hasLoopNormal) {
                short (*fnors)[4][3] = CustomData_get_layer(fdata, CD_TESSLOOPNORMAL);
                float (*lnors)[3] = CustomData_get_layer(ldata, CD_NORMAL);

                for (findex = 0, lidx = loopindices; findex < num_faces; lidx++, findex++, fnors++) {
                        for (j = (mface ? mface[findex].v4 : (*lidx)[3]) ? 4 : 3; j--;) {
                                normal_float_to_short_v3((*fnors)[j], lnors[(*lidx)[j]]);
                        }
                }
        }
}

/**
 * Recreate tessellation.
 *
 * \param do_face_nor_copy: Controls whether the normals from the poly are copied to the tessellated faces.
 *
 * \return number of tessellation faces.
 */
int BKE_mesh_recalc_tessellation(
        CustomData *fdata, CustomData *ldata, CustomData *pdata,
        MVert *mvert,
        int totface, int totloop, int totpoly,
        const bool do_face_nor_copy)
{
        /* use this to avoid locking pthread for _every_ polygon
         * and calling the fill function */

#define USE_TESSFACE_SPEEDUP
#define USE_TESSFACE_QUADS  /* NEEDS FURTHER TESTING */

/* We abuse MFace->edcode to tag quad faces. See below for details. */
#define TESSFACE_IS_QUAD 1

        const int looptris_tot = poly_to_tri_count(totpoly, totloop);

        MPoly *mp, *mpoly;
        MLoop *ml, *mloop;
        MFace *mface, *mf;
        MemArena *arena = NULL;
        int *mface_to_poly_map;
        unsigned int (*lindices)[4];
        int poly_index, mface_index;
        unsigned int j;

        mpoly = CustomData_get_layer(pdata, CD_MPOLY);
        mloop = CustomData_get_layer(ldata, CD_MLOOP);

        /* allocate the length of totfaces, avoid many small reallocs,
         * if all faces are tri's it will be correct, quads == 2x allocs */
        /* take care. we are _not_ calloc'ing so be sure to initialize each field */
        mface_to_poly_map = MEM_mallocN(sizeof(*mface_to_poly_map) * (size_t)looptris_tot, __func__);
        mface             = MEM_mallocN(sizeof(*mface) *             (size_t)looptris_tot, __func__);
        lindices          = MEM_mallocN(sizeof(*lindices) *          (size_t)looptris_tot, __func__);

        mface_index = 0;
        mp = mpoly;
        for (poly_index = 0; poly_index < totpoly; poly_index++, mp++) {
                const unsigned int mp_loopstart = (unsigned int)mp->loopstart;
                const unsigned int mp_totloop = (unsigned int)mp->totloop;
                unsigned int l1, l2, l3, l4;
                unsigned int *lidx;
                if (mp_totloop < 3) {
                        /* do nothing */
                }

#ifdef USE_TESSFACE_SPEEDUP

#define ML_TO_MF(i1, i2, i3)                                                  \
                mface_to_poly_map[mface_index] = poly_index;                          \
                mf = &mface[mface_index];                                             \
                lidx = lindices[mface_index];                                         \
                /* set loop indices, transformed to vert indices later */             \
                l1 = mp_loopstart + i1;                                               \
                l2 = mp_loopstart + i2;                                               \
                l3 = mp_loopstart + i3;                                               \
                mf->v1 = mloop[l1].v;                                                 \
                mf->v2 = mloop[l2].v;                                                 \
                mf->v3 = mloop[l3].v;                                                 \
                mf->v4 = 0;                                                           \
                lidx[0] = l1;                                                         \
                lidx[1] = l2;                                                         \
                lidx[2] = l3;                                                         \
                lidx[3] = 0;                                                          \
                mf->mat_nr = mp->mat_nr;                                              \
                mf->flag = mp->flag;                                                  \
                mf->edcode = 0;                                                       \
                (void)0

/* ALMOST IDENTICAL TO DEFINE ABOVE (see EXCEPTION) */
#define ML_TO_MF_QUAD()                                                       \
                mface_to_poly_map[mface_index] = poly_index;                          \
                mf = &mface[mface_index];                                             \
                lidx = lindices[mface_index];                                         \
                /* set loop indices, transformed to vert indices later */             \
                l1 = mp_loopstart + 0; /* EXCEPTION */                                \
                l2 = mp_loopstart + 1; /* EXCEPTION */                                \
                l3 = mp_loopstart + 2; /* EXCEPTION */                                \
                l4 = mp_loopstart + 3; /* EXCEPTION */                                \
                mf->v1 = mloop[l1].v;                                                 \
                mf->v2 = mloop[l2].v;                                                 \
                mf->v3 = mloop[l3].v;                                                 \
                mf->v4 = mloop[l4].v;                                                 \
                lidx[0] = l1;                                                         \
                lidx[1] = l2;                                                         \
                lidx[2] = l3;                                                         \
                lidx[3] = l4;                                                         \
                mf->mat_nr = mp->mat_nr;                                              \
                mf->flag = mp->flag;                                                  \
                mf->edcode = TESSFACE_IS_QUAD;                                        \
                (void)0


                else if (mp_totloop == 3) {
                        ML_TO_MF(0, 1, 2);
                        mface_index++;
                }
                else if (mp_totloop == 4) {
#ifdef USE_TESSFACE_QUADS
                        ML_TO_MF_QUAD();
                        mface_index++;
#else
                        ML_TO_MF(0, 1, 2);
                        mface_index++;
                        ML_TO_MF(0, 2, 3);
                        mface_index++;
#endif
                }
#endif /* USE_TESSFACE_SPEEDUP */
                else {
                        const float *co_curr, *co_prev;

                        float normal[3];

                        float axis_mat[3][3];
                        float (*projverts)[2];
                        unsigned int (*tris)[3];

                        const unsigned int totfilltri = mp_totloop - 2;

                        if (UNLIKELY(arena == NULL)) {
                                arena = BLI_memarena_new(BLI_MEMARENA_STD_BUFSIZE, __func__);
                        }

                        tris = BLI_memarena_alloc(arena, sizeof(*tris) * (size_t)totfilltri);
                        projverts = BLI_memarena_alloc(arena, sizeof(*projverts) * (size_t)mp_totloop);

                        zero_v3(normal);

                        /* calc normal, flipped: to get a positive 2d cross product */
                        ml = mloop + mp_loopstart;
                        co_prev = mvert[ml[mp_totloop - 1].v].co;
                        for (j = 0; j < mp_totloop; j++, ml++) {
                                co_curr = mvert[ml->v].co;
                                add_newell_cross_v3_v3v3(normal, co_prev, co_curr);
                                co_prev = co_curr;
                        }
                        if (UNLIKELY(normalize_v3(normal) == 0.0f)) {
                                normal[2] = 1.0f;
                        }

                        /* project verts to 2d */
                        axis_dominant_v3_to_m3_negate(axis_mat, normal);

                        ml = mloop + mp_loopstart;
                        for (j = 0; j < mp_totloop; j++, ml++) {
                                mul_v2_m3v3(projverts[j], axis_mat, mvert[ml->v].co);
                        }

                        BLI_polyfill_calc_arena((const float (*)[2])projverts, mp_totloop, 1, tris, arena);

                        /* apply fill */
                        for (j = 0; j < totfilltri; j++) {
                                unsigned int *tri = tris[j];
                                lidx = lindices[mface_index];

                                mface_to_poly_map[mface_index] = poly_index;
                                mf = &mface[mface_index];

                                /* set loop indices, transformed to vert indices later */
                                l1 = mp_loopstart + tri[0];
                                l2 = mp_loopstart + tri[1];
                                l3 = mp_loopstart + tri[2];

                                mf->v1 = mloop[l1].v;
                                mf->v2 = mloop[l2].v;
                                mf->v3 = mloop[l3].v;
                                mf->v4 = 0;

                                lidx[0] = l1;
                                lidx[1] = l2;
                                lidx[2] = l3;
                                lidx[3] = 0;

                                mf->mat_nr = mp->mat_nr;
                                mf->flag = mp->flag;
                                mf->edcode = 0;

                                mface_index++;
                        }

                        BLI_memarena_clear(arena);
                }
        }

        if (arena) {
                BLI_memarena_free(arena);
                arena = NULL;
        }

        CustomData_free(fdata, totface);
        totface = mface_index;

        BLI_assert(totface <= looptris_tot);

        /* not essential but without this we store over-alloc'd memory in the CustomData layers */
        if (LIKELY(looptris_tot != totface)) {
                mface = MEM_reallocN(mface, sizeof(*mface) * (size_t)totface);
                mface_to_poly_map = MEM_reallocN(mface_to_poly_map, sizeof(*mface_to_poly_map) * (size_t)totface);
        }

        CustomData_add_layer(fdata, CD_MFACE, CD_ASSIGN, mface, totface);

        /* CD_ORIGINDEX will contain an array of indices from tessfaces to the polygons
         * they are directly tessellated from */
        CustomData_add_layer(fdata, CD_ORIGINDEX, CD_ASSIGN, mface_to_poly_map, totface);
        CustomData_from_bmeshpoly(fdata, pdata, ldata, totface);

        if (do_face_nor_copy) {
                /* If polys have a normals layer, copying that to faces can help
                 * avoid the need to recalculate normals later */
                if (CustomData_has_layer(pdata, CD_NORMAL)) {
                        float (*pnors)[3] = CustomData_get_layer(pdata, CD_NORMAL);
                        float (*fnors)[3] = CustomData_add_layer(fdata, CD_NORMAL, CD_CALLOC, NULL, totface);
                        for (mface_index = 0; mface_index < totface; mface_index++) {
                                copy_v3_v3(fnors[mface_index], pnors[mface_to_poly_map[mface_index]]);
                        }
                }
        }

        /* NOTE: quad detection issue - forth vertidx vs forth loopidx:
         * Polygons take care of their loops ordering, hence not of their vertices ordering.
         * Currently, our tfaces' forth vertex index might be 0 even for a quad. However, we know our forth loop index is
         * never 0 for quads (because they are sorted for polygons, and our quads are still mere copies of their polygons).
         * So we pass NULL as MFace pointer, and BKE_mesh_loops_to_tessdata will use the forth loop index as quad test.
         * ...
         */
        BKE_mesh_loops_to_tessdata(fdata, ldata, pdata, NULL, mface_to_poly_map, lindices, totface);

        /* NOTE: quad detection issue - forth vertidx vs forth loopidx:
         * ...However, most TFace code uses 'MFace->v4 == 0' test to check whether it is a tri or quad.
         * test_index_face() will check this and rotate the tessellated face if needed.
         */
#ifdef USE_TESSFACE_QUADS
        mf = mface;
        for (mface_index = 0; mface_index < totface; mface_index++, mf++) {
                if (mf->edcode == TESSFACE_IS_QUAD) {
                        test_index_face(mf, fdata, mface_index, 4);
                        mf->edcode = 0;
                }
        }
#endif

        MEM_freeN(lindices);

        return totface;

#undef USE_TESSFACE_SPEEDUP
#undef USE_TESSFACE_QUADS

#undef ML_TO_MF
#undef ML_TO_MF_QUAD

}

/**
 * Calculate tessellation into #MLoopTri which exist only for this purpose.
 */
void BKE_mesh_recalc_looptri(
        const MLoop *mloop, const MPoly *mpoly,
        const MVert *mvert,
        int totloop, int totpoly,
        MLoopTri *mlooptri)
{
        /* use this to avoid locking pthread for _every_ polygon
         * and calling the fill function */

#define USE_TESSFACE_SPEEDUP

        const MPoly *mp;
        const MLoop *ml;
        MLoopTri *mlt;
        MemArena *arena = NULL;
        int poly_index, mlooptri_index;
        unsigned int j;

        mlooptri_index = 0;
        mp = mpoly;
        for (poly_index = 0; poly_index < totpoly; poly_index++, mp++) {
                const unsigned int mp_loopstart = (unsigned int)mp->loopstart;
                const unsigned int mp_totloop = (unsigned int)mp->totloop;
                unsigned int l1, l2, l3;
                if (mp_totloop < 3) {
                        /* do nothing */
                }

#ifdef USE_TESSFACE_SPEEDUP

#define ML_TO_MLT(i1, i2, i3)  { \
                        mlt = &mlooptri[mlooptri_index]; \
                        l1 = mp_loopstart + i1; \
                        l2 = mp_loopstart + i2; \
                        l3 = mp_loopstart + i3; \
                        ARRAY_SET_ITEMS(mlt->tri, l1, l2, l3); \
                        mlt->poly = (unsigned int)poly_index; \
                } ((void)0)

                else if (mp_totloop == 3) {
                        ML_TO_MLT(0, 1, 2);
                        mlooptri_index++;
                }
                else if (mp_totloop == 4) {
                        ML_TO_MLT(0, 1, 2);
                        mlooptri_index++;
                        ML_TO_MLT(0, 2, 3);
                        mlooptri_index++;
                }
#endif /* USE_TESSFACE_SPEEDUP */
                else {
                        const float *co_curr, *co_prev;

                        float normal[3];

                        float axis_mat[3][3];
                        float (*projverts)[2];
                        unsigned int (*tris)[3];

                        const unsigned int totfilltri = mp_totloop - 2;

                        if (UNLIKELY(arena == NULL)) {
                                arena = BLI_memarena_new(BLI_MEMARENA_STD_BUFSIZE, __func__);
                        }

                        tris = BLI_memarena_alloc(arena, sizeof(*tris) * (size_t)totfilltri);
                        projverts = BLI_memarena_alloc(arena, sizeof(*projverts) * (size_t)mp_totloop);

                        zero_v3(normal);

                        /* calc normal, flipped: to get a positive 2d cross product */
                        ml = mloop + mp_loopstart;
                        co_prev = mvert[ml[mp_totloop - 1].v].co;
                        for (j = 0; j < mp_totloop; j++, ml++) {
                                co_curr = mvert[ml->v].co;
                                add_newell_cross_v3_v3v3(normal, co_prev, co_curr);
                                co_prev = co_curr;
                        }
                        if (UNLIKELY(normalize_v3(normal) == 0.0f)) {
                                normal[2] = 1.0f;
                        }

                        /* project verts to 2d */
                        axis_dominant_v3_to_m3_negate(axis_mat, normal);

                        ml = mloop + mp_loopstart;
                        for (j = 0; j < mp_totloop; j++, ml++) {
                                mul_v2_m3v3(projverts[j], axis_mat, mvert[ml->v].co);
                        }

                        BLI_polyfill_calc_arena((const float (*)[2])projverts, mp_totloop, 1, tris, arena);

                        /* apply fill */
                        for (j = 0; j < totfilltri; j++) {
                                unsigned int *tri = tris[j];

                                mlt = &mlooptri[mlooptri_index];

                                /* set loop indices, transformed to vert indices later */
                                l1 = mp_loopstart + tri[0];
                                l2 = mp_loopstart + tri[1];
                                l3 = mp_loopstart + tri[2];

                                ARRAY_SET_ITEMS(mlt->tri, l1, l2, l3);
                                mlt->poly = (unsigned int)poly_index;

                                mlooptri_index++;
                        }

                        BLI_memarena_clear(arena);
                }
        }

        if (arena) {
                BLI_memarena_free(arena);
                arena = NULL;
        }

        BLI_assert(mlooptri_index == poly_to_tri_count(totpoly, totloop));
        UNUSED_VARS_NDEBUG(totloop);

#undef USE_TESSFACE_SPEEDUP
#undef ML_TO_MLT
}

/* -------------------------------------------------------------------- */


#ifdef USE_BMESH_SAVE_AS_COMPAT

/**
 * This function recreates a tessellation.
 * returns number of tessellation faces.
 *
 * for forwards compat only quad->tri polys to mface, skip ngons.
 */
int BKE_mesh_mpoly_to_mface(struct CustomData *fdata, struct CustomData *ldata,
                            struct CustomData *pdata, int totface, int UNUSED(totloop), int totpoly)
{
        MLoop *mloop;

        unsigned int lindex[4];
        int i;
        int k;

        MPoly *mp, *mpoly;
        MFace *mface, *mf;

        const int numTex = CustomData_number_of_layers(pdata, CD_MTEXPOLY);
        const int numCol = CustomData_number_of_layers(ldata, CD_MLOOPCOL);
        const bool hasPCol = CustomData_has_layer(ldata, CD_PREVIEW_MLOOPCOL);
        const bool hasOrigSpace = CustomData_has_layer(ldata, CD_ORIGSPACE_MLOOP);
        const bool hasLNor = CustomData_has_layer(ldata, CD_NORMAL);

        /* over-alloc, ngons will be skipped */
        mface = MEM_mallocN(sizeof(*mface) * (size_t)totpoly, __func__);

        mpoly = CustomData_get_layer(pdata, CD_MPOLY);
        mloop = CustomData_get_layer(ldata, CD_MLOOP);

        mp = mpoly;
        k = 0;
        for (i = 0; i < totpoly; i++, mp++) {
                if (ELEM(mp->totloop, 3, 4)) {
                        const unsigned int mp_loopstart = (unsigned int)mp->loopstart;
                        mf = &mface[k];

                        mf->mat_nr = mp->mat_nr;
                        mf->flag = mp->flag;

                        mf->v1 = mp_loopstart + 0;
                        mf->v2 = mp_loopstart + 1;
                        mf->v3 = mp_loopstart + 2;
                        mf->v4 = (mp->totloop == 4) ? (mp_loopstart + 3) : 0;

                        /* abuse edcode for temp storage and clear next loop */
                        mf->edcode = (char)mp->totloop; /* only ever 3 or 4 */

                        k++;
                }
        }

        CustomData_free(fdata, totface);

        totface = k;

        CustomData_add_layer(fdata, CD_MFACE, CD_ASSIGN, mface, totface);

        CustomData_from_bmeshpoly(fdata, pdata, ldata, totface);

        mp = mpoly;
        k = 0;
        for (i = 0; i < totpoly; i++, mp++) {
                if (ELEM(mp->totloop, 3, 4)) {
                        mf = &mface[k];

                        if (mf->edcode == 3) {
                                /* sort loop indices to ensure winding is correct */
                                /* NO SORT - looks like we can skip this */

                                lindex[0] = mf->v1;
                                lindex[1] = mf->v2;
                                lindex[2] = mf->v3;
                                lindex[3] = 0; /* unused */

                                /* transform loop indices to vert indices */
                                mf->v1 = mloop[mf->v1].v;
                                mf->v2 = mloop[mf->v2].v;
                                mf->v3 = mloop[mf->v3].v;

                                BKE_mesh_loops_to_mface_corners(fdata, ldata, pdata,
                                                                lindex, k, i, 3,
                                                                numTex, numCol, hasPCol, hasOrigSpace, hasLNor);
                                test_index_face(mf, fdata, k, 3);
                        }
                        else {
                                /* sort loop indices to ensure winding is correct */
                                /* NO SORT - looks like we can skip this */

                                lindex[0] = mf->v1;
                                lindex[1] = mf->v2;
                                lindex[2] = mf->v3;
                                lindex[3] = mf->v4;

                                /* transform loop indices to vert indices */
                                mf->v1 = mloop[mf->v1].v;
                                mf->v2 = mloop[mf->v2].v;
                                mf->v3 = mloop[mf->v3].v;
                                mf->v4 = mloop[mf->v4].v;

                                BKE_mesh_loops_to_mface_corners(fdata, ldata, pdata,
                                                                lindex, k, i, 4,
                                                                numTex, numCol, hasPCol, hasOrigSpace, hasLNor);
                                test_index_face(mf, fdata, k, 4);
                        }

                        mf->edcode = 0;

                        k++;
                }
        }

        return k;
}
#endif /* USE_BMESH_SAVE_AS_COMPAT */


static void bm_corners_to_loops_ex(ID *id, CustomData *fdata, CustomData *ldata, CustomData *pdata,
                                   MFace *mface, int totloop, int findex, int loopstart, int numTex, int numCol)
{
        MTFace *texface;
        MTexPoly *texpoly;
        MCol *mcol;
        MLoopCol *mloopcol;
        MLoopUV *mloopuv;
        MFace *mf;
        int i;

        mf = mface + findex;

        for (i = 0; i < numTex; i++) {
                texface = CustomData_get_n(fdata, CD_MTFACE, findex, i);
                texpoly = CustomData_get_n(pdata, CD_MTEXPOLY, findex, i);

                ME_MTEXFACE_CPY(texpoly, texface);

                mloopuv = CustomData_get_n(ldata, CD_MLOOPUV, loopstart, i);
                copy_v2_v2(mloopuv->uv, texface->uv[0]); mloopuv++;
                copy_v2_v2(mloopuv->uv, texface->uv[1]); mloopuv++;
                copy_v2_v2(mloopuv->uv, texface->uv[2]); mloopuv++;

                if (mf->v4) {
                        copy_v2_v2(mloopuv->uv, texface->uv[3]); mloopuv++;
                }
        }

        for (i = 0; i < numCol; i++) {
                mloopcol = CustomData_get_n(ldata, CD_MLOOPCOL, loopstart, i);
                mcol = CustomData_get_n(fdata, CD_MCOL, findex, i);

                MESH_MLOOPCOL_FROM_MCOL(mloopcol, &mcol[0]); mloopcol++;
                MESH_MLOOPCOL_FROM_MCOL(mloopcol, &mcol[1]); mloopcol++;
                MESH_MLOOPCOL_FROM_MCOL(mloopcol, &mcol[2]); mloopcol++;
                if (mf->v4) {
                        MESH_MLOOPCOL_FROM_MCOL(mloopcol, &mcol[3]); mloopcol++;
                }
        }

        if (CustomData_has_layer(fdata, CD_TESSLOOPNORMAL)) {
                float (*lnors)[3] = CustomData_get(ldata, loopstart, CD_NORMAL);
                short (*tlnors)[3] = CustomData_get(fdata, findex, CD_TESSLOOPNORMAL);
                const int max = mf->v4 ? 4 : 3;

                for (i = 0; i < max; i++, lnors++, tlnors++) {
                        normal_short_to_float_v3(*lnors, *tlnors);
                }
        }

        if (CustomData_has_layer(fdata, CD_MDISPS)) {
                MDisps *ld = CustomData_get(ldata, loopstart, CD_MDISPS);
                MDisps *fd = CustomData_get(fdata, findex, CD_MDISPS);
                float (*disps)[3] = fd->disps;
                int tot = mf->v4 ? 4 : 3;
                int corners;

                if (CustomData_external_test(fdata, CD_MDISPS)) {
                        if (id && fdata->external) {
                                CustomData_external_add(ldata, id, CD_MDISPS,
                                                        totloop, fdata->external->filename);
                        }
                }

                corners = multires_mdisp_corners(fd);

                if (corners == 0) {
                        /* Empty MDisp layers appear in at least one of the sintel.blend files.
                         * Not sure why this happens, but it seems fine to just ignore them here.
                         * If (corners == 0) for a non-empty layer though, something went wrong. */
                        BLI_assert(fd->totdisp == 0);
                }
                else {
                        const int side = (int)sqrtf((float)(fd->totdisp / corners));
                        const int side_sq = side * side;
                        const size_t disps_size = sizeof(float[3]) * (size_t)side_sq;

                        for (i = 0; i < tot; i++, disps += side_sq, ld++) {
                                ld->totdisp = side_sq;
                                ld->level = (int)(logf((float)side - 1.0f) / (float)M_LN2) + 1;

                                if (ld->disps)
                                        MEM_freeN(ld->disps);

                                ld->disps = MEM_mallocN(disps_size, "converted loop mdisps");
                                if (fd->disps) {
                                        memcpy(ld->disps, disps, disps_size);
                                }
                                else {
                                        memset(ld->disps, 0, disps_size);
                                }
                        }
                }
        }
}


void BKE_mesh_convert_mfaces_to_mpolys(Mesh *mesh)
{
        BKE_mesh_convert_mfaces_to_mpolys_ex(&mesh->id, &mesh->fdata, &mesh->ldata, &mesh->pdata,
                                             mesh->totedge, mesh->totface, mesh->totloop, mesh->totpoly,
                                             mesh->medge, mesh->mface,
                                             &mesh->totloop, &mesh->totpoly, &mesh->mloop, &mesh->mpoly);

        BKE_mesh_update_customdata_pointers(mesh, true);
}

/* the same as BKE_mesh_convert_mfaces_to_mpolys but oriented to be used in do_versions from readfile.c
 * the difference is how active/render/clone/stencil indices are handled here
 *
 * normally thay're being set from pdata which totally makes sense for meshes which are already
 * converted to bmesh structures, but when loading older files indices shall be updated in other
 * way around, so newly added pdata and ldata would have this indices set based on fdata layer
 *
 * this is normally only needed when reading older files, in all other cases BKE_mesh_convert_mfaces_to_mpolys
 * shall be always used
 */
void BKE_mesh_do_versions_convert_mfaces_to_mpolys(Mesh *mesh)
{
        BKE_mesh_convert_mfaces_to_mpolys_ex(&mesh->id, &mesh->fdata, &mesh->ldata, &mesh->pdata,
                                             mesh->totedge, mesh->totface, mesh->totloop, mesh->totpoly,
                                             mesh->medge, mesh->mface,
                                             &mesh->totloop, &mesh->totpoly, &mesh->mloop, &mesh->mpoly);

        CustomData_bmesh_do_versions_update_active_layers(&mesh->fdata, &mesh->pdata, &mesh->ldata);

        BKE_mesh_update_customdata_pointers(mesh, true);
}

void BKE_mesh_convert_mfaces_to_mpolys_ex(ID *id, CustomData *fdata, CustomData *ldata, CustomData *pdata,
                                          int totedge_i, int totface_i, int totloop_i, int totpoly_i,
                                          MEdge *medge, MFace *mface,
                                          int *r_totloop, int *r_totpoly,
                                          MLoop **r_mloop, MPoly **r_mpoly)
{
        MFace *mf;
        MLoop *ml, *mloop;
        MPoly *mp, *mpoly;
        MEdge *me;
        EdgeHash *eh;
        int numTex, numCol;
        int i, j, totloop, totpoly, *polyindex;

        /* old flag, clear to allow for reuse */
#define ME_FGON (1 << 3)

        /* just in case some of these layers are filled in (can happen with python created meshes) */
        CustomData_free(ldata, totloop_i);
        CustomData_free(pdata, totpoly_i);

        totpoly = totface_i;
        mpoly = MEM_callocN(sizeof(MPoly) * (size_t)totpoly, "mpoly converted");
        CustomData_add_layer(pdata, CD_MPOLY, CD_ASSIGN, mpoly, totpoly);

        numTex = CustomData_number_of_layers(fdata, CD_MTFACE);
        numCol = CustomData_number_of_layers(fdata, CD_MCOL);

        totloop = 0;
        mf = mface;
        for (i = 0; i < totface_i; i++, mf++) {
                totloop += mf->v4 ? 4 : 3;
        }

        mloop = MEM_callocN(sizeof(MLoop) * (size_t)totloop, "mloop converted");

        CustomData_add_layer(ldata, CD_MLOOP, CD_ASSIGN, mloop, totloop);

        CustomData_to_bmeshpoly(fdata, pdata, ldata, totloop, totpoly);

        if (id) {
                /* ensure external data is transferred */
                CustomData_external_read(fdata, id, CD_MASK_MDISPS, totface_i);
        }

        eh = BLI_edgehash_new_ex(__func__, (unsigned int)totedge_i);

        /* build edge hash */
        me = medge;
        for (i = 0; i < totedge_i; i++, me++) {
                BLI_edgehash_insert(eh, me->v1, me->v2, SET_UINT_IN_POINTER(i));

                /* unrelated but avoid having the FGON flag enabled, so we can reuse it later for something else */
                me->flag &= ~ME_FGON;
        }

        polyindex = CustomData_get_layer(fdata, CD_ORIGINDEX);

        j = 0; /* current loop index */
        ml = mloop;
        mf = mface;
        mp = mpoly;
        for (i = 0; i < totface_i; i++, mf++, mp++) {
                mp->loopstart = j;

                mp->totloop = mf->v4 ? 4 : 3;

                mp->mat_nr = mf->mat_nr;
                mp->flag = mf->flag;

#       define ML(v1, v2) { \
                        ml->v = mf->v1; \
                        ml->e = GET_UINT_FROM_POINTER(BLI_edgehash_lookup(eh, mf->v1, mf->v2)); \
                        ml++; j++; \
                } (void)0

                ML(v1, v2);
                ML(v2, v3);
                if (mf->v4) {
                        ML(v3, v4);
                        ML(v4, v1);
                }
                else {
                        ML(v3, v1);
                }

#       undef ML

                bm_corners_to_loops_ex(id, fdata, ldata, pdata, mface, totloop, i, mp->loopstart, numTex, numCol);