blender-archive/source/blender/gpencil_modifiers/intern/lineart/lineart_cpu.c

/* SPDX-License-Identifier: GPL-2.0-or-later
 * Copyright 2019 Blender Foundation. All rights reserved. */

/* \file
 * \ingroup editors
 */

#include "MOD_gpencil_lineart.h"
#include "MOD_lineart.h"

#include "BLI_edgehash.h"
#include "BLI_linklist.h"
#include "BLI_listbase.h"
#include "BLI_math.h"
#include "BLI_task.h"
#include "BLI_utildefines.h"

#include "PIL_time.h"

#include "BKE_camera.h"
#include "BKE_collection.h"
#include "BKE_customdata.h"
#include "BKE_deform.h"
#include "BKE_duplilist.h"
#include "BKE_editmesh.h"
#include "BKE_global.h"
#include "BKE_gpencil.h"
#include "BKE_gpencil_geom.h"
#include "BKE_gpencil_modifier.h"
#include "BKE_lib_id.h"
#include "BKE_material.h"
#include "BKE_mesh.h"
#include "BKE_mesh_mapping.h"
#include "BKE_mesh_runtime.h"
#include "BKE_object.h"
#include "BKE_pointcache.h"
#include "BKE_scene.h"
#include "DEG_depsgraph_query.h"
#include "DNA_camera_types.h"
#include "DNA_collection_types.h"
#include "DNA_gpencil_types.h"
#include "DNA_material_types.h"
#include "DNA_mesh_types.h"
#include "DNA_meshdata_types.h"
#include "DNA_modifier_types.h"
#include "DNA_scene_types.h"
#include "MEM_guardedalloc.h"

#include "bmesh.h"
#include "bmesh_class.h"
#include "bmesh_tools.h"

#include "lineart_intern.h"

typedef struct LineartIsecSingle {
  float v1[3], v2[3];
  LineartTriangle *tri1, *tri2;
} LineartIsecSingle;

typedef struct LineartIsecThread {
  int thread_id;

  /* Scheduled work range. */
  LineartElementLinkNode *pending_from;
  LineartElementLinkNode *pending_to;
  int index_from;
  int index_to;

  /* Thread intersection result data. */
  LineartIsecSingle *array;
  int current;
  int max;
  int count_test;

  /* For individual thread reference.*/
  LineartRenderBuffer *rb;
} LineartIsecThread;

typedef struct LineartIsecData {
  LineartRenderBuffer *rb;
  LineartIsecThread *threads;
  int thread_count;
} LineartIsecData;

static LineartBoundingArea *lineart_edge_first_bounding_area(LineartRenderBuffer *rb,
                                                             LineartEdge *e);

static void lineart_bounding_area_link_edge(LineartRenderBuffer *rb,
                                            LineartBoundingArea *root_ba,
                                            LineartEdge *e);

static LineartBoundingArea *lineart_bounding_area_next(LineartBoundingArea *this,
                                                       LineartEdge *e,
                                                       double x,
                                                       double y,
                                                       double k,
                                                       int positive_x,
                                                       int positive_y,
                                                       double *next_x,
                                                       double *next_y);

static bool lineart_get_edge_bounding_areas(LineartRenderBuffer *rb,
                                            LineartEdge *e,
                                            int *rowbegin,
                                            int *rowend,
                                            int *colbegin,
                                            int *colend);

static bool lineart_triangle_edge_image_space_occlusion(SpinLock *spl,
                                                        const LineartTriangle *tri,
                                                        const LineartEdge *e,
                                                        const double *override_camera_loc,
                                                        const bool override_cam_is_persp,
                                                        const bool allow_overlapping_edges,
                                                        const double vp[4][4],
                                                        const double *camera_dir,
                                                        const float cam_shift_x,
                                                        const float cam_shift_y,
                                                        double *from,
                                                        double *to);

static void lineart_add_edge_to_array(LineartPendingEdges *pe, LineartEdge *e);

static void lineart_bounding_area_link_triangle(LineartRenderBuffer *rb,
                                                LineartBoundingArea *root_ba,
                                                LineartTriangle *tri,
                                                double *LRUB,
                                                int recursive,
                                                int recursive_level,
                                                bool do_intersection,
                                                struct LineartIsecThread *th);

static void lineart_free_bounding_area_memory(LineartBoundingArea *ba, bool recursive);

static void lineart_free_bounding_area_memories(LineartRenderBuffer *rb);

static LineartCache *lineart_init_cache(void);

static void lineart_discard_segment(LineartRenderBuffer *rb, LineartEdgeSegment *es)
{
  BLI_spin_lock(&rb->lock_cuts);

  memset(es, 0, sizeof(LineartEdgeSegment));

  /* Storing the node for potentially reuse the memory for new segment data.
   * Line Art data is not freed after all calculations are done. */
  BLI_addtail(&rb->wasted_cuts, es);

  BLI_spin_unlock(&rb->lock_cuts);
}

static LineartEdgeSegment *lineart_give_segment(LineartRenderBuffer *rb)
{
  BLI_spin_lock(&rb->lock_cuts);

  /* See if there is any already allocated memory we can reuse. */
  if (rb->wasted_cuts.first) {
    LineartEdgeSegment *es = (LineartEdgeSegment *)BLI_pophead(&rb->wasted_cuts);
    BLI_spin_unlock(&rb->lock_cuts);
    memset(es, 0, sizeof(LineartEdgeSegment));
    return es;
  }
  BLI_spin_unlock(&rb->lock_cuts);

  /* Otherwise allocate some new memory. */
  return (LineartEdgeSegment *)lineart_mem_acquire_thread(&rb->render_data_pool,
                                                          sizeof(LineartEdgeSegment));
}

/**
 * Cuts the edge in image space and mark occlusion level for each segment.
 */
static void lineart_edge_cut(LineartRenderBuffer *rb,
                             LineartEdge *e,
                             double start,
                             double end,
                             uchar material_mask_bits,
                             uchar mat_occlusion)
{
  LineartEdgeSegment *es, *ies, *next_es, *prev_es;
  LineartEdgeSegment *cut_start_before = 0, *cut_end_before = 0;
  LineartEdgeSegment *ns = 0, *ns2 = 0;
  int untouched = 0;

  /* If for some reason the occlusion function may give a result that has zero length, or reversed
   * in direction, or NAN, we take care of them here. */
  if (LRT_DOUBLE_CLOSE_ENOUGH(start, end)) {
    return;
  }
  if (LRT_DOUBLE_CLOSE_ENOUGH(start, 1) || LRT_DOUBLE_CLOSE_ENOUGH(end, 0)) {
    return;
  }
  if (UNLIKELY(start != start)) {
    start = 0;
  }
  if (UNLIKELY(end != end)) {
    end = 0;
  }

  if (start > end) {
    double t = start;
    start = end;
    end = t;
  }

  /* Begin looking for starting position of the segment. */
  /* Not using a list iteration macro because of it more clear when using for loops to iterate
   * through the segments. */
  for (es = e->segments.first; es; es = es->next) {
    if (LRT_DOUBLE_CLOSE_ENOUGH(es->at, start)) {
      cut_start_before = es;
      ns = cut_start_before;
      break;
    }
    if (es->next == NULL) {
      break;
    }
    ies = es->next;
    if (ies->at > start + 1e-09 && start > es->at) {
      cut_start_before = ies;
      ns = lineart_give_segment(rb);
      break;
    }
  }
  if (!cut_start_before && LRT_DOUBLE_CLOSE_ENOUGH(1, end)) {
    untouched = 1;
  }
  for (es = cut_start_before; es; es = es->next) {
    /* We tried to cut at existing cutting point (e.g. where the line's occluded by a triangle
     * strip). */
    if (LRT_DOUBLE_CLOSE_ENOUGH(es->at, end)) {
      cut_end_before = es;
      ns2 = cut_end_before;
      break;
    }
    /* This check is to prevent `es->at == 1.0` (where we don't need to cut because we are at the
     * end point). */
    if (!es->next && LRT_DOUBLE_CLOSE_ENOUGH(1, end)) {
      cut_end_before = es;
      ns2 = cut_end_before;
      untouched = 1;
      break;
    }
    /* When an actual cut is needed in the line. */
    if (es->at > end) {
      cut_end_before = es;
      ns2 = lineart_give_segment(rb);
      break;
    }
  }

  /* When we still can't find any existing cut in the line, we allocate new ones. */
  if (ns == NULL) {
    ns = lineart_give_segment(rb);
  }
  if (ns2 == NULL) {
    if (untouched) {
      ns2 = ns;
      cut_end_before = ns2;
    }
    else {
      ns2 = lineart_give_segment(rb);
    }
  }

  if (cut_start_before) {
    if (cut_start_before != ns) {
      /* Insert cutting points for when a new cut is needed. */
      ies = cut_start_before->prev ? cut_start_before->prev : NULL;
      ns->occlusion = ies ? ies->occlusion : 0;
      ns->material_mask_bits = ies->material_mask_bits;
      BLI_insertlinkbefore(&e->segments, cut_start_before, ns);
    }
    /* Otherwise we already found a existing cutting point, no need to insert a new one. */
  }
  else {
    /* We have yet to reach a existing cutting point even after we searched the whole line, so we
     * append the new cut to the end. */
    ies = e->segments.last;
    ns->occlusion = ies->occlusion;
    ns->material_mask_bits = ies->material_mask_bits;
    BLI_addtail(&e->segments, ns);
  }
  if (cut_end_before) {
    /* The same manipulation as on "cut_start_before". */
    if (cut_end_before != ns2) {
      ies = cut_end_before->prev ? cut_end_before->prev : NULL;
      ns2->occlusion = ies ? ies->occlusion : 0;
      ns2->material_mask_bits = ies ? ies->material_mask_bits : 0;
      BLI_insertlinkbefore(&e->segments, cut_end_before, ns2);
    }
  }
  else {
    ies = e->segments.last;
    ns2->occlusion = ies->occlusion;
    ns2->material_mask_bits = ies->material_mask_bits;
    BLI_addtail(&e->segments, ns2);
  }

  /* If we touched the cut list, we assign the new cut position based on new cut position,
   * this way we accommodate precision lost due to multiple cut inserts. */
  ns->at = start;
  if (!untouched) {
    ns2->at = end;
  }
  else {
    /* For the convenience of the loop below. */
    ns2 = ns2->next;
  }

  /* Register 1 level of occlusion for all touched segments. */
  for (es = ns; es && es != ns2; es = es->next) {
    es->occlusion += mat_occlusion;
    es->material_mask_bits |= material_mask_bits;
  }

  /* Reduce adjacent cutting points of the same level, which saves memory. */
  char min_occ = 127;
  prev_es = NULL;
  for (es = e->segments.first; es; es = next_es) {
    next_es = es->next;

    if (prev_es && prev_es->occlusion == es->occlusion &&
        prev_es->material_mask_bits == es->material_mask_bits) {
      BLI_remlink(&e->segments, es);
      /* This puts the node back to the render buffer, if more cut happens, these unused nodes get
       * picked first. */
      lineart_discard_segment(rb, es);
      continue;
    }

    min_occ = MIN2(min_occ, es->occlusion);

    prev_es = es;
  }
  e->min_occ = min_occ;
}

/**
 * To see if given line is connected to an adjacent intersection line.
 */
BLI_INLINE bool lineart_occlusion_is_adjacent_intersection(LineartEdge *e, LineartTriangle *tri)
{
  LineartVertIntersection *v1 = (void *)e->v1;
  LineartVertIntersection *v2 = (void *)e->v2;
  return ((v1->base.flag && v1->intersecting_with == tri) ||
          (v2->base.flag && v2->intersecting_with == tri));
}

static void lineart_bounding_area_triangle_reallocate(LineartBoundingArea *ba)
{
  ba->max_triangle_count *= 2;
  ba->linked_triangles = MEM_recallocN(ba->linked_triangles,
                                       sizeof(LineartTriangle *) * ba->max_triangle_count);
}

static void lineart_bounding_area_line_add(LineartBoundingArea *ba, LineartEdge *e)
{
  /* In case of too many lines concentrating in one point, do not add anymore, these lines will
   * be either shorter than a single pixel, or will still be added into the list of other less
   * dense areas. */
  if (ba->line_count >= 65535) {
    return;
  }
  if (ba->line_count >= ba->max_line_count) {
    LineartEdge **new_array = MEM_mallocN(sizeof(LineartEdge *) * ba->max_line_count * 2,
                                          "new ba_line_array");
    memcpy(new_array, ba->linked_lines, sizeof(LineartEdge *) * ba->max_line_count);
    ba->max_line_count *= 2;
    MEM_freeN(ba->linked_lines);
    ba->linked_lines = new_array;
  }
  ba->linked_lines[ba->line_count] = e;
  ba->line_count++;
}

static void lineart_occlusion_single_line(LineartRenderBuffer *rb, LineartEdge *e, int thread_id)
{
  double x = e->v1->fbcoord[0], y = e->v1->fbcoord[1];
  LineartBoundingArea *ba = lineart_edge_first_bounding_area(rb, e);
  LineartBoundingArea *nba = ba;
  LineartTriangleThread *tri;

  /* These values are used for marching along the line. */
  double l, r;
  double k = (e->v2->fbcoord[1] - e->v1->fbcoord[1]) /
             (e->v2->fbcoord[0] - e->v1->fbcoord[0] + 1e-30);
  int positive_x = (e->v2->fbcoord[0] - e->v1->fbcoord[0]) > 0 ?
                       1 :
                       (e->v2->fbcoord[0] == e->v1->fbcoord[0] ? 0 : -1);
  int positive_y = (e->v2->fbcoord[1] - e->v1->fbcoord[1]) > 0 ?
                       1 :
                       (e->v2->fbcoord[1] == e->v1->fbcoord[1] ? 0 : -1);

  while (nba) {

    for (int i = 0; i < nba->triangle_count; i++) {
      tri = (LineartTriangleThread *)nba->linked_triangles[i];
      /* If we are already testing the line in this thread, then don't do it. */
      if (tri->testing_e[thread_id] == e || (tri->base.flags & LRT_TRIANGLE_INTERSECTION_ONLY) ||
          /* Ignore this triangle if an intersection line directly comes from it, */
          lineart_occlusion_is_adjacent_intersection(e, (LineartTriangle *)tri) ||
          /* Or if this triangle isn't effectively occluding anything nor it's providing a
           * material flag. */
          ((!tri->base.mat_occlusion) && (!tri->base.material_mask_bits))) {
        continue;
      }
      tri->testing_e[thread_id] = e;
      if (lineart_triangle_edge_image_space_occlusion(&rb->lock_task,
                                                      (const LineartTriangle *)tri,
                                                      e,
                                                      rb->camera_pos,
                                                      rb->cam_is_persp,
                                                      rb->allow_overlapping_edges,
                                                      rb->view_projection,
                                                      rb->view_vector,
                                                      rb->shift_x,
                                                      rb->shift_y,
                                                      &l,
                                                      &r)) {
        lineart_edge_cut(rb, e, l, r, tri->base.material_mask_bits, tri->base.mat_occlusion);
        if (e->min_occ > rb->max_occlusion_level) {
          /* No need to calculate any longer on this line because no level more than set value is
           * going to show up in the rendered result. */
          return;
        }
      }
    }
    /* Marching along `e->v1` to `e->v2`, searching each possible bounding areas it may touch. */
    nba = lineart_bounding_area_next(nba, e, x, y, k, positive_x, positive_y, &x, &y);
  }
}

static int lineart_occlusion_make_task_info(LineartRenderBuffer *rb, LineartRenderTaskInfo *rti)
{
  int res = 0;
  int starting_index;

  BLI_spin_lock(&rb->lock_task);

  starting_index = rb->scheduled_count;
  rb->scheduled_count += LRT_THREAD_EDGE_COUNT;

  BLI_spin_unlock(&rb->lock_task);

  if (starting_index >= rb->pending_edges.next) {
    res = 0;
  }
  else {
    rti->pending_edges.array = &rb->pending_edges.array[starting_index];
    int remaining = rb->pending_edges.next - starting_index;
    rti->pending_edges.max = MIN2(remaining, LRT_THREAD_EDGE_COUNT);
    res = 1;
  }

  return res;
}

static void lineart_occlusion_worker(TaskPool *__restrict UNUSED(pool), LineartRenderTaskInfo *rti)
{
  LineartRenderBuffer *rb = rti->rb;
  LineartEdge *eip;

  while (lineart_occlusion_make_task_info(rb, rti)) {
    for (int i = 0; i < rti->pending_edges.max; i++) {
      eip = rti->pending_edges.array[i];
      lineart_occlusion_single_line(rb, eip, rti->thread_id);
    }
  }
}

/**
 * All internal functions starting with lineart_main_ is called inside
 * #MOD_lineart_compute_feature_lines function.
 * This function handles all occlusion calculation.
 */
static void lineart_main_occlusion_begin(LineartRenderBuffer *rb)
{
  int thread_count = rb->thread_count;
  LineartRenderTaskInfo *rti = MEM_callocN(sizeof(LineartRenderTaskInfo) * thread_count,
                                           "Task Pool");
  int i;

  TaskPool *tp = BLI_task_pool_create(NULL, TASK_PRIORITY_HIGH);

  for (i = 0; i < thread_count; i++) {
    rti[i].thread_id = i;
    rti[i].rb = rb;
    BLI_task_pool_push(tp, (TaskRunFunction)lineart_occlusion_worker, &rti[i], 0, NULL);
  }
  BLI_task_pool_work_and_wait(tp);
  BLI_task_pool_free(tp);

  MEM_freeN(rti);
}

/**
 * Test if v lies with in the triangle formed by v0, v1, and v2.
 * Returns false when v is exactly on the edge.
 *
 * For v to be inside the triangle, it needs to be at the same side of v0->v1, v1->v2, and
 * `v2->v0`, where the "side" is determined by checking the sign of `cross(v1-v0, v1-v)` and so on.
 */
static bool lineart_point_inside_triangle(const double v[2],
                                          const double v0[2],
                                          const double v1[2],
                                          const double v2[2])
{
  double cl, c;

  cl = (v0[0] - v[0]) * (v1[1] - v[1]) - (v0[1] - v[1]) * (v1[0] - v[0]);
  c = cl;

  cl = (v1[0] - v[0]) * (v2[1] - v[1]) - (v1[1] - v[1]) * (v2[0] - v[0]);
  if (c * cl <= 0) {
    return false;
  }

  c = cl;

  cl = (v2[0] - v[0]) * (v0[1] - v[1]) - (v2[1] - v[1]) * (v0[0] - v[0]);
  if (c * cl <= 0) {
    return false;
  }

  c = cl;

  cl = (v0[0] - v[0]) * (v1[1] - v[1]) - (v0[1] - v[1]) * (v1[0] - v[0]);
  if (c * cl <= 0) {
    return false;
  }

  return true;
}

static int lineart_point_on_line_segment(double v[2], double v0[2], double v1[2])
{
  /* `c1 != c2` by default. */
  double c1 = 1, c2 = 0;
  double l0[2], l1[2];

  sub_v2_v2v2_db(l0, v, v0);
  sub_v2_v2v2_db(l1, v, v1);

  if (v1[0] == v0[0] && v1[1] == v0[1]) {
    return 0;
  }

  if (!LRT_DOUBLE_CLOSE_ENOUGH(v1[0], v0[0])) {
    c1 = ratiod(v0[0], v1[0], v[0]);
  }
  else {
    if (LRT_DOUBLE_CLOSE_ENOUGH(v[0], v1[0])) {
      c2 = ratiod(v0[1], v1[1], v[1]);
      return (c2 >= -DBL_TRIANGLE_LIM && c2 <= 1 + DBL_TRIANGLE_LIM);
    }
    return false;
  }

  if (!LRT_DOUBLE_CLOSE_ENOUGH(v1[1], v0[1])) {
    c2 = ratiod(v0[1], v1[1], v[1]);
  }
  else {
    if (LRT_DOUBLE_CLOSE_ENOUGH(v[1], v1[1])) {
      c1 = ratiod(v0[0], v1[0], v[0]);
      return (c1 >= -DBL_TRIANGLE_LIM && c1 <= 1 + DBL_TRIANGLE_LIM);
    }
    return false;
  }

  if (LRT_DOUBLE_CLOSE_ENOUGH(c1, c2) && c1 >= 0 && c1 <= 1) {
    return 1;
  }

  return 0;
}

/**
 * Same algorithm as lineart_point_inside_triangle(), but returns differently:
 * 0-outside 1-on the edge 2-inside.
 */
static int lineart_point_triangle_relation(double v[2], double v0[2], double v1[2], double v2[2])
{
  double cl, c;
  double r;
  if (lineart_point_on_line_segment(v, v0, v1) || lineart_point_on_line_segment(v, v1, v2) ||
      lineart_point_on_line_segment(v, v2, v0)) {
    return 1;
  }

  cl = (v0[0] - v[0]) * (v1[1] - v[1]) - (v0[1] - v[1]) * (v1[0] - v[0]);
  c = cl;

  cl = (v1[0] - v[0]) * (v2[1] - v[1]) - (v1[1] - v[1]) * (v2[0] - v[0]);
  if ((r = c * cl) < 0) {
    return 0;
  }

  c = cl;

  cl = (v2[0] - v[0]) * (v0[1] - v[1]) - (v2[1] - v[1]) * (v0[0] - v[0]);
  if ((r = c * cl) < 0) {
    return 0;
  }

  c = cl;

  cl = (v0[0] - v[0]) * (v1[1] - v[1]) - (v0[1] - v[1]) * (v1[0] - v[0]);
  if ((r = c * cl) < 0) {
    return 0;
  }

  if (r == 0) {
    return 1;
  }

  return 2;
}

/**
 * Similar with #lineart_point_inside_triangle, but in 3d.
 * Returns false when not co-planar.
 */
static bool lineart_point_inside_triangle3d(double v[3], double v0[3], double v1[3], double v2[3])
{
  double l[3], r[3];
  double N1[3], N2[3];
  double d;

  sub_v3_v3v3_db(l, v1, v0);
  sub_v3_v3v3_db(r, v, v1);
  cross_v3_v3v3_db(N1, l, r);

  sub_v3_v3v3_db(l, v2, v1);
  sub_v3_v3v3_db(r, v, v2);
  cross_v3_v3v3_db(N2, l, r);

  if ((d = dot_v3v3_db(N1, N2)) < 0) {
    return false;
  }

  sub_v3_v3v3_db(l, v0, v2);
  sub_v3_v3v3_db(r, v, v0);
  cross_v3_v3v3_db(N1, l, r);

  if ((d = dot_v3v3_db(N1, N2)) < 0) {
    return false;
  }

  sub_v3_v3v3_db(l, v1, v0);
  sub_v3_v3v3_db(r, v, v1);
  cross_v3_v3v3_db(N2, l, r);

  if ((d = dot_v3v3_db(N1, N2)) < 0) {
    return false;
  }

  return true;
}

/**
 * The following `lineart_memory_get_XXX_space` functions are for allocating new memory for some
 * modified geometries in the culling stage.
 */
static LineartElementLinkNode *lineart_memory_get_triangle_space(LineartRenderBuffer *rb)
{
  LineartElementLinkNode *eln;

  /* We don't need to allocate a whole bunch of triangles because the amount of clipped triangles
   * are relatively small. */
  LineartTriangle *render_triangles = lineart_mem_acquire(&rb->render_data_pool,
                                                          64 * rb->triangle_size);

  eln = lineart_list_append_pointer_pool_sized(&rb->triangle_buffer_pointers,
                                               &rb->render_data_pool,
                                               render_triangles,
                                               sizeof(LineartElementLinkNode));
  eln->element_count = 64;
  eln->flags |= LRT_ELEMENT_IS_ADDITIONAL;

  return eln;
}

static LineartElementLinkNode *lineart_memory_get_vert_space(LineartRenderBuffer *rb)
{
  LineartElementLinkNode *eln;

  LineartVert *render_vertices = lineart_mem_acquire(&rb->render_data_pool,
                                                     sizeof(LineartVert) * 64);

  eln = lineart_list_append_pointer_pool_sized(&rb->vertex_buffer_pointers,
                                               &rb->render_data_pool,
                                               render_vertices,
                                               sizeof(LineartElementLinkNode));
  eln->element_count = 64;
  eln->flags |= LRT_ELEMENT_IS_ADDITIONAL;

  return eln;
}

static LineartElementLinkNode *lineart_memory_get_edge_space(LineartRenderBuffer *rb)
{
  LineartElementLinkNode *eln;

  LineartEdge *render_edges = lineart_mem_acquire(&rb->render_data_pool, sizeof(LineartEdge) * 64);

  eln = lineart_list_append_pointer_pool_sized(&rb->line_buffer_pointers,
                                               &rb->render_data_pool,
                                               render_edges,
                                               sizeof(LineartElementLinkNode));
  eln->element_count = 64;
  eln->crease_threshold = rb->crease_threshold;
  eln->flags |= LRT_ELEMENT_IS_ADDITIONAL;

  return eln;
}

static void lineart_triangle_post(LineartTriangle *tri, LineartTriangle *orig)
{
  /* Just re-assign normal and set cull flag. */
  copy_v3_v3_db(tri->gn, orig->gn);
  tri->flags = LRT_CULL_GENERATED;
  tri->material_mask_bits = orig->material_mask_bits;
  tri->mat_occlusion = orig->mat_occlusion;
}

static void lineart_triangle_set_cull_flag(LineartTriangle *tri, uchar flag)
{
  uchar intersection_only = (tri->flags & LRT_TRIANGLE_INTERSECTION_ONLY);
  tri->flags = flag;
  tri->flags |= intersection_only;
}

static bool lineart_edge_match(LineartTriangle *tri, LineartEdge *e, int v1, int v2)
{
  return ((tri->v[v1] == e->v1 && tri->v[v2] == e->v2) ||
          (tri->v[v2] == e->v1 && tri->v[v1] == e->v2));
}

static void lineart_discard_duplicated_edges(LineartEdge *old_e)
{
  LineartEdge *e = old_e;
  while (e->flags & LRT_EDGE_FLAG_NEXT_IS_DUPLICATION) {
    e++;
    e->flags |= LRT_EDGE_FLAG_CHAIN_PICKED;
  }
}

/**
 * Does near-plane cut on 1 triangle only. When cutting with far-plane, the camera vectors gets
 * reversed by the caller so don't need to implement one in a different direction.
 */
static void lineart_triangle_cull_single(LineartRenderBuffer *rb,
                                         LineartTriangle *tri,
                                         int in0,
                                         int in1,
                                         int in2,
                                         double *cam_pos,
                                         double *view_dir,
                                         bool allow_boundaries,
                                         double (*vp)[4],
                                         Object *ob,
                                         int *r_v_count,
                                         int *r_e_count,
                                         int *r_t_count,
                                         LineartElementLinkNode *v_eln,
                                         LineartElementLinkNode *e_eln,
                                         LineartElementLinkNode *t_eln)
{
  double vv1[3], vv2[3], dot1, dot2;
  double a;
  int v_count = *r_v_count;
  int e_count = *r_e_count;
  int t_count = *r_t_count;
  uint16_t new_flag = 0;

  LineartEdge *new_e, *e, *old_e;
  LineartEdgeSegment *es;
  LineartTriangleAdjacent *ta;

  if (tri->flags & (LRT_CULL_USED | LRT_CULL_GENERATED | LRT_CULL_DISCARD)) {
    return;
  }

  /* See definition of tri->intersecting_verts and the usage in
   * lineart_geometry_object_load() for details. */
  ta = (void *)tri->intersecting_verts;

  LineartVert *vt = &((LineartVert *)v_eln->pointer)[v_count];
  LineartTriangle *tri1 = (void *)(((uchar *)t_eln->pointer) + rb->triangle_size * t_count);
  LineartTriangle *tri2 = (void *)(((uchar *)t_eln->pointer) + rb->triangle_size * (t_count + 1));

  new_e = &((LineartEdge *)e_eln->pointer)[e_count];
  /* Init `edge` to the last `edge` entry. */
  e = new_e;

#define INCREASE_EDGE \
  new_e = &((LineartEdge *)e_eln->pointer)[e_count]; \
  e_count++; \
  e = new_e; \
  es = lineart_mem_acquire(&rb->render_data_pool, sizeof(LineartEdgeSegment)); \
  BLI_addtail(&e->segments, es);

#define SELECT_EDGE(e_num, v1_link, v2_link, new_tri) \
  if (ta->e[e_num]) { \
    old_e = ta->e[e_num]; \
    new_flag = old_e->flags; \
    old_e->flags = LRT_EDGE_FLAG_CHAIN_PICKED; \
    lineart_discard_duplicated_edges(old_e); \
    INCREASE_EDGE \
    e->v1 = (v1_link); \
    e->v2 = (v2_link); \
    e->v1->index = (v1_link)->index; \
    e->v2->index = (v1_link)->index; \
    e->flags = new_flag; \
    e->object_ref = ob; \
    e->t1 = ((old_e->t1 == tri) ? (new_tri) : (old_e->t1)); \
    e->t2 = ((old_e->t2 == tri) ? (new_tri) : (old_e->t2)); \
    lineart_add_edge_to_array(&rb->pending_edges, e); \
  }

#define RELINK_EDGE(e_num, new_tri) \
  if (ta->e[e_num]) { \
    old_e = ta->e[e_num]; \
    old_e->t1 = ((old_e->t1 == tri) ? (new_tri) : (old_e->t1)); \
    old_e->t2 = ((old_e->t2 == tri) ? (new_tri) : (old_e->t2)); \
  }

#define REMOVE_TRIANGLE_EDGE \
  if (ta->e[0]) { \
    ta->e[0]->flags = LRT_EDGE_FLAG_CHAIN_PICKED; \
    lineart_discard_duplicated_edges(ta->e[0]); \
  } \
  if (ta->e[1]) { \
    ta->e[1]->flags = LRT_EDGE_FLAG_CHAIN_PICKED; \
    lineart_discard_duplicated_edges(ta->e[1]); \
  } \
  if (ta->e[2]) { \
    ta->e[2]->flags = LRT_EDGE_FLAG_CHAIN_PICKED; \
    lineart_discard_duplicated_edges(ta->e[2]); \
  }

  switch (in0 + in1 + in2) {
    case 0: /* Triangle is visible. Ignore this triangle. */
      return;
    case 3:
      /* Triangle completely behind near plane, throw it away
       * also remove render lines form being computed. */
      lineart_triangle_set_cull_flag(tri, LRT_CULL_DISCARD);
      REMOVE_TRIANGLE_EDGE
      return;
    case 2:
      /* Two points behind near plane, cut those and
       * generate 2 new points, 3 lines and 1 triangle. */
      lineart_triangle_set_cull_flag(tri, LRT_CULL_USED);

      /**
       * (!in0) means "when point 0 is visible".
       * conditions for point 1, 2 are the same idea.
       *
       * \code{.txt}identify
       * 1-----|-------0
       * |     |   ---
       * |     |---
       * |  ---|
       * 2--   |
       *     (near)---------->(far)
       * Will become:
       *       |N******0
       *       |*  ***
       *       |N**
       *       |
       *       |
       *     (near)---------->(far)
       * \endcode
       */
      if (!in0) {

        /* Cut point for line 2---|-----0. */
        sub_v3_v3v3_db(vv1, tri->v[0]->gloc, cam_pos);
        sub_v3_v3v3_db(vv2, cam_pos, tri->v[2]->gloc);
        dot1 = dot_v3v3_db(vv1, view_dir);
        dot2 = dot_v3v3_db(vv2, view_dir);
        a = dot1 / (dot1 + dot2);
        /* Assign it to a new point. */
        interp_v3_v3v3_db(vt[0].gloc, tri->v[0]->gloc, tri->v[2]->gloc, a);
        mul_v4_m4v3_db(vt[0].fbcoord, vp, vt[0].gloc);
        vt[0].index = tri->v[2]->index;

        /* Cut point for line 1---|-----0. */
        sub_v3_v3v3_db(vv1, tri->v[0]->gloc, cam_pos);
        sub_v3_v3v3_db(vv2, cam_pos, tri->v[1]->gloc);
        dot1 = dot_v3v3_db(vv1, view_dir);
        dot2 = dot_v3v3_db(vv2, view_dir);
        a = dot1 / (dot1 + dot2);
        /* Assign it to another new point. */
        interp_v3_v3v3_db(vt[1].gloc, tri->v[0]->gloc, tri->v[1]->gloc, a);
        mul_v4_m4v3_db(vt[1].fbcoord, vp, vt[1].gloc);
        vt[1].index = tri->v[1]->index;

        /* New line connecting two new points. */
        INCREASE_EDGE
        if (allow_boundaries) {
          e->flags = LRT_EDGE_FLAG_CONTOUR;
          lineart_add_edge_to_array(&rb->pending_edges, e);
        }
        /* NOTE: inverting `e->v1/v2` (left/right point) doesn't matter as long as
         * `tri->edge` and `tri->v` has the same sequence. and the winding direction
         * can be either CW or CCW but needs to be consistent throughout the calculation. */
        e->v1 = &vt[1];
        e->v2 = &vt[0];
        /* Only one adjacent triangle, because the other side is the near plane. */
        /* Use `tl` or `tr` doesn't matter. */
        e->t1 = tri1;
        e->object_ref = ob;

        /* New line connecting original point 0 and a new point, only when it's a selected line. */
        SELECT_EDGE(2, tri->v[0], &vt[0], tri1)
        /* New line connecting original point 0 and another new point. */
        SELECT_EDGE(0, tri->v[0], &vt[1], tri1)

        /* Re-assign triangle point array to two new points. */
        tri1->v[0] = tri->v[0];
        tri1->v[1] = &vt[1];
        tri1->v[2] = &vt[0];

        lineart_triangle_post(tri1, tri);

        v_count += 2;
        t_count += 1;
      }
      else if (!in2) {
        sub_v3_v3v3_db(vv1, tri->v[2]->gloc, cam_pos);
        sub_v3_v3v3_db(vv2, cam_pos, tri->v[0]->gloc);
        dot1 = dot_v3v3_db(vv1, view_dir);
        dot2 = dot_v3v3_db(vv2, view_dir);
        a = dot1 / (dot1 + dot2);
        interp_v3_v3v3_db(vt[0].gloc, tri->v[2]->gloc, tri->v[0]->gloc, a);
        mul_v4_m4v3_db(vt[0].fbcoord, vp, vt[0].gloc);
        vt[0].index = tri->v[0]->index;

        sub_v3_v3v3_db(vv1, tri->v[2]->gloc, cam_pos);
        sub_v3_v3v3_db(vv2, cam_pos, tri->v[1]->gloc);
        dot1 = dot_v3v3_db(vv1, view_dir);
        dot2 = dot_v3v3_db(vv2, view_dir);
        a = dot1 / (dot1 + dot2);
        interp_v3_v3v3_db(vt[1].gloc, tri->v[2]->gloc, tri->v[1]->gloc, a);
        mul_v4_m4v3_db(vt[1].fbcoord, vp, vt[1].gloc);
        vt[1].index = tri->v[1]->index;

        INCREASE_EDGE
        if (allow_boundaries) {
          e->flags = LRT_EDGE_FLAG_CONTOUR;
          lineart_add_edge_to_array(&rb->pending_edges, e);
        }
        e->v1 = &vt[0];
        e->v2 = &vt[1];
        e->t1 = tri1;
        e->object_ref = ob;

        SELECT_EDGE(2, tri->v[2], &vt[0], tri1)
        SELECT_EDGE(1, tri->v[2], &vt[1], tri1)

        tri1->v[0] = &vt[0];
        tri1->v[1] = &vt[1];
        tri1->v[2] = tri->v[2];

        lineart_triangle_post(tri1, tri);

        v_count += 2;
        t_count += 1;
      }
      else if (!in1) {
        sub_v3_v3v3_db(vv1, tri->v[1]->gloc, cam_pos);
        sub_v3_v3v3_db(vv2, cam_pos, tri->v[2]->gloc);
        dot1 = dot_v3v3_db(vv1, view_dir);
        dot2 = dot_v3v3_db(vv2, view_dir);
        a = dot1 / (dot1 + dot2);
        interp_v3_v3v3_db(vt[0].gloc, tri->v[1]->gloc, tri->v[2]->gloc, a);
        mul_v4_m4v3_db(vt[0].fbcoord, vp, vt[0].gloc);
        vt[0].index = tri->v[2]->index;

        sub_v3_v3v3_db(vv1, tri->v[1]->gloc, cam_pos);
        sub_v3_v3v3_db(vv2, cam_pos, tri->v[0]->gloc);
        dot1 = dot_v3v3_db(vv1, view_dir);
        dot2 = dot_v3v3_db(vv2, view_dir);
        a = dot1 / (dot1 + dot2);
        interp_v3_v3v3_db(vt[1].gloc, tri->v[1]->gloc, tri->v[0]->gloc, a);
        mul_v4_m4v3_db(vt[1].fbcoord, vp, vt[1].gloc);
        vt[1].index = tri->v[0]->index;

        INCREASE_EDGE
        if (allow_boundaries) {
          e->flags = LRT_EDGE_FLAG_CONTOUR;
          lineart_add_edge_to_array(&rb->pending_edges, e);
        }
        e->v1 = &vt[1];
        e->v2 = &vt[0];
        e->t1 = tri1;
        e->object_ref = ob;

        SELECT_EDGE(1, tri->v[1], &vt[0], tri1)
        SELECT_EDGE(0, tri->v[1], &vt[1], tri1)

        tri1->v[0] = &vt[0];
        tri1->v[1] = tri->v[1];
        tri1->v[2] = &vt[1];

        lineart_triangle_post(tri1, tri);

        v_count += 2;
        t_count += 1;
      }
      break;
    case 1:
      /* One point behind near plane, cut those and
       * generate 2 new points, 4 lines and 2 triangles. */
      lineart_triangle_set_cull_flag(tri, LRT_CULL_USED);

      /**
       * (in0) means "when point 0 is invisible".
       * conditions for point 1, 2 are the same idea.
       * \code{.txt}
       * 0------|----------1
       *   --   |          |
       *     ---|          |
       *        |--        |
       *        |  ---     |
       *        |     ---  |
       *        |        --2
       *      (near)---------->(far)
       * Will become:
       *        |N*********1
       *        |*     *** |
       *        |*  ***    |
       *        |N**       |
       *        |  ***     |
       *        |     ***  |
       *        |        **2
       *      (near)---------->(far)
       * \endcode
       */
      if (in0) {
        /* Cut point for line 0---|------1. */
        sub_v3_v3v3_db(vv1, tri->v[1]->gloc, cam_pos);
        sub_v3_v3v3_db(vv2, cam_pos, tri->v[0]->gloc);
        dot1 = dot_v3v3_db(vv1, view_dir);
        dot2 = dot_v3v3_db(vv2, view_dir);
        a = dot2 / (dot1 + dot2);
        /* Assign to a new point. */
        interp_v3_v3v3_db(vt[0].gloc, tri->v[0]->gloc, tri->v[1]->gloc, a);
        mul_v4_m4v3_db(vt[0].fbcoord, vp, vt[0].gloc);
        vt[0].index = tri->v[0]->index;

        /* Cut point for line 0---|------2. */
        sub_v3_v3v3_db(vv1, tri->v[2]->gloc, cam_pos);
        sub_v3_v3v3_db(vv2, cam_pos, tri->v[0]->gloc);
        dot1 = dot_v3v3_db(vv1, view_dir);
        dot2 = dot_v3v3_db(vv2, view_dir);
        a = dot2 / (dot1 + dot2);
        /* Assign to other new point. */
        interp_v3_v3v3_db(vt[1].gloc, tri->v[0]->gloc, tri->v[2]->gloc, a);
        mul_v4_m4v3_db(vt[1].fbcoord, vp, vt[1].gloc);
        vt[1].index = tri->v[0]->index;

        /* New line connects two new points. */
        INCREASE_EDGE
        if (allow_boundaries) {
          e->flags = LRT_EDGE_FLAG_CONTOUR;
          lineart_add_edge_to_array(&rb->pending_edges, e);
        }
        e->v1 = &vt[1];
        e->v2 = &vt[0];
        e->t1 = tri1;
        e->object_ref = ob;

        /* New line connects new point 0 and old point 1,
         * this is a border line. */

        SELECT_EDGE(0, tri->v[1], &vt[0], tri1)
        SELECT_EDGE(2, tri->v[2], &vt[1], tri2)
        RELINK_EDGE(1, tri2)

        /* We now have one triangle closed. */
        tri1->v[0] = tri->v[1];
        tri1->v[1] = &vt[1];
        tri1->v[2] = &vt[0];
        /* Close the second triangle. */
        tri2->v[0] = &vt[1];
        tri2->v[1] = tri->v[1];
        tri2->v[2] = tri->v[2];

        lineart_triangle_post(tri1, tri);
        lineart_triangle_post(tri2, tri);

        v_count += 2;
        t_count += 2;
      }
      else if (in1) {

        sub_v3_v3v3_db(vv1, tri->v[1]->gloc, cam_pos);
        sub_v3_v3v3_db(vv2, cam_pos, tri->v[2]->gloc);
        dot1 = dot_v3v3_db(vv1, view_dir);
        dot2 = dot_v3v3_db(vv2, view_dir);
        a = dot1 / (dot1 + dot2);
        interp_v3_v3v3_db(vt[0].gloc, tri->v[1]->gloc, tri->v[2]->gloc, a);
        mul_v4_m4v3_db(vt[0].fbcoord, vp, vt[0].gloc);
        vt[0].index = tri->v[1]->index;

        sub_v3_v3v3_db(vv1, tri->v[1]->gloc, cam_pos);
        sub_v3_v3v3_db(vv2, cam_pos, tri->v[0]->gloc);
        dot1 = dot_v3v3_db(vv1, view_dir);
        dot2 = dot_v3v3_db(vv2, view_dir);
        a = dot1 / (dot1 + dot2);
        interp_v3_v3v3_db(vt[1].gloc, tri->v[1]->gloc, tri->v[0]->gloc, a);
        mul_v4_m4v3_db(vt[1].fbcoord, vp, vt[1].gloc);
        vt[1].index = tri->v[1]->index;

        INCREASE_EDGE
        if (allow_boundaries) {
          e->flags = LRT_EDGE_FLAG_CONTOUR;
          lineart_add_edge_to_array(&rb->pending_edges, e);
        }
        e->v1 = &vt[1];
        e->v2 = &vt[0];

        e->t1 = tri1;
        e->object_ref = ob;

        SELECT_EDGE(1, tri->v[2], &vt[0], tri1)
        SELECT_EDGE(0, tri->v[0], &vt[1], tri2)
        RELINK_EDGE(2, tri2)

        tri1->v[0] = tri->v[2];
        tri1->v[1] = &vt[1];
        tri1->v[2] = &vt[0];

        tri2->v[0] = &vt[1];
        tri2->v[1] = tri->v[2];
        tri2->v[2] = tri->v[0];

        lineart_triangle_post(tri1, tri);
        lineart_triangle_post(tri2, tri);

        v_count += 2;
        t_count += 2;
      }
      else if (in2) {

        sub_v3_v3v3_db(vv1, tri->v[2]->gloc, cam_pos);
        sub_v3_v3v3_db(vv2, cam_pos, tri->v[0]->gloc);
        dot1 = dot_v3v3_db(vv1, view_dir);
        dot2 = dot_v3v3_db(vv2, view_dir);
        a = dot1 / (dot1 + dot2);
        interp_v3_v3v3_db(vt[0].gloc, tri->v[2]->gloc, tri->v[0]->gloc, a);
        mul_v4_m4v3_db(vt[0].fbcoord, vp, vt[0].gloc);
        vt[0].index = tri->v[2]->index;

        sub_v3_v3v3_db(vv1, tri->v[2]->gloc, cam_pos);
        sub_v3_v3v3_db(vv2, cam_pos, tri->v[1]->gloc);
        dot1 = dot_v3v3_db(vv1, view_dir);
        dot2 = dot_v3v3_db(vv2, view_dir);
        a = dot1 / (dot1 + dot2);
        interp_v3_v3v3_db(vt[1].gloc, tri->v[2]->gloc, tri->v[1]->gloc, a);
        mul_v4_m4v3_db(vt[1].fbcoord, vp, vt[1].gloc);
        vt[1].index = tri->v[2]->index;

        INCREASE_EDGE
        if (allow_boundaries) {
          e->flags = LRT_EDGE_FLAG_CONTOUR;
          lineart_add_edge_to_array(&rb->pending_edges, e);
        }
        e->v1 = &vt[1];
        e->v2 = &vt[0];

        e->t1 = tri1;
        e->object_ref = ob;

        SELECT_EDGE(2, tri->v[0], &vt[0], tri1)
        SELECT_EDGE(1, tri->v[1], &vt[1], tri2)
        RELINK_EDGE(0, tri2)

        tri1->v[0] = tri->v[0];
        tri1->v[1] = &vt[1];
        tri1->v[2] = &vt[0];

        tri2->v[0] = &vt[1];
        tri2->v[1] = tri->v[0];
        tri2->v[2] = tri->v[1];

        lineart_triangle_post(tri1, tri);
        lineart_triangle_post(tri2, tri);

        v_count += 2;
        t_count += 2;
      }
      break;
  }
  *r_v_count = v_count;
  *r_e_count = e_count;
  *r_t_count = t_count;

#undef INCREASE_EDGE
#undef SELECT_EDGE
#undef RELINK_EDGE
#undef REMOVE_TRIANGLE_EDGE
}

/**
 * This function cuts triangles with near- or far-plane. Setting clip_far = true for cutting with
 * far-plane. For triangles that's crossing the plane, it will generate new 1 or 2 triangles with
 * new topology that represents the trimmed triangle. (which then became a triangle or a square
 * formed by two triangles)
 */
static void lineart_main_cull_triangles(LineartRenderBuffer *rb, bool clip_far)
{
  LineartTriangle *tri;
  LineartElementLinkNode *v_eln, *t_eln, *e_eln;
  double(*vp)[4] = rb->view_projection;
  int i;
  int v_count = 0, t_count = 0, e_count = 0;
  Object *ob;
  bool allow_boundaries = rb->allow_boundaries;
  double cam_pos[3];
  double clip_start = rb->near_clip, clip_end = rb->far_clip;
  double view_dir[3], clip_advance[3];

  copy_v3_v3_db(view_dir, rb->view_vector);
  copy_v3_v3_db(clip_advance, rb->view_vector);
  copy_v3_v3_db(cam_pos, rb->camera_pos);

  if (clip_far) {
    /* Move starting point to end plane. */
    mul_v3db_db(clip_advance, -clip_end);
    add_v3_v3_db(cam_pos, clip_advance);

    /* "reverse looking". */
    mul_v3db_db(view_dir, -1.0f);
  }
  else {
    /* Clip Near. */
    mul_v3db_db(clip_advance, -clip_start);
    add_v3_v3_db(cam_pos, clip_advance);
  }

  v_eln = lineart_memory_get_vert_space(rb);
  t_eln = lineart_memory_get_triangle_space(rb);
  e_eln = lineart_memory_get_edge_space(rb);

  /* Additional memory space for storing generated points and triangles. */
#define LRT_CULL_ENSURE_MEMORY \
  if (v_count > 60) { \
    v_eln->element_count = v_count; \
    v_eln = lineart_memory_get_vert_space(rb); \
    v_count = 0; \
  } \
  if (t_count > 60) { \
    t_eln->element_count = t_count; \
    t_eln = lineart_memory_get_triangle_space(rb); \
    t_count = 0; \
  } \
  if (e_count > 60) { \
    e_eln->element_count = e_count; \
    e_eln = lineart_memory_get_edge_space(rb); \
    e_count = 0; \
  }

#define LRT_CULL_DECIDE_INSIDE \
  /* These three represents points that are in the clipping range or not. */ \
  in0 = 0, in1 = 0, in2 = 0; \
  if (clip_far) { \
    /* Point outside far plane. */ \
    if (tri->v[0]->fbcoord[use_w] > clip_end) { \
      in0 = 1; \
    } \
    if (tri->v[1]->fbcoord[use_w] > clip_end) { \
      in1 = 1; \
    } \
    if (tri->v[2]->fbcoord[use_w] > clip_end) { \
      in2 = 1; \
    } \
  } \
  else { \
    /* Point inside near plane. */ \
    if (tri->v[0]->fbcoord[use_w] < clip_start) { \
      in0 = 1; \
    } \
    if (tri->v[1]->fbcoord[use_w] < clip_start) { \
      in1 = 1; \
    } \
    if (tri->v[2]->fbcoord[use_w] < clip_start) { \
      in2 = 1; \
    } \
  }

  int use_w = 3;
  int in0 = 0, in1 = 0, in2 = 0;

  if (!rb->cam_is_persp) {
    clip_start = -1;
    clip_end = 1;
    use_w = 2;
  }

  /* Then go through all the other triangles. */
  LISTBASE_FOREACH (LineartElementLinkNode *, eln, &rb->triangle_buffer_pointers) {
    if (eln->flags & LRT_ELEMENT_IS_ADDITIONAL) {
      continue;
    }
    ob = eln->object_ref;
    for (i = 0; i < eln->element_count; i++) {
      /* Select the triangle in the array. */
      tri = (void *)(((uchar *)eln->pointer) + rb->triangle_size * i);

      if (tri->flags & LRT_CULL_DISCARD) {
        continue;
      }

      LRT_CULL_DECIDE_INSIDE
      LRT_CULL_ENSURE_MEMORY
      lineart_triangle_cull_single(rb,
                                   tri,
                                   in0,
                                   in1,
                                   in2,
                                   cam_pos,
                                   view_dir,
                                   allow_boundaries,
                                   vp,
                                   ob,
                                   &v_count,
                                   &e_count,
                                   &t_count,
                                   v_eln,
                                   e_eln,
                                   t_eln);
    }
    t_eln->element_count = t_count;
    v_eln->element_count = v_count;
  }

#undef LRT_CULL_ENSURE_MEMORY
#undef LRT_CULL_DECIDE_INSIDE
}

/**
 * Adjacent data is only used during the initial stages of computing.
 * So we can free it using this function when it is not needed anymore.
 */
static void lineart_main_free_adjacent_data(LineartRenderBuffer *rb)
{
  LinkData *ld;
  while ((ld = BLI_pophead(&rb->triangle_adjacent_pointers)) != NULL) {
    MEM_freeN(ld->data);
  }
  LISTBASE_FOREACH (LineartElementLinkNode *, eln, &rb->triangle_buffer_pointers) {
    LineartTriangle *tri = eln->pointer;
    int i;
    for (i = 0; i < eln->element_count; i++) {
      /* See definition of tri->intersecting_verts and the usage in
       * lineart_geometry_object_load() for detailed. */
      tri->intersecting_verts = NULL;
      tri = (LineartTriangle *)(((uchar *)tri) + rb->triangle_size);
    }
  }
}

static void lineart_main_perspective_division(LineartRenderBuffer *rb)
{
  LineartVert *vt;
  int i;

  LISTBASE_FOREACH (LineartElementLinkNode *, eln, &rb->vertex_buffer_pointers) {
    vt = eln->pointer;
    for (i = 0; i < eln->element_count; i++) {
      if (rb->cam_is_persp) {
        /* Do not divide Z, we use Z to back transform cut points in later chaining process. */
        vt[i].fbcoord[0] /= vt[i].fbcoord[3];
        vt[i].fbcoord[1] /= vt[i].fbcoord[3];
        /* Re-map z into (0-1) range, because we no longer need NDC (Normalized Device Coordinates)
         * at the moment.
         * The algorithm currently doesn't need Z for operation, we use W instead. If Z is needed
         * in the future, the line below correctly transforms it to view space coordinates. */
        // `vt[i].fbcoord[2] = -2 * vt[i].fbcoord[2] / (far - near) - (far + near) / (far - near);
      }
      /* Shifting is always needed. */
      vt[i].fbcoord[0] -= rb->shift_x * 2;
      vt[i].fbcoord[1] -= rb->shift_y * 2;
    }
  }
}

static void lineart_main_discard_out_of_frame_edges(LineartRenderBuffer *rb)
{
  LineartEdge *e;
  int i;

#define LRT_VERT_OUT_OF_BOUND(v) \
  (v && (v->fbcoord[0] < -1 || v->fbcoord[0] > 1 || v->fbcoord[1] < -1 || v->fbcoord[1] > 1))

  LISTBASE_FOREACH (LineartElementLinkNode *, eln, &rb->line_buffer_pointers) {
    e = (LineartEdge *)eln->pointer;
    for (i = 0; i < eln->element_count; i++) {
      if ((LRT_VERT_OUT_OF_BOUND(e[i].v1) && LRT_VERT_OUT_OF_BOUND(e[i].v2))) {
        e[i].flags = LRT_EDGE_FLAG_CHAIN_PICKED;
      }
    }
  }
}

typedef struct LineartEdgeNeighbor {
  int e;
  uint16_t flags;
  int v1, v2;
} LineartEdgeNeighbor;

typedef struct VertData {
  MVert *mvert;
  LineartVert *v_arr;
  double (*model_view)[4];
  double (*model_view_proj)[4];
} VertData;

static void lineart_mvert_transform_task(void *__restrict userdata,
                                         const int i,
                                         const TaskParallelTLS *__restrict UNUSED(tls))
{
  VertData *vert_task_data = (VertData *)userdata;
  MVert *m_v = &vert_task_data->mvert[i];
  double co[4];
  LineartVert *v = &vert_task_data->v_arr[i];
  copy_v3db_v3fl(co, m_v->co);
  mul_v3_m4v3_db(v->gloc, vert_task_data->model_view, co);
  mul_v4_m4v3_db(v->fbcoord, vert_task_data->model_view_proj, co);
  v->index = i;
}

#define LRT_EDGE_FLAG_TYPE_MAX_BITS 6

static int lineart_edge_type_duplication_count(char eflag)
{
  int count = 0;
  /* See eLineartEdgeFlag for details. */
  for (int i = 0; i < LRT_EDGE_FLAG_TYPE_MAX_BITS; i++) {
    if (eflag & (1 << i)) {
      count++;
    }
  }
  return count;
}

/**
 * Because we have a variable size for #LineartTriangle, we need an access helper.
 * See #LineartTriangleThread for more info.
 */
static LineartTriangle *lineart_triangle_from_index(LineartRenderBuffer *rb,
                                                    LineartTriangle *rt_array,
                                                    int index)
{
  char *b = (char *)rt_array;
  b += (index * rb->triangle_size);
  return (LineartTriangle *)b;
}

typedef struct EdgeFeatData {
  LineartRenderBuffer *rb;
  Mesh *me;
  const MLoopTri *mlooptri;
  LineartTriangle *tri_array;
  LineartVert *v_array;
  float crease_threshold;
  bool use_auto_smooth;
  bool use_freestyle_face;
  int freestyle_face_index;
  bool use_freestyle_edge;
  int freestyle_edge_index;
  LineartEdgeNeighbor *edge_nabr;
} EdgeFeatData;

typedef struct EdgeFeatReduceData {
  int feat_edges;
} EdgeFeatReduceData;

static void feat_data_sum_reduce(const void *__restrict UNUSED(userdata),
                                 void *__restrict chunk_join,
                                 void *__restrict chunk)
{
  EdgeFeatReduceData *feat_chunk_join = (EdgeFeatReduceData *)chunk_join;
  EdgeFeatReduceData *feat_chunk = (EdgeFeatReduceData *)chunk;
  feat_chunk_join->feat_edges += feat_chunk->feat_edges;
}

static void lineart_identify_mlooptri_feature_edges(void *__restrict userdata,
                                                    const int i,
                                                    const TaskParallelTLS *__restrict tls)
{
  EdgeFeatData *e_feat_data = (EdgeFeatData *)userdata;
  EdgeFeatReduceData *reduce_data = (EdgeFeatReduceData *)tls->userdata_chunk;
  Mesh *me = e_feat_data->me;
  LineartEdgeNeighbor *edge_nabr = e_feat_data->edge_nabr;
  const MLoopTri *mlooptri = e_feat_data->mlooptri;

  uint16_t edge_flag_result = 0;

  /* Because the edge neighbor array contains loop edge pairs, we only need to process the first
   * edge in the pair. Otherwise we would add the same edge that the loops represent twice. */
  if (i < edge_nabr[i].e) {
    return;
  }

  bool face_mark_filtered = false;
  bool enable_face_mark = (e_feat_data->use_freestyle_face && e_feat_data->rb->filter_face_mark);
  bool only_contour = false;
  if (enable_face_mark) {
    FreestyleFace *ff1, *ff2;
    int index = e_feat_data->freestyle_face_index;
    if (index > -1) {
      ff1 = &((FreestyleFace *)me->pdata.layers[index].data)[mlooptri[i / 3].poly];
    }
    if (edge_nabr[i].e > -1) {
      ff2 = &((FreestyleFace *)me->pdata.layers[index].data)[mlooptri[edge_nabr[i].e / 3].poly];
    }
    else {
      /* Handle mesh boundary cases: We want mesh boundaries to respect
       * `filter_face_mark_boundaries` option the same way as face mark boundaries, and the code
       * path is simper when it's assuming both ff1 and ff2 not NULL. */
      ff2 = ff1;
    }
    if (e_feat_data->rb->filter_face_mark_boundaries ^ e_feat_data->rb->filter_face_mark_invert) {
      if ((ff1->flag & FREESTYLE_FACE_MARK) || (ff2->flag & FREESTYLE_FACE_MARK)) {
        face_mark_filtered = true;
      }
    }
    else {
      if ((ff1->flag & FREESTYLE_FACE_MARK) && (ff2->flag & FREESTYLE_FACE_MARK) && (ff2 != ff1)) {
        face_mark_filtered = true;
      }
    }
    if (e_feat_data->rb->filter_face_mark_invert) {
      face_mark_filtered = !face_mark_filtered;
    }
    if (!face_mark_filtered) {
      edge_nabr[i].flags = LRT_EDGE_FLAG_INHIBIT;
      if (e_feat_data->rb->filter_face_mark_keep_contour) {
        only_contour = true;
      }
    }
  }

  if (enable_face_mark && !face_mark_filtered && !only_contour) {
    return;
  }

  /* Mesh boundary */
  if (edge_nabr[i].e == -1) {
    edge_nabr[i].flags = LRT_EDGE_FLAG_CONTOUR;
    reduce_data->feat_edges += 1;
    return;
  }

  LineartTriangle *tri1, *tri2;
  LineartVert *vert;
  LineartRenderBuffer *rb = e_feat_data->rb;

  int f1 = i / 3, f2 = edge_nabr[i].e / 3;

  /* The mesh should already be triangulated now, so we can assume each face is a triangle. */
  tri1 = lineart_triangle_from_index(rb, e_feat_data->tri_array, f1);
  tri2 = lineart_triangle_from_index(rb, e_feat_data->tri_array, f2);

  vert = &e_feat_data->v_array[edge_nabr[i].v1];

  double view_vector_persp[3];
  double *view_vector = view_vector_persp;
  double dot_1 = 0, dot_2 = 0;
  double result;
  bool material_back_face = ((tri1->flags | tri2->flags) & LRT_TRIANGLE_MAT_BACK_FACE_CULLING);

  if (rb->use_contour || rb->use_back_face_culling || material_back_face) {
    if (rb->cam_is_persp) {
      sub_v3_v3v3_db(view_vector, rb->camera_pos, vert->gloc);
    }
    else {
      view_vector = rb->view_vector;
    }

    dot_1 = dot_v3v3_db(view_vector, tri1->gn);
    dot_2 = dot_v3v3_db(view_vector, tri2->gn);

    if ((result = dot_1 * dot_2) <= 0 && (dot_1 + dot_2)) {
      edge_flag_result |= LRT_EDGE_FLAG_CONTOUR;
    }

    if (rb->use_back_face_culling) {
      if (dot_1 < 0) {
        tri1->flags |= LRT_CULL_DISCARD;
      }
      if (dot_2 < 0) {
        tri2->flags |= LRT_CULL_DISCARD;
      }
    }
    if (material_back_face) {
      if (tri1->flags & LRT_TRIANGLE_MAT_BACK_FACE_CULLING && dot_1 < 0) {
        tri1->flags |= LRT_CULL_DISCARD;
      }
      if (tri2->flags & LRT_TRIANGLE_MAT_BACK_FACE_CULLING && dot_2 < 0) {
        tri2->flags |= LRT_CULL_DISCARD;
      }
    }
  }

  if (!only_contour) {

    if (rb->use_crease) {
      bool do_crease = true;
      if (!rb->force_crease && !e_feat_data->use_auto_smooth &&
          (me->mpoly[mlooptri[f1].poly].flag & ME_SMOOTH) &&
          (me->mpoly[mlooptri[f2].poly].flag & ME_SMOOTH)) {
        do_crease = false;
      }
      if (do_crease && (dot_v3v3_db(tri1->gn, tri2->gn) < e_feat_data->crease_threshold)) {
        edge_flag_result |= LRT_EDGE_FLAG_CREASE;
      }
    }

    int mat1 = me->mpoly[mlooptri[f1].poly].mat_nr;
    int mat2 = me->mpoly[mlooptri[f2].poly].mat_nr;

    if (rb->use_material && mat1 != mat2) {
      edge_flag_result |= LRT_EDGE_FLAG_MATERIAL;
    }
  }
  else {                     /* only_contour */
    if (!edge_flag_result) { /* Other edge types inhibited */
      return;
    }
  }

  int real_edges[3];
  BKE_mesh_looptri_get_real_edges(me, &mlooptri[i / 3], real_edges);

  if (real_edges[i % 3] >= 0) {
    MEdge *medge = &me->medge[real_edges[i % 3]];

    if (rb->use_crease && rb->sharp_as_crease && (medge->flag & ME_SHARP)) {
      edge_flag_result |= LRT_EDGE_FLAG_CREASE;
    }

    if (rb->use_edge_marks && e_feat_data->use_freestyle_edge) {
      FreestyleEdge *fe;
      int index = e_feat_data->freestyle_edge_index;
      fe = &((FreestyleEdge *)me->edata.layers[index].data)[real_edges[i % 3]];
      if (fe->flag & FREESTYLE_EDGE_MARK) {
        edge_flag_result |= LRT_EDGE_FLAG_EDGE_MARK;
      }
    }
  }

  edge_nabr[i].flags = edge_flag_result;

  if (edge_flag_result) {
    /* Only allocate for feature edge (instead of all edges) to save memory.
     * If allow duplicated edges, one edge gets added multiple times if it has multiple types.
     */
    reduce_data->feat_edges += e_feat_data->rb->allow_duplicated_types ?
                                   lineart_edge_type_duplication_count(edge_flag_result) :
                                   1;
  }
}

typedef struct LooseEdgeData {
  int loose_count;
  int loose_max;
  MEdge **loose_array;
  Mesh *me;
} LooseEdgeData;

static void lineart_loose_data_reallocate(LooseEdgeData *loose_data, int count)
{
  MEdge **new_arr = MEM_callocN(sizeof(MEdge *) * count, "loose edge array");
  if (loose_data->loose_array) {
    memcpy(new_arr, loose_data->loose_array, sizeof(MEdge *) * loose_data->loose_max);
    MEM_freeN(loose_data->loose_array);
  }
  loose_data->loose_max = count;
  loose_data->loose_array = new_arr;
}

static void lineart_join_loose_edge_arr(LooseEdgeData *loose_data, LooseEdgeData *to_be_joined)
{
  if (!to_be_joined->loose_array) {
    return;
  }
  int new_count = loose_data->loose_count + to_be_joined->loose_count;
  if (new_count >= loose_data->loose_max) {
    lineart_loose_data_reallocate(loose_data, new_count);
  }
  memcpy(&loose_data->loose_array[loose_data->loose_count],
         to_be_joined->loose_array,
         sizeof(MEdge *) * to_be_joined->loose_count);
  loose_data->loose_count += to_be_joined->loose_count;
  MEM_freeN(to_be_joined->loose_array);
  to_be_joined->loose_array = NULL;
}

static void lineart_add_loose_edge(LooseEdgeData *loose_data, MEdge *e)
{
  if (loose_data->loose_count >= loose_data->loose_max) {
    int min_amount = MAX2(100, loose_data->loose_count * 2);
    lineart_loose_data_reallocate(loose_data, min_amount);
  }
  loose_data->loose_array[loose_data->loose_count] = e;
  loose_data->loose_count++;
}

static void lineart_identify_loose_edges(void *__restrict UNUSED(userdata),
                                         const int i,
                                         const TaskParallelTLS *__restrict tls)
{
  LooseEdgeData *loose_data = (LooseEdgeData *)tls->userdata_chunk;
  Mesh *me = loose_data->me;

  if (me->medge[i].flag & ME_LOOSEEDGE) {
    lineart_add_loose_edge(loose_data, &me->medge[i]);
  }
}

static void loose_data_sum_reduce(const void *__restrict UNUSED(userdata),
                                  void *__restrict chunk_join,
                                  void *__restrict chunk)
{
  LooseEdgeData *final = (LooseEdgeData *)chunk_join;
  LooseEdgeData *loose_chunk = (LooseEdgeData *)chunk;
  lineart_join_loose_edge_arr(final, loose_chunk);
}

static void lineart_add_edge_to_array(LineartPendingEdges *pe, LineartEdge *e)
{
  if (pe->next >= pe->max || !pe->max) {
    if (!pe->max) {
      pe->max = 1000;
    }

    LineartEdge **new_array = MEM_mallocN(sizeof(LineartEdge *) * pe->max * 2,
                                          "LineartPendingEdges array");
    if (LIKELY(pe->array)) {
      memcpy(new_array, pe->array, sizeof(LineartEdge *) * pe->max);
      MEM_freeN(pe->array);
    }
    pe->max *= 2;
    pe->array = new_array;
  }
  pe->array[pe->next] = e;
  pe->next++;
}

static void lineart_add_edge_to_array_thread(LineartObjectInfo *obi, LineartEdge *e)
{
  lineart_add_edge_to_array(&obi->pending_edges, e);
}

/* Note: For simplicity, this function doesn't actually do anything if you already have data in
 * #pe.  */
static void lineart_finalize_object_edge_array_reserve(LineartPendingEdges *pe, int count)
{
  if (pe->max || pe->array) {
    return;
  }

  pe->max = count;
  LineartEdge **new_array = MEM_mallocN(sizeof(LineartEdge *) * pe->max,
                                        "LineartPendingEdges array final");
  pe->array = new_array;
}

static void lineart_finalize_object_edge_array(LineartPendingEdges *pe, LineartObjectInfo *obi)
{
  /* In case of line art "occlusion only" or contour not enabled, it's possible for an object to
   * not produce any feature lines. */
  if (!obi->pending_edges.array) {
    return;
  }
  memcpy(&pe->array[pe->next],
         obi->pending_edges.array,
         sizeof(LineartEdge *) * obi->pending_edges.next);
  MEM_freeN(obi->pending_edges.array);
  pe->next += obi->pending_edges.next;
}

static void lineart_triangle_adjacent_assign(LineartTriangle *tri,
                                             LineartTriangleAdjacent *ta,
                                             LineartEdge *e)
{
  if (lineart_edge_match(tri, e, 0, 1)) {
    ta->e[0] = e;
  }
  else if (lineart_edge_match(tri, e, 1, 2)) {
    ta->e[1] = e;
  }
  else if (lineart_edge_match(tri, e, 2, 0)) {
    ta->e[2] = e;
  }
}

typedef struct TriData {
  LineartObjectInfo *ob_info;
  const MLoopTri *mlooptri;
  LineartVert *vert_arr;
  LineartTriangle *tri_arr;
  int lineart_triangle_size;
  LineartTriangleAdjacent *tri_adj;
} TriData;

static void lineart_load_tri_task(void *__restrict userdata,
                                  const int i,
                                  const TaskParallelTLS *__restrict UNUSED(tls))
{
  TriData *tri_task_data = (TriData *)userdata;
  Mesh *me = tri_task_data->ob_info->original_me;
  LineartObjectInfo *ob_info = tri_task_data->ob_info;
  const MLoopTri *mlooptri = &tri_task_data->mlooptri[i];
  LineartVert *vert_arr = tri_task_data->vert_arr;
  LineartTriangle *tri = tri_task_data->tri_arr;

  tri = (LineartTriangle *)(((uchar *)tri) + tri_task_data->lineart_triangle_size * i);

  int v1 = me->mloop[mlooptri->tri[0]].v;
  int v2 = me->mloop[mlooptri->tri[1]].v;
  int v3 = me->mloop[mlooptri->tri[2]].v;

  tri->v[0] = &vert_arr[v1];
  tri->v[1] = &vert_arr[v2];
  tri->v[2] = &vert_arr[v3];

  /* Material mask bits and occlusion effectiveness assignment. */
  Material *mat = BKE_object_material_get(ob_info->original_ob,
                                          me->mpoly[mlooptri->poly].mat_nr + 1);
  tri->material_mask_bits |= ((mat && (mat->lineart.flags & LRT_MATERIAL_MASK_ENABLED)) ?
                                  mat->lineart.material_mask_bits :
                                  0);
  tri->mat_occlusion |= (mat ? mat->lineart.mat_occlusion : 1);
  tri->flags |= (mat && (mat->blend_flag & MA_BL_CULL_BACKFACE)) ?
                    LRT_TRIANGLE_MAT_BACK_FACE_CULLING :
                    0;

  tri->intersection_mask = ob_info->override_intersection_mask;

  double gn[3];
  float no[3];
  normal_tri_v3(no, me->mvert[v1].co, me->mvert[v2].co, me->mvert[v3].co);
  copy_v3db_v3fl(gn, no);
  mul_v3_mat3_m4v3_db(tri->gn, ob_info->normal, gn);
  normalize_v3_db(tri->gn);

  if (ob_info->usage == OBJECT_LRT_INTERSECTION_ONLY) {
    tri->flags |= LRT_TRIANGLE_INTERSECTION_ONLY;
  }
  else if (ob_info->usage == OBJECT_LRT_NO_INTERSECTION ||
           ob_info->usage == OBJECT_LRT_OCCLUSION_ONLY) {
    tri->flags |= LRT_TRIANGLE_NO_INTERSECTION;
  }

  /* Re-use this field to refer to adjacent info, will be cleared after culling stage. */
  tri->intersecting_verts = (void *)&tri_task_data->tri_adj[i];
}
typedef struct EdgeNeighborData {
  LineartEdgeNeighbor *edge_nabr;
  LineartAdjacentEdge *adj_e;
  MLoopTri *mlooptri;
  MLoop *mloop;
} EdgeNeighborData;

static void lineart_edge_neighbor_init_task(void *__restrict userdata,
                                            const int i,
                                            const TaskParallelTLS *__restrict UNUSED(tls))
{
  EdgeNeighborData *en_data = (EdgeNeighborData *)userdata;
  LineartAdjacentEdge *adj_e = &en_data->adj_e[i];
  MLoopTri *looptri = &en_data->mlooptri[i / 3];
  LineartEdgeNeighbor *edge_nabr = &en_data->edge_nabr[i];
  MLoop *mloop = en_data->mloop;

  adj_e->e = i;
  adj_e->v1 = mloop[looptri->tri[i % 3]].v;
  adj_e->v2 = mloop[looptri->tri[(i + 1) % 3]].v;
  if (adj_e->v1 > adj_e->v2) {
    SWAP(unsigned int, adj_e->v1, adj_e->v2);
  }
  edge_nabr->e = -1;

  edge_nabr->v1 = adj_e->v1;
  edge_nabr->v2 = adj_e->v2;
  edge_nabr->flags = 0;
}

static LineartEdgeNeighbor *lineart_build_edge_neighbor(Mesh *me, int total_edges)
{
  /* Because the mesh is triangulated, so `me->totedge` should be reliable? */
  LineartAdjacentEdge *adj_e = MEM_mallocN(sizeof(LineartAdjacentEdge) * total_edges,
                                           "LineartAdjacentEdge arr");
  LineartEdgeNeighbor *edge_nabr = MEM_mallocN(sizeof(LineartEdgeNeighbor) * total_edges,
                                               "LineartEdgeNeighbor arr");

  MLoopTri *mlooptri = me->runtime.looptris.array;

  TaskParallelSettings en_settings;
  BLI_parallel_range_settings_defaults(&en_settings);
  /* Set the minimum amount of edges a thread has to process. */
  en_settings.min_iter_per_thread = 50000;

  EdgeNeighborData en_data;
  en_data.adj_e = adj_e;
  en_data.edge_nabr = edge_nabr;
  en_data.mlooptri = mlooptri;
  en_data.mloop = me->mloop;

  BLI_task_parallel_range(0, total_edges, &en_data, lineart_edge_neighbor_init_task, &en_settings);

  lineart_sort_adjacent_items(adj_e, total_edges);

  for (int i = 0; i < total_edges - 1; i++) {
    if (adj_e[i].v1 == adj_e[i + 1].v1 && adj_e[i].v2 == adj_e[i + 1].v2) {
      edge_nabr[adj_e[i].e].e = adj_e[i + 1].e;
      edge_nabr[adj_e[i + 1].e].e = adj_e[i].e;
    }
  }

  MEM_freeN(adj_e);

  return edge_nabr;
}

static void lineart_geometry_object_load(LineartObjectInfo *ob_info, LineartRenderBuffer *re_buf)
{
  LineartElementLinkNode *elem_link_node;
  LineartVert *la_v_arr;
  LineartEdge *la_edge_arr;
  LineartEdgeSegment *la_seg_arr;
  LineartTriangle *la_tri_arr;

  Mesh *me = ob_info->original_me;

  if (!me->totedge) {
    return;
  }

  /* Triangulate. */
  const MLoopTri *mlooptri = BKE_mesh_runtime_looptri_ensure(me);
  const int tot_tri = BKE_mesh_runtime_looptri_len(me);

  /* Check if we should look for custom data tags like Freestyle edges or faces. */
  bool can_find_freestyle_edge = false;
  int layer_index = CustomData_get_active_layer_index(&me->edata, CD_FREESTYLE_EDGE);
  if (layer_index != -1) {
    can_find_freestyle_edge = true;
  }

  bool can_find_freestyle_face = false;
  layer_index = CustomData_get_active_layer_index(&me->pdata, CD_FREESTYLE_FACE);
  if (layer_index != -1) {
    can_find_freestyle_face = true;
  }

  /* If we allow duplicated edges, one edge should get added multiple times if is has been
   * classified as more than one edge type. This is so we can create multiple different line type
   * chains containing the same edge. */
  la_v_arr = lineart_mem_acquire_thread(&re_buf->render_data_pool,
                                        sizeof(LineartVert) * me->totvert);
  la_tri_arr = lineart_mem_acquire_thread(&re_buf->render_data_pool,
                                          tot_tri * re_buf->triangle_size);

  Object *orig_ob = ob_info->original_ob;

  BLI_spin_lock(&re_buf->lock_task);
  elem_link_node = lineart_list_append_pointer_pool_sized_thread(&re_buf->vertex_buffer_pointers,
                                                                 &re_buf->render_data_pool,
                                                                 la_v_arr,
                                                                 sizeof(LineartElementLinkNode));
  BLI_spin_unlock(&re_buf->lock_task);

  elem_link_node->element_count = me->totvert;
  elem_link_node->object_ref = orig_ob;
  ob_info->v_eln = elem_link_node;

  bool use_auto_smooth = false;
  float crease_angle = 0;
  if (orig_ob->lineart.flags & OBJECT_LRT_OWN_CREASE) {
    crease_angle = cosf(M_PI - orig_ob->lineart.crease_threshold);
  }
  else if (ob_info->original_me->flag & ME_AUTOSMOOTH) {
    crease_angle = cosf(ob_info->original_me->smoothresh);
    use_auto_smooth = true;
  }
  else {
    crease_angle = re_buf->crease_threshold;
  }

  /* FIXME(Yiming): Hack for getting clean 3D text, the seam that extruded text object creates
   * erroneous detection on creases. Future configuration should allow options. */
  if (orig_ob->type == OB_FONT) {
    elem_link_node->flags |= LRT_ELEMENT_BORDER_ONLY;
  }

  BLI_spin_lock(&re_buf->lock_task);
  elem_link_node = lineart_list_append_pointer_pool_sized_thread(&re_buf->triangle_buffer_pointers,
                                                                 &re_buf->render_data_pool,
                                                                 la_tri_arr,
                                                                 sizeof(LineartElementLinkNode));
  BLI_spin_unlock(&re_buf->lock_task);

  int usage = ob_info->usage;

  elem_link_node->element_count = tot_tri;
  elem_link_node->object_ref = orig_ob;
  elem_link_node->flags |= (usage == OBJECT_LRT_NO_INTERSECTION ? LRT_ELEMENT_NO_INTERSECTION : 0);

  /* Note this memory is not from pool, will be deleted after culling. */
  LineartTriangleAdjacent *tri_adj = MEM_callocN(sizeof(LineartTriangleAdjacent) * tot_tri,
                                                 "LineartTriangleAdjacent");
  /* Link is minimal so we use pool anyway. */
  BLI_spin_lock(&re_buf->lock_task);
  lineart_list_append_pointer_pool_thread(
      &re_buf->triangle_adjacent_pointers, &re_buf->render_data_pool, tri_adj);
  BLI_spin_unlock(&re_buf->lock_task);

  /* Convert all vertices to lineart verts. */
  TaskParallelSettings vert_settings;
  BLI_parallel_range_settings_defaults(&vert_settings);
  /* Set the minimum amount of verts a thread has to process. */
  vert_settings.min_iter_per_thread = 4000;

  VertData vert_data;
  vert_data.mvert = me->mvert;
  vert_data.v_arr = la_v_arr;
  vert_data.model_view = ob_info->model_view;
  vert_data.model_view_proj = ob_info->model_view_proj;

  BLI_task_parallel_range(
      0, me->totvert, &vert_data, lineart_mvert_transform_task, &vert_settings);

  /* Convert all mesh triangles into lineart triangles.
   * Also create an edge map to get connectivity between edges and triangles. */
  TaskParallelSettings tri_settings;
  BLI_parallel_range_settings_defaults(&tri_settings);
  /* Set the minimum amount of triangles a thread has to process. */
  tri_settings.min_iter_per_thread = 4000;

  TriData tri_data;
  tri_data.ob_info = ob_info;
  tri_data.mlooptri = mlooptri;
  tri_data.vert_arr = la_v_arr;
  tri_data.tri_arr = la_tri_arr;
  tri_data.lineart_triangle_size = re_buf->triangle_size;
  tri_data.tri_adj = tri_adj;

  unsigned int total_edges = tot_tri * 3;

  BLI_task_parallel_range(0, tot_tri, &tri_data, lineart_load_tri_task, &tri_settings);

  /* Check for contour lines in the mesh.
   * IE check if the triangle edges lies in area where the triangles go from front facing to back
   * facing.
   */
  EdgeFeatReduceData edge_reduce = {0};
  TaskParallelSettings edge_feat_settings;
  BLI_parallel_range_settings_defaults(&edge_feat_settings);
  /* Set the minimum amount of edges a thread has to process. */
  edge_feat_settings.min_iter_per_thread = 4000;
  edge_feat_settings.userdata_chunk = &edge_reduce;
  edge_feat_settings.userdata_chunk_size = sizeof(EdgeFeatReduceData);
  edge_feat_settings.func_reduce = feat_data_sum_reduce;

  EdgeFeatData edge_feat_data = {0};
  edge_feat_data.rb = re_buf;
  edge_feat_data.me = me;
  edge_feat_data.mlooptri = mlooptri;
  edge_feat_data.edge_nabr = lineart_build_edge_neighbor(me, total_edges);
  edge_feat_data.tri_array = la_tri_arr;
  edge_feat_data.v_array = la_v_arr;
  edge_feat_data.crease_threshold = crease_angle;
  edge_feat_data.use_auto_smooth = use_auto_smooth;
  edge_feat_data.use_freestyle_face = can_find_freestyle_face;
  edge_feat_data.use_freestyle_edge = can_find_freestyle_edge;
  if (edge_feat_data.use_freestyle_face) {
    edge_feat_data.freestyle_face_index = CustomData_get_layer_index(&me->pdata,
                                                                     CD_FREESTYLE_FACE);
  }
  if (edge_feat_data.use_freestyle_edge) {
    edge_feat_data.freestyle_edge_index = CustomData_get_layer_index(&me->edata,
                                                                     CD_FREESTYLE_EDGE);
  }

  BLI_task_parallel_range(0,
                          total_edges,
                          &edge_feat_data,
                          lineart_identify_mlooptri_feature_edges,
                          &edge_feat_settings);

  LooseEdgeData loose_data = {0};
  if (re_buf->use_loose) {
    /* Only identifying floating edges at this point because other edges has been taken care of
     * inside #lineart_identify_mlooptri_feature_edges function. */
    TaskParallelSettings edge_loose_settings;
    BLI_parallel_range_settings_defaults(&edge_loose_settings);
    edge_loose_settings.min_iter_per_thread = 4000;
    edge_loose_settings.func_reduce = loose_data_sum_reduce;
    edge_loose_settings.userdata_chunk = &loose_data;
    edge_loose_settings.userdata_chunk_size = sizeof(LooseEdgeData);
    loose_data.me = me;
    BLI_task_parallel_range(
        0, me->totedge, &loose_data, lineart_identify_loose_edges, &edge_loose_settings);
  }

  int allocate_la_e = edge_reduce.feat_edges + loose_data.loose_count;

  la_edge_arr = lineart_mem_acquire_thread(&re_buf->render_data_pool,
                                           sizeof(LineartEdge) * allocate_la_e);
  la_seg_arr = lineart_mem_acquire_thread(&re_buf->render_data_pool,
                                          sizeof(LineartEdgeSegment) * allocate_la_e);
  BLI_spin_lock(&re_buf->lock_task);
  elem_link_node = lineart_list_append_pointer_pool_sized_thread(&re_buf->line_buffer_pointers,
                                                                 &re_buf->render_data_pool,
                                                                 la_edge_arr,
                                                                 sizeof(LineartElementLinkNode));
  BLI_spin_unlock(&re_buf->lock_task);
  elem_link_node->element_count = allocate_la_e;
  elem_link_node->object_ref = orig_ob;

  /* Start of the edge/seg arr */
  LineartEdge *la_edge;
  LineartEdgeSegment *la_seg;
  la_edge = la_edge_arr;
  la_seg = la_seg_arr;

  for (int i = 0; i < total_edges; i++) {
    LineartEdgeNeighbor *edge_nabr = &edge_feat_data.edge_nabr[i];

    if (i < edge_nabr->e) {
      continue;
    }

    /* Not a feature line, so we skip. */
    if (edge_nabr->flags == 0) {
      continue;
    }

    LineartEdge *edge_added = NULL;

    /* See eLineartEdgeFlag for details. */
    for (int flag_bit = 0; flag_bit < LRT_EDGE_FLAG_TYPE_MAX_BITS; flag_bit++) {
      char use_type = 1 << flag_bit;
      if (!(use_type & edge_nabr->flags)) {
        continue;
      }

      la_edge->v1 = &la_v_arr[edge_nabr->v1];
      la_edge->v2 = &la_v_arr[edge_nabr->v2];
      int findex = i / 3;
      la_edge->t1 = lineart_triangle_from_index(re_buf, la_tri_arr, findex);
      if (!edge_added) {
        lineart_triangle_adjacent_assign(la_edge->t1, &tri_adj[findex], la_edge);
      }
      if (edge_nabr->e != -1) {
        findex = edge_nabr->e / 3;
        la_edge->t2 = lineart_triangle_from_index(re_buf, la_tri_arr, findex);
        if (!edge_added) {
          lineart_triangle_adjacent_assign(la_edge->t2, &tri_adj[findex], la_edge);
        }
      }
      la_edge->flags = use_type;
      la_edge->object_ref = orig_ob;
      BLI_addtail(&la_edge->segments, la_seg);
      if (usage == OBJECT_LRT_INHERIT || usage == OBJECT_LRT_INCLUDE ||
          usage == OBJECT_LRT_NO_INTERSECTION) {
        lineart_add_edge_to_array_thread(ob_info, la_edge);
      }

      if (edge_added) {
        edge_added->flags |= LRT_EDGE_FLAG_NEXT_IS_DUPLICATION;
      }

      edge_added = la_edge;

      la_edge++;
      la_seg++;

      if (!re_buf->allow_duplicated_types) {
        break;
      }
    }
  }

  if (loose_data.loose_array) {
    for (int i = 0; i < loose_data.loose_count; i++) {
      la_edge->v1 = &la_v_arr[loose_data.loose_array[i]->v1];
      la_edge->v2 = &la_v_arr[loose_data.loose_array[i]->v2];
      la_edge->flags = LRT_EDGE_FLAG_LOOSE;
      la_edge->object_ref = orig_ob;
      BLI_addtail(&la_edge->segments, la_seg);
      if (usage == OBJECT_LRT_INHERIT || usage == OBJECT_LRT_INCLUDE ||
          usage == OBJECT_LRT_NO_INTERSECTION) {
        lineart_add_edge_to_array_thread(ob_info, la_edge);
      }
      la_edge++;
      la_seg++;
    }
    MEM_freeN(loose_data.loose_array);
  }

  MEM_freeN(edge_feat_data.edge_nabr);

  if (ob_info->free_use_mesh) {
    BKE_id_free(NULL, me);
  }
}

static void lineart_object_load_worker(TaskPool *__restrict UNUSED(pool),
                                       LineartObjectLoadTaskInfo *olti)
{
  for (LineartObjectInfo *obi = olti->pending; obi; obi = obi->next) {
    lineart_geometry_object_load(obi, olti->rb);
    if (G.debug_value == 4000) {
      printf("thread id: %d processed: %d\n", olti->thread_id, obi->original_me->totpoly);
    }
  }
}

static uchar lineart_intersection_mask_check(Collection *c, Object *ob)
{
  LISTBASE_FOREACH (CollectionChild *, cc, &c->children) {
    uchar result = lineart_intersection_mask_check(cc->collection, ob);
    if (result) {
      return result;
    }
  }

  if (BKE_collection_has_object(c, (Object *)(ob->id.orig_id))) {
    if (c->lineart_flags & COLLECTION_LRT_USE_INTERSECTION_MASK) {
      return c->lineart_intersection_mask;
    }
  }

  return 0;
}

/**
 * See if this object in such collection is used for generating line art,
 * Disabling a collection for line art will doable all objects inside.
 */
static int lineart_usage_check(Collection *c, Object *ob, bool is_render)
{

  if (!c) {
    return OBJECT_LRT_INHERIT;
  }

  int object_has_special_usage = (ob->lineart.usage != OBJECT_LRT_INHERIT);

  if (object_has_special_usage) {
    return ob->lineart.usage;
  }

  if (c->gobject.first) {
    if (BKE_collection_has_object(c, (Object *)(ob->id.orig_id))) {
      if ((is_render && (c->flag & COLLECTION_HIDE_RENDER)) ||
          ((!is_render) && (c->flag & COLLECTION_HIDE_VIEWPORT))) {
        return OBJECT_LRT_EXCLUDE;
      }
      if (ob->lineart.usage == OBJECT_LRT_INHERIT) {
        switch (c->lineart_usage) {
          case COLLECTION_LRT_OCCLUSION_ONLY:
            return OBJECT_LRT_OCCLUSION_ONLY;
          case COLLECTION_LRT_EXCLUDE:
            return OBJECT_LRT_EXCLUDE;
          case COLLECTION_LRT_INTERSECTION_ONLY:
            return OBJECT_LRT_INTERSECTION_ONLY;
          case COLLECTION_LRT_NO_INTERSECTION:
            return OBJECT_LRT_NO_INTERSECTION;
        }
        return OBJECT_LRT_INHERIT;
      }
      return ob->lineart.usage;
    }
  }

  LISTBASE_FOREACH (CollectionChild *, cc, &c->children) {
    int result = lineart_usage_check(cc->collection, ob, is_render);
    if (result > OBJECT_LRT_INHERIT) {
      return result;
    }
  }

  return OBJECT_LRT_INHERIT;
}

static void lineart_geometry_load_assign_thread(LineartObjectLoadTaskInfo *olti_list,
                                                LineartObjectInfo *obi,
                                                int thread_count,
                                                int this_face_count)
{
  LineartObjectLoadTaskInfo *use_olti = olti_list;
  long unsigned int min_face = use_olti->total_faces;
  for (int i = 0; i < thread_count; i++) {
    if (olti_list[i].total_faces < min_face) {
      min_face = olti_list[i].total_faces;
      use_olti = &olti_list[i];
    }
  }

  use_olti->total_faces += this_face_count;
  obi->next = use_olti->pending;
  use_olti->pending = obi;
}

static bool lineart_geometry_check_visible(double (*model_view_proj)[4],
                                           double shift_x,
                                           double shift_y,
                                           Mesh *use_mesh)
{
  if (!use_mesh) {
    return false;
  }
  float mesh_min[3], mesh_max[3];
  INIT_MINMAX(mesh_min, mesh_max);
  BKE_mesh_minmax(use_mesh, mesh_min, mesh_max);
  BoundBox bb = {0};
  BKE_boundbox_init_from_minmax(&bb, mesh_min, mesh_max);

  double co[8][4];
  double tmp[3];
  for (int i = 0; i < 8; i++) {
    copy_v3db_v3fl(co[i], bb.vec[i]);
    copy_v3_v3_db(tmp, co[i]);
    mul_v4_m4v3_db(co[i], model_view_proj, tmp);
    co[i][0] -= shift_x * 2 * co[i][3];
    co[i][1] -= shift_y * 2 * co[i][3];
  }

  bool cond[6] = {true, true, true, true, true, true};
  /* Because for a point to be inside clip space, it must satisfy `-Wc <= XYCc <= Wc`, here if
   * all verts falls to the same side of the clip space border, we know it's outside view. */
  for (int i = 0; i < 8; i++) {
    cond[0] &= (co[i][0] < -co[i][3]);
    cond[1] &= (co[i][0] > co[i][3]);
    cond[2] &= (co[i][1] < -co[i][3]);
    cond[3] &= (co[i][1] > co[i][3]);
    cond[4] &= (co[i][2] < -co[i][3]);
    cond[5] &= (co[i][2] > co[i][3]);
  }
  for (int i = 0; i < 6; i++) {
    if (cond[i]) {
      return false;
    }
  }
  return true;
}

static void lineart_object_load_single_instance(LineartRenderBuffer *rb,
                                                Depsgraph *depsgraph,
                                                Scene *scene,
                                                Object *ob,
                                                Object *ref_ob,
                                                float use_mat[4][4],
                                                bool is_render,
                                                LineartObjectLoadTaskInfo *olti,
                                                int thread_count)
{
  LineartObjectInfo *obi = lineart_mem_acquire(&rb->render_data_pool, sizeof(LineartObjectInfo));
  obi->usage = lineart_usage_check(scene->master_collection, ob, is_render);
  obi->override_intersection_mask = lineart_intersection_mask_check(scene->master_collection, ob);
  Mesh *use_mesh;

  if (obi->usage == OBJECT_LRT_EXCLUDE) {
    return;
  }

  /* Prepare the matrix used for transforming this specific object (instance). This has to be
   * done before mesh boundbox check because the function needs that. */
  mul_m4db_m4db_m4fl_uniq(obi->model_view_proj, rb->view_projection, use_mat);
  mul_m4db_m4db_m4fl_uniq(obi->model_view, rb->view, use_mat);

  if (!ELEM(ob->type, OB_MESH, OB_MBALL, OB_CURVES_LEGACY, OB_SURF, OB_FONT)) {
    return;
  }
  if (ob->type == OB_MESH) {
    use_mesh = BKE_object_get_evaluated_mesh(ob);
    if (use_mesh->edit_mesh) {
      /* If the object is being edited, then the mesh is not evaluated fully into the final
       * result, do not load them. */
      return;
    }
  }
  else {
    use_mesh = BKE_mesh_new_from_object(depsgraph, ob, true, true);
  }

  /* In case we still can not get any mesh geometry data from the object */
  if (!use_mesh) {
    return;
  }

  if (!lineart_geometry_check_visible(obi->model_view_proj, rb->shift_x, rb->shift_y, use_mesh)) {
    return;
  }

  if (ob->type != OB_MESH) {
    obi->free_use_mesh = true;
  }

  /* Make normal matrix. */
  float imat[4][4];
  invert_m4_m4(imat, use_mat);
  transpose_m4(imat);
  copy_m4d_m4(obi->normal, imat);

  obi->original_me = use_mesh;
  obi->original_ob = (ref_ob->id.orig_id ? (Object *)ref_ob->id.orig_id : (Object *)ref_ob);
  lineart_geometry_load_assign_thread(olti, obi, thread_count, use_mesh->totpoly);
}

static void lineart_main_load_geometries(
    Depsgraph *depsgraph,
    Scene *scene,
    Object *camera /* Still use camera arg for convenience. */,
    LineartRenderBuffer *rb,
    bool allow_duplicates)
{
  double proj[4][4], view[4][4], result[4][4];
  float inv[4][4];
  Camera *cam = camera->data;
  float sensor = BKE_camera_sensor_size(cam->sensor_fit, cam->sensor_x, cam->sensor_y);
  int fit = BKE_camera_sensor_fit(cam->sensor_fit, rb->w, rb->h);
  double asp = ((double)rb->w / (double)rb->h);

  int bound_box_discard_count = 0;

  if (cam->type == CAM_PERSP) {
    if (fit == CAMERA_SENSOR_FIT_VERT && asp > 1) {
      sensor *= asp;
    }
    if (fit == CAMERA_SENSOR_FIT_HOR && asp < 1) {
      sensor /= asp;
    }
    const double fov = focallength_to_fov(cam->lens / (1 + rb->overscan), sensor);
    lineart_matrix_perspective_44d(proj, fov, asp, cam->clip_start, cam->clip_end);
  }
  else if (cam->type == CAM_ORTHO) {
    const double w = cam->ortho_scale / 2;
    lineart_matrix_ortho_44d(proj, -w, w, -w / asp, w / asp, cam->clip_start, cam->clip_end);
  }

  double t_start;

  if (G.debug_value == 4000) {
    t_start = PIL_check_seconds_timer();
  }

  invert_m4_m4(inv, rb->cam_obmat);
  mul_m4db_m4db_m4fl_uniq(result, proj, inv);
  copy_m4_m4_db(proj, result);
  copy_m4_m4_db(rb->view_projection, proj);

  unit_m4_db(view);
  copy_m4_m4_db(rb->view, view);

  BLI_listbase_clear(&rb->triangle_buffer_pointers);
  BLI_listbase_clear(&rb->vertex_buffer_pointers);

  int thread_count = rb->thread_count;

  /* This memory is in render buffer memory pool. so we don't need to free those after loading.
   */
  LineartObjectLoadTaskInfo *olti = lineart_mem_acquire(
      &rb->render_data_pool, sizeof(LineartObjectLoadTaskInfo) * thread_count);

  eEvaluationMode eval_mode = DEG_get_mode(depsgraph);
  bool is_render = eval_mode == DAG_EVAL_RENDER;

  int flags = DEG_ITER_OBJECT_FLAG_LINKED_DIRECTLY | DEG_ITER_OBJECT_FLAG_LINKED_VIA_SET |
              DEG_ITER_OBJECT_FLAG_VISIBLE;

  /* Instance duplicated & particles. */
  if (allow_duplicates) {
    flags |= DEG_ITER_OBJECT_FLAG_DUPLI;
  }

  /* XXX(@Yiming): Temporary solution, this iterator is technically unsafe to use *during*
   * depsgraph evaluation, see D14997 for detailed explanations. */
  DEG_OBJECT_ITER_BEGIN (depsgraph, ob, flags) {
    Object *eval_ob = DEG_get_evaluated_object(depsgraph, ob);

    if (!eval_ob) {
      continue;
    }

    /* DEG_OBJECT_ITER_BEGIN will include the instanced mesh of these curve object types, so don't
     * load them twice. */
    if (allow_duplicates && ELEM(ob->type, OB_CURVES_LEGACY, OB_FONT, OB_SURF)) {
      continue;
    }

    if (BKE_object_visibility(eval_ob, eval_mode) & OB_VISIBLE_SELF) {
      lineart_object_load_single_instance(
          rb, depsgraph, scene, eval_ob, eval_ob, eval_ob->obmat, is_render, olti, thread_count);
    }
  }
  DEG_OBJECT_ITER_END;

  TaskPool *tp = BLI_task_pool_create(NULL, TASK_PRIORITY_HIGH);

  if (G.debug_value == 4000) {
    printf("thread count: %d\n", thread_count);
  }
  for (int i = 0; i < thread_count; i++) {
    olti[i].rb = rb;
    olti[i].thread_id = i;
    BLI_task_pool_push(tp, (TaskRunFunction)lineart_object_load_worker, &olti[i], 0, NULL);
  }
  BLI_task_pool_work_and_wait(tp);
  BLI_task_pool_free(tp);

  /* The step below is to serialize vertex index in the whole scene, so
   * lineart_triangle_share_edge() can work properly from the lack of triangle adjacent info. */
  int global_i = 0;

  int edge_count = 0;
  for (int i = 0; i < thread_count; i++) {
    for (LineartObjectInfo *obi = olti[i].pending; obi; obi = obi->next) {
      if (!obi->v_eln) {
        continue;
      }
      edge_count += obi->pending_edges.next;
    }
  }
  lineart_finalize_object_edge_array_reserve(&rb->pending_edges, edge_count);

  for (int i = 0; i < thread_count; i++) {
    for (LineartObjectInfo *obi = olti[i].pending; obi; obi = obi->next) {
      if (!obi->v_eln) {
        continue;
      }
      LineartVert *v = (LineartVert *)obi->v_eln->pointer;
      int v_count = obi->v_eln->element_count;
      for (int vi = 0; vi < v_count; vi++) {
        v[vi].index += global_i;
      }
      /* Register a global index increment. See #lineart_triangle_share_edge() and
       * #lineart_main_load_geometries() for detailed. It's okay that global_vindex might
       * eventually overflow, in such large scene it's virtually impossible for two vertex of the
       * same numeric index to come close together. */
      obi->global_i_offset = global_i;
      global_i += v_count;
      lineart_finalize_object_edge_array(&rb->pending_edges, obi);
    }
  }

  if (G.debug_value == 4000) {
    double t_elapsed = PIL_check_seconds_timer() - t_start;
    printf("Line art loading time: %lf\n", t_elapsed);
    printf("Discarded %d object from bound box check\n", bound_box_discard_count);
  }
}

/**
 * Returns the two other verts of the triangle given a vertex. Returns false if the given vertex
 * doesn't belong to this triangle.
 */
static bool lineart_triangle_get_other_verts(const LineartTriangle *tri,
                                             const LineartVert *vt,
                                             LineartVert **l,
                                             LineartVert **r)
{
  if (tri->v[0] == vt) {
    *l = tri->v[1];
    *r = tri->v[2];
    return true;
  }
  if (tri->v[1] == vt) {
    *l = tri->v[2];
    *r = tri->v[0];
    return true;
  }
  if (tri->v[2] == vt) {
    *l = tri->v[0];
    *r = tri->v[1];
    return true;
  }
  return false;
}

static bool lineart_edge_from_triangle(const LineartTriangle *tri,
                                       const LineartEdge *e,
                                       bool allow_overlapping_edges)
{
  /* Normally we just determine from the pointer address. */
  if (e->t1 == tri || e->t2 == tri) {
    return true;
  }
  /* If allows overlapping, then we compare the vertex coordinates one by one to determine if one
   * edge is from specific triangle. This is slower but can handle edge split cases very well. */
  if (allow_overlapping_edges) {
#define LRT_TRI_SAME_POINT(tri, i, pt) \
  ((LRT_DOUBLE_CLOSE_ENOUGH(tri->v[i]->gloc[0], pt->gloc[0]) && \
    LRT_DOUBLE_CLOSE_ENOUGH(tri->v[i]->gloc[1], pt->gloc[1]) && \
    LRT_DOUBLE_CLOSE_ENOUGH(tri->v[i]->gloc[2], pt->gloc[2])) || \
   (LRT_DOUBLE_CLOSE_ENOUGH(tri->v[i]->gloc[0], pt->gloc[0]) && \
    LRT_DOUBLE_CLOSE_ENOUGH(tri->v[i]->gloc[1], pt->gloc[1]) && \
    LRT_DOUBLE_CLOSE_ENOUGH(tri->v[i]->gloc[2], pt->gloc[2])))
    if ((LRT_TRI_SAME_POINT(tri, 0, e->v1) || LRT_TRI_SAME_POINT(tri, 1, e->v1) ||
         LRT_TRI_SAME_POINT(tri, 2, e->v1)) &&
        (LRT_TRI_SAME_POINT(tri, 0, e->v2) || LRT_TRI_SAME_POINT(tri, 1, e->v2) ||
         LRT_TRI_SAME_POINT(tri, 2, e->v2))) {
      return true;
    }
#undef LRT_TRI_SAME_POINT
  }
  return false;
}

/* Sorting three intersection points from min to max,
 * the order for each intersection is set in `lst[0]` to `lst[2]`. */
#define INTERSECT_SORT_MIN_TO_MAX_3(ia, ib, ic, lst) \
  { \
    lst[0] = LRT_MIN3_INDEX(ia, ib, ic); \
    lst[1] = (((ia <= ib && ib <= ic) || (ic <= ib && ib <= ia)) ? \
                  1 : \
                  (((ic <= ia && ia <= ib) || (ib < ia && ia <= ic)) ? 0 : 2)); \
    lst[2] = LRT_MAX3_INDEX(ia, ib, ic); \
  }

/* `ia ib ic` are ordered. */
#define INTERSECT_JUST_GREATER(is, order, num, index) \
  { \
    index = (num < is[order[0]] ? \
                 order[0] : \
                 (num < is[order[1]] ? order[1] : (num < is[order[2]] ? order[2] : -1))); \
  }

/* `ia ib ic` are ordered. */
#define INTERSECT_JUST_SMALLER(is, order, num, index) \
  { \
    index = (num > is[order[2]] ? \
                 order[2] : \
                 (num > is[order[1]] ? order[1] : (num > is[order[0]] ? order[0] : -1))); \
  }

/**
 * This is the main function to calculate
 * the occlusion status between 1(one) triangle and 1(one) line.
 * if returns true, then from/to will carry the occluded segments
 * in ratio from `e->v1` to `e->v2`. The line is later cut with these two values.
 *
 * TODO(@Yiming): This function uses a convoluted method that needs to be redesigned.
 *
 * 1) The #lineart_intersect_seg_seg() and #lineart_point_triangle_relation() are separate calls,
 * which would potentially return results that doesn't agree, especially when it's an edge
 * extruding from one of the triangle's point. To get the information using one math process can
 * solve this problem.
 *
 * 2) Currently using discrete a/b/c/pa/pb/pc/is[3] values for storing
 * intersection/edge_aligned/intersection_order info, which isn't optimal, needs a better
 * representation (likely a struct) for readability and clarity of code path.
 *
 * I keep this function as-is because it's still fast, and more importantly the output value
 * threshold is already in tune with the cutting function in the next stage.
 * While current "edge aligned" fix isn't ideal, it does solve most of the precision issue
 * especially in orthographic camera mode.
 */
static bool lineart_triangle_edge_image_space_occlusion(SpinLock *UNUSED(spl),
                                                        const LineartTriangle *tri,
                                                        const LineartEdge *e,
                                                        const double *override_camera_loc,
                                                        const bool override_cam_is_persp,
                                                        const bool allow_overlapping_edges,
                                                        const double vp[4][4],
                                                        const double *camera_dir,
                                                        const float cam_shift_x,
                                                        const float cam_shift_y,
                                                        double *from,
                                                        double *to)
{
  double is[3] = {0};
  int order[3];
  int LCross = -1, RCross = -1;
  int a, b, c;     /* Crossing info. */
  bool pa, pb, pc; /* Parallel info. */
  int st_l = 0, st_r = 0;

  double Lv[3];
  double Rv[3];
  double vd4[4];
  double Cv[3];
  double dot_l, dot_r, dot_la, dot_ra;
  double dot_f;
  double gloc[4], trans[4];
  double cut = -1;

  double *LFBC = e->v1->fbcoord, *RFBC = e->v2->fbcoord, *FBC0 = tri->v[0]->fbcoord,
         *FBC1 = tri->v[1]->fbcoord, *FBC2 = tri->v[2]->fbcoord;

  /* Overlapping not possible, return early. */
  if ((MAX3(FBC0[0], FBC1[0], FBC2[0]) < MIN2(LFBC[0], RFBC[0])) ||
      (MIN3(FBC0[0], FBC1[0], FBC2[0]) > MAX2(LFBC[0], RFBC[0])) ||
      (MAX3(FBC0[1], FBC1[1], FBC2[1]) < MIN2(LFBC[1], RFBC[1])) ||
      (MIN3(FBC0[1], FBC1[1], FBC2[1]) > MAX2(LFBC[1], RFBC[1])) ||
      (MIN3(FBC0[3], FBC1[3], FBC2[3]) > MAX2(LFBC[3], RFBC[3]))) {
    return false;
  }

  /* If the line is one of the edge in the triangle, then it's not occluded. */
  if (lineart_edge_from_triangle(tri, e, allow_overlapping_edges)) {
    return false;
  }

  /* Check if the line visually crosses one of the edge in the triangle. */
  a = lineart_intersect_seg_seg(LFBC, RFBC, FBC0, FBC1, &is[0], &pa);
  b = lineart_intersect_seg_seg(LFBC, RFBC, FBC1, FBC2, &is[1], &pb);
  c = lineart_intersect_seg_seg(LFBC, RFBC, FBC2, FBC0, &is[2], &pc);

  /* Sort the intersection distance. */
  INTERSECT_SORT_MIN_TO_MAX_3(is[0], is[1], is[2], order);

  sub_v3_v3v3_db(Lv, e->v1->gloc, tri->v[0]->gloc);
  sub_v3_v3v3_db(Rv, e->v2->gloc, tri->v[0]->gloc);

  copy_v3_v3_db(Cv, camera_dir);

  if (override_cam_is_persp) {
    copy_v3_v3_db(vd4, override_camera_loc);
  }
  else {
    copy_v4_v4_db(vd4, override_camera_loc);
  }
  if (override_cam_is_persp) {
    sub_v3_v3v3_db(Cv, vd4, tri->v[0]->gloc);
  }

  dot_l = dot_v3v3_db(Lv, tri->gn);
  dot_r = dot_v3v3_db(Rv, tri->gn);
  dot_f = dot_v3v3_db(Cv, tri->gn);

  /* NOTE(Yiming): When we don't use `dot_f==0` here, it's theoretically possible that _some_
   * faces in perspective mode would get erroneously caught in this condition where they really
   * are legit faces that would produce occlusion, but haven't encountered those yet in my test
   * files.
   */
  if (fabs(dot_f) < FLT_EPSILON) {
    return false;
  }

  /* If the edge doesn't visually cross any edge of the triangle... */
  if (!a && !b && !c) {
    /* And if both end point from the edge is outside of the triangle... */
    if (!(st_l = lineart_point_triangle_relation(LFBC, FBC0, FBC1, FBC2)) &&
        !(st_r = lineart_point_triangle_relation(RFBC, FBC0, FBC1, FBC2))) {
      return 0; /* We don't have any occlusion. */
    }
  }

  /* Whether two end points are inside/on_the_edge/outside of the triangle. */
  st_l = lineart_point_triangle_relation(LFBC, FBC0, FBC1, FBC2);
  st_r = lineart_point_triangle_relation(RFBC, FBC0, FBC1, FBC2);

  /* Determine the cut position. */

  dot_la = fabs(dot_l);
  if (dot_la < DBL_EPSILON) {
    dot_la = 0;
    dot_l = 0;
  }
  dot_ra = fabs(dot_r);
  if (dot_ra < DBL_EPSILON) {
    dot_ra = 0;
    dot_r = 0;
  }
  if (dot_l - dot_r == 0) {
    cut = 100000;
  }
  else if (dot_l * dot_r <= 0) {
    cut = dot_la / fabs(dot_l - dot_r);
  }
  else {
    cut = fabs(dot_r + dot_l) / fabs(dot_l - dot_r);
    cut = dot_ra > dot_la ? 1 - cut : cut;
  }

  /* Transform the cut from geometry space to image space. */
  if (override_cam_is_persp) {
    interp_v3_v3v3_db(gloc, e->v1->gloc, e->v2->gloc, cut);
    mul_v4_m4v3_db(trans, vp, gloc);
    mul_v3db_db(trans, (1 / trans[3]));
    trans[0] -= cam_shift_x * 2;
    trans[1] -= cam_shift_y * 2;
    /* To accommodate `k=0` and `k=inf` (vertical) lines. here the cut is in image space. */
    if (fabs(e->v1->fbcoord[0] - e->v2->fbcoord[0]) >
        fabs(e->v1->fbcoord[1] - e->v2->fbcoord[1])) {
      cut = ratiod(e->v1->fbcoord[0], e->v2->fbcoord[0], trans[0]);
    }
    else {
      cut = ratiod(e->v1->fbcoord[1], e->v2->fbcoord[1], trans[1]);
    }
  }

#define LRT_GUARD_NOT_FOUND \
  if (LCross < 0 || RCross < 0) { \
    return false; \
  }

  /* Determine the pair of edges that the line has crossed. The "|" symbol in the comment
   * indicates triangle boundary. DBL_TRIANGLE_LIM is needed to for floating point precision
   * tolerance. */

  if (st_l == 2) {
    /* Left side is in the triangle. */
    if (st_r == 2) {
      /* |   l---r   | */
      INTERSECT_JUST_SMALLER(is, order, DBL_TRIANGLE_LIM, LCross);
      INTERSECT_JUST_GREATER(is, order, 1 - DBL_TRIANGLE_LIM, RCross);
    }
    else if (st_r == 1) {
      /* |   l------r| */
      INTERSECT_JUST_SMALLER(is, order, DBL_TRIANGLE_LIM, LCross);
      INTERSECT_JUST_GREATER(is, order, 1 - DBL_TRIANGLE_LIM, RCross);
    }
    else if (st_r == 0) {
      /* |   l-------|------r */
      INTERSECT_JUST_SMALLER(is, order, DBL_TRIANGLE_LIM, LCross);
      INTERSECT_JUST_GREATER(is, order, 0, RCross);
    }
  }
  else if (st_l == 1) {
    /* Left side is on some edge of the triangle. */
    if (st_r == 2) {
      /* |l------r   | */
      INTERSECT_JUST_SMALLER(is, order, DBL_TRIANGLE_LIM, LCross);
      INTERSECT_JUST_GREATER(is, order, 1 - DBL_TRIANGLE_LIM, RCross);
    }
    else if (st_r == 1) {
      /* |l---------r| */
      INTERSECT_JUST_SMALLER(is, order, DBL_TRIANGLE_LIM, LCross);
      INTERSECT_JUST_GREATER(is, order, 1 - DBL_TRIANGLE_LIM, RCross);
    }
    else if (st_r == 0) {
      /*           |l----------|-------r (crossing the triangle) [OR]
       * r---------|l          |         (not crossing the triangle) */
      INTERSECT_JUST_GREATER(is, order, DBL_TRIANGLE_LIM, RCross);
      if (RCross >= 0 && LRT_ABC(RCross) && is[RCross] > (DBL_TRIANGLE_LIM)) {
        INTERSECT_JUST_SMALLER(is, order, DBL_TRIANGLE_LIM, LCross);
      }
      else {
        INTERSECT_JUST_SMALLER(is, order, DBL_TRIANGLE_LIM, RCross);
        if (RCross > 0) {
          INTERSECT_JUST_SMALLER(is, order, is[RCross], LCross);
        }
      }
      LRT_GUARD_NOT_FOUND
      /* We could have the edge being completely parallel to the triangle where there isn't a
       * viable occlusion result. */
      if ((LRT_PABC(LCross) && !LRT_ABC(LCross)) || (LRT_PABC(RCross) && !LRT_ABC(RCross))) {
        return false;
      }
    }
  }
  else if (st_l == 0) {
    /* Left side is outside of the triangle. */
    if (st_r == 2) {
      /* l---|---r   | */
      INTERSECT_JUST_SMALLER(is, order, 1 - DBL_TRIANGLE_LIM, LCross);
      INTERSECT_JUST_GREATER(is, order, 1 - DBL_TRIANGLE_LIM, RCross);
    }
    else if (st_r == 1) {
      /*           |r----------|-------l (crossing the triangle) [OR]
       * l---------|r          |         (not crossing the triangle) */
      INTERSECT_JUST_SMALLER(is, order, 1 - DBL_TRIANGLE_LIM, LCross);
      if (LCross >= 0 && LRT_ABC(LCross) && is[LCross] < (1 - DBL_TRIANGLE_LIM)) {
        INTERSECT_JUST_GREATER(is, order, 1 - DBL_TRIANGLE_LIM, RCross);
      }
      else {
        INTERSECT_JUST_GREATER(is, order, 1 - DBL_TRIANGLE_LIM, LCross);
        if (LCross > 0) {
          INTERSECT_JUST_GREATER(is, order, is[LCross], RCross);
        }
      }
      LRT_GUARD_NOT_FOUND
      /* The same logic applies as above case. */
      if ((LRT_PABC(LCross) && !LRT_ABC(LCross)) || (LRT_PABC(RCross) && !LRT_ABC(RCross))) {
        return false;
      }
    }
    else if (st_r == 0) {
      /*      l---|----|----r (crossing the triangle) [OR]
       * l----r   |    |      (not crossing the triangle) */
      INTERSECT_JUST_GREATER(is, order, -DBL_TRIANGLE_LIM, LCross);
      if (LCross >= 0 && LRT_ABC(LCross)) {
        INTERSECT_JUST_GREATER(is, order, is[LCross], RCross);
      }
      else {
        if (LCross >= 0) {
          INTERSECT_JUST_GREATER(is, order, is[LCross], LCross);
          if (LCross >= 0) {
            INTERSECT_JUST_GREATER(is, order, is[LCross], RCross);
          }
        }
      }
    }
  }

  LRT_GUARD_NOT_FOUND

  double LF = dot_l * dot_f, RF = dot_r * dot_f;

  /* Determine the start and end point of image space cut on a line. */
  if (LF <= 0 && RF <= 0 && (dot_l || dot_r)) {
    *from = MAX2(0, is[LCross]);
    *to = MIN2(1, is[RCross]);
    if (*from >= *to) {
      return false;
    }
    return true;
  }
  if (LF >= 0 && RF <= 0 && (dot_l || dot_r)) {
    *from = MAX2(cut, is[LCross]);
    *to = MIN2(1, is[RCross]);
    if (*from >= *to) {
      return false;
    }
    return true;
  }
  if (LF <= 0 && RF >= 0 && (dot_l || dot_r)) {
    *from = MAX2(0, is[LCross]);
    *to = MIN2(cut, is[RCross]);
    if (*from >= *to) {
      return false;
    }
    return true;
  }

  /* Unlikely, but here's the default failed value if anything fall through. */
  return false;
}

#undef INTERSECT_SORT_MIN_TO_MAX_3
#undef INTERSECT_JUST_GREATER
#undef INTERSECT_JUST_SMALLER

/**
 * At this stage of the computation we don't have triangle adjacent info anymore,
 * so we can only compare the global vert index.
 */
static bool lineart_triangle_share_edge(const LineartTriangle *l, const LineartTriangle *r)
{
  if (l->v[0]->index == r->v[0]->index) {
    if (l->v[1]->index == r->v[1]->index || l->v[1]->index == r->v[2]->index ||
        l->v[2]->index == r->v[2]->index || l->v[2]->index == r->v[1]->index) {
      return true;
    }
  }
  if (l->v[0]->index == r->v[1]->index) {
    if (l->v[1]->index == r->v[0]->index || l->v[1]->index == r->v[2]->index ||
        l->v[2]->index == r->v[2]->index || l->v[2]->index == r->v[0]->index) {
      return true;
    }
  }
  if (l->v[0]->index == r->v[2]->index) {
    if (l->v[1]->index == r->v[1]->index || l->v[1]->index == r->v[0]->index ||
        l->v[2]->index == r->v[0]->index || l->v[2]->index == r->v[1]->index) {
      return true;
    }
  }
  if (l->v[1]->index == r->v[0]->index) {
    if (l->v[2]->index == r->v[1]->index || l->v[2]->index == r->v[2]->index ||
        l->v[0]->index == r->v[2]->index || l->v[0]->index == r->v[1]->index) {
      return true;
    }
  }
  if (l->v[1]->index == r->v[1]->index) {
    if (l->v[2]->index == r->v[0]->index || l->v[2]->index == r->v[2]->index ||
        l->v[0]->index == r->v[2]->index || l->v[0]->index == r->v[0]->index) {
      return true;
    }
  }
  if (l->v[1]->index == r->v[2]->index) {
    if (l->v[2]->index == r->v[1]->index || l->v[2]->index == r->v[0]->index ||
        l->v[0]->index == r->v[0]->index || l->v[0]->index == r->v[1]->index) {
      return true;
    }
  }

  /* Otherwise not possible. */
  return false;
}

static LineartVert *lineart_triangle_share_point(const LineartTriangle *l,
                                                 const LineartTriangle *r)
{
  if (l->v[0] == r->v[0]) {
    return r->v[0];
  }
  if (l->v[0] == r->v[1]) {
    return r->v[1];
  }
  if (l->v[0] == r->v[2]) {
    return r->v[2];
  }
  if (l->v[1] == r->v[0]) {
    return r->v[0];
  }
  if (l->v[1] == r->v[1]) {
    return r->v[1];
  }
  if (l->v[1] == r->v[2]) {
    return r->v[2];
  }
  if (l->v[2] == r->v[0]) {
    return r->v[0];
  }
  if (l->v[2] == r->v[1]) {
    return r->v[1];
  }
  if (l->v[2] == r->v[2]) {
    return r->v[2];
  }
  return NULL;
}

static bool lineart_triangle_2v_intersection_math(
    LineartVert *v1, LineartVert *v2, LineartTriangle *t2, double *last, double *rv)
{
  double Lv[3];
  double Rv[3];
  double dot_l, dot_r;
  double gloc[3];
  LineartVert *l = v1, *r = v2;

  sub_v3_v3v3_db(Lv, l->gloc, t2->v[0]->gloc);
  sub_v3_v3v3_db(Rv, r->gloc, t2->v[0]->gloc);

  dot_l = dot_v3v3_db(Lv, t2->gn);
  dot_r = dot_v3v3_db(Rv, t2->gn);

  if (dot_l * dot_r > 0 || (!dot_l && !dot_r)) {
    return false;
  }

  dot_l = fabs(dot_l);
  dot_r = fabs(dot_r);

  interp_v3_v3v3_db(gloc, l->gloc, r->gloc, dot_l / (dot_l + dot_r));

  /* Due to precision issue, we might end up with the same point as the one we already detected.
   */
  if (last && LRT_DOUBLE_CLOSE_ENOUGH(last[0], gloc[0]) &&
      LRT_DOUBLE_CLOSE_ENOUGH(last[1], gloc[1]) && LRT_DOUBLE_CLOSE_ENOUGH(last[2], gloc[2])) {
    return false;
  }

  if (!(lineart_point_inside_triangle3d(gloc, t2->v[0]->gloc, t2->v[1]->gloc, t2->v[2]->gloc))) {
    return false;
  }

  copy_v3_v3_db(rv, gloc);

  return true;
}

static bool lineart_triangle_intersect_math(LineartTriangle *tri,
                                            LineartTriangle *t2,
                                            double *v1,
                                            double *v2)
{
  double *next = v1, *last = NULL;
  LineartVert *sv1, *sv2;

  LineartVert *share = lineart_triangle_share_point(t2, tri);

  if (share) {
    /* If triangles have sharing points like `abc` and `acd`, then we only need to detect `bc`
     * against `acd` or `cd` against `abc`. */

    lineart_triangle_get_other_verts(tri, share, &sv1, &sv2);

    copy_v3_v3_db(v1, share->gloc);

    if (!lineart_triangle_2v_intersection_math(sv1, sv2, t2, 0, v2)) {
      lineart_triangle_get_other_verts(t2, share, &sv1, &sv2);
      if (lineart_triangle_2v_intersection_math(sv1, sv2, tri, 0, v2)) {
        return true;
      }
    }
  }
  else {
    /* If not sharing any points, then we need to try all the possibilities. */

    if (lineart_triangle_2v_intersection_math(tri->v[0], tri->v[1], t2, 0, v1)) {
      next = v2;
      last = v1;
    }

    if (lineart_triangle_2v_intersection_math(tri->v[1], tri->v[2], t2, last, next)) {
      if (last) {
        return true;
      }
      next = v2;
      last = v1;
    }
    if (lineart_triangle_2v_intersection_math(tri->v[2], tri->v[0], t2, last, next)) {
      if (last) {
        return true;
      }
      next = v2;
      last = v1;
    }

    if (lineart_triangle_2v_intersection_math(t2->v[0], t2->v[1], tri, last, next)) {
      if (last) {
        return true;
      }
      next = v2;
      last = v1;
    }
    if (lineart_triangle_2v_intersection_math(t2->v[1], t2->v[2], tri, last, next)) {
      if (last) {
        return true;
      }
      next = v2;
      last = v1;
    }
    if (lineart_triangle_2v_intersection_math(t2->v[2], t2->v[0], tri, last, next)) {
      if (last) {
        return true;
      }
      next = v2;
      last = v1;
    }
  }
  return false;
}

static void lineart_add_isec_thread(LineartIsecThread *th,
                                    const double *v1,
                                    const double *v2,
                                    LineartTriangle *tri1,
                                    LineartTriangle *tri2)
{
  if (th->current == th->max) {

    LineartIsecSingle *new_array = MEM_mallocN(sizeof(LineartIsecSingle) * th->max * 2,
                                               "LineartIsecSingle");
    memcpy(new_array, th->array, sizeof(LineartIsecSingle) * th->max);
    th->max *= 2;
    MEM_freeN(th->array);
    th->array = new_array;
  }
  LineartIsecSingle *is = &th->array[th->current];
  copy_v3fl_v3db(is->v1, v1);
  copy_v3fl_v3db(is->v2, v2);
  is->tri1 = tri1;
  is->tri2 = tri2;
  th->current++;
}

#define LRT_ISECT_TRIANGLE_PER_THREAD 4096

static bool lineart_schedule_new_triangle_task(LineartIsecThread *th)
{
  LineartRenderBuffer *rb = th->rb;
  int remaining = LRT_ISECT_TRIANGLE_PER_THREAD;

  BLI_spin_lock(&rb->lock_task);
  LineartElementLinkNode *eln = rb->isect_scheduled_up_to;

  if (!eln) {
    BLI_spin_unlock(&rb->lock_task);
    return false;
  }

  th->pending_from = eln;
  th->index_from = rb->isect_scheduled_up_to_index;

  while (remaining > 0 && eln) {
    int remaining_this_eln = eln->element_count - rb->isect_scheduled_up_to_index;
    int added_count = MIN2(remaining, remaining_this_eln);
    remaining -= added_count;
    if (remaining || added_count == remaining_this_eln) {
      eln = eln->next;
      rb->isect_scheduled_up_to = eln;
      rb->isect_scheduled_up_to_index = 0;
    }
    else {
      rb->isect_scheduled_up_to_index += added_count;
    }
  }

  th->pending_to = eln ? eln : rb->triangle_buffer_pointers.last;
  th->index_to = rb->isect_scheduled_up_to_index;

  BLI_spin_unlock(&rb->lock_task);

  return true;
}

/* This function initializes two things:
 * 1) Triangle array scheduling info, for each worker thread to get its chunk from the scheduler.
 * 2) Per-thread intersection result array. Does not store actual #LineartEdge, these results will
 * be finalized by #lineart_create_edges_from_isec_data
 */
static void lineart_init_isec_thread(LineartIsecData *d, LineartRenderBuffer *rb, int thread_count)
{
  d->threads = MEM_callocN(sizeof(LineartIsecThread) * thread_count, "LineartIsecThread arr");
  d->rb = rb;
  d->thread_count = thread_count;

  rb->isect_scheduled_up_to = rb->triangle_buffer_pointers.first;
  rb->isect_scheduled_up_to_index = 0;

  for (int i = 0; i < thread_count; i++) {
    LineartIsecThread *it = &d->threads[i];
    it->array = MEM_mallocN(sizeof(LineartIsecSingle) * 100, "LineartIsecSingle arr");
    it->max = 100;
    it->current = 0;
    it->thread_id = i;
    it->rb = rb;
  }
}

static void lineart_destroy_isec_thread(LineartIsecData *d)
{
  for (int i = 0; i < d->thread_count; i++) {
    LineartIsecThread *it = &d->threads[i];
    MEM_freeN(it->array);
  }
  MEM_freeN(d->threads);
}

static void lineart_triangle_intersect_in_bounding_area(LineartTriangle *tri,
                                                        LineartBoundingArea *ba,
                                                        LineartIsecThread *th,
                                                        int up_to)
{
  BLI_assert(th != NULL);

  if (!th) {
    return;
  }

  double *G0 = tri->v[0]->gloc, *G1 = tri->v[1]->gloc, *G2 = tri->v[2]->gloc;

  /* If this _is_ the smallest subdivision bounding area, then do the intersections there. */
  for (int i = 0; i < up_to; i++) {
    /* Testing_triangle->testing[0] is used to store pairing triangle reference.
     * See definition of LineartTriangleThread for more info. */
    LineartTriangle *testing_triangle = ba->linked_triangles[i];
    LineartTriangleThread *tt = (LineartTriangleThread *)testing_triangle;

    if (testing_triangle == tri || tt->testing_e[th->thread_id] == (LineartEdge *)tri) {
      continue;
    }
    tt->testing_e[th->thread_id] = (LineartEdge *)tri;

    if ((testing_triangle->flags & LRT_TRIANGLE_NO_INTERSECTION) ||
        ((testing_triangle->flags & LRT_TRIANGLE_INTERSECTION_ONLY) &&
         (tri->flags & LRT_TRIANGLE_INTERSECTION_ONLY))) {
      continue;
    }

    double *RG0 = testing_triangle->v[0]->gloc, *RG1 = testing_triangle->v[1]->gloc,
           *RG2 = testing_triangle->v[2]->gloc;

    /* Bounding box not overlapping or triangles share edges, not potential of intersecting. */
    if ((MIN3(G0[2], G1[2], G2[2]) > MAX3(RG0[2], RG1[2], RG2[2])) ||
        (MAX3(G0[2], G1[2], G2[2]) < MIN3(RG0[2], RG1[2], RG2[2])) ||
        (MIN3(G0[0], G1[0], G2[0]) > MAX3(RG0[0], RG1[0], RG2[0])) ||
        (MAX3(G0[0], G1[0], G2[0]) < MIN3(RG0[0], RG1[0], RG2[0])) ||
        (MIN3(G0[1], G1[1], G2[1]) > MAX3(RG0[1], RG1[1], RG2[1])) ||
        (MAX3(G0[1], G1[1], G2[1]) < MIN3(RG0[1], RG1[1], RG2[1])) ||
        lineart_triangle_share_edge(tri, testing_triangle)) {
      continue;
    }

    /* If we do need to compute intersection, then finally do it. */

    double iv1[3], iv2[3];
    if (lineart_triangle_intersect_math(tri, testing_triangle, iv1, iv2)) {
      lineart_add_isec_thread(th, iv1, iv2, tri, testing_triangle);
    }
  }
}

/**
 * The calculated view vector will point towards the far-plane from the camera position.
 */
static void lineart_main_get_view_vector(LineartRenderBuffer *rb)
{
  float direction[3] = {0, 0, 1};
  float trans[3];
  float inv[4][4];
  float obmat_no_scale[4][4];

  copy_m4_m4(obmat_no_scale, rb->cam_obmat);

  normalize_v3(obmat_no_scale[0]);
  normalize_v3(obmat_no_scale[1]);
  normalize_v3(obmat_no_scale[2]);
  invert_m4_m4(inv, obmat_no_scale);
  transpose_m4(inv);
  mul_v3_mat3_m4v3(trans, inv, direction);
  copy_m4_m4(rb->cam_obmat, obmat_no_scale);
  copy_v3db_v3fl(rb->view_vector, trans);
}

static void lineart_destroy_render_data(LineartRenderBuffer *rb)
{
  if (rb == NULL) {
    return;
  }

  BLI_listbase_clear(&rb->chains);
  BLI_listbase_clear(&rb->wasted_cuts);

  BLI_listbase_clear(&rb->vertex_buffer_pointers);
  BLI_listbase_clear(&rb->line_buffer_pointers);
  BLI_listbase_clear(&rb->triangle_buffer_pointers);

  BLI_spin_end(&rb->lock_task);
  BLI_spin_end(&rb->lock_cuts);
  BLI_spin_end(&rb->render_data_pool.lock_mem);

  if (rb->pending_edges.array) {
    MEM_freeN(rb->pending_edges.array);
  }

  lineart_free_bounding_area_memories(rb);

  lineart_mem_destroy(&rb->render_data_pool);
}

void MOD_lineart_destroy_render_data(LineartGpencilModifierData *lmd)
{
  LineartRenderBuffer *rb = lmd->render_buffer_ptr;

  lineart_destroy_render_data(rb);

  if (rb) {
    MEM_freeN(rb);
    lmd->render_buffer_ptr = NULL;
  }

  if (G.debug_value == 4000) {
    printf("LRT: Destroyed render data.\n");
  }
}

static LineartCache *lineart_init_cache(void)
{
  LineartCache *lc = MEM_callocN(sizeof(LineartCache), "Lineart Cache");
  return lc;
}

void MOD_lineart_clear_cache(struct LineartCache **lc)
{
  if (!(*lc)) {
    return;
  }
  lineart_mem_destroy(&((*lc)->chain_data_pool));
  MEM_freeN(*lc);
  (*lc) = NULL;
}

static LineartRenderBuffer *lineart_create_render_buffer(Scene *scene,
                                                         LineartGpencilModifierData *lmd,
                                                         Object *camera,
                                                         Object *active_camera,
                                                         LineartCache *lc)
{
  LineartRenderBuffer *rb = MEM_callocN(sizeof(LineartRenderBuffer), "Line Art render buffer");

  lmd->cache = lc;
  lmd->render_buffer_ptr = rb;
  lc->rb_edge_types = lmd->edge_types_override;

  if (!scene || !camera || !lc) {
    return NULL;
  }
  Camera *c = camera->data;
  double clipping_offset = 0;

  if (lmd->calculation_flags & LRT_ALLOW_CLIPPING_BOUNDARIES) {
    /* This way the clipped lines are "stably visible" by prevents depth buffer artifacts. */
    clipping_offset = 0.0001;
  }

  copy_v3db_v3fl(rb->camera_pos, camera->obmat[3]);
  if (active_camera) {
    copy_v3db_v3fl(rb->active_camera_pos, active_camera->obmat[3]);
  }
  copy_m4_m4(rb->cam_obmat, camera->obmat);
  rb->cam_is_persp = (c->type == CAM_PERSP);
  rb->near_clip = c->clip_start + clipping_offset;
  rb->far_clip = c->clip_end - clipping_offset;
  rb->w = scene->r.xsch;
  rb->h = scene->r.ysch;

  if (rb->cam_is_persp) {
    rb->tile_recursive_level = LRT_TILE_RECURSIVE_PERSPECTIVE;
  }
  else {
    rb->tile_recursive_level = LRT_TILE_RECURSIVE_ORTHO;
  }

  double asp = ((double)rb->w / (double)rb->h);
  int fit = BKE_camera_sensor_fit(c->sensor_fit, rb->w, rb->h);
  rb->shift_x = fit == CAMERA_SENSOR_FIT_HOR ? c->shiftx : c->shiftx / asp;
  rb->shift_y = fit == CAMERA_SENSOR_FIT_VERT ? c->shifty : c->shifty * asp;

  rb->overscan = lmd->overscan;

  rb->shift_x /= (1 + rb->overscan);
  rb->shift_y /= (1 + rb->overscan);

  rb->crease_threshold = cos(M_PI - lmd->crease_threshold);
  rb->chaining_image_threshold = lmd->chaining_image_threshold;
  rb->angle_splitting_threshold = lmd->angle_splitting_threshold;
  rb->chain_smooth_tolerance = lmd->chain_smooth_tolerance;

  rb->fuzzy_intersections = (lmd->calculation_flags & LRT_INTERSECTION_AS_CONTOUR) != 0;
  rb->fuzzy_everything = (lmd->calculation_flags & LRT_EVERYTHING_AS_CONTOUR) != 0;
  rb->allow_boundaries = (lmd->calculation_flags & LRT_ALLOW_CLIPPING_BOUNDARIES) != 0;
  rb->use_loose_as_contour = (lmd->calculation_flags & LRT_LOOSE_AS_CONTOUR) != 0;
  rb->use_loose_edge_chain = (lmd->calculation_flags & LRT_CHAIN_LOOSE_EDGES) != 0;
  rb->use_geometry_space_chain = (lmd->calculation_flags & LRT_CHAIN_GEOMETRY_SPACE) != 0;
  rb->use_image_boundary_trimming = (lmd->calculation_flags & LRT_USE_IMAGE_BOUNDARY_TRIMMING) !=
                                    0;

  /* See lineart_edge_from_triangle() for how this option may impact performance. */
  rb->allow_overlapping_edges = (lmd->calculation_flags & LRT_ALLOW_OVERLAPPING_EDGES) != 0;

  rb->allow_duplicated_types = (lmd->calculation_flags & LRT_ALLOW_OVERLAP_EDGE_TYPES) != 0;

  rb->force_crease = (lmd->calculation_flags & LRT_USE_CREASE_ON_SMOOTH_SURFACES) != 0;
  rb->sharp_as_crease = (lmd->calculation_flags & LRT_USE_CREASE_ON_SHARP_EDGES) != 0;

  rb->chain_preserve_details = (lmd->calculation_flags & LRT_CHAIN_PRESERVE_DETAILS) != 0;

  /* This is used to limit calculation to a certain level to save time, lines who have higher
   * occlusion levels will get ignored. */
  rb->max_occlusion_level = lmd->level_end_override;

  rb->use_back_face_culling = (lmd->calculation_flags & LRT_USE_BACK_FACE_CULLING) != 0;

  int16_t edge_types = lmd->edge_types_override;

  rb->use_contour = (edge_types & LRT_EDGE_FLAG_CONTOUR) != 0;
  rb->use_crease = (edge_types & LRT_EDGE_FLAG_CREASE) != 0;
  rb->use_material = (edge_types & LRT_EDGE_FLAG_MATERIAL) != 0;
  rb->use_edge_marks = (edge_types & LRT_EDGE_FLAG_EDGE_MARK) != 0;
  rb->use_intersections = (edge_types & LRT_EDGE_FLAG_INTERSECTION) != 0;
  rb->use_loose = (edge_types & LRT_EDGE_FLAG_LOOSE) != 0;

  rb->filter_face_mark_invert = (lmd->calculation_flags & LRT_FILTER_FACE_MARK_INVERT) != 0;
  rb->filter_face_mark = (lmd->calculation_flags & LRT_FILTER_FACE_MARK) != 0;
  rb->filter_face_mark_boundaries = (lmd->calculation_flags & LRT_FILTER_FACE_MARK_BOUNDARIES) !=
                                    0;
  rb->filter_face_mark_keep_contour = (lmd->calculation_flags &
                                       LRT_FILTER_FACE_MARK_KEEP_CONTOUR) != 0;

  rb->chain_data_pool = &lc->chain_data_pool;

  BLI_spin_init(&rb->lock_task);
  BLI_spin_init(&rb->lock_cuts);
  BLI_spin_init(&rb->render_data_pool.lock_mem);

  rb->thread_count = BKE_render_num_threads(&scene->r);

  return rb;
}

static int lineart_triangle_size_get(LineartRenderBuffer *rb)
{
  return sizeof(LineartTriangle) + (sizeof(LineartEdge *) * (rb->thread_count));
}

static void lineart_main_bounding_area_make_initial(LineartRenderBuffer *rb)
{
  /* Initial tile split is defined as 4 (subdivided as 4*4), increasing the value allows the
   * algorithm to build the acceleration structure for bigger scenes a little faster but not as
   * efficient at handling medium to small scenes. */
  int sp_w = LRT_BA_ROWS;
  int sp_h = LRT_BA_ROWS;
  int row, col;
  LineartBoundingArea *ba;

  /* Always make sure the shortest side has at least LRT_BA_ROWS tiles. */
  if (rb->w > rb->h) {
    sp_w = sp_h * rb->w / rb->h;
  }
  else {
    sp_h = sp_w * rb->h / rb->w;
  }

  /* Because NDC (Normalized Device Coordinates) range is (-1,1),
   * so the span for each initial tile is double of that in the (0,1) range. */
  double span_w = (double)1 / sp_w * 2.0;
  double span_h = (double)1 / sp_h * 2.0;

  rb->tile_count_x = sp_w;
  rb->tile_count_y = sp_h;
  rb->width_per_tile = span_w;
  rb->height_per_tile = span_h;

  rb->bounding_area_count = sp_w * sp_h;
  rb->initial_bounding_areas = lineart_mem_acquire(
      &rb->render_data_pool, sizeof(LineartBoundingArea) * rb->bounding_area_count);

  /* Initialize tiles. */
  for (row = 0; row < sp_h; row++) {
    for (col = 0; col < sp_w; col++) {
      ba = &rb->initial_bounding_areas[row * rb->tile_count_x + col];

      /* Set the four direction limits. */
      ba->l = span_w * col - 1.0;
      ba->r = (col == sp_w - 1) ? 1.0 : (span_w * (col + 1) - 1.0);
      ba->u = 1.0 - span_h * row;
      ba->b = (row == sp_h - 1) ? -1.0 : (1.0 - span_h * (row + 1));

      ba->cx = (ba->l + ba->r) / 2;
      ba->cy = (ba->u + ba->b) / 2;

      /* Init linked_triangles array. */
      ba->max_triangle_count = LRT_TILE_SPLITTING_TRIANGLE_LIMIT;
      ba->max_line_count = LRT_TILE_EDGE_COUNT_INITIAL;
      ba->linked_triangles = MEM_callocN(sizeof(LineartTriangle *) * ba->max_triangle_count,
                                         "ba_linked_triangles");
      ba->linked_lines = MEM_callocN(sizeof(LineartEdge *) * ba->max_line_count,
                                     "ba_linked_lines");

      BLI_spin_init(&ba->lock);
    }
  }
}

/**
 * Re-link adjacent tiles after one gets subdivided.
 */
static void lineart_bounding_areas_connect_new(LineartRenderBuffer *rb, LineartBoundingArea *root)
{
  LineartBoundingArea *ba = root->child, *tba;
  LinkData *lip2, *next_lip;
  LineartStaticMemPool *mph = &rb->render_data_pool;

  /* Inter-connection with newly created 4 child bounding areas. */
  lineart_list_append_pointer_pool(&ba[1].rp, mph, &ba[0]);
  lineart_list_append_pointer_pool(&ba[0].lp, mph, &ba[1]);
  lineart_list_append_pointer_pool(&ba[1].bp, mph, &ba[2]);
  lineart_list_append_pointer_pool(&ba[2].up, mph, &ba[1]);
  lineart_list_append_pointer_pool(&ba[2].rp, mph, &ba[3]);
  lineart_list_append_pointer_pool(&ba[3].lp, mph, &ba[2]);
  lineart_list_append_pointer_pool(&ba[3].up, mph, &ba[0]);
  lineart_list_append_pointer_pool(&ba[0].bp, mph, &ba[3]);

  /* Connect 4 child bounding areas to other areas that are
   * adjacent to their original parents. */
  LISTBASE_FOREACH (LinkData *, lip, &root->lp) {

    /* For example, we are dealing with parent's left side
     * "tba" represents each adjacent neighbor of the parent. */
    tba = lip->data;

    /* if this neighbor is adjacent to
     * the two new areas on the left side of the parent,
     * then add them to the adjacent list as well. */
    if (ba[1].u > tba->b && ba[1].b < tba->u) {
      lineart_list_append_pointer_pool(&ba[1].lp, mph, tba);
      lineart_list_append_pointer_pool(&tba->rp, mph, &ba[1]);
    }
    if (ba[2].u > tba->b && ba[2].b < tba->u) {
      lineart_list_append_pointer_pool(&ba[2].lp, mph, tba);
      lineart_list_append_pointer_pool(&tba->rp, mph, &ba[2]);
    }
  }
  LISTBASE_FOREACH (LinkData *, lip, &root->rp) {
    tba = lip->data;
    if (ba[0].u > tba->b && ba[0].b < tba->u) {
      lineart_list_append_pointer_pool(&ba[0].rp, mph, tba);
      lineart_list_append_pointer_pool(&tba->lp, mph, &ba[0]);
    }
    if (ba[3].u > tba->b && ba[3].b < tba->u) {
      lineart_list_append_pointer_pool(&ba[3].rp, mph, tba);
      lineart_list_append_pointer_pool(&tba->lp, mph, &ba[3]);
    }
  }
  LISTBASE_FOREACH (LinkData *, lip, &root->up) {
    tba = lip->data;
    if (ba[0].r > tba->l && ba[0].l < tba->r) {
      lineart_list_append_pointer_pool(&ba[0].up, mph, tba);
      lineart_list_append_pointer_pool(&tba->bp, mph, &ba[0]);
    }
    if (ba[1].r > tba->l && ba[1].l < tba->r) {
      lineart_list_append_pointer_pool(&ba[1].up, mph, tba);
      lineart_list_append_pointer_pool(&tba->bp, mph, &ba[1]);
    }
  }
  LISTBASE_FOREACH (LinkData *, lip, &root->bp) {
    tba = lip->data;
    if (ba[2].r > tba->l && ba[2].l < tba->r) {
      lineart_list_append_pointer_pool(&ba[2].bp, mph, tba);
      lineart_list_append_pointer_pool(&tba->up, mph, &ba[2]);
    }
    if (ba[3].r > tba->l && ba[3].l < tba->r) {
      lineart_list_append_pointer_pool(&ba[3].bp, mph, tba);
      lineart_list_append_pointer_pool(&tba->up, mph, &ba[3]);
    }
  }

  /* Then remove the parent bounding areas from
   * their original adjacent areas. */
  LISTBASE_FOREACH (LinkData *, lip, &root->lp) {
    for (lip2 = ((LineartBoundingArea *)lip->data)->rp.first; lip2; lip2 = next_lip) {
      next_lip = lip2->next;
      tba = lip2->data;
      if (tba == root) {
        lineart_list_remove_pointer_item_no_free(&((LineartBoundingArea *)lip->data)->rp, lip2);
        if (ba[1].u > tba->b && ba[1].b < tba->u) {
          lineart_list_append_pointer_pool(&tba->rp, mph, &ba[1]);
        }
        if (ba[2].u > tba->b && ba[2].b < tba->u) {
          lineart_list_append_pointer_pool(&tba->rp, mph, &ba[2]);
        }
      }
    }
  }
  LISTBASE_FOREACH (LinkData *, lip, &root->rp) {
    for (lip2 = ((LineartBoundingArea *)lip->data)->lp.first; lip2; lip2 = next_lip) {
      next_lip = lip2->next;
      tba = lip2->data;
      if (tba == root) {
        lineart_list_remove_pointer_item_no_free(&((LineartBoundingArea *)lip->data)->lp, lip2);
        if (ba[0].u > tba->b && ba[0].b < tba->u) {
          lineart_list_append_pointer_pool(&tba->lp, mph, &ba[0]);
        }
        if (ba[3].u > tba->b && ba[3].b < tba->u) {
          lineart_list_append_pointer_pool(&tba->lp, mph, &ba[3]);
        }
      }
    }
  }
  LISTBASE_FOREACH (LinkData *, lip, &root->up) {
    for (lip2 = ((LineartBoundingArea *)lip->data)->bp.first; lip2; lip2 = next_lip) {
      next_lip = lip2->next;
      tba = lip2->data;
      if (tba == root) {
        lineart_list_remove_pointer_item_no_free(&((LineartBoundingArea *)lip->data)->bp, lip2);
        if (ba[0].r > tba->l && ba[0].l < tba->r) {
          lineart_list_append_pointer_pool(&tba->up, mph, &ba[0]);
        }
        if (ba[1].r > tba->l && ba[1].l < tba->r) {
          lineart_list_append_pointer_pool(&tba->up, mph, &ba[1]);
        }
      }
    }
  }
  LISTBASE_FOREACH (LinkData *, lip, &root->bp) {
    for (lip2 = ((LineartBoundingArea *)lip->data)->up.first; lip2; lip2 = next_lip) {
      next_lip = lip2->next;
      tba = lip2->data;
      if (tba == root) {
        lineart_list_remove_pointer_item_no_free(&((LineartBoundingArea *)lip->data)->up, lip2);
        if (ba[2].r > tba->l && ba[2].l < tba->r) {
          lineart_list_append_pointer_pool(&tba->bp, mph, &ba[2]);
        }
        if (ba[3].r > tba->l && ba[3].l < tba->r) {
          lineart_list_append_pointer_pool(&tba->bp, mph, &ba[3]);
        }
      }
    }
  }

  /* Finally clear parent's adjacent list. */
  BLI_listbase_clear(&root->lp);
  BLI_listbase_clear(&root->rp);
  BLI_listbase_clear(&root->up);
  BLI_listbase_clear(&root->bp);
}

static void lineart_bounding_areas_connect_recursive(LineartRenderBuffer *rb,
                                                     LineartBoundingArea *root)
{
  if (root->child) {
    lineart_bounding_areas_connect_new(rb, root);
    for (int i = 0; i < 4; i++) {
      lineart_bounding_areas_connect_recursive(rb, &root->child[i]);
    }
  }
}

static void lineart_main_bounding_areas_connect_post(LineartRenderBuffer *rb)
{
  int total_tile_initial = rb->tile_count_x * rb->tile_count_y;
  int tiles_per_row = rb->tile_count_x;

  for (int row = 0; row < rb->tile_count_y; row++) {
    for (int col = 0; col < rb->tile_count_x; col++) {
      LineartBoundingArea *ba = &rb->initial_bounding_areas[row * tiles_per_row + col];
      /* Link adjacent ones. */
      if (row) {
        lineart_list_append_pointer_pool(
            &ba->up,
            &rb->render_data_pool,
            &rb->initial_bounding_areas[(row - 1) * tiles_per_row + col]);
      }
      if (col) {
        lineart_list_append_pointer_pool(
            &ba->lp,
            &rb->render_data_pool,
            &rb->initial_bounding_areas[row * tiles_per_row + col - 1]);
      }
      if (row != rb->tile_count_y - 1) {
        lineart_list_append_pointer_pool(
            &ba->bp,
            &rb->render_data_pool,
            &rb->initial_bounding_areas[(row + 1) * tiles_per_row + col]);
      }
      if (col != rb->tile_count_x - 1) {
        lineart_list_append_pointer_pool(
            &ba->rp,
            &rb->render_data_pool,
            &rb->initial_bounding_areas[row * tiles_per_row + col + 1]);
      }
    }
  }
  for (int i = 0; i < total_tile_initial; i++) {
    lineart_bounding_areas_connect_recursive(rb, &rb->initial_bounding_areas[i]);
  }
}

/**
 * Subdivide a tile after one tile contains too many triangles, then re-link triangles into all the
 * child tiles.
 */
static void lineart_bounding_area_split(LineartRenderBuffer *rb,
                                        LineartBoundingArea *root,
                                        int recursive_level)
{

  LineartBoundingArea *ba = lineart_mem_acquire_thread(&rb->render_data_pool,
                                                       sizeof(LineartBoundingArea) * 4);
  ba[0].l = root->cx;
  ba[0].r = root->r;
  ba[0].u = root->u;
  ba[0].b = root->cy;
  ba[0].cx = (ba[0].l + ba[0].r) / 2;
  ba[0].cy = (ba[0].u + ba[0].b) / 2;

  ba[1].l = root->l;
  ba[1].r = root->cx;
  ba[1].u = root->u;
  ba[1].b = root->cy;
  ba[1].cx = (ba[1].l + ba[1].r) / 2;
  ba[1].cy = (ba[1].u + ba[1].b) / 2;

  ba[2].l = root->l;
  ba[2].r = root->cx;
  ba[2].u = root->cy;
  ba[2].b = root->b;
  ba[2].cx = (ba[2].l + ba[2].r) / 2;
  ba[2].cy = (ba[2].u + ba[2].b) / 2;

  ba[3].l = root->cx;
  ba[3].r = root->r;
  ba[3].u = root->cy;
  ba[3].b = root->b;
  ba[3].cx = (ba[3].l + ba[3].r) / 2;
  ba[3].cy = (ba[3].u + ba[3].b) / 2;

  /* Init linked_triangles array and locks. */
  for (int i = 0; i < 4; i++) {
    ba[i].max_triangle_count = LRT_TILE_SPLITTING_TRIANGLE_LIMIT;
    ba[i].max_line_count = LRT_TILE_EDGE_COUNT_INITIAL;
    ba[i].linked_triangles = MEM_callocN(sizeof(LineartTriangle *) * ba[i].max_triangle_count,
                                         "ba_linked_triangles");
    ba[i].linked_lines = MEM_callocN(sizeof(LineartEdge *) * ba[i].max_line_count,
                                     "ba_linked_lines");
    BLI_spin_init(&ba[i].lock);
  }

  for (int i = 0; i < root->triangle_count; i++) {
    LineartTriangle *tri = root->linked_triangles[i];

    double b[4];
    b[0] = MIN3(tri->v[0]->fbcoord[0], tri->v[1]->fbcoord[0], tri->v[2]->fbcoord[0]);
    b[1] = MAX3(tri->v[0]->fbcoord[0], tri->v[1]->fbcoord[0], tri->v[2]->fbcoord[0]);
    b[2] = MAX3(tri->v[0]->fbcoord[1], tri->v[1]->fbcoord[1], tri->v[2]->fbcoord[1]);
    b[3] = MIN3(tri->v[0]->fbcoord[1], tri->v[1]->fbcoord[1], tri->v[2]->fbcoord[1]);

    /* Re-link triangles into child tiles, not doing intersection lines during this because this
     * batch of triangles are all tested with each other for intersections. */
    if (LRT_BOUND_AREA_CROSSES(b, &ba[0].l)) {
      lineart_bounding_area_link_triangle(rb, &ba[0], tri, b, 0, recursive_level + 1, false, NULL);
    }
    if (LRT_BOUND_AREA_CROSSES(b, &ba[1].l)) {
      lineart_bounding_area_link_triangle(rb, &ba[1], tri, b, 0, recursive_level + 1, false, NULL);
    }
    if (LRT_BOUND_AREA_CROSSES(b, &ba[2].l)) {
      lineart_bounding_area_link_triangle(rb, &ba[2], tri, b, 0, recursive_level + 1, false, NULL);
    }
    if (LRT_BOUND_AREA_CROSSES(b, &ba[3].l)) {
      lineart_bounding_area_link_triangle(rb, &ba[3], tri, b, 0, recursive_level + 1, false, NULL);
    }
  }

  /* At this point the child tiles are fully initialized and it's safe for new triangles to be
   * inserted, so assign root->child for #lineart_bounding_area_link_triangle to use. */
  root->child = ba;

  rb->bounding_area_count += 3;
}

static bool lineart_bounding_area_edge_intersect(LineartRenderBuffer *UNUSED(fb),
                                                 const double l[2],
                                                 const double r[2],
                                                 LineartBoundingArea *ba)
{
  double vx, vy;
  double converted[4];
  double c1, c;

  if (((converted[0] = (double)ba->l) > MAX2(l[0], r[0])) ||
      ((converted[1] = (double)ba->r) < MIN2(l[0], r[0])) ||
      ((converted[2] = (double)ba->b) > MAX2(l[1], r[1])) ||
      ((converted[3] = (double)ba->u) < MIN2(l[1], r[1]))) {
    return false;
  }

  vx = l[0] - r[0];
  vy = l[1] - r[1];

  c1 = vx * (converted[2] - l[1]) - vy * (converted[0] - l[0]);
  c = c1;

  c1 = vx * (converted[2] - l[1]) - vy * (converted[1] - l[0]);
  if (c1 * c <= 0) {
    return true;
  }
  c = c1;

  c1 = vx * (converted[3] - l[1]) - vy * (converted[0] - l[0]);
  if (c1 * c <= 0) {
    return true;
  }
  c = c1;

  c1 = vx * (converted[3] - l[1]) - vy * (converted[1] - l[0]);
  if (c1 * c <= 0) {
    return true;
  }
  c = c1;

  return false;
}

static bool lineart_bounding_area_triangle_intersect(LineartRenderBuffer *fb,
                                                     LineartTriangle *tri,
                                                     LineartBoundingArea *ba)
{
  double p1[2], p2[2], p3[2], p4[2];
  double *FBC1 = tri->v[0]->fbcoord, *FBC2 = tri->v[1]->fbcoord, *FBC3 = tri->v[2]->fbcoord;

  p3[0] = p1[0] = (double)ba->l;
  p2[1] = p1[1] = (double)ba->b;
  p2[0] = p4[0] = (double)ba->r;
  p3[1] = p4[1] = (double)ba->u;

  if ((FBC1[0] >= p1[0] && FBC1[0] <= p2[0] && FBC1[1] >= p1[1] && FBC1[1] <= p3[1]) ||
      (FBC2[0] >= p1[0] && FBC2[0] <= p2[0] && FBC2[1] >= p1[1] && FBC2[1] <= p3[1]) ||
      (FBC3[0] >= p1[0] && FBC3[0] <= p2[0] && FBC3[1] >= p1[1] && FBC3[1] <= p3[1])) {
    return true;
  }

  if (lineart_point_inside_triangle(p1, FBC1, FBC2, FBC3) ||
      lineart_point_inside_triangle(p2, FBC1, FBC2, FBC3) ||
      lineart_point_inside_triangle(p3, FBC1, FBC2, FBC3) ||
      lineart_point_inside_triangle(p4, FBC1, FBC2, FBC3)) {
    return true;
  }

  if (lineart_bounding_area_edge_intersect(fb, FBC1, FBC2, ba) ||
      lineart_bounding_area_edge_intersect(fb, FBC2, FBC3, ba) ||
      lineart_bounding_area_edge_intersect(fb, FBC3, FBC1, ba)) {
    return true;
  }

  return false;
}

/**
 * This function does two things:
 *
 * 1) Builds a quad-tree under rb->InitialBoundingAreas to achieve good geometry separation for
 * fast overlapping test between triangles and lines. This acceleration structure makes the
 * occlusion stage much faster.
 *
 * 2) Test triangles with other triangles that are previously linked into each tile
 * (#LineartBoundingArea) for intersection lines. When splitting the tile into 4 children and
 * re-linking triangles into the child tiles, intersections are inhibited so we don't get
 * duplicated intersection lines.
 *
 */
static void lineart_bounding_area_link_triangle(LineartRenderBuffer *rb,
                                                LineartBoundingArea *root_ba,
                                                LineartTriangle *tri,
                                                double *LRUB,
                                                int recursive,
                                                int recursive_level,
                                                bool do_intersection,
                                                struct LineartIsecThread *th)
{
  if (!lineart_bounding_area_triangle_intersect(rb, tri, root_ba)) {
    return;
  }

  LineartBoundingArea *old_ba = root_ba;

  if (old_ba->child) {
    /* If old_ba->child is not NULL, then tile splitting is fully finished, safe to directly insert
     * into child tiles. */
    double *B1 = LRUB;
    double b[4];
    if (!LRUB) {
      b[0] = MIN3(tri->v[0]->fbcoord[0], tri->v[1]->fbcoord[0], tri->v[2]->fbcoord[0]);
      b[1] = MAX3(tri->v[0]->fbcoord[0], tri->v[1]->fbcoord[0], tri->v[2]->fbcoord[0]);
      b[2] = MAX3(tri->v[0]->fbcoord[1], tri->v[1]->fbcoord[1], tri->v[2]->fbcoord[1]);
      b[3] = MIN3(tri->v[0]->fbcoord[1], tri->v[1]->fbcoord[1], tri->v[2]->fbcoord[1]);
      B1 = b;
    }
    for (int iba = 0; iba < 4; iba++) {
      if (LRT_BOUND_AREA_CROSSES(B1, &old_ba->child[iba].l)) {
        lineart_bounding_area_link_triangle(
            rb, &old_ba->child[iba], tri, B1, recursive, recursive_level + 1, do_intersection, th);
      }
    }
    return;
  }

  /* When splitting tiles, triangles are relinked into new tiles by a single thread, #th is NULL
   * in that situation. */
  if (th) {
    BLI_spin_lock(&old_ba->lock);
  }

  /* If there are still space left in this tile for insertion. */
  if (old_ba->triangle_count < old_ba->max_triangle_count) {
    const uint32_t old_tri_count = old_ba->triangle_count;

    old_ba->linked_triangles[old_ba->triangle_count++] = tri;

    /* Do intersections in place. */
    if (do_intersection && rb->use_intersections) {
      lineart_triangle_intersect_in_bounding_area(tri, old_ba, th, old_tri_count);
    }

    if (th) {
      BLI_spin_unlock(&old_ba->lock);
    }
  }
  else { /* We need to wait for either splitting or array extension to be done. */

    if (recursive_level < rb->tile_recursive_level) {
      if (!old_ba->child) {
        /* old_ba->child==NULL, means we are the thread that's doing the splitting. */
        lineart_bounding_area_split(rb, old_ba, recursive_level);
      } /* Otherwise other thread has completed the splitting process. */
    }
    else {
      if (old_ba->triangle_count == old_ba->max_triangle_count) {
        /* Means we are the thread that's doing the extension. */
        lineart_bounding_area_triangle_reallocate(old_ba);
      } /* Otherwise other thread has completed the extending the array. */
    }

    /* Unlock before going into recursive call. */
    if (th) {
      BLI_spin_unlock(&old_ba->lock);
    }

    /* Of course we still have our own triangle needs to be added. */
    lineart_bounding_area_link_triangle(
        rb, root_ba, tri, LRUB, recursive, recursive_level, do_intersection, th);
  }
}

static void lineart_free_bounding_area_memory(LineartBoundingArea *ba, bool recursive)
{
  if (ba->linked_lines) {
    MEM_freeN(ba->linked_lines);
  }
  if (ba->linked_triangles) {
    MEM_freeN(ba->linked_triangles);
  }
  if (recursive && ba->child) {
    for (int i = 0; i < 4; i++) {
      lineart_free_bounding_area_memory(&ba->child[i], recursive);
    }
  }
}
static void lineart_free_bounding_area_memories(LineartRenderBuffer *rb)
{
  for (int i = 0; i < rb->tile_count_y; i++) {
    for (int j = 0; j < rb->tile_count_x; j++) {
      lineart_free_bounding_area_memory(&rb->initial_bounding_areas[i * rb->tile_count_x + j],
                                        true);
    }
  }
}

static void lineart_bounding_area_link_edge(LineartRenderBuffer *rb,
                                            LineartBoundingArea *root_ba,
                                            LineartEdge *e)
{
  if (root_ba->child == NULL) {
    lineart_bounding_area_line_add(root_ba, e);
  }
  else {
    if (lineart_bounding_area_edge_intersect(
            rb, e->v1->fbcoord, e->v2->fbcoord, &root_ba->child[0])) {
      lineart_bounding_area_link_edge(rb, &root_ba->child[0], e);
    }
    if (lineart_bounding_area_edge_intersect(
            rb, e->v1->fbcoord, e->v2->fbcoord, &root_ba->child[1])) {
      lineart_bounding_area_link_edge(rb, &root_ba->child[1], e);
    }
    if (lineart_bounding_area_edge_intersect(
            rb, e->v1->fbcoord, e->v2->fbcoord, &root_ba->child[2])) {
      lineart_bounding_area_link_edge(rb, &root_ba->child[2], e);
    }
    if (lineart_bounding_area_edge_intersect(
            rb, e->v1->fbcoord, e->v2->fbcoord, &root_ba->child[3])) {
      lineart_bounding_area_link_edge(rb, &root_ba->child[3], e);
    }
  }
}

/**
 * Link lines to their respective bounding areas.
 */
static void lineart_main_link_lines(LineartRenderBuffer *rb)
{
  LRT_ITER_ALL_LINES_BEGIN
  {
    int r1, r2, c1, c2, row, col;
    if (lineart_get_edge_bounding_areas(rb, e, &r1, &r2, &c1, &c2)) {
      for (row = r1; row != r2 + 1; row++) {
        for (col = c1; col != c2 + 1; col++) {
          lineart_bounding_area_link_edge(
              rb, &rb->initial_bounding_areas[row * rb->tile_count_x + col], e);
        }
      }
    }
  }
  LRT_ITER_ALL_LINES_END
}

static bool lineart_get_triangle_bounding_areas(LineartRenderBuffer *rb,
                                                LineartTriangle *tri,
                                                int *rowbegin,
                                                int *rowend,
                                                int *colbegin,
                                                int *colend)
{
  double sp_w = rb->width_per_tile, sp_h = rb->height_per_tile;
  double b[4];

  if (!tri->v[0] || !tri->v[1] || !tri->v[2]) {
    return false;
  }

  b[0] = MIN3(tri->v[0]->fbcoord[0], tri->v[1]->fbcoord[0], tri->v[2]->fbcoord[0]);
  b[1] = MAX3(tri->v[0]->fbcoord[0], tri->v[1]->fbcoord[0], tri->v[2]->fbcoord[0]);
  b[2] = MIN3(tri->v[0]->fbcoord[1], tri->v[1]->fbcoord[1], tri->v[2]->fbcoord[1]);
  b[3] = MAX3(tri->v[0]->fbcoord[1], tri->v[1]->fbcoord[1], tri->v[2]->fbcoord[1]);

  if (b[0] > 1 || b[1] < -1 || b[2] > 1 || b[3] < -1) {
    return false;
  }

  (*colbegin) = (int)((b[0] + 1.0) / sp_w);
  (*colend) = (int)((b[1] + 1.0) / sp_w);
  (*rowend) = rb->tile_count_y - (int)((b[2] + 1.0) / sp_h) - 1;
  (*rowbegin) = rb->tile_count_y - (int)((b[3] + 1.0) / sp_h) - 1;

  if ((*colend) >= rb->tile_count_x) {
    (*colend) = rb->tile_count_x - 1;
  }
  if ((*rowend) >= rb->tile_count_y) {
    (*rowend) = rb->tile_count_y - 1;
  }
  if ((*colbegin) < 0) {
    (*colbegin) = 0;
  }
  if ((*rowbegin) < 0) {
    (*rowbegin) = 0;
  }

  return true;
}

static bool lineart_get_edge_bounding_areas(LineartRenderBuffer *rb,
                                            LineartEdge *e,
                                            int *rowbegin,
                                            int *rowend,
                                            int *colbegin,
                                            int *colend)
{
  double sp_w = rb->width_per_tile, sp_h = rb->height_per_tile;
  double b[4];

  if (!e->v1 || !e->v2) {
    return false;
  }

  if (e->v1->fbcoord[0] != e->v1->fbcoord[0] || e->v2->fbcoord[0] != e->v2->fbcoord[0]) {
    return false;
  }

  b[0] = MIN2(e->v1->fbcoord[0], e->v2->fbcoord[0]);
  b[1] = MAX2(e->v1->fbcoord[0], e->v2->fbcoord[0]);
  b[2] = MIN2(e->v1->fbcoord[1], e->v2->fbcoord[1]);
  b[3] = MAX2(e->v1->fbcoord[1], e->v2->fbcoord[1]);

  if (b[0] > 1 || b[1] < -1 || b[2] > 1 || b[3] < -1) {
    return false;
  }

  (*colbegin) = (int)((b[0] + 1.0) / sp_w);
  (*colend) = (int)((b[1] + 1.0) / sp_w);
  (*rowend) = rb->tile_count_y - (int)((b[2] + 1.0) / sp_h) - 1;
  (*rowbegin) = rb->tile_count_y - (int)((b[3] + 1.0) / sp_h) - 1;

  /* It's possible that the line stretches too much out to the side, resulting negative value. */
  if ((*rowend) < (*rowbegin)) {
    (*rowend) = rb->tile_count_y - 1;
  }

  if ((*colend) < (*colbegin)) {
    (*colend) = rb->tile_count_x - 1;
  }

  CLAMP((*colbegin), 0, rb->tile_count_x - 1);
  CLAMP((*rowbegin), 0, rb->tile_count_y - 1);
  CLAMP((*colend), 0, rb->tile_count_x - 1);
  CLAMP((*rowend), 0, rb->tile_count_y - 1);

  return true;
}

LineartBoundingArea *MOD_lineart_get_parent_bounding_area(LineartRenderBuffer *rb,
                                                          double x,
                                                          double y)
{
  double sp_w = rb->width_per_tile, sp_h = rb->height_per_tile;
  int col, row;

  if (x > 1 || x < -1 || y > 1 || y < -1) {
    return 0;
  }

  col = (int)((x + 1.0) / sp_w);
  row = rb->tile_count_y - (int)((y + 1.0) / sp_h) - 1;

  if (col >= rb->tile_count_x) {
    col = rb->tile_count_x - 1;
  }
  if (row >= rb->tile_count_y) {
    row = rb->tile_count_y - 1;
  }
  if (col < 0) {
    col = 0;
  }
  if (row < 0) {
    row = 0;
  }

  return &rb->initial_bounding_areas[row * rb->tile_count_x + col];
}

static LineartBoundingArea *lineart_get_bounding_area(LineartRenderBuffer *rb, double x, double y)
{
  LineartBoundingArea *iba;
  double sp_w = rb->width_per_tile, sp_h = rb->height_per_tile;
  int c = (int)((x + 1.0) / sp_w);
  int r = rb->tile_count_y - (int)((y + 1.0) / sp_h) - 1;
  if (r < 0) {
    r = 0;
  }
  if (c < 0) {
    c = 0;
  }
  if (r >= rb->tile_count_y) {
    r = rb->tile_count_y - 1;
  }
  if (c >= rb->tile_count_x) {
    c = rb->tile_count_x - 1;
  }

  iba = &rb->initial_bounding_areas[r * rb->tile_count_x + c];
  while (iba->child) {
    if (x > iba->cx) {
      if (y > iba->cy) {
        iba = &iba->child[0];
      }
      else {
        iba = &iba->child[3];
      }
    }
    else {
      if (y > iba->cy) {
        iba = &iba->child[1];
      }
      else {
        iba = &iba->child[2];
      }
    }
  }
  return iba;
}

LineartBoundingArea *MOD_lineart_get_bounding_area(LineartRenderBuffer *rb, double x, double y)
{
  LineartBoundingArea *ba;
  if ((ba = MOD_lineart_get_parent_bounding_area(rb, x, y)) != NULL) {
    return lineart_get_bounding_area(rb, x, y);
  }
  return NULL;
}

static void lineart_add_triangles_worker(TaskPool *__restrict UNUSED(pool), LineartIsecThread *th)
{
  LineartRenderBuffer *rb = th->rb;
  int _dir_control = 0;
  while (lineart_schedule_new_triangle_task(th)) {
    for (LineartElementLinkNode *eln = th->pending_from; eln != th->pending_to->next;
         eln = eln->next) {
      int index_start = eln == th->pending_from ? th->index_from : 0;
      int index_end = eln == th->pending_to ? th->index_to : eln->element_count;
      LineartTriangle *tri = (void *)(((uchar *)eln->pointer) + rb->triangle_size * index_start);
      for (int ei = index_start; ei < index_end; ei++) {
        int x1, x2, y1, y2;
        int r, co;
        if ((tri->flags & LRT_CULL_USED) || (tri->flags & LRT_CULL_DISCARD)) {
          tri = (void *)(((uchar *)tri) + rb->triangle_size);
          continue;
        }
        if (lineart_get_triangle_bounding_areas(rb, tri, &y1, &y2, &x1, &x2)) {
          _dir_control++;
          for (co = x1; co <= x2; co++) {
            for (r = y1; r <= y2; r++) {
              lineart_bounding_area_link_triangle(
                  rb,
                  &rb->initial_bounding_areas[r * rb->tile_count_x + co],
                  tri,
                  0,
                  1,
                  0,
                  (!(tri->flags & LRT_TRIANGLE_NO_INTERSECTION)),
                  th);
            }
          }
        } /* Else throw away. */
        tri = (void *)(((uchar *)tri) + rb->triangle_size);
      }
    }
  }
}

static void lineart_create_edges_from_isec_data(LineartIsecData *d)
{
  LineartRenderBuffer *rb = d->rb;
  double ZMax = rb->far_clip;
  double ZMin = rb->near_clip;

  for (int i = 0; i < d->thread_count; i++) {
    LineartIsecThread *th = &d->threads[i];
    if (G.debug_value == 4000) {
      printf("Thread %d isec generated %d lines.\n", i, th->current);
    }
    if (!th->current) {
      continue;
    }
    /* We don't care about removing duplicated vert in this method, chaining can handle that,
     * and it saves us from using locks and look up tables. */
    LineartVertIntersection *v = lineart_mem_acquire(
        &rb->render_data_pool, sizeof(LineartVertIntersection) * th->current * 2);
    LineartEdge *e = lineart_mem_acquire(&rb->render_data_pool, sizeof(LineartEdge) * th->current);
    LineartEdgeSegment *es = lineart_mem_acquire(&rb->render_data_pool,
                                                 sizeof(LineartEdgeSegment) * th->current);
    for (int j = 0; j < th->current; j++) {
      LineartVertIntersection *v1i = v;
      LineartVertIntersection *v2i = v + 1;
      LineartIsecSingle *is = &th->array[j];
      v1i->intersecting_with = is->tri1;
      v2i->intersecting_with = is->tri2;
      LineartVert *v1 = (LineartVert *)v1i;
      LineartVert *v2 = (LineartVert *)v2i;
      v1->flag |= LRT_VERT_HAS_INTERSECTION_DATA;
      v2->flag |= LRT_VERT_HAS_INTERSECTION_DATA;
      copy_v3db_v3fl(v1->gloc, is->v1);
      copy_v3db_v3fl(v2->gloc, is->v2);
      /* The intersection line has been generated only in geometry space, so we need to transform
       * them as well. */
      mul_v4_m4v3_db(v1->fbcoord, rb->view_projection, v1->gloc);
      mul_v4_m4v3_db(v2->fbcoord, rb->view_projection, v2->gloc);
      mul_v3db_db(v1->fbcoord, (1 / v1->fbcoord[3]));
      mul_v3db_db(v2->fbcoord, (1 / v2->fbcoord[3]));

      v1->fbcoord[0] -= rb->shift_x * 2;
      v1->fbcoord[1] -= rb->shift_y * 2;
      v2->fbcoord[0] -= rb->shift_x * 2;
      v2->fbcoord[1] -= rb->shift_y * 2;

      /* This z transformation is not the same as the rest of the part, because the data don't go
       * through normal perspective division calls in the pipeline, but this way the 3D result and
       * occlusion on the generated line is correct, and we don't really use 2D for viewport stroke
       * generation anyway. */
      v1->fbcoord[2] = ZMin * ZMax / (ZMax - fabs(v1->fbcoord[2]) * (ZMax - ZMin));
      v2->fbcoord[2] = ZMin * ZMax / (ZMax - fabs(v2->fbcoord[2]) * (ZMax - ZMin));
      e->v1 = v1;
      e->v2 = v2;
      e->t1 = is->tri1;
      e->t2 = is->tri2;
      e->flags = LRT_EDGE_FLAG_INTERSECTION;
      e->intersection_mask = (is->tri1->intersection_mask | is->tri2->intersection_mask);
      BLI_addtail(&e->segments, es);

      lineart_add_edge_to_array(&rb->pending_edges, e);

      v += 2;
      e++;
      es++;
    }
  }
}

/**
 * Sequentially add triangles into render buffer, intersection lines between those triangles will
 * also be computed at the same time.
 */
static void lineart_main_add_triangles(LineartRenderBuffer *rb)
{
  double t_start;
  if (G.debug_value == 4000) {
    t_start = PIL_check_seconds_timer();
  }

  /* Initialize per-thread data for thread task scheduling information and storing intersection
   * results.  */
  LineartIsecData d = {0};
  lineart_init_isec_thread(&d, rb, rb->thread_count);

  TaskPool *tp = BLI_task_pool_create(NULL, TASK_PRIORITY_HIGH);
  for (int i = 0; i < rb->thread_count; i++) {
    BLI_task_pool_push(tp, (TaskRunFunction)lineart_add_triangles_worker, &d.threads[i], 0, NULL);
  }
  BLI_task_pool_work_and_wait(tp);
  BLI_task_pool_free(tp);

  /* Create actual lineart edges from intersection results.  */
  lineart_create_edges_from_isec_data(&d);

  lineart_destroy_isec_thread(&d);

  if (G.debug_value == 4000) {
    double t_elapsed = PIL_check_seconds_timer() - t_start;
    printf("Line art intersection time: %f\n", t_elapsed);
  }
}

/**
 * This function gets the tile for the point `e->v1`, and later use #lineart_bounding_area_next()
 * to get next along the way.
 */
static LineartBoundingArea *lineart_edge_first_bounding_area(LineartRenderBuffer *rb,
                                                             LineartEdge *e)
{
  double data[2] = {e->v1->fbcoord[0], e->v1->fbcoord[1]};
  double LU[2] = {-1, 1}, RU[2] = {1, 1}, LB[2] = {-1, -1}, RB[2] = {1, -1};
  double r = 1, sr = 1;
  bool p_unused;

  if (data[0] > -1 && data[0] < 1 && data[1] > -1 && data[1] < 1) {
    return lineart_get_bounding_area(rb, data[0], data[1]);
  }

  if (lineart_intersect_seg_seg(e->v1->fbcoord, e->v2->fbcoord, LU, RU, &sr, &p_unused) &&
      sr < r && sr > 0) {
    r = sr;
  }
  if (lineart_intersect_seg_seg(e->v1->fbcoord, e->v2->fbcoord, LB, RB, &sr, &p_unused) &&
      sr < r && sr > 0) {
    r = sr;
  }
  if (lineart_intersect_seg_seg(e->v1->fbcoord, e->v2->fbcoord, LB, LU, &sr, &p_unused) &&
      sr < r && sr > 0) {
    r = sr;
  }
  if (lineart_intersect_seg_seg(e->v1->fbcoord, e->v2->fbcoord, RB, RU, &sr, &p_unused) &&
      sr < r && sr > 0) {
    r = sr;
  }
  interp_v2_v2v2_db(data, e->v1->fbcoord, e->v2->fbcoord, r);

  return lineart_get_bounding_area(rb, data[0], data[1]);
}

/**
 * This march along one render line in image space and
 * get the next bounding area the line is crossing.
 */
static LineartBoundingArea *lineart_bounding_area_next(LineartBoundingArea *this,
                                                       LineartEdge *e,
                                                       double x,
                                                       double y,
                                                       double k,
                                                       int positive_x,
                                                       int positive_y,
                                                       double *next_x,
                                                       double *next_y)
{
  double rx, ry, ux, uy, lx, ly, bx, by;
  double r1, r2;
  LineartBoundingArea *ba;

  /* If we are marching towards the right. */
  if (positive_x > 0) {
    rx = this->r;
    ry = y + k * (rx - x);

    /* If we are marching towards the top. */
    if (positive_y > 0) {
      uy = this->u;
      ux = x + (uy - y) / k;
      r1 = ratiod(e->v1->fbcoord[0], e->v2->fbcoord[0], rx);
      r2 = ratiod(e->v1->fbcoord[0], e->v2->fbcoord[0], ux);
      if (MIN2(r1, r2) > 1) {
        return 0;
      }

      /* We reached the right side before the top side. */
      if (r1 <= r2) {
        LISTBASE_FOREACH (LinkData *, lip, &this->rp) {
          ba = lip->data;
          if (ba->u >= ry && ba->b < ry) {
            *next_x = rx;
            *next_y = ry;
            return ba;
          }
        }
      }
      /* We reached the top side before the right side. */
      else {
        LISTBASE_FOREACH (LinkData *, lip, &this->up) {
          ba = lip->data;
          if (ba->r >= ux && ba->l < ux) {
            *next_x = ux;
            *next_y = uy;
            return ba;
          }
        }
      }
    }
    /* If we are marching towards the bottom. */
    else if (positive_y < 0) {
      by = this->b;
      bx = x + (by - y) / k;
      r1 = ratiod(e->v1->fbcoord[0], e->v2->fbcoord[0], rx);
      r2 = ratiod(e->v1->fbcoord[0], e->v2->fbcoord[0], bx);
      if (MIN2(r1, r2) > 1) {
        return 0;
      }
      if (r1 <= r2) {
        LISTBASE_FOREACH (LinkData *, lip, &this->rp) {
          ba = lip->data;
          if (ba->u >= ry && ba->b < ry) {
            *next_x = rx;
            *next_y = ry;
            return ba;
          }
        }
      }
      else {
        LISTBASE_FOREACH (LinkData *, lip, &this->bp) {
          ba = lip->data;
          if (ba->r >= bx && ba->l < bx) {
            *next_x = bx;
            *next_y = by;
            return ba;
          }
        }
      }
    }
    /* If the line is completely horizontal, in which Y difference == 0. */
    else {
      r1 = ratiod(e->v1->fbcoord[0], e->v2->fbcoord[0], this->r);
      if (r1 > 1) {
        return 0;
      }
      LISTBASE_FOREACH (LinkData *, lip, &this->rp) {
        ba = lip->data;
        if (ba->u >= y && ba->b < y) {
          *next_x = this->r;
          *next_y = y;
          return ba;
        }
      }
    }
  }

  /* If we are marching towards the left. */
  else if (positive_x < 0) {
    lx = this->l;
    ly = y + k * (lx - x);

    /* If we are marching towards the top. */
    if (positive_y > 0) {
      uy = this->u;
      ux = x + (uy - y) / k;
      r1 = ratiod(e->v1->fbcoord[0], e->v2->fbcoord[0], lx);
      r2 = ratiod(e->v1->fbcoord[0], e->v2->fbcoord[0], ux);
      if (MIN2(r1, r2) > 1) {
        return 0;
      }
      if (r1 <= r2) {
        LISTBASE_FOREACH (LinkData *, lip, &this->lp) {
          ba = lip->data;
          if (ba->u >= ly && ba->b < ly) {
            *next_x = lx;
            *next_y = ly;
            return ba;
          }
        }
      }
      else {
        LISTBASE_FOREACH (LinkData *, lip, &this->up) {
          ba = lip->data;
          if (ba->r >= ux && ba->l < ux) {
            *next_x = ux;
            *next_y = uy;
            return ba;
          }
        }
      }
    }

    /* If we are marching towards the bottom. */
    else if (positive_y < 0) {
      by = this->b;
      bx = x + (by - y) / k;
      r1 = ratiod(e->v1->fbcoord[0], e->v2->fbcoord[0], lx);
      r2 = ratiod(e->v1->fbcoord[0], e->v2->fbcoord[0], bx);
      if (MIN2(r1, r2) > 1) {
        return 0;
      }
      if (r1 <= r2) {
        LISTBASE_FOREACH (LinkData *, lip, &this->lp) {
          ba = lip->data;
          if (ba->u >= ly && ba->b < ly) {
            *next_x = lx;
            *next_y = ly;
            return ba;
          }
        }
      }
      else {
        LISTBASE_FOREACH (LinkData *, lip, &this->bp) {
          ba = lip->data;
          if (ba->r >= bx && ba->l < bx) {
            *next_x = bx;
            *next_y = by;
            return ba;
          }
        }
      }
    }
    /* Again, horizontal. */
    else {
      r1 = ratiod(e->v1->fbcoord[0], e->v2->fbcoord[0], this->l);
      if (r1 > 1) {
        return 0;
      }
      LISTBASE_FOREACH (LinkData *, lip, &this->lp) {
        ba = lip->data;
        if (ba->u >= y && ba->b < y) {
          *next_x = this->l;
          *next_y = y;
          return ba;
        }
      }
    }
  }
  /* If the line is completely vertical, hence X difference == 0. */
  else {
    if (positive_y > 0) {
      r1 = ratiod(e->v1->fbcoord[1], e->v2->fbcoord[1], this->u);
      if (r1 > 1) {
        return 0;
      }
      LISTBASE_FOREACH (LinkData *, lip, &this->up) {
        ba = lip->data;
        if (ba->r > x && ba->l <= x) {
          *next_x = x;
          *next_y = this->u;
          return ba;
        }
      }
    }
    else if (positive_y < 0) {
      r1 = ratiod(e->v1->fbcoord[1], e->v2->fbcoord[1], this->b);
      if (r1 > 1) {
        return 0;
      }
      LISTBASE_FOREACH (LinkData *, lip, &this->bp) {
        ba = lip->data;
        if (ba->r > x && ba->l <= x) {
          *next_x = x;
          *next_y = this->b;
          return ba;
        }
      }
    }
    else {
      /* Segment has no length. */
      return 0;
    }
  }
  return 0;
}

bool MOD_lineart_compute_feature_lines(Depsgraph *depsgraph,
                                       LineartGpencilModifierData *lmd,
                                       LineartCache **cached_result,
                                       bool enable_stroke_depth_offset)
{
  LineartRenderBuffer *rb;
  Scene *scene = DEG_get_evaluated_scene(depsgraph);
  int intersections_only = 0; /* Not used right now, but preserve for future. */
  Object *use_camera;

  double t_start;

  if (G.debug_value == 4000) {
    t_start = PIL_check_seconds_timer();
  }

  BKE_scene_camera_switch_update(scene);

  if (lmd->calculation_flags & LRT_USE_CUSTOM_CAMERA) {
    if (!lmd->source_camera ||
        (use_camera = DEG_get_evaluated_object(depsgraph, lmd->source_camera))->type !=
            OB_CAMERA) {
      return false;
    }
  }
  else {
    if (!scene->camera) {
      return false;
    }
    use_camera = scene->camera;
  }

  LineartCache *lc = lineart_init_cache();
  *cached_result = lc;

  rb = lineart_create_render_buffer(scene, lmd, use_camera, scene->camera, lc);

  /* Triangle thread testing data size varies depending on the thread count.
   * See definition of LineartTriangleThread for details. */
  rb->triangle_size = lineart_triangle_size_get(rb);

  /* FIXME(Yiming): See definition of int #LineartRenderBuffer::_source_type for detailed. */
  rb->_source_type = lmd->source_type;
  rb->_source_collection = lmd->source_collection;
  rb->_source_object = lmd->source_object;

  /* Get view vector before loading geometries, because we detect feature lines there. */
  lineart_main_get_view_vector(rb);
  lineart_main_load_geometries(
      depsgraph, scene, use_camera, rb, lmd->calculation_flags & LRT_ALLOW_DUPLI_OBJECTS);

  if (!rb->vertex_buffer_pointers.first) {
    /* No geometry loaded, return early. */
    return true;
  }

  /* Initialize the bounding box acceleration structure, it's a lot like BVH in 3D. */
  lineart_main_bounding_area_make_initial(rb);

  /* We need to get cut into triangles that are crossing near/far plans, only this way can we get
   * correct coordinates of those clipped lines. Done in two steps,
   * setting clip_far==false for near plane. */
  lineart_main_cull_triangles(rb, false);
  /* `clip_far == true` for far plane. */
  lineart_main_cull_triangles(rb, true);

  /* At this point triangle adjacent info pointers is no longer needed, free them. */
  lineart_main_free_adjacent_data(rb);

  /* Do the perspective division after clipping is done. */
  lineart_main_perspective_division(rb);

  lineart_main_discard_out_of_frame_edges(rb);

  /* Triangle intersections are done here during sequential adding of them. Only after this,
   * triangles and lines are all linked with acceleration structure, and the 2D occlusion stage
   * can do its job. */
  lineart_main_add_triangles(rb);

  /* Re-link bounding areas because they have been subdivided by worker threads and we need
   * adjacent info. */
  lineart_main_bounding_areas_connect_post(rb);

  /* Link lines to acceleration structure, this can only be done after perspective division, if
   * we do it after triangles being added, the acceleration structure has already been
   * subdivided, this way we do less list manipulations. */
  lineart_main_link_lines(rb);

  /* "intersection_only" is preserved for being called in a standalone fashion.
   * If so the data will already be available at the stage. Otherwise we do the occlusion and
   * chaining etc. */

  if (!intersections_only) {

    /* Occlusion is work-and-wait. This call will not return before work is completed. */
    lineart_main_occlusion_begin(rb);

    /* Chaining is all single threaded. See lineart_chain.c
     * In this particular call, only lines that are geometrically connected (share the _exact_
     * same end point) will be chained together. */
    MOD_lineart_chain_feature_lines(rb);

    /* We are unable to take care of occlusion if we only connect end points, so here we do a
     * spit, where the splitting point could be any cut in e->segments. */
    MOD_lineart_chain_split_for_fixed_occlusion(rb);

    /* Then we connect chains based on the _proximity_ of their end points in image space, here's
     * the place threshold value gets involved. */
    MOD_lineart_chain_connect(rb);

    float *t_image = &lmd->chaining_image_threshold;
    /* This configuration ensures there won't be accidental lost of short unchained segments. */
    MOD_lineart_chain_discard_short(rb, MIN2(*t_image, 0.001f) - FLT_EPSILON);

    if (rb->chain_smooth_tolerance > FLT_EPSILON) {
      /* Keeping UI range of 0-1 for ease of read while scaling down the actual value for best
       * effective range in image-space (Coordinate only goes from -1 to 1). This value is
       * somewhat arbitrary, but works best for the moment. */
      MOD_lineart_smooth_chains(rb, rb->chain_smooth_tolerance / 50);
    }

    if (rb->use_image_boundary_trimming) {
      MOD_lineart_chain_clip_at_border(rb);
    }

    if (rb->angle_splitting_threshold > FLT_EPSILON) {
      MOD_lineart_chain_split_angle(rb, rb->angle_splitting_threshold);
    }

    if (enable_stroke_depth_offset && lmd->stroke_depth_offset > FLT_EPSILON) {
      MOD_lineart_chain_offset_towards_camera(
          rb, lmd->stroke_depth_offset, lmd->flags & LRT_GPENCIL_OFFSET_TOWARDS_CUSTOM_CAMERA);
    }

    /* Finally transfer the result list into cache. */
    memcpy(&lc->chains, &rb->chains, sizeof(ListBase));

    /* At last, we need to clear flags so we don't confuse GPencil generation calls. */
    MOD_lineart_chain_clear_picked_flag(lc);
  }

  if (G.debug_value == 4000) {
    lineart_count_and_print_render_buffer_memory(rb);

    double t_elapsed = PIL_check_seconds_timer() - t_start;
    printf("Line art total time: %lf\n", t_elapsed);
  }

  return true;
}

static int UNUSED_FUNCTION(lineart_rb_edge_types)(LineartRenderBuffer *rb)
{
  int types = 0;
  types |= rb->use_contour ? LRT_EDGE_FLAG_CONTOUR : 0;
  types |= rb->use_crease ? LRT_EDGE_FLAG_CREASE : 0;
  types |= rb->use_material ? LRT_EDGE_FLAG_MATERIAL : 0;
  types |= rb->use_edge_marks ? LRT_EDGE_FLAG_EDGE_MARK : 0;
  types |= rb->use_intersections ? LRT_EDGE_FLAG_INTERSECTION : 0;
  types |= rb->use_loose ? LRT_EDGE_FLAG_LOOSE : 0;
  return types;
}

static void lineart_gpencil_generate(LineartCache *cache,
                                     Depsgraph *depsgraph,
                                     Object *gpencil_object,
                                     float (*gp_obmat_inverse)[4],
                                     bGPDlayer *UNUSED(gpl),
                                     bGPDframe *gpf,
                                     int level_start,
                                     int level_end,
                                     int material_nr,
                                     Object *source_object,
                                     Collection *source_collection,
                                     int types,
                                     uchar mask_switches,
                                     uchar material_mask_bits,
                                     uchar intersection_mask,
                                     short thickness,
                                     float opacity,
                                     const char *source_vgname,
                                     const char *vgname,
                                     int modifier_flags)
{
  if (cache == NULL) {
    if (G.debug_value == 4000) {
      printf("NULL Lineart cache!\n");
    }
    return;
  }

  int stroke_count = 0;
  int color_idx = 0;

  Object *orig_ob = NULL;
  if (source_object) {
    orig_ob = source_object->id.orig_id ? (Object *)source_object->id.orig_id : source_object;
  }

  Collection *orig_col = NULL;
  if (source_collection) {
    orig_col = source_collection->id.orig_id ? (Collection *)source_collection->id.orig_id :
                                               source_collection;
  }

  /* (!orig_col && !orig_ob) means the whole scene is selected. */

  int enabled_types = cache->rb_edge_types;
  bool invert_input = modifier_flags & LRT_GPENCIL_INVERT_SOURCE_VGROUP;
  bool match_output = modifier_flags & LRT_GPENCIL_MATCH_OUTPUT_VGROUP;

  LISTBASE_FOREACH (LineartEdgeChain *, ec, &cache->chains) {

    if (ec->picked) {
      continue;
    }
    if (!(ec->type & (types & enabled_types))) {
      continue;
    }
    if (ec->level > level_end || ec->level < level_start) {
      continue;
    }
    if (orig_ob && orig_ob != ec->object_ref) {
      continue;
    }
    if (orig_col && ec->object_ref) {
      if (BKE_collection_has_object_recursive_instanced(orig_col, (Object *)ec->object_ref)) {
        if (modifier_flags & LRT_GPENCIL_INVERT_COLLECTION) {
          continue;
        }
      }
      else {
        if (!(modifier_flags & LRT_GPENCIL_INVERT_COLLECTION)) {
          continue;
        }
      }
    }
    if (mask_switches & LRT_GPENCIL_MATERIAL_MASK_ENABLE) {
      if (mask_switches & LRT_GPENCIL_MATERIAL_MASK_MATCH) {
        if (ec->material_mask_bits != material_mask_bits) {
          continue;
        }
      }
      else {
        if (!(ec->material_mask_bits & material_mask_bits)) {
          continue;
        }
      }
    }
    if (ec->type & LRT_EDGE_FLAG_INTERSECTION) {
      if (mask_switches & LRT_GPENCIL_INTERSECTION_MATCH) {
        if (ec->intersection_mask != intersection_mask) {
          continue;
        }
      }
      else {
        if ((intersection_mask) && !(ec->intersection_mask & intersection_mask)) {
          continue;
        }
      }
    }

    /* Preserved: If we ever do asynchronous generation, this picked flag should be set here. */
    // ec->picked = 1;

    const int count = MOD_lineart_chain_count(ec);
    bGPDstroke *gps = BKE_gpencil_stroke_add(gpf, color_idx, count, thickness, false);

    int i;
    LISTBASE_FOREACH_INDEX (LineartEdgeChainItem *, eci, &ec->chain, i) {
      bGPDspoint *point = &gps->points[i];
      mul_v3_m4v3(&point->x, gp_obmat_inverse, eci->gpos);
      point->pressure = 1.0f;
      point->strength = opacity;
    }

    BKE_gpencil_dvert_ensure(gps);
    gps->mat_nr = max_ii(material_nr, 0);

    if (source_vgname && vgname) {
      Object *eval_ob = DEG_get_evaluated_object(depsgraph, ec->object_ref);
      int gpdg = -1;
      if ((match_output || (gpdg = BKE_object_defgroup_name_index(gpencil_object, vgname)) >= 0)) {
        if (eval_ob && eval_ob->type == OB_MESH) {
          int dindex = 0;
          Mesh *me = BKE_object_get_evaluated_mesh(eval_ob);
          if (me->dvert) {
            LISTBASE_FOREACH (bDeformGroup *, db, &me->vertex_group_names) {
              if ((!source_vgname) || strstr(db->name, source_vgname) == db->name) {
                if (match_output) {
                  gpdg = BKE_object_defgroup_name_index(gpencil_object, db->name);
                  if (gpdg < 0) {
                    continue;
                  }
                }
                int sindex = 0, vindex;
                LISTBASE_FOREACH (LineartEdgeChainItem *, eci, &ec->chain) {
                  vindex = eci->index;
                  if (vindex >= me->totvert) {
                    break;
                  }
                  MDeformWeight *mdw = BKE_defvert_ensure_index(&me->dvert[vindex], dindex);
                  MDeformWeight *gdw = BKE_defvert_ensure_index(&gps->dvert[sindex], gpdg);

                  float use_weight = mdw->weight;
                  if (invert_input) {
                    use_weight = 1 - use_weight;
                  }
                  gdw->weight = MAX2(use_weight, gdw->weight);

                  sindex++;
                }
              }
              dindex++;
            }
          }
        }
      }
    }

    if (G.debug_value == 4000) {
      BKE_gpencil_stroke_set_random_color(gps);
    }
    BKE_gpencil_stroke_geometry_update(gpencil_object->data, gps);
    stroke_count++;
  }

  if (G.debug_value == 4000) {
    printf("LRT: Generated %d strokes.\n", stroke_count);
  }
}

void MOD_lineart_gpencil_generate(LineartCache *cache,
                                  Depsgraph *depsgraph,
                                  Object *ob,
                                  bGPDlayer *gpl,
                                  bGPDframe *gpf,
                                  char source_type,
                                  void *source_reference,
                                  int level_start,
                                  int level_end,
                                  int mat_nr,
                                  short edge_types,
                                  uchar mask_switches,
                                  uchar material_mask_bits,
                                  uchar intersection_mask,
                                  short thickness,
                                  float opacity,
                                  const char *source_vgname,
                                  const char *vgname,
                                  int modifier_flags)
{

  if (!gpl || !gpf || !ob) {
    return;
  }

  Object *source_object = NULL;
  Collection *source_collection = NULL;
  short use_types = 0;
  if (source_type == LRT_SOURCE_OBJECT) {
    if (!source_reference) {
      return;
    }
    source_object = (Object *)source_reference;
    /* Note that intersection lines will only be in collection. */
    use_types = edge_types & (~LRT_EDGE_FLAG_INTERSECTION);
  }
  else if (source_type == LRT_SOURCE_COLLECTION) {
    if (!source_reference) {
      return;
    }
    source_collection = (Collection *)source_reference;
    use_types = edge_types;
  }
  else {
    /* Whole scene. */
    use_types = edge_types;
  }
  float gp_obmat_inverse[4][4];
  invert_m4_m4(gp_obmat_inverse, ob->obmat);
  lineart_gpencil_generate(cache,
                           depsgraph,
                           ob,
                           gp_obmat_inverse,
                           gpl,
                           gpf,
                           level_start,
                           level_end,
                           mat_nr,
                           source_object,
                           source_collection,
                           use_types,
                           mask_switches,
                           material_mask_bits,
                           intersection_mask,
                           thickness,
                           opacity,
                           source_vgname,
                           vgname,
                           modifier_flags);
}