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

/** \file
 * \ingroup edgpencil
 */

#include <stdio.h>

#include "MEM_guardedalloc.h"

#include "BLI_utildefines.h"
#include "BLI_blenlib.h"
#include "BLI_math.h"
#include "BLI_stack.h"

#include "BLT_translation.h"

#include "DNA_brush_types.h"
#include "DNA_gpencil_types.h"
#include "DNA_image_types.h"
#include "DNA_meshdata_types.h"
#include "DNA_object_types.h"
#include "DNA_windowmanager_types.h"

#include "BKE_main.h"
#include "BKE_brush.h"
#include "BKE_deform.h"
#include "BKE_image.h"
#include "BKE_gpencil.h"
#include "BKE_material.h"
#include "BKE_context.h"
#include "BKE_screen.h"
#include "BKE_paint.h"

#include "ED_gpencil.h"
#include "ED_screen.h"
#include "ED_space_api.h"
#include "ED_view3d.h"

#include "RNA_access.h"
#include "RNA_define.h"

#include "IMB_imbuf.h"
#include "IMB_imbuf_types.h"

#include "GPU_immediate.h"
#include "GPU_draw.h"
#include "GPU_matrix.h"
#include "GPU_framebuffer.h"
#include "GPU_state.h"

#include "UI_interface.h"

#include "WM_api.h"
#include "WM_types.h"

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

#include "gpencil_intern.h"

#define LEAK_HORZ 0
#define LEAK_VERT 1

/* Temporary fill operation data (op->customdata) */
typedef struct tGPDfill {
  bContext *C;
  struct Main *bmain;
  struct Depsgraph *depsgraph;
  /** window where painting originated */
  struct wmWindow *win;
  /** current scene from context */
  struct Scene *scene;
  /** current active gp object */
  struct Object *ob;
  /** area where painting originated */
  struct ScrArea *sa;
  /** region where painting originated */
  struct RegionView3D *rv3d;
  /** view3 where painting originated */
  struct View3D *v3d;
  /** region where painting originated */
  struct ARegion *ar;
  /** current GP datablock */
  struct bGPdata *gpd;
  /** current material */
  struct Material *mat;
  /** layer */
  struct bGPDlayer *gpl;
  /** frame */
  struct bGPDframe *gpf;

  /** flags */
  short flag;
  /** avoid too fast events */
  short oldkey;
  /** send to back stroke */
  bool on_back;

  /** mouse fill center position */
  int center[2];
  /** windows width */
  int sizex;
  /** window height */
  int sizey;
  /** lock to viewport axis */
  int lock_axis;

  /** number of pixel to consider the leak is too small (x 2) */
  short fill_leak;
  /** factor for transparency */
  float fill_threshold;
  /** number of simplify steps */
  int fill_simplylvl;
  /** boundary limits drawing mode */
  int fill_draw_mode;
  /* scaling factor */
  short fill_factor;

  /** number of elements currently in cache */
  short sbuffer_size;
  /** temporary points */
  void *sbuffer;
  /** depth array for reproject */
  float *depth_arr;

  /** temp image */
  Image *ima;
  /** temp points data */
  BLI_Stack *stack;
  /** handle for drawing strokes while operator is running 3d stuff */
  void *draw_handle_3d;

  /* tmp size x */
  int bwinx;
  /* tmp size y */
  int bwiny;
  rcti brect;

} tGPDfill;

/* draw a given stroke using same thickness and color for all points */
static void gp_draw_basic_stroke(tGPDfill *tgpf,
                                 bGPDstroke *gps,
                                 const float diff_mat[4][4],
                                 const bool cyclic,
                                 const float ink[4],
                                 const int flag,
                                 const float thershold)
{
  bGPDspoint *points = gps->points;

  Material *ma = tgpf->mat;
  MaterialGPencilStyle *gp_style = ma->gp_style;

  int totpoints = gps->totpoints;
  float fpt[3];
  float col[4];

  copy_v4_v4(col, ink);

  /* if cyclic needs more vertex */
  int cyclic_add = (cyclic) ? 1 : 0;

  GPUVertFormat *format = immVertexFormat();
  uint pos = GPU_vertformat_attr_add(format, "pos", GPU_COMP_F32, 3, GPU_FETCH_FLOAT);
  uint color = GPU_vertformat_attr_add(format, "color", GPU_COMP_F32, 4, GPU_FETCH_FLOAT);

  immBindBuiltinProgram(GPU_SHADER_3D_FLAT_COLOR);

  /* draw stroke curve */
  GPU_line_width(1.0f);
  immBeginAtMost(GPU_PRIM_LINE_STRIP, totpoints + cyclic_add);
  const bGPDspoint *pt = points;

  for (int i = 0; i < totpoints; i++, pt++) {

    if (flag & GP_BRUSH_FILL_HIDE) {
      float alpha = gp_style->stroke_rgba[3] * pt->strength;
      CLAMP(alpha, 0.0f, 1.0f);
      col[3] = alpha <= thershold ? 0.0f : 1.0f;
    }
    else {
      col[3] = 1.0f;
    }
    /* set point */
    immAttr4fv(color, col);
    mul_v3_m4v3(fpt, diff_mat, &pt->x);
    immVertex3fv(pos, fpt);
  }

  if (cyclic && totpoints > 2) {
    /* draw line to first point to complete the cycle */
    immAttr4fv(color, col);
    mul_v3_m4v3(fpt, diff_mat, &points->x);
    immVertex3fv(pos, fpt);
  }

  immEnd();
  immUnbindProgram();
}

/* loop all layers */
static void gp_draw_datablock(tGPDfill *tgpf, const float ink[4])
{
  /* duplicated: etempFlags */
  enum {
    GP_DRAWFILLS_NOSTATUS = (1 << 0), /* don't draw status info */
    GP_DRAWFILLS_ONLY3D = (1 << 1),   /* only draw 3d-strokes */
  };

  Object *ob = tgpf->ob;
  bGPdata *gpd = tgpf->gpd;
  int cfra_eval = (int)DEG_get_ctime(tgpf->depsgraph);

  tGPDdraw tgpw;
  tgpw.rv3d = tgpf->rv3d;
  tgpw.depsgraph = tgpf->depsgraph;
  tgpw.ob = ob;
  tgpw.gpd = gpd;
  tgpw.offsx = 0;
  tgpw.offsy = 0;
  tgpw.winx = tgpf->ar->winx;
  tgpw.winy = tgpf->ar->winy;
  tgpw.dflag = 0;
  tgpw.disable_fill = 1;
  tgpw.dflag |= (GP_DRAWFILLS_ONLY3D | GP_DRAWFILLS_NOSTATUS);

  GPU_blend(true);

  for (bGPDlayer *gpl = gpd->layers.first; gpl; gpl = gpl->next) {
    /* calculate parent position */
    ED_gpencil_parent_location(tgpw.depsgraph, ob, gpd, gpl, tgpw.diff_mat);

    /* do not draw layer if hidden */
    if (gpl->flag & GP_LAYER_HIDE) {
      continue;
    }

    /* if active layer and no keyframe, create a new one */
    if (gpl == tgpf->gpl) {
      if ((gpl->actframe == NULL) || (gpl->actframe->framenum != cfra_eval)) {
        BKE_gpencil_layer_getframe(gpl, cfra_eval, GP_GETFRAME_ADD_NEW);
      }
    }

    /* get frame to draw */
    bGPDframe *gpf = BKE_gpencil_layer_getframe(gpl, cfra_eval, GP_GETFRAME_USE_PREV);
    if (gpf == NULL) {
      continue;
    }

    for (bGPDstroke *gps = gpf->strokes.first; gps; gps = gps->next) {
      /* check if stroke can be drawn */
      if ((gps->points == NULL) || (gps->totpoints < 2)) {
        continue;
      }
      /* check if the color is visible */
      MaterialGPencilStyle *gp_style = BKE_material_gpencil_settings_get(ob, gps->mat_nr + 1);
      if ((gp_style == NULL) || (gp_style->flag & GP_STYLE_COLOR_HIDE)) {
        continue;
      }

      tgpw.gps = gps;
      tgpw.gpl = gpl;
      tgpw.gpf = gpf;
      tgpw.t_gpf = gpf;

      /* reduce thickness to avoid gaps */
      tgpw.is_fill_stroke = (tgpf->fill_draw_mode == GP_FILL_DMODE_CONTROL) ? false : true;
      tgpw.lthick = gpl->line_change;
      tgpw.opacity = 1.0;
      copy_v4_v4(tgpw.tintcolor, ink);
      tgpw.onion = true;
      tgpw.custonion = true;

      bool textured_stroke = (gp_style->stroke_style == GP_STYLE_STROKE_STYLE_TEXTURE);

      /* normal strokes */
      if (((tgpf->fill_draw_mode == GP_FILL_DMODE_STROKE) ||
           (tgpf->fill_draw_mode == GP_FILL_DMODE_BOTH)) &&
          !textured_stroke) {
        ED_gp_draw_fill(&tgpw);
      }

      /* 3D Lines with basic shapes and invisible lines */
      if ((tgpf->fill_draw_mode == GP_FILL_DMODE_CONTROL) ||
          (tgpf->fill_draw_mode == GP_FILL_DMODE_BOTH) || textured_stroke) {
        gp_draw_basic_stroke(tgpf,
                             gps,
                             tgpw.diff_mat,
                             gps->flag & GP_STROKE_CYCLIC,
                             ink,
                             tgpf->flag,
                             tgpf->fill_threshold);
      }
    }
  }

  GPU_blend(false);
}

/* draw strokes in offscreen buffer */
static bool gp_render_offscreen(tGPDfill *tgpf)
{
  bool is_ortho = false;
  float winmat[4][4];

  if (!tgpf->gpd) {
    return false;
  }

  /* set temporary new size */
  tgpf->bwinx = tgpf->ar->winx;
  tgpf->bwiny = tgpf->ar->winy;
  tgpf->brect = tgpf->ar->winrct;

  /* resize ar */
  tgpf->ar->winrct.xmin = 0;
  tgpf->ar->winrct.ymin = 0;
  tgpf->ar->winrct.xmax = (int)tgpf->ar->winx * tgpf->fill_factor;
  tgpf->ar->winrct.ymax = (int)tgpf->ar->winy * tgpf->fill_factor;
  tgpf->ar->winx = (short)abs(tgpf->ar->winrct.xmax - tgpf->ar->winrct.xmin);
  tgpf->ar->winy = (short)abs(tgpf->ar->winrct.ymax - tgpf->ar->winrct.ymin);

  /* save new size */
  tgpf->sizex = (int)tgpf->ar->winx;
  tgpf->sizey = (int)tgpf->ar->winy;

  /* adjust center */
  float center[2];
  center[0] = (float)tgpf->center[0] * ((float)tgpf->ar->winx / (float)tgpf->bwinx);
  center[1] = (float)tgpf->center[1] * ((float)tgpf->ar->winy / (float)tgpf->bwiny);
  round_v2i_v2fl(tgpf->center, center);

  char err_out[256] = "unknown";
  GPUOffScreen *offscreen = GPU_offscreen_create(
      tgpf->sizex, tgpf->sizey, 0, true, false, err_out);
  if (offscreen == NULL) {
    printf("GPencil - Fill - Unable to create fill buffer\n");
    return false;
  }

  GPU_offscreen_bind(offscreen, true);
  uint flag = IB_rect | IB_rectfloat;
  ImBuf *ibuf = IMB_allocImBuf(tgpf->sizex, tgpf->sizey, 32, flag);

  rctf viewplane;
  float clip_start, clip_end;

  is_ortho = ED_view3d_viewplane_get(tgpf->depsgraph,
                                     tgpf->v3d,
                                     tgpf->rv3d,
                                     tgpf->sizex,
                                     tgpf->sizey,
                                     &viewplane,
                                     &clip_start,
                                     &clip_end,
                                     NULL);
  if (is_ortho) {
    orthographic_m4(winmat,
                    viewplane.xmin,
                    viewplane.xmax,
                    viewplane.ymin,
                    viewplane.ymax,
                    -clip_end,
                    clip_end);
  }
  else {
    perspective_m4(winmat,
                   viewplane.xmin,
                   viewplane.xmax,
                   viewplane.ymin,
                   viewplane.ymax,
                   clip_start,
                   clip_end);
  }

  GPU_matrix_push_projection();
  GPU_matrix_identity_set();
  GPU_matrix_push();
  GPU_matrix_identity_set();

  glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
  glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

  ED_view3d_update_viewmat(
      tgpf->depsgraph, tgpf->scene, tgpf->v3d, tgpf->ar, NULL, winmat, NULL, true);
  /* set for opengl */
  GPU_matrix_projection_set(tgpf->rv3d->winmat);
  GPU_matrix_set(tgpf->rv3d->viewmat);

  /* draw strokes */
  float ink[4] = {1.0f, 0.0f, 0.0f, 1.0f};
  gp_draw_datablock(tgpf, ink);

  GPU_matrix_pop_projection();
  GPU_matrix_pop();

  /* create a image to see result of template */
  if (ibuf->rect_float) {
    GPU_offscreen_read_pixels(offscreen, GL_FLOAT, ibuf->rect_float);
  }
  else if (ibuf->rect) {
    GPU_offscreen_read_pixels(offscreen, GL_UNSIGNED_BYTE, ibuf->rect);
  }
  if (ibuf->rect_float && ibuf->rect) {
    IMB_rect_from_float(ibuf);
  }

  tgpf->ima = BKE_image_add_from_imbuf(tgpf->bmain, ibuf, "GP_fill");
  tgpf->ima->id.tag |= LIB_TAG_DOIT;

  BKE_image_release_ibuf(tgpf->ima, ibuf, NULL);

  /* switch back to window-system-provided framebuffer */
  GPU_offscreen_unbind(offscreen, true);
  GPU_offscreen_free(offscreen);

  return true;
}

/* return pixel data (rgba) at index */
static void get_pixel(const ImBuf *ibuf, const int idx, float r_col[4])
{
  if (ibuf->rect_float) {
    const float *frgba = &ibuf->rect_float[idx * 4];
    copy_v4_v4(r_col, frgba);
  }
  else {
    /* XXX: This case probably doesn't happen, as we only write to the float buffer,
     * but we get compiler warnings about uninitialized vars otherwise
     */
    BLI_assert(!"gpencil_fill.c - get_pixel() non-float case is used!");
    zero_v4(r_col);
  }
}

/* set pixel data (rgba) at index */
static void set_pixel(ImBuf *ibuf, int idx, const float col[4])
{
  // BLI_assert(idx <= ibuf->x * ibuf->y);
  if (ibuf->rect) {
    uint *rrect = &ibuf->rect[idx];
    uchar ccol[4];

    rgba_float_to_uchar(ccol, col);
    *rrect = *((uint *)ccol);
  }

  if (ibuf->rect_float) {
    float *rrectf = &ibuf->rect_float[idx * 4];
    copy_v4_v4(rrectf, col);
  }
}

/* check if the size of the leak is narrow to determine if the stroke is closed
 * this is used for strokes with small gaps between them to get a full fill
 * and do not get a full screen fill.
 *
 * \param ibuf: Image pixel data
 * \param maxpixel: Maximum index
 * \param limit: Limit of pixels to analyze
 * \param index: Index of current pixel
 * \param type: 0-Horizontal 1-Vertical
 */
static bool is_leak_narrow(ImBuf *ibuf, const int maxpixel, int limit, int index, int type)
{
  float rgba[4];
  int i;
  int pt;
  bool t_a = false;
  bool t_b = false;

  /* Horizontal leak (check vertical pixels)
   * X
   * X
   * xB7
   * X
   * X
   */
  if (type == LEAK_HORZ) {
    /* pixels on top */
    for (i = 1; i <= limit; i++) {
      pt = index + (ibuf->x * i);
      if (pt <= maxpixel) {
        get_pixel(ibuf, pt, rgba);
        if (rgba[0] == 1.0f) {
          t_a = true;
          break;
        }
      }
      else {
        /* edge of image*/
        t_a = true;
        break;
      }
    }
    /* pixels on bottom */
    for (i = 1; i <= limit; i++) {
      pt = index - (ibuf->x * i);
      if (pt >= 0) {
        get_pixel(ibuf, pt, rgba);
        if (rgba[0] == 1.0f) {
          t_b = true;
          break;
        }
      }
      else {
        /* edge of image*/
        t_b = true;
        break;
      }
    }
  }

  /* Vertical leak (check horizontal pixels)
   *
   * XXXxB7XX
   */
  if (type == LEAK_VERT) {
    /* get pixel range of the row */
    int row = index / ibuf->x;
    int lowpix = row * ibuf->x;
    int higpix = lowpix + ibuf->x - 1;

    /* pixels to right */
    for (i = 0; i < limit; i++) {
      pt = index - (limit - i);
      if (pt >= lowpix) {
        get_pixel(ibuf, pt, rgba);
        if (rgba[0] == 1.0f) {
          t_a = true;
          break;
        }
      }
      else {
        t_a = true; /* edge of image*/
        break;
      }
    }
    /* pixels to left */
    for (i = 0; i < limit; i++) {
      pt = index + (limit - i);
      if (pt <= higpix) {
        get_pixel(ibuf, pt, rgba);
        if (rgba[0] == 1.0f) {
          t_b = true;
          break;
        }
      }
      else {
        t_b = true; /* edge of image */
        break;
      }
    }
  }
  return (bool)(t_a && t_b);
}

/* Boundary fill inside strokes
 * Fills the space created by a set of strokes using the stroke color as the boundary
 * of the shape to fill.
 *
 * \param tgpf: Temporary fill data
 */
static void gpencil_boundaryfill_area(tGPDfill *tgpf)
{
  ImBuf *ibuf;
  float rgba[4];
  void *lock;
  const float fill_col[4] = {0.0f, 1.0f, 0.0f, 1.0f};
  ibuf = BKE_image_acquire_ibuf(tgpf->ima, NULL, &lock);
  const int maxpixel = (ibuf->x * ibuf->y) - 1;

  BLI_Stack *stack = BLI_stack_new(sizeof(int), __func__);

  /* calculate index of the seed point using the position of the mouse */
  int index = (tgpf->sizex * tgpf->center[1]) + tgpf->center[0];
  if ((index >= 0) && (index <= maxpixel)) {
    BLI_stack_push(stack, &index);
  }

  /* the fill use a stack to save the pixel list instead of the common recursive
   * 4-contact point method.
   * The problem with recursive calls is that for big fill areas, we can get max limit
   * of recursive calls and STACK_OVERFLOW error.
   *
   * The 4-contact point analyze the pixels to the left, right, bottom and top
   *      -----------
   *      |    X    |
   *      |   XoX   |
   *      |    X    |
   *      -----------
   */
  while (!BLI_stack_is_empty(stack)) {
    int v;

    BLI_stack_pop(stack, &v);

    get_pixel(ibuf, v, rgba);

    if (true) { /* Was: 'rgba' */
      /* check if no border(red) or already filled color(green) */
      if ((rgba[0] != 1.0f) && (rgba[1] != 1.0f)) {
        /* fill current pixel with green */
        set_pixel(ibuf, v, fill_col);

        /* add contact pixels */
        /* pixel left */
        if (v - 1 >= 0) {
          index = v - 1;
          if (!is_leak_narrow(ibuf, maxpixel, tgpf->fill_leak, v, LEAK_HORZ)) {
            BLI_stack_push(stack, &index);
          }
        }
        /* pixel right */
        if (v + 1 <= maxpixel) {
          index = v + 1;
          if (!is_leak_narrow(ibuf, maxpixel, tgpf->fill_leak, v, LEAK_HORZ)) {
            BLI_stack_push(stack, &index);
          }
        }
        /* pixel top */
        if (v + ibuf->x <= maxpixel) {
          index = v + ibuf->x;
          if (!is_leak_narrow(ibuf, maxpixel, tgpf->fill_leak, v, LEAK_VERT)) {
            BLI_stack_push(stack, &index);
          }
        }
        /* pixel bottom */
        if (v - ibuf->x >= 0) {
          index = v - ibuf->x;
          if (!is_leak_narrow(ibuf, maxpixel, tgpf->fill_leak, v, LEAK_VERT)) {
            BLI_stack_push(stack, &index);
          }
        }
      }
    }
  }

  /* release ibuf */
  if (ibuf) {
    BKE_image_release_ibuf(tgpf->ima, ibuf, lock);
  }

  tgpf->ima->id.tag |= LIB_TAG_DOIT;
  /* free temp stack data */
  BLI_stack_free(stack);
}

/* clean external border of image to avoid infinite loops */
static void gpencil_clean_borders(tGPDfill *tgpf)
{
  ImBuf *ibuf;
  void *lock;
  const float fill_col[4] = {0.0f, 0.0f, 0.0f, 0.0f};
  ibuf = BKE_image_acquire_ibuf(tgpf->ima, NULL, &lock);
  int idx;
  int pixel = 0;

  /* horizontal lines */
  for (idx = 0; idx < ibuf->x; idx++) {
    /* bottom line */
    set_pixel(ibuf, idx, fill_col);
    /* top line */
    pixel = idx + (ibuf->x * (ibuf->y - 1));
    set_pixel(ibuf, pixel, fill_col);
  }
  /* vertical lines */
  for (idx = 0; idx < ibuf->y; idx++) {
    /* left line */
    set_pixel(ibuf, ibuf->x * idx, fill_col);
    /* right line */
    pixel = ibuf->x * idx + (ibuf->x - 1);
    set_pixel(ibuf, pixel, fill_col);
  }

  /* release ibuf */
  if (ibuf) {
    BKE_image_release_ibuf(tgpf->ima, ibuf, lock);
  }

  tgpf->ima->id.tag |= LIB_TAG_DOIT;
}

/* Naive dilate
 *
 * Expand green areas into enclosing red areas.
 * Using stack prevents creep when replacing colors directly.
 * -----------
 *  XXXXXXX
 *  XoooooX
 *  XXooXXX
 *   XXXX
 * -----------
 */
static void dilate(ImBuf *ibuf)
{
  BLI_Stack *stack = BLI_stack_new(sizeof(int), __func__);
  const float green[4] = {0.0f, 1.0f, 0.0f, 1.0f};
  const int maxpixel = (ibuf->x * ibuf->y) - 1;
  /* detect pixels and expand into red areas */
  for (int v = maxpixel; v != 0; v--) {
    float color[4];
    int index;
    int tp = 0;
    int bm = 0;
    int lt = 0;
    int rt = 0;
    get_pixel(ibuf, v, color);
    if (color[1] == 1.0f) {
      /* pixel left */
      if (v - 1 >= 0) {
        index = v - 1;
        get_pixel(ibuf, index, color);
        if (color[0] == 1.0f) {
          BLI_stack_push(stack, &index);
          lt = index;
        }
      }
      /* pixel right */
      if (v + 1 <= maxpixel) {
        index = v + 1;
        get_pixel(ibuf, index, color);
        if (color[0] == 1.0f) {
          BLI_stack_push(stack, &index);
          rt = index;
        }
      }
      /* pixel top */
      if (v + ibuf->x <= maxpixel) {
        index = v + ibuf->x;
        get_pixel(ibuf, index, color);
        if (color[0] == 1.0f) {
          BLI_stack_push(stack, &index);
          tp = index;
        }
      }
      /* pixel bottom */
      if (v - ibuf->x >= 0) {
        index = v - ibuf->x;
        get_pixel(ibuf, index, color);
        if (color[0] == 1.0f) {
          BLI_stack_push(stack, &index);
          bm = index;
        }
      }
      /* pixel top-left */
      if (tp && lt) {
        index = tp - 1;
        get_pixel(ibuf, index, color);
        if (color[0] == 1.0f) {
          BLI_stack_push(stack, &index);
        }
      }
      /* pixel top-right */
      if (tp && rt) {
        index = tp + 1;
        get_pixel(ibuf, index, color);
        if (color[0] == 1.0f) {
          BLI_stack_push(stack, &index);
        }
      }
      /* pixel bottom-left */
      if (bm && lt) {
        index = bm - 1;
        get_pixel(ibuf, index, color);
        if (color[0] == 1.0f) {
          BLI_stack_push(stack, &index);
        }
      }
      /* pixel bottom-right */
      if (bm && rt) {
        index = bm + 1;
        get_pixel(ibuf, index, color);
        if (color[0] == 1.0f) {
          BLI_stack_push(stack, &index);
        }
      }
    }
  }
  /* set dilated pixels */
  while (!BLI_stack_is_empty(stack)) {
    int v;
    BLI_stack_pop(stack, &v);
    set_pixel(ibuf, v, green);
  }
  BLI_stack_free(stack);
}

/* Get the outline points of a shape using Moore Neighborhood algorithm
 *
 * This is a Blender customized version of the general algorithm described
 * in https://en.wikipedia.org/wiki/Moore_neighborhood
 */
static void gpencil_get_outline_points(tGPDfill *tgpf)
{
  ImBuf *ibuf;
  float rgba[4];
  void *lock;
  int v[2];
  int boundary_co[2];
  int start_co[2];
  int backtracked_co[2];
  int current_check_co[2];
  int prev_check_co[2];
  int backtracked_offset[1][2] = {{0, 0}};
  // bool boundary_found = false;
  bool start_found = false;
  const int NEIGHBOR_COUNT = 8;

  const int offset[8][2] = {
      {-1, -1},
      {0, -1},
      {1, -1},
      {1, 0},
      {1, 1},
      {0, 1},
      {-1, 1},
      {-1, 0},
  };

  tgpf->stack = BLI_stack_new(sizeof(int[2]), __func__);

  ibuf = BKE_image_acquire_ibuf(tgpf->ima, NULL, &lock);
  int imagesize = ibuf->x * ibuf->y;

  /* dilate */
  dilate(ibuf);

  /* find the initial point to start outline analysis */
  for (int idx = imagesize - 1; idx != 0; idx--) {
    get_pixel(ibuf, idx, rgba);
    if (rgba[1] == 1.0f) {
      boundary_co[0] = idx % ibuf->x;
      boundary_co[1] = idx / ibuf->x;
      copy_v2_v2_int(start_co, boundary_co);
      backtracked_co[0] = (idx - 1) % ibuf->x;
      backtracked_co[1] = (idx - 1) / ibuf->x;
      backtracked_offset[0][0] = backtracked_co[0] - boundary_co[0];
      backtracked_offset[0][1] = backtracked_co[1] - boundary_co[1];
      copy_v2_v2_int(prev_check_co, start_co);

      BLI_stack_push(tgpf->stack, &boundary_co);
      start_found = true;
      break;
    }
  }

  while (start_found) {
    int cur_back_offset = -1;
    for (int i = 0; i < NEIGHBOR_COUNT; i++) {
      if (backtracked_offset[0][0] == offset[i][0] && backtracked_offset[0][1] == offset[i][1]) {
        /* Finding the bracktracked pixel offset index */
        cur_back_offset = i;
        break;
      }
    }

    int loop = 0;
    while (loop < (NEIGHBOR_COUNT - 1) && cur_back_offset != -1) {
      int offset_idx = (cur_back_offset + 1) % NEIGHBOR_COUNT;
      current_check_co[0] = boundary_co[0] + offset[offset_idx][0];
      current_check_co[1] = boundary_co[1] + offset[offset_idx][1];

      int image_idx = ibuf->x * current_check_co[1] + current_check_co[0];
      get_pixel(ibuf, image_idx, rgba);

      /* find next boundary pixel */
      if (rgba[1] == 1.0f) {
        copy_v2_v2_int(boundary_co, current_check_co);
        copy_v2_v2_int(backtracked_co, prev_check_co);
        backtracked_offset[0][0] = backtracked_co[0] - boundary_co[0];
        backtracked_offset[0][1] = backtracked_co[1] - boundary_co[1];

        BLI_stack_push(tgpf->stack, &boundary_co);

        break;
      }
      copy_v2_v2_int(prev_check_co, current_check_co);
      cur_back_offset++;
      loop++;
    }
    /* current pixel is equal to starting pixel */
    if (boundary_co[0] == start_co[0] && boundary_co[1] == start_co[1]) {
      BLI_stack_pop(tgpf->stack, &v);
      // boundary_found = true;
      break;
    }
  }

  /* release ibuf */
  if (ibuf) {
    BKE_image_release_ibuf(tgpf->ima, ibuf, lock);
  }
}

/* get z-depth array to reproject on surface */
static void gpencil_get_depth_array(tGPDfill *tgpf)
{
  tGPspoint *ptc;
  ToolSettings *ts = tgpf->scene->toolsettings;
  int totpoints = tgpf->sbuffer_size;
  int i = 0;

  if (totpoints == 0) {
    return;
  }

  /* for surface sketching, need to set the right OpenGL context stuff so that
   * the conversions will project the values correctly...
   */
  if (ts->gpencil_v3d_align & GP_PROJECT_DEPTH_VIEW) {
    /* need to restore the original projection settings before packing up */
    view3d_region_operator_needs_opengl(tgpf->win, tgpf->ar);
    ED_view3d_autodist_init(tgpf->depsgraph, tgpf->ar, tgpf->v3d, 0);

    /* Since strokes are so fine, when using their depth we need a margin
     * otherwise they might get missed. */
    int depth_margin = 0;

    /* get an array of depths, far depths are blended */
    int mval_prev[2] = {0};
    int interp_depth = 0;
    int found_depth = 0;

    tgpf->depth_arr = MEM_mallocN(sizeof(float) * totpoints, "depth_points");

    for (i = 0, ptc = tgpf->sbuffer; i < totpoints; i++, ptc++) {

      int mval_i[2];
      round_v2i_v2fl(mval_i, &ptc->x);

      if ((ED_view3d_autodist_depth(tgpf->ar, mval_i, depth_margin, tgpf->depth_arr + i) == 0) &&
          (i && (ED_view3d_autodist_depth_seg(
                     tgpf->ar, mval_i, mval_prev, depth_margin + 1, tgpf->depth_arr + i) == 0))) {
        interp_depth = true;
      }
      else {
        found_depth = true;
      }

      copy_v2_v2_int(mval_prev, mval_i);
    }

    if (found_depth == false) {
      /* eeh... not much we can do.. :/, ignore depth in this case */
      for (i = totpoints - 1; i >= 0; i--) {
        tgpf->depth_arr[i] = 0.9999f;
      }
    }
    else {
      if (interp_depth) {
        interp_sparse_array(tgpf->depth_arr, totpoints, FLT_MAX);
      }
    }
  }
}

/* create array of points using stack as source */
static void gpencil_points_from_stack(tGPDfill *tgpf)
{
  tGPspoint *point2D;
  int totpoints = BLI_stack_count(tgpf->stack);
  if (totpoints == 0) {
    return;
  }

  tgpf->sbuffer_size = (short)totpoints;
  tgpf->sbuffer = MEM_callocN(sizeof(tGPspoint) * totpoints, __func__);

  point2D = tgpf->sbuffer;
  while (!BLI_stack_is_empty(tgpf->stack)) {
    int v[2];
    BLI_stack_pop(tgpf->stack, &v);
    copy_v2fl_v2i(&point2D->x, v);
    /* shift points to center of pixel */
    add_v2_fl(&point2D->x, 0.5f);
    point2D->pressure = 1.0f;
    point2D->strength = 1.0f;
    point2D->time = 0.0f;
    point2D++;
  }
}

/* create a grease pencil stroke using points in buffer */
static void gpencil_stroke_from_buffer(tGPDfill *tgpf)
{
  const int cfra_eval = (int)DEG_get_ctime(tgpf->depsgraph);

  ToolSettings *ts = tgpf->scene->toolsettings;
  const char *align_flag = &ts->gpencil_v3d_align;
  const bool is_depth = (bool)(*align_flag & (GP_PROJECT_DEPTH_VIEW | GP_PROJECT_DEPTH_STROKE));
  const bool is_camera = (bool)(ts->gp_sculpt.lock_axis == 0) &&
                         (tgpf->rv3d->persp == RV3D_CAMOB) && (!is_depth);
  Brush *brush = BKE_paint_brush(&ts->gp_paint->paint);
  if (brush == NULL) {
    return;
  }

  bGPDspoint *pt;
  MDeformVert *dvert = NULL;
  tGPspoint *point2D;

  if (tgpf->sbuffer_size == 0) {
    return;
  }

  /* get frame or create a new one */
  tgpf->gpf = BKE_gpencil_layer_getframe(tgpf->gpl, cfra_eval, GP_GETFRAME_ADD_NEW);

  /* create new stroke */
  bGPDstroke *gps = MEM_callocN(sizeof(bGPDstroke), "bGPDstroke");
  gps->thickness = brush->size;
  gps->gradient_f = brush->gpencil_settings->gradient_f;
  copy_v2_v2(gps->gradient_s, brush->gpencil_settings->gradient_s);
  gps->inittime = 0.0f;

  /* the polygon must be closed, so enabled cyclic */
  gps->flag |= GP_STROKE_CYCLIC;
  gps->flag |= GP_STROKE_3DSPACE;

  gps->mat_nr = BKE_gpencil_object_material_ensure(tgpf->bmain, tgpf->ob, tgpf->mat);

  /* allocate memory for storage points */
  gps->totpoints = tgpf->sbuffer_size;
  gps->points = MEM_callocN(sizeof(bGPDspoint) * tgpf->sbuffer_size, "gp_stroke_points");

  /* initialize triangle memory to dummy data */
  gps->tot_triangles = 0;
  gps->triangles = NULL;
  gps->flag |= GP_STROKE_RECALC_GEOMETRY;

  /* add stroke to frame */
  if ((ts->gpencil_flags & GP_TOOL_FLAG_PAINT_ONBACK) || (tgpf->on_back == true)) {
    BLI_addhead(&tgpf->gpf->strokes, gps);
  }
  else {
    BLI_addtail(&tgpf->gpf->strokes, gps);
  }

  /* add points */
  pt = gps->points;
  point2D = (tGPspoint *)tgpf->sbuffer;

  const int def_nr = tgpf->ob->actdef - 1;
  const bool have_weight = (bool)BLI_findlink(&tgpf->ob->defbase, def_nr);

  if ((ts->gpencil_flags & GP_TOOL_FLAG_CREATE_WEIGHTS) && (have_weight)) {
    BKE_gpencil_dvert_ensure(gps);
    dvert = gps->dvert;
  }

  for (int i = 0; i < tgpf->sbuffer_size && point2D; i++, point2D++, pt++) {
    /* convert screen-coordinates to 3D coordinates */
    gp_stroke_convertcoords_tpoint(tgpf->scene,
                                   tgpf->ar,
                                   tgpf->ob,
                                   tgpf->gpl,
                                   point2D,
                                   tgpf->depth_arr ? tgpf->depth_arr + i : NULL,
                                   &pt->x);

    pt->pressure = 1.0f;
    pt->strength = 1.0f;
    pt->time = 0.0f;

    if ((ts->gpencil_flags & GP_TOOL_FLAG_CREATE_WEIGHTS) && (have_weight)) {
      MDeformWeight *dw = defvert_verify_index(dvert, def_nr);
      if (dw) {
        dw->weight = ts->vgroup_weight;
      }

      dvert++;
    }
    else {
      if (dvert != NULL) {
        dvert->totweight = 0;
        dvert->dw = NULL;
        dvert++;
      }
    }
  }

  /* smooth stroke */
  float reduce = 0.0f;
  float smoothfac = 1.0f;
  for (int r = 0; r < 1; r++) {
    for (int i = 0; i < gps->totpoints; i++) {
      BKE_gpencil_smooth_stroke(gps, i, smoothfac - reduce);
    }
    reduce += 0.25f;  // reduce the factor
  }

  /* if axis locked, reproject to plane locked */
  if ((tgpf->lock_axis > GP_LOCKAXIS_VIEW) &&
      ((ts->gpencil_v3d_align & GP_PROJECT_DEPTH_VIEW) == 0)) {
    float origin[3];
    ED_gp_get_drawing_reference(tgpf->scene, tgpf->ob, tgpf->gpl, ts->gpencil_v3d_align, origin);
    ED_gp_project_stroke_to_plane(
        tgpf->scene, tgpf->ob, tgpf->rv3d, gps, origin, tgpf->lock_axis - 1);
  }

  /* if parented change position relative to parent object */
  for (int a = 0; a < tgpf->sbuffer_size; a++) {
    pt = &gps->points[a];
    gp_apply_parent_point(tgpf->depsgraph, tgpf->ob, tgpf->gpd, tgpf->gpl, pt);
  }

  /* if camera view, reproject flat to view to avoid perspective effect */
  if (is_camera) {
    ED_gpencil_project_stroke_to_view(tgpf->C, tgpf->gpl, gps);
  }

  /* simplify stroke */
  for (int b = 0; b < tgpf->fill_simplylvl; b++) {
    BKE_gpencil_simplify_fixed(gps);
  }
}

/* ----------------------- */
/* Drawing                 */
/* Helper: Draw status message while the user is running the operator */
static void gpencil_fill_status_indicators(bContext *C, tGPDfill *UNUSED(tgpf))
{
  const char *status_str = TIP_("Fill: ESC/RMB cancel, LMB Fill, Shift Draw on Back");
  ED_workspace_status_text(C, status_str);
}

/* draw boundary lines to see fill limits */
static void gpencil_draw_boundary_lines(const bContext *UNUSED(C), tGPDfill *tgpf)
{
  if (!tgpf->gpd) {
    return;
  }
  const float ink[4] = {1.0f, 0.0f, 0.0f, 1.0f};
  gp_draw_datablock(tgpf, ink);
}

/* Drawing callback for modal operator in 3d mode */
static void gpencil_fill_draw_3d(const bContext *C, ARegion *UNUSED(ar), void *arg)
{
  tGPDfill *tgpf = (tGPDfill *)arg;
  /* draw only in the region that originated operator. This is required for multiwindow */
  ARegion *ar = CTX_wm_region(C);
  if (ar != tgpf->ar) {
    return;
  }

  gpencil_draw_boundary_lines(C, tgpf);
}

/* check if context is suitable for filling */
static bool gpencil_fill_poll(bContext *C)
{
  Object *obact = CTX_data_active_object(C);

  if (ED_operator_regionactive(C)) {
    ScrArea *sa = CTX_wm_area(C);
    if (sa->spacetype == SPACE_VIEW3D) {
      if ((obact == NULL) || (obact->type != OB_GPENCIL) ||
          (obact->mode != OB_MODE_PAINT_GPENCIL)) {
        return false;
      }

      return true;
    }
    else {
      CTX_wm_operator_poll_msg_set(C, "Active region not valid for filling operator");
      return false;
    }
  }
  else {
    CTX_wm_operator_poll_msg_set(C, "Active region not set");
    return false;
  }
}

/* Allocate memory and initialize values */
static tGPDfill *gp_session_init_fill(bContext *C, wmOperator *UNUSED(op))
{
  tGPDfill *tgpf = MEM_callocN(sizeof(tGPDfill), "GPencil Fill Data");

  /* define initial values */
  ToolSettings *ts = CTX_data_tool_settings(C);
  bGPdata *gpd = CTX_data_gpencil_data(C);
  Main *bmain = CTX_data_main(C);

  /* set current scene and window info */
  tgpf->C = C;
  tgpf->bmain = CTX_data_main(C);
  tgpf->scene = CTX_data_scene(C);
  tgpf->ob = CTX_data_active_object(C);
  tgpf->sa = CTX_wm_area(C);
  tgpf->ar = CTX_wm_region(C);
  tgpf->rv3d = tgpf->ar->regiondata;
  tgpf->v3d = tgpf->sa->spacedata.first;
  tgpf->depsgraph = CTX_data_depsgraph(C);
  tgpf->win = CTX_wm_window(C);

  /* set GP datablock */
  tgpf->gpd = gpd;
  tgpf->gpl = BKE_gpencil_layer_getactive(gpd);
  if (tgpf->gpl == NULL) {
    tgpf->gpl = BKE_gpencil_layer_addnew(tgpf->gpd, DATA_("GP_Layer"), true);
  }
  tgpf->lock_axis = ts->gp_sculpt.lock_axis;

  tgpf->oldkey = -1;
  tgpf->sbuffer_size = 0;
  tgpf->sbuffer = NULL;
  tgpf->depth_arr = NULL;

  /* save filling parameters */
  Brush *brush = BKE_paint_brush(&ts->gp_paint->paint);
  tgpf->flag = brush->gpencil_settings->flag;
  tgpf->fill_leak = brush->gpencil_settings->fill_leak;
  tgpf->fill_threshold = brush->gpencil_settings->fill_threshold;
  tgpf->fill_simplylvl = brush->gpencil_settings->fill_simplylvl;
  tgpf->fill_draw_mode = brush->gpencil_settings->fill_draw_mode;
  tgpf->fill_factor = (short)max_ii(1, min_ii((int)brush->gpencil_settings->fill_factor, 8));

  int totcol = tgpf->ob->totcol;

  /* get color info */
  Material *ma = BKE_gpencil_object_material_ensure_from_active_input_brush(
      bmain, tgpf->ob, brush);

  tgpf->mat = ma;

  /* check whether the material was newly added */
  if (totcol != tgpf->ob->totcol) {
    WM_event_add_notifier(C, NC_SPACE | ND_SPACE_PROPERTIES, NULL);
  }

  /* init undo */
  gpencil_undo_init(tgpf->gpd);

  /* return context data for running operator */
  return tgpf;
}

/* end operator */
static void gpencil_fill_exit(bContext *C, wmOperator *op)
{
  Main *bmain = CTX_data_main(C);
  Object *ob = CTX_data_active_object(C);

  /* clear undo stack */
  gpencil_undo_finish();

  /* restore cursor to indicate end of fill */
  WM_cursor_modal_restore(CTX_wm_window(C));

  tGPDfill *tgpf = op->customdata;

  /* don't assume that operator data exists at all */
  if (tgpf) {
    /* clear status message area */
    ED_workspace_status_text(C, NULL);

    MEM_SAFE_FREE(tgpf->sbuffer);
    MEM_SAFE_FREE(tgpf->depth_arr);

    /* remove drawing handler */
    if (tgpf->draw_handle_3d) {
      ED_region_draw_cb_exit(tgpf->ar->type, tgpf->draw_handle_3d);
    }

    /* delete temp image */
    if (tgpf->ima) {
      for (Image *ima = bmain->images.first; ima; ima = ima->id.next) {
        if (ima == tgpf->ima) {
          BLI_remlink(&bmain->images, ima);
          BKE_image_free(tgpf->ima);
          MEM_SAFE_FREE(tgpf->ima);
          break;
        }
      }
    }

    /* finally, free memory used by temp data */
    MEM_freeN(tgpf);
  }

  /* clear pointer */
  op->customdata = NULL;

  /* drawing batch cache is dirty now */
  if ((ob) && (ob->type == OB_GPENCIL) && (ob->data)) {
    bGPdata *gpd2 = ob->data;
    DEG_id_tag_update(&gpd2->id, ID_RECALC_TRANSFORM | ID_RECALC_GEOMETRY);
    gpd2->flag |= GP_DATA_CACHE_IS_DIRTY;
  }

  WM_event_add_notifier(C, NC_GPENCIL | NA_EDITED, NULL);
}

static void gpencil_fill_cancel(bContext *C, wmOperator *op)
{
  /* this is just a wrapper around exit() */
  gpencil_fill_exit(C, op);
}

/* Init: Allocate memory and set init values */
static int gpencil_fill_init(bContext *C, wmOperator *op)
{
  tGPDfill *tgpf;
  /* cannot paint in locked layer */
  bGPdata *gpd = CTX_data_gpencil_data(C);
  bGPDlayer *gpl = BKE_gpencil_layer_getactive(gpd);
  if ((gpl) && (gpl->flag & GP_LAYER_LOCKED)) {
    return 0;
  }

  /* check context */
  tgpf = op->customdata = gp_session_init_fill(C, op);
  if (tgpf == NULL) {
    /* something wasn't set correctly in context */
    gpencil_fill_exit(C, op);
    return 0;
  }

  /* everything is now setup ok */
  return 1;
}

/* start of interactive part of operator */
static int gpencil_fill_invoke(bContext *C, wmOperator *op, const wmEvent *UNUSED(event))
{
  tGPDfill *tgpf = NULL;

  /* try to initialize context data needed */
  if (!gpencil_fill_init(C, op)) {
    gpencil_fill_exit(C, op);
    if (op->customdata) {
      MEM_freeN(op->customdata);
    }
    return OPERATOR_CANCELLED;
  }
  else {
    tgpf = op->customdata;
  }

  /* Enable custom drawing handlers to show help lines */
  if (tgpf->flag & GP_BRUSH_FILL_SHOW_HELPLINES) {
    tgpf->draw_handle_3d = ED_region_draw_cb_activate(
        tgpf->ar->type, gpencil_fill_draw_3d, tgpf, REGION_DRAW_POST_VIEW);
  }

  WM_cursor_modal_set(CTX_wm_window(C), BC_PAINTBRUSHCURSOR);

  gpencil_fill_status_indicators(C, tgpf);

  DEG_id_tag_update(&tgpf->gpd->id, ID_RECALC_TRANSFORM | ID_RECALC_GEOMETRY);
  WM_event_add_notifier(C, NC_GPENCIL | NA_EDITED, NULL);

  /* add a modal handler for this operator*/
  WM_event_add_modal_handler(C, op);

  return OPERATOR_RUNNING_MODAL;
}

/* events handling during interactive part of operator */
static int gpencil_fill_modal(bContext *C, wmOperator *op, const wmEvent *event)
{
  tGPDfill *tgpf = op->customdata;

  int estate = OPERATOR_PASS_THROUGH; /* default exit state - pass through */

  switch (event->type) {
    case ESCKEY:
    case RIGHTMOUSE:
      estate = OPERATOR_CANCELLED;
      break;
    case LEFTMOUSE:
      tgpf->on_back = RNA_boolean_get(op->ptr, "on_back");
      /* first time the event is not enabled to show help lines */
      if ((tgpf->oldkey != -1) || ((tgpf->flag & GP_BRUSH_FILL_SHOW_HELPLINES) == 0)) {
        ARegion *ar = BKE_area_find_region_xy(CTX_wm_area(C), RGN_TYPE_ANY, event->x, event->y);
        if (ar) {
          bool in_bounds = false;

          /* Perform bounds check */
          in_bounds = BLI_rcti_isect_pt(&ar->winrct, event->x, event->y);

          if ((in_bounds) && (ar->regiontype == RGN_TYPE_WINDOW)) {
            /* TODO GPXX: Verify the mouse click is right for any window size */
            tgpf->center[0] = event->mval[0];
            tgpf->center[1] = event->mval[1];

            /* render screen to temp image */
            if (gp_render_offscreen(tgpf)) {

              /* apply boundary fill */
              gpencil_boundaryfill_area(tgpf);

              /* clean borders to avoid infinite loops */
              gpencil_clean_borders(tgpf);

              /* analyze outline */
              gpencil_get_outline_points(tgpf);

              /* create array of points from stack */
              gpencil_points_from_stack(tgpf);

              /* create z-depth array for reproject */
              gpencil_get_depth_array(tgpf);

              /* create stroke and reproject */
              gpencil_stroke_from_buffer(tgpf);
            }

            /* restore size */
            tgpf->ar->winx = (short)tgpf->bwinx;
            tgpf->ar->winy = (short)tgpf->bwiny;
            tgpf->ar->winrct = tgpf->brect;

            /* free temp stack data */
            if (tgpf->stack) {
              BLI_stack_free(tgpf->stack);
            }

            /* push undo data */
            gpencil_undo_push(tgpf->gpd);

            estate = OPERATOR_FINISHED;
          }
          else {
            estate = OPERATOR_CANCELLED;
          }
        }
        else {
          estate = OPERATOR_CANCELLED;
        }
      }
      tgpf->oldkey = event->type;
      break;
  }
  /* process last operations before exiting */
  switch (estate) {
    case OPERATOR_FINISHED:
      gpencil_fill_exit(C, op);
      WM_event_add_notifier(C, NC_GPENCIL | NA_EDITED, NULL);
      break;

    case OPERATOR_CANCELLED:
      gpencil_fill_exit(C, op);
      break;

    case OPERATOR_RUNNING_MODAL | OPERATOR_PASS_THROUGH:
      break;
  }

  /* return status code */
  return estate;
}

void GPENCIL_OT_fill(wmOperatorType *ot)
{
  PropertyRNA *prop;

  /* identifiers */
  ot->name = "Grease Pencil Fill";
  ot->idname = "GPENCIL_OT_fill";
  ot->description = "Fill with color the shape formed by strokes";

  /* api callbacks */
  ot->invoke = gpencil_fill_invoke;
  ot->modal = gpencil_fill_modal;
  ot->poll = gpencil_fill_poll;
  ot->cancel = gpencil_fill_cancel;

  /* flags */
  ot->flag = OPTYPE_UNDO | OPTYPE_BLOCKING;

  prop = RNA_def_boolean(ot->srna, "on_back", false, "Draw On Back", "Send new stroke to Back");
  RNA_def_property_flag(prop, PROP_SKIP_SAVE);
}
