text: /*
   * 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) 2008, Blender Foundation
   * This is a new part of Blender
   */
  
  /** \file
   * \ingroup edgpencil
   */
  
  #include <math.h>
  #include <stddef.h>
  #include <stdio.h>
  #include <stdlib.h>
  #include <string.h>
  
  #include "MEM_guardedalloc.h"
  
  #include "BLI_blenlib.h"
  #include "BLI_hash.h"
  #include "BLI_math.h"
  #include "BLI_math_geom.h"
  #include "BLI_rand.h"
  #include "BLI_utildefines.h"
  
  #include "BLT_translation.h"
  
  #include "PIL_time.h"
  
  #include "DNA_brush_types.h"
  #include "DNA_gpencil_types.h"
  #include "DNA_material_types.h"
  #include "DNA_meshdata_types.h"
  #include "DNA_object_types.h"
  #include "DNA_scene_types.h"
  #include "DNA_windowmanager_types.h"
  
  #include "BKE_brush.h"
  #include "BKE_colortools.h"
  #include "BKE_context.h"
  #include "BKE_deform.h"
  #include "BKE_global.h"
  #include "BKE_gpencil.h"
  #include "BKE_gpencil_geom.h"
  #include "BKE_layer.h"
  #include "BKE_main.h"
  #include "BKE_material.h"
  #include "BKE_paint.h"
  #include "BKE_report.h"
  #include "BKE_screen.h"
  #include "BKE_tracking.h"
  
  #include "UI_view2d.h"
  
  #include "ED_clip.h"
  #include "ED_gpencil.h"
  #include "ED_object.h"
  #include "ED_screen.h"
  #include "ED_view3d.h"
  
  #include "GPU_immediate.h"
  #include "GPU_immediate_util.h"
  #include "GPU_state.h"
  
  #include "RNA_access.h"
  #include "RNA_define.h"
  
  #include "WM_api.h"
  #include "WM_types.h"
  
  #include "DEG_depsgraph.h"
  #include "DEG_depsgraph_query.h"
  
  #include "gpencil_intern.h"
  
  /* ******************************************* */
  /* 'Globals' and Defines */
  
  /* values for tGPsdata->status */
  typedef enum eGPencil_PaintStatus {
    GP_STATUS_IDLING = 0, /* stroke isn't in progress yet */
    GP_STATUS_PAINTING,   /* a stroke is in progress */
    GP_STATUS_ERROR,      /* something wasn't correctly set up */
    GP_STATUS_DONE,       /* painting done */
  } eGPencil_PaintStatus;
  
  /* Return flags for adding points to stroke buffer */
  typedef enum eGP_StrokeAdd_Result {
    GP_STROKEADD_INVALID = -2,  /* error occurred - insufficient info to do so */
    GP_STROKEADD_OVERFLOW = -1, /* error occurred - cannot fit any more points */
    GP_STROKEADD_NORMAL,        /* point was successfully added */
    GP_STROKEADD_FULL,          /* cannot add any more points to buffer */
  } eGP_StrokeAdd_Result;
  
  /* Runtime flags */
  typedef enum eGPencil_PaintFlags {
    GP_PAINTFLAG_FIRSTRUN = (1 << 0), /* operator just started */
    GP_PAINTFLAG_STROKEADDED = (1 << 1),
    GP_PAINTFLAG_SELECTMASK = (1 << 3),
    GP_PAINTFLAG_HARD_ERASER = (1 << 4),
    GP_PAINTFLAG_STROKE_ERASER = (1 << 5),
    GP_PAINTFLAG_REQ_VECTOR = (1 << 6),
  } eGPencil_PaintFlags;
  
  /* Temporary Guide data */
  typedef struct tGPguide {
    /** guide spacing */
    float spacing;
    /** half guide spacing */
    float half_spacing;
    /** origin */
    float origin[2];
    /** rotated point */
    float rot_point[2];
    /** rotated point */
    float rot_angle;
    /** initial stroke direction */
    float stroke_angle;
    /** initial origin direction */
    float origin_angle;
    /** initial origin distance */
    float origin_distance;
    /** initial line for guides */
    float unit[2];
  } tGPguide;
  
  /* Temporary 'Stroke' Operation data
   *   "p" = op->customdata
   */
  typedef struct tGPsdata {
    bContext *C;
  
    /** main database pointer. */
    Main *bmain;
    /** current scene from context. */
    Scene *scene;
    struct Depsgraph *depsgraph;
  
    /** current object. */
    Object *ob;
    /** Obeject eval. */
    Object *ob_eval;
    /** window where painting originated. */
    wmWindow *win;
    /** area where painting originated. */
    ScrArea *area;
    /** region where painting originated. */
    ARegion *region;
    /** needed for GP_STROKE_2DSPACE. */
    View2D *v2d;
    /** for using the camera rect within the 3d view. */
    rctf *subrect;
    rctf subrect_data;
  
    /** settings to pass to gp_points_to_xy(). */
    GP_SpaceConversion gsc;
  
    /** pointer to owner of gp-datablock. */
    PointerRNA ownerPtr;
    /** gp-datablock layer comes from. */
    bGPdata *gpd;
    /** layer we're working on. */
    bGPDlayer *gpl;
    /** frame we're working on. */
    bGPDframe *gpf;
  
    /** projection-mode flags (toolsettings - eGPencil_Placement_Flags) */
    char *align_flag;
  
    /** current status of painting. */
    eGPencil_PaintStatus status;
    /** mode for painting. */
    eGPencil_PaintModes paintmode;
    /** flags that can get set during runtime (eGPencil_PaintFlags) */
    eGPencil_PaintFlags flags;
  
    /** radius of influence for eraser. */
    short radius;
  
    /** current mouse-position. */
    float mval[2];
    /** previous recorded mouse-position. */
    float mvalo[2];
    /** initial recorded mouse-position */
    float mvali[2];
  
    /** current stylus pressure. */
    float pressure;
    /** previous stylus pressure. */
    float opressure;
  
    /* These need to be doubles, as (at least under unix) they are in seconds since epoch,
     * float (and its 7 digits precision) is definitively not enough here!
     * double, with its 15 digits precision,
     * ensures us millisecond precision for a few centuries at least.
     */
    /** Used when converting to path. */
    double inittime;
    /** Used when converting to path. */
    double curtime;
    /** Used when converting to path. */
    double ocurtime;
  
    /** Inverted transformation matrix applying when converting coords from screen-space
     * to region space. */
    float imat[4][4];
    float mat[4][4];
  
    float diff_mat[4][4];
  
    /** custom color - hack for enforcing a particular color for track/mask editing. */
    float custom_color[4];
  
    /** radial cursor data for drawing eraser. */
    void *erasercursor;
  
    /* mat settings are only used for 3D view */
    /** current material */
    Material *material;
    /** current drawing brush */
    Brush *brush;
    /** default eraser brush */
    Brush *eraser;
  
    /** 1: line horizontal, 2: line vertical, other: not defined */
    short straight;
    /** lock drawing to one axis */
    int lock_axis;
    /** the stroke is no fill mode */
    bool disable_fill;
  
    RNG *rng;
  
    /** key used for invoking the operator */
    short keymodifier;
    /** shift modifier flag */
    short shift;
    /** size in pixels for uv calculation */
    float totpixlen;
  
    /* guide */
    tGPguide guide;
  
    ReportList *reports;
  
    /** Random settings by stroke */
    GpRandomSettings random_settings;
  
  } tGPsdata;
  
  /* ------ */
  
  #define STROKE_HORIZONTAL 1
  #define STROKE_VERTICAL 2
  
  /* Macros for accessing sensitivity thresholds... */
  /* minimum number of pixels mouse should move before new point created */
  #define MIN_MANHATTEN_PX (U.gp_manhattandist)
  /* minimum length of new segment before new point can be added */
  #define MIN_EUCLIDEAN_PX (U.gp_euclideandist)
  
  static void gpencil_update_cache(bGPdata *gpd)
  {
    if (gpd) {
      DEG_id_tag_update(&gpd->id, ID_RECALC_TRANSFORM | ID_RECALC_GEOMETRY);
      gpd->flag |= GP_DATA_CACHE_IS_DIRTY;
    }
  }
  
  static void gpencil_stroke_added_enable(tGPsdata *p)
  {
    BLI_assert(p->gpf->strokes.last != NULL);
    p->flags |= GP_PAINTFLAG_STROKEADDED;
  
    /* drawing batch cache is dirty now */
    gpencil_update_cache(p->gpd);
  }
  
  /* ------ */
  /* Forward defines for some functions... */
  
  static void gpencil_session_validatebuffer(tGPsdata *p);
  
  /* ******************************************* */
  /* Context Wrangling... */
  
  /* check if context is suitable for drawing */
  static bool gpencil_draw_poll(bContext *C)
  {
    if (ED_operator_regionactive(C)) {
      ScrArea *area = CTX_wm_area(C);
      /* 3D Viewport */
      if (area->spacetype != SPACE_VIEW3D) {
        return false;
      }
  
      /* check if Grease Pencil isn't already running */
      if (ED_gpencil_session_active() != 0) {
        CTX_wm_operator_poll_msg_set(C, "Grease Pencil operator is already active");
        return false;
      }
  
      /* only grease pencil object type */
      Object *ob = CTX_data_active_object(C);
      if ((ob == NULL) || (ob->type != OB_GPENCIL)) {
        return false;
      }
  
      bGPdata *gpd = (bGPdata *)ob->data;
      if (!GPENCIL_PAINT_MODE(gpd)) {
        return false;
      }
  
      ToolSettings *ts = CTX_data_scene(C)->toolsettings;
      if (!ts->gp_paint->paint.brush) {
        CTX_wm_operator_poll_msg_set(C, "Grease Pencil has no active paint tool");
        return false;
      }
  
      return true;
    }
  
    CTX_wm_operator_poll_msg_set(C, "Active region not set");
    return false;
  }
  
  /* check if projecting strokes into 3d-geometry in the 3D-View */
  static bool gpencil_project_check(tGPsdata *p)
  {
    bGPdata *gpd = p->gpd;
    return ((gpd->runtime.sbuffer_sflag & GP_STROKE_3DSPACE) &&
            (*p->align_flag & (GP_PROJECT_DEPTH_VIEW | GP_PROJECT_DEPTH_STROKE)));
  }
  
  /* ******************************************* */
  /* Calculations/Conversions */
  
  /* Utilities --------------------------------- */
  
  /* get the reference point for stroke-point conversions */
  static void gpencil_get_3d_reference(tGPsdata *p, float vec[3])
  {
    Object *ob = NULL;
    if (p->ownerPtr.type == &RNA_Object) {
      ob = (Object *)p->ownerPtr.data;
    }
    ED_gpencil_drawing_reference_get(p->scene, ob, *p->align_flag, vec);
  }
  
  /* Stroke Editing ---------------------------- */
  /* check if the current mouse position is suitable for adding a new point */
  static bool gpencil_stroke_filtermval(tGPsdata *p, const float mval[2], float mvalo[2])
  {
    Brush *brush = p->brush;
    int dx = (int)fabsf(mval[0] - mvalo[0]);
    int dy = (int)fabsf(mval[1] - mvalo[1]);
    brush->gpencil_settings->flag &= ~GP_BRUSH_STABILIZE_MOUSE_TEMP;
  
    /* if buffer is empty, just let this go through (i.e. so that dots will work) */
    if (p->gpd->runtime.sbuffer_used == 0) {
      return true;
    }
    /* if lazy mouse, check minimum distance */
    if (GPENCIL_LAZY_MODE(brush, p->shift)) {
      brush->gpencil_settings->flag |= GP_BRUSH_STABILIZE_MOUSE_TEMP;
      if ((dx * dx + dy * dy) > (brush->smooth_stroke_radius * brush->smooth_stroke_radius)) {
        return true;
      }
  
      /* If the mouse is moving within the radius of the last move,
       * don't update the mouse position. This allows sharp turns. */
      copy_v2_v2(p->mval, p->mvalo);
      return false;
    }
    /* check if mouse moved at least certain distance on both axes (best case)
     * - aims to eliminate some jitter-noise from input when trying to draw straight lines freehand
     */
    if ((dx > MIN_MANHATTEN_PX) && (dy > MIN_MANHATTEN_PX)) {
      return true;
    }
    /* Check if the distance since the last point is significant enough:
     * - Prevents points being added too densely
     * - Distance here doesn't use sqrt to prevent slowness.
     *   We should still be safe from overflows though.
     */
    if ((dx * dx + dy * dy) > MIN_EUCLIDEAN_PX * MIN_EUCLIDEAN_PX) {
      return true;
    }
    /* mouse 'didn't move' */
    return false;
  }
  
  /* reproject stroke to plane locked to axis in 3d cursor location */
  static void gpencil_reproject_toplane(tGPsdata *p, bGPDstroke *gps)
  {
    bGPdata *gpd = p->gpd;
    Object *obact = (Object *)p->ownerPtr.data;
  
    float origin[3];
    RegionView3D *rv3d = p->region->regiondata;
  
    /* verify the stroke mode is CURSOR 3d space mode */
    if ((gpd->runtime.sbuffer_sflag & GP_STROKE_3DSPACE) == 0) {
      return;
    }
    if ((*p->align_flag & GP_PROJECT_VIEWSPACE) == 0) {
      return;
    }
    if ((*p->align_flag & GP_PROJECT_DEPTH_VIEW) || (*p->align_flag & GP_PROJECT_DEPTH_STROKE)) {
      return;
    }
  
    /* get drawing origin */
    gpencil_get_3d_reference(p, origin);
    ED_gpencil_project_stroke_to_plane(p->scene, obact, rv3d, gps, origin, p->lock_axis - 1);
  }
  
  /* convert screen-coordinates to buffer-coordinates */
  static void gpencil_stroke_convertcoords(tGPsdata *p,
                                           const float mval[2],
                                           float out[3],
                                           float *depth)
  {
    bGPdata *gpd = p->gpd;
  
    /* in 3d-space - pt->x/y/z are 3 side-by-side floats */
    if (gpd->runtime.sbuffer_sflag & GP_STROKE_3DSPACE) {
  
      /* add small offset to keep stroke over the surface */
      if ((depth) && (gpd->zdepth_offset > 0.0f) && (*p->align_flag & GP_PROJECT_DEPTH_VIEW)) {
        *depth *= (1.0f - (gpd->zdepth_offset / 1000.0f));
      }
  
      int mval_i[2];
      float rmval[2];
      rmval[0] = mval[0] - 0.5f;
      rmval[1] = mval[1] - 0.5f;
      round_v2i_v2fl(mval_i, rmval);
  
      if (gpencil_project_check(p) &&
          (ED_view3d_autodist_simple(p->region, mval_i, out, 0, depth))) {
        /* projecting onto 3D-Geometry
         * - nothing more needs to be done here, since view_autodist_simple() has already done it
         */
  
        /* verify valid zdepth, if it's wrong, the default drawing mode is used
         * and the function doesn't return now */
        if ((depth == NULL) || (*depth <= 1.0f)) {
          return;
        }
      }
  
      float mval_prj[2];
      float rvec[3], dvec[3];
      float mval_f[2];
      float zfac;
  
      /* Current method just converts each point in screen-coordinates to
       * 3D-coordinates using the 3D-cursor as reference. In general, this
       * works OK, but it could of course be improved. */
  
      gpencil_get_3d_reference(p, rvec);
      zfac = ED_view3d_calc_zfac(p->region->regiondata, rvec, NULL);
  
      if (ED_view3d_project_float_global(p->region, rvec, mval_prj, V3D_PROJ_TEST_NOP) ==
          V3D_PROJ_RET_OK) {
        sub_v2_v2v2(mval_f, mval_prj, mval);
        ED_view3d_win_to_delta(p->region, mval_f, dvec, zfac);
        sub_v3_v3v3(out, rvec, dvec);
      }
      else {
        zero_v3(out);
      }
    }
  }
  
  /* Apply jitter to stroke point. */
  static void gpencil_brush_jitter(bGPdata *gpd, tGPspoint *pt, const float amplitude)
  {
    const float axis[2] = {0.0f, 1.0f};
    /* Jitter is applied perpendicular to the mouse movement vector (2D space). */
    float mvec[2];
    /* Mouse movement in ints -> floats. */
    if (gpd->runtime.sbuffer_used > 1) {
      tGPspoint *pt_prev = pt - 1;
      sub_v2_v2v2(mvec, &pt->x, &pt_prev->x);
      normalize_v2(mvec);
      /* Rotate mvec by 90 degrees... */
      float angle = angle_v2v2(mvec, axis);
      /* Reduce noise in the direction of the stroke. */
      mvec[0] *= cos(angle);
      mvec[1] *= sin(angle);
  
      /* Scale by displacement amount, and apply. */
      madd_v2_v2fl(&pt->x, mvec, amplitude * 10.0f);
    }
  }
  
  /* Apply pressure change depending of the angle of the stroke to simulate a pen with shape */
  static void gpencil_brush_angle(bGPdata *gpd, Brush *brush, tGPspoint *pt, const float mval[2])
  {
    float mvec[2];
    float sen = brush->gpencil_settings->draw_angle_factor; /* sensitivity */
    float fac;
  
    /* default angle of brush in radians */
    float angle = brush->gpencil_settings->draw_angle;
    /* angle vector of the brush with full thickness */
    float v0[2] = {cos(angle), sin(angle)};
  
    /* Apply to first point (only if there are 2 points because before no data to do it ) */
    if (gpd->runtime.sbuffer_used == 1) {
      mvec[0] = (mval[0] - (pt - 1)->x);
      mvec[1] = (mval[1] - (pt - 1)->y);
      normalize_v2(mvec);
  
      /* uses > 1.0f to get a smooth transition in first point */
      fac = 1.4f - fabs(dot_v2v2(v0, mvec)); /* 0.0 to 1.0 */
      (pt - 1)->pressure = (pt - 1)->pressure - (sen * fac);
  
      CLAMP((pt - 1)->pressure, GPENCIL_ALPHA_OPACITY_THRESH, 1.0f);
    }
  
    /* apply from second point */
    if (gpd->runtime.sbuffer_used >= 1) {
      mvec[0] = (mval[0] - (pt - 1)->x);
      mvec[1] = (mval[1] - (pt - 1)->y);
      normalize_v2(mvec);
  
      fac = 1.0f - fabs(dot_v2v2(v0, mvec)); /* 0.0 to 1.0 */
      /* interpolate with previous point for smoother transitions */
      pt->pressure = interpf(pt->pressure - (sen * fac), (pt - 1)->pressure, 0.3f);
      CLAMP(pt->pressure, GPENCIL_ALPHA_OPACITY_THRESH, 1.0f);
    }
  }
  
  /**
   * Apply smooth to buffer while drawing
   * to smooth point C, use 2 before (A, B) and current point (D):
   *
   * `A----B-----C------D`
   *
   * \param p: Temp data
   * \param inf: Influence factor
   * \param idx: Index of the last point (need minimum 3 points in the array)
   */
  static void gpencil_smooth_buffer(tGPsdata *p, float inf, int idx)
  {
    bGPdata *gpd = p->gpd;
    GP_Sculpt_Guide *guide = &p->scene->toolsettings->gp_sculpt.guide;
    const short num_points = gpd->runtime.sbuffer_used;
  
    /* Do nothing if not enough points to smooth out */
    if ((num_points < 3) || (idx < 3) || (inf == 0.0f)) {
      return;
    }
  
    tGPspoint *points = (tGPspoint *)gpd->runtime.sbuffer;
    const float steps = (idx < 4) ? 3.0f : 4.0f;
  
    tGPspoint *pta = idx >= 4 ? &points[idx - 4] : NULL;
    tGPspoint *ptb = idx >= 3 ? &points[idx - 3] : NULL;
    tGPspoint *ptc = idx >= 2 ? &points[idx - 2] : NULL;
    tGPspoint *ptd = &points[idx - 1];
  
    float sco[2] = {0.0f};
    float a[2], b[2], c[2], d[2];
    float pressure = 0.0f;
    float strength = 0.0f;
    const float average_fac = 1.0f / steps;
  
    /* Compute smoothed coordinate by taking the ones nearby */
    if (pta) {
      copy_v2_v2(a, &pta->x);
      madd_v2_v2fl(sco, a, average_fac);
      pressure += pta->pressure * average_fac;
      strength += pta->strength * average_fac;
    }
    if (ptb) {
      copy_v2_v2(b, &ptb->x);
      madd_v2_v2fl(sco, b, average_fac);
      pressure += ptb->pressure * average_fac;
      strength += ptb->strength * average_fac;
    }
    if (ptc) {
      copy_v2_v2(c, &ptc->x);
      madd_v2_v2fl(sco, c, average_fac);
      pressure += ptc->pressure * average_fac;
      strength += ptc->strength * average_fac;
    }
    if (ptd) {
      copy_v2_v2(d, &ptd->x);
      madd_v2_v2fl(sco, d, average_fac);
      pressure += ptd->pressure * average_fac;
      strength += ptd->strength * average_fac;
    }
  
    /* Based on influence factor, blend between original and optimal smoothed coordinate but not
     * for Guide mode. */
    if (!guide->use_guide) {
      interp_v2_v2v2(c, c, sco, inf);
      copy_v2_v2(&ptc->x, c);
    }
    /* Interpolate pressure. */
    ptc->pressure = interpf(ptc->pressure, pressure, inf);
    /* Interpolate strength. */
    ptc->strength = interpf(ptc->strength, strength, inf);
  }
  
  /* Helper: Apply smooth to segment from Index to Index */
  static void gpencil_smooth_segment(bGPdata *gpd, const float inf, int from_idx, int to_idx)
  {
    const short num_points = to_idx - from_idx;
    /* Do nothing if not enough points to smooth out */
    if ((num_points < 3) || (inf == 0.0f)) {
      return;
    }
  
    if (from_idx <= 2) {
      return;
    }
  
    tGPspoint *points = (tGPspoint *)gpd->runtime.sbuffer;
    const float average_fac = 0.25f;
  
    for (int i = from_idx; i < to_idx + 1; i++) {
  
      tGPspoint *pta = i >= 3 ? &points[i - 3] : NULL;
      tGPspoint *ptb = i >= 2 ? &points[i - 2] : NULL;
      tGPspoint *ptc = i >= 1 ? &points[i - 1] : &points[i];
      tGPspoint *ptd = &points[i];
  
      float sco[2] = {0.0f};
      float pressure = 0.0f;
      float strength = 0.0f;
  
      /* Compute smoothed coordinate by taking the ones nearby */
      if (pta) {
        madd_v2_v2fl(sco, &pta->x, average_fac);
        pressure += pta->pressure * average_fac;
        strength += pta->strength * average_fac;
      }
      else {
        madd_v2_v2fl(sco, &ptc->x, average_fac);
        pressure += ptc->pressure * average_fac;
        strength += ptc->strength * average_fac;
      }
  
      if (ptb) {
        madd_v2_v2fl(sco, &ptb->x, average_fac);
        pressure += ptb->pressure * average_fac;
        strength += ptb->strength * average_fac;
      }
      else {
        madd_v2_v2fl(sco, &ptc->x, average_fac);
        pressure += ptc->pressure * average_fac;
        strength += ptc->strength * average_fac;
      }
  
      madd_v2_v2fl(sco, &ptc->x, average_fac);
      pressure += ptc->pressure * average_fac;
      strength += ptc->strength * average_fac;
  
      madd_v2_v2fl(sco, &ptd->x, average_fac);
      pressure += ptd->pressure * average_fac;
      strength += ptd->strength * average_fac;
  
      /* Based on influence factor, blend between original and optimal smoothed coordinate. */
      interp_v2_v2v2(&ptc->x, &ptc->x, sco, inf);
  
      /* Interpolate pressure. */
      ptc->pressure = interpf(ptc->pressure, pressure, inf);
      /* Interpolate strength. */
      ptc->strength = interpf(ptc->strength, strength, inf);
    }
  }
  
  static void gpencil_apply_randomness(tGPsdata *p,
                                       BrushGpencilSettings *brush_settings,
                                       tGPspoint *pt,
                                       const bool press,
                                       const bool strength,
                                       const bool uv)
  {
    bGPdata *gpd = p->gpd;
    GpRandomSettings random_settings = p->random_settings;
    float value = 0.0f;
    /* Apply randomness to pressure. */
    if ((brush_settings->draw_random_press > 0.0f) && (press)) {
      if ((brush_settings->flag2 & GP_BRUSH_USE_PRESS_AT_STROKE) == 0) {
        float rand = BLI_rng_get_float(p->rng) * 2.0f - 1.0f;
        value = 1.0 + rand * 2.0 * brush_settings->draw_random_press;
      }
      else {
        value = 1.0 + random_settings.pressure * brush_settings->draw_random_press;
      }
  
      /* Apply random curve. */
      if (brush_settings->flag2 & GP_BRUSH_USE_PRESSURE_RAND_PRESS) {
        value *= BKE_curvemapping_evaluateF(
            brush_settings->curve_rand_pressure, 0, random_settings.pen_press);
      }
  
      pt->pressure *= value;
      CLAMP(pt->pressure, 0.1f, 1.0f);
    }
  
    /* Apply randomness to color strength. */
    if ((brush_settings->draw_random_strength) && (strength)) {
      if ((brush_settings->flag2 & GP_BRUSH_USE_STRENGTH_AT_STROKE) == 0) {
        float rand = BLI_rng_get_float(p->rng) * 2.0f - 1.0f;
        value = 1.0 + rand * brush_settings->draw_random_strength;
      }
      else {
        value = 1.0 + random_settings.strength * brush_settings->draw_random_strength;
      }
  
      /* Apply random curve. */
      if (brush_settings->flag2 & GP_BRUSH_USE_STRENGTH_RAND_PRESS) {
        value *= BKE_curvemapping_evaluateF(
            brush_settings->curve_rand_pressure, 0, random_settings.pen_press);
      }
  
      pt->strength *= value;
      CLAMP(pt->strength, GPENCIL_STRENGTH_MIN, 1.0f);
    }
  
    /* Apply randomness to uv texture rotation. */
    if ((brush_settings->uv_random > 0.0f) && (uv)) {
      if ((brush_settings->flag2 & GP_BRUSH_USE_UV_AT_STROKE) == 0) {
        float rand = BLI_hash_int_01(BLI_hash_int_2d((int)pt->x, gpd->runtime.sbuffer_used)) * 2.0f -
                     1.0f;
        value = rand * M_PI_2 * brush_settings->uv_random;
      }
      else {
        value = random_settings.uv * M_PI_2 * brush_settings->uv_random;
      }
  
      /* Apply random curve. */
      if (brush_settings->flag2 & GP_BRUSH_USE_UV_RAND_PRESS) {
        value *= BKE_curvemapping_evaluateF(
            brush_settings->curve_rand_uv, 0, random_settings.pen_press);
      }
  
      pt->uv_rot += value;
      CLAMP(pt->uv_rot, -M_PI_2, M_PI_2);
    }
  }
  
  /* add current stroke-point to buffer (returns whether point was successfully added) */
  static short gpencil_stroke_addpoint(tGPsdata *p,
                                       const float mval[2],
                                       float pressure,
                                       double curtime)
  {
    bGPdata *gpd = p->gpd;
    Brush *brush = p->brush;
    BrushGpencilSettings *brush_settings = p->brush->gpencil_settings;
    tGPspoint *pt;
    Object *obact = (Object *)p->ownerPtr.data;
    RegionView3D *rv3d = p->region->regiondata;
  
    /* check painting mode */
    if (p->paintmode == GP_PAINTMODE_DRAW_STRAIGHT) {
      /* straight lines only - i.e. only store start and end point in buffer */
      if (gpd->runtime.sbuffer_used == 0) {
        /* first point in buffer (start point) */
        pt = (tGPspoint *)(gpd->runtime.sbuffer);
  
        /* store settings */
        copy_v2_v2(&pt->x, mval);
        /* T44932 - Pressure vals are unreliable, so ignore for now */
        pt->pressure = 1.0f;
        pt->strength = 1.0f;
        pt->time = (float)(curtime - p->inittime);
  
        /* increment buffer size */
        gpd->runtime.sbuffer_used++;
      }
      else {
        /* just reset the endpoint to the latest value
         * - assume that pointers for this are always valid...
         */
        pt = ((tGPspoint *)(gpd->runtime.sbuffer) + 1);
  
        /* store settings */
        copy_v2_v2(&pt->x, mval);
        /* T44932 - Pressure vals are unreliable, so ignore for now */
        pt->pressure = 1.0f;
        pt->strength = 1.0f;
        pt->time = (float)(curtime - p->inittime);
  
        /* now the buffer has 2 points (and shouldn't be allowed to get any larger) */
        gpd->runtime.sbuffer_used = 2;
      }
  
      /* can keep carrying on this way :) */
      return GP_STROKEADD_NORMAL;
    }
  
    if (p->paintmode == GP_PAINTMODE_DRAW) { /* normal drawing */
      /* check if still room in buffer or add more */
      gpd->runtime.sbuffer = ED_gpencil_sbuffer_ensure(
          gpd->runtime.sbuffer, &gpd->runtime.sbuffer_size, &gpd->runtime.sbuffer_used, false);
  
      /* Check the buffer was created. */
      if (gpd->runtime.sbuffer == NULL) {
        return GP_STROKEADD_INVALID;
      }
  
      /* get pointer to destination point */
      pt = ((tGPspoint *)(gpd->runtime.sbuffer) + gpd->runtime.sbuffer_used);
  
      /* store settings */
      pt->strength = brush_settings->draw_strength;
      pt->pressure = 1.0f;
      pt->uv_rot = 0.0f;
      copy_v2_v2(&pt->x, mval);
  
      /* pressure */
      if (brush_settings->flag & GP_BRUSH_USE_PRESSURE) {
        pt->pressure *= BKE_curvemapping_evaluateF(brush_settings->curve_sensitivity, 0, pressure);
      }
  
      /* color strength */
      if (brush_settings->flag & GP_BRUSH_USE_STENGTH_PRESSURE) {
        pt->strength *= BKE_curvemapping_evaluateF(brush_settings->curve_strength, 0, pressure);
        CLAMP(pt->strength, GPENCIL_STRENGTH_MIN, 1.0f);
      }
  
      /* Set vertex colors for buffer. */
      ED_gpencil_sbuffer_vertex_color_set(p->depsgraph,
                                          p->ob,
                                          p->scene->toolsettings,
                                          p->brush,
                                          p->material,
                                          p->random_settings.hsv,
                                          p->random_settings.pen_press);
  
      if (brush_settings->flag & GP_BRUSH_GROUP_RANDOM) {
        /* Apply jitter to position */
        if (brush_settings->draw_jitter > 0.0f) {
          float rand = BLI_rng_get_float(p->rng) * 2.0f - 1.0f;
          float jitpress = 1.0f;
          if (brush_settings->flag & GP_BRUSH_USE_JITTER_PRESSURE) {
            jitpress = BKE_curvemapping_evaluateF(brush_settings->curve_jitter, 0, pressure);
          }
          /* FIXME the +2 means minimum jitter is 4 which is a bit strange for UX. */
          const float exp_factor = brush_settings->draw_jitter + 2.0f;
          const float fac = rand * square_f(exp_factor) * jitpress;
          gpencil_brush_jitter(gpd, pt, fac);
        }
  
        /* Apply other randomness. */
        gpencil_apply_randomness(p, brush_settings, pt, true, true, true);
      }
  
      /* apply angle of stroke to brush size */
      if (brush_settings->draw_angle_factor != 0.0f) {
        gpencil_brush_angle(gpd, brush, pt, mval);
      }
  
      /* point time */
      pt->time = (float)(curtime - p->inittime);
  
      /* point uv (only 3d view) */
      if ((p->area->spacetype == SPACE_VIEW3D) && (gpd->runtime.sbuffer_used > 0)) {
        tGPspoint *ptb = (tGPspoint *)gpd->runtime.sbuffer + gpd->runtime.sbuffer_used - 1;
        bGPDspoint spt, spt2;
  
        /* get origin to reproject point */
        float origin[3];
        gpencil_get_3d_reference(p, origin);
        /* reproject current */
        ED_gpencil_tpoint_to_point(p->region, origin, pt, &spt);
        ED_gpencil_project_point_to_plane(p->scene, obact, rv3d, origin, p->lock_axis - 1, &spt);
  
        /* reproject previous */
        ED_gpencil_tpoint_to_point(p->region, origin, ptb, &spt2);
        ED_gpencil_project_point_to_plane(p->scene, obact, rv3d, origin, p->lock_axis - 1, &spt2);
        p->totpixlen += len_v3v3(&spt.x, &spt2.x);
        pt->uv_fac = p->totpixlen;
      }
      else {
        p->totpixlen = 0.0f;
        pt->uv_fac = 0.0f;
      }
  
      /* increment counters */
      gpd->runtime.sbuffer_used++;
  
      /* Smooth while drawing previous points with a reduction factor for previous. */
      if (brush->gpencil_settings->active_smooth > 0.0f) {
        for (int s = 0; s < 3; s++) {
          gpencil_smooth_buffer(p,
                                brush->gpencil_settings->active_smooth * ((3.0f - s) / 3.0f),
                                gpd->runtime.sbuffer_used - s);
        }
      }
  
      /* Update evaluated data. */
      ED_gpencil_sbuffer_update_eval(gpd, p->ob_eval);
  
      return GP_STROKEADD_NORMAL;
    }
    /* return invalid state for now... */
    return GP_STROKEADD_INVALID;
  }
  
  /* make a new stroke from the buffer data */
  static void gpencil_stroke_newfrombuffer(tGPsdata *p)
  {
    bGPdata *gpd = p->gpd;
    bGPDlayer *gpl = p->gpl;
    bGPDstroke *gps;
    bGPDspoint *pt;
    tGPspoint *ptc;
    MDeformVert *dvert = NULL;
    Brush *brush = p->brush;
    ToolSettings *ts = p->scene->toolsettings;
    Depsgraph *depsgraph = p->depsgraph;
    Object *obact = (Object *)p->ownerPtr.data;
    RegionView3D *rv3d = p->region->regiondata;
    const int def_nr = obact->actdef - 1;
    const bool have_weight = (bool)BLI_findlink(&obact->defbase, def_nr);
    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) && (rv3d->persp == RV3D_CAMOB) &&
                           (!is_depth);
    int i, totelem;
  
    /* For very low pressure at the end, truncate stroke. */
    if (p->paintmode == GP_PAINTMODE_DRAW) {
      int last_i = gpd->runtime.sbuffer_used - 1;
      while (last_i > 0) {
        ptc = (tGPspoint *)gpd->runtime.sbuffer + last_i;
        if (ptc->pressure > 0.001f) {
          break;
        }
        gpd->runtime.sbuffer_used = last_i - 1;
        CLAMP_MIN(gpd->runtime.sbuffer_used, 1);
  
        last_i--;
      }
    }
    /* Since strokes are so fine,
     * when using their depth we need a margin otherwise they might get missed. */
    int depth_margin = (ts->gpencil_v3d_align & GP_PROJECT_DEPTH_STROKE) ? 4 : 0;
  
    /* get total number of points to allocate space for
     * - drawing straight-lines only requires the endpoints
     */
    if (p->paintmode == GP_PAINTMODE_DRAW_STRAIGHT) {
      totelem = (gpd->runtime.sbuffer_used >= 2) ? 2 : gpd->runtime.sbuffer_used;
    }
    else {
      totelem = gpd->runtime.sbuffer_used;
    }
  
    /* exit with error if no valid points from this stroke */
    if (totelem == 0) {
      if (G.debug & G_DEBUG) {
        printf("Error: No valid points in stroke buffer to convert (tot=%d)\n",
               gpd->runtime.sbuffer_used);
      }
      return;
    }
  
    /* allocate memory for a new stroke */
    gps = MEM_callocN(sizeof(bGPDstroke), "gp_stroke");
  
    /* copy appropriate settings for stroke */
    gps->totpoints = totelem;
    gps->thickness = brush->size;
    gps->fill_opacity_fac = 1.0f;
    gps->hardeness = brush->gpencil_settings->hardeness;
    copy_v2_v2(gps->aspect_ratio, brush->gpencil_settings->aspect_ratio);
    gps->flag = gpd->runtime.sbuffer_sflag;
    gps->inittime = p->inittime;
    gps->uv_scale = 1.0f;
  
    /* allocate enough memory for a continuous array for storage points */
    const int subdivide = brush->gpencil_settings->draw_subdivide;
  
    gps->points = MEM_callocN(sizeof(bGPDspoint) * gps->totpoints, "gp_stroke_points");
    gps->dvert = NULL;
  
    /* drawing batch cache is dirty now */
    gpencil_update_cache(p->gpd);
    /* set pointer to first non-initialized point */
    pt = gps->points + (gps->totpoints - totelem);
    if (gps->dvert != NULL) {
      dvert = gps->dvert + (gps->totpoints - totelem);
    }
  
    /* Apply the vertex color to fill. */
    ED_gpencil_fill_vertex_color_set(ts, brush, gps);
  
    /* copy points from the buffer to the stroke */
    if (p->paintmode == GP_PAINTMODE_DRAW_STRAIGHT) {
      /* straight lines only -> only endpoints */
      {
        /* first point */
        ptc = gpd->runtime.sbuffer;
  
        /* convert screen-coordinates to appropriate coordinates (and store them) */
        gpencil_stroke_convertcoords(p, &ptc->x, &pt->x, NULL);
        /* copy pressure and time */
        pt->pressure = ptc->pressure;
        pt->strength = ptc->strength;
        CLAMP(pt->strength, GPENCIL_STRENGTH_MIN, 1.0f);
        copy_v4_v4(pt->vert_color, ptc->vert_color);
        pt->time = ptc->time;
        /* Apply the vertex color to point. */
        ED_gpencil_point_vertex_color_set(ts, brush, pt, ptc);
  
        pt++;
  
        if ((ts->gpencil_flags & GP_TOOL_FLAG_CREATE_WEIGHTS) && (have_weight)) {
          BKE_gpencil_dvert_ensure(gps);
          MDeformWeight *dw = BKE_defvert_ensure_index(dvert, def_nr);
          if (dw) {
            dw->weight = ts->vgroup_weight;
          }
          dvert++;
        }
        else {
          if (dvert != NULL) {
            dvert->totweight = 0;
            dvert->dw = NULL;
            dvert++;
          }
        }
      }
  
      if (totelem == 2) {
        /* last point if applicable */
        ptc = ((tGPspoint *)gpd->runtime.sbuffer) + (gpd->runtime.sbuffer_used - 1);
  
        /* convert screen-coordinates to appropriate coordinates (and store them) */
        gpencil_stroke_convertcoords(p, &ptc->x, &pt->x, NULL);
        /* copy pressure and time */
        pt->pressure = ptc->pressure;
        pt->strength = ptc->strength;
        CLAMP(pt->strength, GPENCIL_STRENGTH_MIN, 1.0f);
        pt->time = ptc->time;
        /* Apply the vertex color to point. */
        ED_gpencil_point_vertex_color_set(ts, brush, pt, ptc);
  
        if ((ts->gpencil_flags & GP_TOOL_FLAG_CREATE_WEIGHTS) && (have_weight)) {
          BKE_gpencil_dvert_ensure(gps);
          MDeformWeight *dw = BKE_defvert_ensure_index(dvert, def_nr);
          if (dw) {
            dw->weight = ts->vgroup_weight;
          }
        }
        else {
          if (dvert != NULL) {
            dvert->totweight = 0;
            dvert->dw = NULL;
          }
        }
      }
  
      /* reproject to plane (only in 3d space) */
      gpencil_reproject_toplane(p, gps);
      pt = gps->points;
      for (i = 0; i < gps->totpoints; i++, pt++) {
        /* if parented change position relative to parent object */
        gpencil_apply_parent_point(depsgraph, obact, gpl, pt);
      }
  
      /* if camera view, reproject flat to view to avoid perspective effect */
      if (is_camera) {
        ED_gpencil_project_stroke_to_view(p->C, p->gpl, gps);
      }
    }
    else {
      float *depth_arr = NULL;
  
      /* get an array of depths, far depths are blended */
      if (gpencil_project_check(p)) {
        int mval_i[2], mval_prev[2] = {0};
        int interp_depth = 0;
        int found_depth = 0;
  
        depth_arr = MEM_mallocN(sizeof(float) * gpd->runtime.sbuffer_used, "depth_points");
  
        for (i = 0, ptc = gpd->runtime.sbuffer; i < gpd->runtime.sbuffer_used; i++, ptc++, pt++) {
  
          round_v2i_v2fl(mval_i, &ptc->x);
  
          if ((ED_view3d_autodist_depth(p->region, mval_i, depth_margin, depth_arr + i) == 0) &&
              (i && (ED_view3d_autodist_depth_seg(
                         p->region, mval_i, mval_prev, depth_margin + 1, 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, use the 3D cursor */
          for (i = gpd->runtime.sbuffer_used - 1; i >= 0; i--) {
            depth_arr[i] = 0.9999f;
          }
        }
        else {
          if ((ts->gpencil_v3d_align & GP_PROJECT_DEPTH_STROKE) &&
              ((ts->gpencil_v3d_align & GP_PROJECT_DEPTH_STROKE_ENDPOINTS) ||
               (ts->gpencil_v3d_align & GP_PROJECT_DEPTH_STROKE_FIRST))) {
            int first_valid = 0;
            int last_valid = 0;
  
            /* find first valid contact point */
            for (i = 0; i < gpd->runtime.sbuffer_used; i++) {
              if (depth_arr[i] != FLT_MAX) {
                break;
              }
            }
            first_valid = i;
  
            /* find last valid contact point */
            if (ts->gpencil_v3d_align & GP_PROJECT_DEPTH_STROKE_FIRST) {
              last_valid = first_valid;
            }
            else {
              for (i = gpd->runtime.sbuffer_used - 1; i >= 0; i--) {
                if (depth_arr[i] != FLT_MAX) {
                  break;
                }
              }
              last_valid = i;
            }
            /* invalidate any other point, to interpolate between
             * first and last contact in an imaginary line between them */
            for (i = 0; i < gpd->runtime.sbuffer_used; i++) {
              if ((i != first_valid) && (i != last_valid)) {
                depth_arr[i] = FLT_MAX;
              }
            }
            interp_depth = true;
          }
  
          if (interp_depth) {
            interp_sparse_array(depth_arr, gpd->runtime.sbuffer_used, FLT_MAX);
          }
        }
      }
  
      pt = gps->points;
      dvert = gps->dvert;
  
      /* convert all points (normal behavior) */
      for (i = 0, ptc = gpd->runtime.sbuffer; i < gpd->runtime.sbuffer_used && ptc;
           i++, ptc++, pt++) {
        /* convert screen-coordinates to appropriate coordinates (and store them) */
        gpencil_stroke_convertcoords(p, &ptc->x, &pt->x, depth_arr ? depth_arr + i : NULL);
  
        /* copy pressure and time */
        pt->pressure = ptc->pressure;
        pt->strength = ptc->strength;
        CLAMP(pt->strength, GPENCIL_STRENGTH_MIN, 1.0f);
        copy_v4_v4(pt->vert_color, ptc->vert_color);
        pt->time = ptc->time;
        pt->uv_fac = ptc->uv_fac;
        pt->uv_rot = ptc->uv_rot;
        /* Apply the vertex color to point. */
        ED_gpencil_point_vertex_color_set(ts, brush, pt, ptc);
  
        if (dvert != NULL) {
          dvert->totweight = 0;
          dvert->dw = NULL;
          dvert++;
        }
      }
  
      /* subdivide and smooth the stroke */
      if ((brush->gpencil_settings->flag & GP_BRUSH_GROUP_SETTINGS) && (subdivide > 0)) {
        gpencil_subdivide_stroke(gps, subdivide);
      }
  
      /* Smooth stroke after subdiv - only if there's something to do for each iteration,
       * the factor is reduced to get a better smoothing
       * without changing too much the original stroke. */
      if ((brush->gpencil_settings->flag & GP_BRUSH_GROUP_SETTINGS) &&
          (brush->gpencil_settings->draw_smoothfac > 0.0f)) {
        float reduce = 0.0f;
        for (int r = 0; r < brush->gpencil_settings->draw_smoothlvl; r++) {
          for (i = 0; i < gps->totpoints - 1; i++) {
            BKE_gpencil_stroke_smooth(gps, i, brush->gpencil_settings->draw_smoothfac - reduce);
            BKE_gpencil_stroke_smooth_strength(gps, i, brush->gpencil_settings->draw_smoothfac);
          }
          reduce += 0.25f; /* reduce the factor */
        }
      }
      /* If reproject the stroke using Stroke mode, need to apply a smooth because
       * the reprojection creates small jitter. */
      if (ts->gpencil_v3d_align & GP_PROJECT_DEPTH_STROKE) {
        float ifac = (float)brush->gpencil_settings->input_samples / 10.0f;
        float sfac = interpf(1.0f, 0.2f, ifac);
        for (i = 0; i < gps->totpoints - 1; i++) {
          BKE_gpencil_stroke_smooth(gps, i, sfac);
          BKE_gpencil_stroke_smooth_strength(gps, i, sfac);
        }
      }
  
      /* Simplify adaptive */
      if ((brush->gpencil_settings->flag & GP_BRUSH_GROUP_SETTINGS) &&
          (brush->gpencil_settings->simplify_f > 0.0f)) {
        BKE_gpencil_stroke_simplify_adaptive(gps, brush->gpencil_settings->simplify_f);
      }
  
      /* reproject to plane (only in 3d space) */
      gpencil_reproject_toplane(p, gps);
      /* change position relative to parent object */
      gpencil_apply_parent(depsgraph, obact, gpl, gps);
      /* if camera view, reproject flat to view to avoid perspective effect */
      if (is_camera) {
        ED_gpencil_project_stroke_to_view(p->C, p->gpl, gps);
      }
  
      if (depth_arr) {
        MEM_freeN(depth_arr);
      }
    }
  
    /* Save material index */
    gps->mat_nr = BKE_gpencil_object_material_get_index_from_brush(p->ob, p->brush);
    if (gps->mat_nr < 0) {
      if (p->ob->actcol - 1 < 0) {
        gps->mat_nr = 0;
      }
      else {
        gps->mat_nr = p->ob->actcol - 1;
      }
    }
  
    /* add stroke to frame, usually on tail of the listbase, but if on back is enabled the stroke
     * is added on listbase head because the drawing order is inverse and the head stroke is the
     * first to draw. This is very useful for artist when drawing the background.
     */
    if (ts->gpencil_flags & GP_TOOL_FLAG_PAINT_ONBACK) {
      BLI_addhead(&p->gpf->strokes, gps);
    }
    else {
      BLI_addtail(&p->gpf->strokes, gps);
    }
    /* add weights */
    if ((ts->gpencil_flags & GP_TOOL_FLAG_CREATE_WEIGHTS) && (have_weight)) {
      BKE_gpencil_dvert_ensure(gps);
      for (i = 0; i < gps->totpoints; i++) {
        MDeformVert *ve = &gps->dvert[i];
        MDeformWeight *dw = BKE_defvert_ensure_index(ve, def_nr);
        if (dw) {
          dw->weight = ts->vgroup_weight;
        }
      }
    }
  
    /* post process stroke */
    if ((p->brush->gpencil_settings->flag & GP_BRUSH_GROUP_SETTINGS) &&
        p->brush->gpencil_settings->flag & GP_BRUSH_TRIM_STROKE) {
      BKE_gpencil_stroke_trim(gps);
    }
  
    /* Calc geometry data. */
    BKE_gpencil_stroke_geometry_update(gps);
  
    gpencil_stroke_added_enable(p);
  }
  
  /* --- 'Eraser' for 'Paint' Tool ------ */
  
  /**
   * Which which point is in front (result should only be used for comparison).
   */
  static float view3d_point_depth(const RegionView3D *rv3d, const float co[3])
  {
    if (rv3d->is_persp) {
      return ED_view3d_calc_zfac(rv3d, co, NULL);
    }
    return -dot_v3v3(rv3d->viewinv[2], co);
  }
  
  /* only erase stroke points that are visible */
  static bool gpencil_stroke_eraser_is_occluded(tGPsdata *p,
                                                const bGPDspoint *pt,
                                                const int x,
                                                const int y)
  {
    Object *obact = (Object *)p->ownerPtr.data;
    Brush *brush = p->brush;
    Brush *eraser = p->eraser;
    BrushGpencilSettings *gp_settings = NULL;
  
    if (brush->gpencil_tool == GPAINT_TOOL_ERASE) {
      gp_settings = brush->gpencil_settings;
    }
    else if ((eraser != NULL) & (eraser->gpencil_tool == GPAINT_TOOL_ERASE)) {
      gp_settings = eraser->gpencil_settings;
    }
  
    if ((gp_settings != NULL) && (p->area->spacetype == SPACE_VIEW3D) &&
        (gp_settings->flag & GP_BRUSH_OCCLUDE_ERASER)) {
      RegionView3D *rv3d = p->region->regiondata;
      bGPDlayer *gpl = p->gpl;
  
      const int mval_i[2] = {x, y};
      float mval_3d[3];
      float fpt[3];
  
      float diff_mat[4][4];
      /* calculate difference matrix if parent object */
      BKE_gpencil_parent_matrix_get(p->depsgraph, obact, gpl, diff_mat);
  
      if (ED_view3d_autodist_simple(p->region, mval_i, mval_3d, 0, NULL)) {
        const float depth_mval = view3d_point_depth(rv3d, mval_3d);
  
        mul_v3_m4v3(fpt, diff_mat, &pt->x);
        const float depth_pt = view3d_point_depth(rv3d, fpt);
  
        if (depth_pt > depth_mval) {
          return true;
        }
      }
    }
    return false;
  }
  
  /* apply a falloff effect to brush strength, based on distance */
  static float gpencil_stroke_eraser_calc_influence(tGPsdata *p,
                                                    const float mval[2],
                                                    const int radius,
                                                    const int co[2])
  {
    Brush *brush = p->brush;
    /* Linear Falloff... */
    int mval_i[2];
    round_v2i_v2fl(mval_i, mval);
    float distance = (float)len_v2v2_int(mval_i, co);
    float fac;
  
    CLAMP(distance, 0.0f, (float)radius);
    fac = 1.0f - (distance / (float)radius);
  
    /* apply strength factor */
    fac *= brush->gpencil_settings->draw_strength;
  
    /* Control this further using pen pressure */
    if (brush->gpencil_settings->flag & GP_BRUSH_USE_PRESSURE) {
      fac *= p->pressure;
    }
    /* Return influence factor computed here */
    return fac;
  }
  
  /* helper to free a stroke */
  static void gpencil_free_stroke(bGPdata *gpd, bGPDframe *gpf, bGPDstroke *gps)
  {
    if (gps->points) {
      MEM_freeN(gps->points);
    }
  
    if (gps->dvert) {
      BKE_gpencil_free_stroke_weights(gps);
      MEM_freeN(gps->dvert);
    }
  
    if (gps->triangles) {
      MEM_freeN(gps->triangles);
    }
    BLI_freelinkN(&gpf->strokes, gps);
    gpencil_update_cache(gpd);
  }
  
  /**
   * Analyze points to be removed when soft eraser is used
   * to avoid that segments gets the end points rounded.
   * The round caps breaks the artistic effect.
   */
  static void gpencil_stroke_soft_refine(bGPDstroke *gps)
  {
    bGPDspoint *pt = NULL;
    bGPDspoint *pt2 = NULL;
    int i;
  
    /* check if enough points*/
    if (gps->totpoints < 3) {
      return;
    }
  
    /* loop all points to untag any point that next is not tagged */
    pt = gps->points;
    for (i = 1; i < gps->totpoints - 1; i++, pt++) {
      if (pt->flag & GP_SPOINT_TAG) {
        pt2 = &gps->points[i + 1];
        if ((pt2->flag & GP_SPOINT_TAG) == 0) {
          pt->flag &= ~GP_SPOINT_TAG;
        }
      }
    }
  
    /* loop reverse all points to untag any point that previous is not tagged */
    pt = &gps->points[gps->totpoints - 1];
    for (i = gps->totpoints - 1; i > 0; i--, pt--) {
      if (pt->flag & GP_SPOINT_TAG) {
        pt2 = &gps->points[i - 1];
        if ((pt2->flag & GP_SPOINT_TAG) == 0) {
          pt->flag &= ~GP_SPOINT_TAG;
        }
      }
    }
  }
  
  /* eraser tool - evaluation per stroke */
  static void gpencil_stroke_eraser_dostroke(tGPsdata *p,
                                             bGPDframe *gpf,
                                             bGPDstroke *gps,
                                             const float mval[2],
                                             const int radius,
                                             const rcti *rect)
  {
    Brush *eraser = p->eraser;
    bGPDspoint *pt0, *pt1, *pt2;
    int pc0[2] = {0};
    int pc1[2] = {0};
    int pc2[2] = {0};
    int i;
    int mval_i[2];
    round_v2i_v2fl(mval_i, mval);
  
    if (gps->totpoints == 0) {
      /* just free stroke */
      gpencil_free_stroke(p->gpd, gpf, gps);
    }
    else if (gps->totpoints == 1) {
      /* only process if it hasn't been masked out... */
      if (!(p->flags & GP_PAINTFLAG_SELECTMASK) || (gps->points->flag & GP_SPOINT_SELECT)) {
        bGPDspoint pt_temp;
        gpencil_point_to_parent_space(gps->points, p->diff_mat, &pt_temp);
        gpencil_point_to_xy(&p->gsc, gps, &pt_temp, &pc1[0], &pc1[1]);
        /* do boundbox check first */
        if ((!ELEM(V2D_IS_CLIPPED, pc1[0], pc1[1])) && BLI_rcti_isect_pt(rect, pc1[0], pc1[1])) {
          /* only check if point is inside */
          if (len_v2v2_int(mval_i, pc1) <= radius) {
            /* free stroke */
            gpencil_free_stroke(p->gpd, gpf, gps);
          }
        }
      }
    }
    else if ((p->flags & GP_PAINTFLAG_STROKE_ERASER) ||
             (eraser->gpencil_settings->eraser_mode == GP_BRUSH_ERASER_STROKE)) {
      for (i = 0; (i + 1) < gps->totpoints; i++) {
  
        /* only process if it hasn't been masked out... */
        if ((p->flags & GP_PAINTFLAG_SELECTMASK) && !(gps->points->flag & GP_SPOINT_SELECT)) {
          continue;
        }
  
        /* get points to work with */
        pt1 = gps->points + i;
        bGPDspoint npt;
        gpencil_point_to_parent_space(pt1, p->diff_mat, &npt);
        gpencil_point_to_xy(&p->gsc, gps, &npt, &pc1[0], &pc1[1]);
  
        /* do boundbox check first */
        if ((!ELEM(V2D_IS_CLIPPED, pc1[0], pc1[1])) && BLI_rcti_isect_pt(rect, pc1[0], pc1[1])) {
          /* only check if point is inside */
          if (len_v2v2_int(mval_i, pc1) <= radius) {
            /* free stroke */
            gpencil_free_stroke(p->gpd, gpf, gps);
            return;
          }
        }
      }
    }
    else {
      /* Pressure threshold at which stroke should be culled */
      const float cull_thresh = 0.005f;
  
      /* Amount to decrease the pressure of each point with each stroke */
      const float strength = 0.1f;
  
      /* Perform culling? */
      bool do_cull = false;
  
      /* Clear Tags
       *
       * Note: It's better this way, as we are sure that
       * we don't miss anything, though things will be
       * slightly slower as a result
       */
      for (i = 0; i < gps->totpoints; i++) {
        bGPDspoint *pt = &gps->points[i];
        pt->flag &= ~GP_SPOINT_TAG;
      }
  
      /* First Pass: Loop over the points in the stroke
       *   1) Thin out parts of the stroke under the brush
       *   2) Tag "too thin" parts for removal (in second pass)
       */
      for (i = 0; (i + 1) < gps->totpoints; i++) {
        /* get points to work with */
        pt0 = i > 0 ? gps->points + i - 1 : NULL;
        pt1 = gps->points + i;
        pt2 = gps->points + i + 1;
  
        /* only process if it hasn't been masked out... */
        if ((p->flags & GP_PAINTFLAG_SELECTMASK) && !(gps->points->flag & GP_SPOINT_SELECT)) {
          continue;
        }
  
        bGPDspoint npt;
        if (pt0) {
          gpencil_point_to_parent_space(pt0, p->diff_mat, &npt);
          gpencil_point_to_xy(&p->gsc, gps, &npt, &pc0[0], &pc0[1]);
        }
        else {
          /* avoid null values */
          copy_v2_v2_int(pc0, pc1);
        }
  
        gpencil_point_to_parent_space(pt1, p->diff_mat, &npt);
        gpencil_point_to_xy(&p->gsc, gps, &npt, &pc1[0], &pc1[1]);
  
        gpencil_point_to_parent_space(pt2, p->diff_mat, &npt);
        gpencil_point_to_xy(&p->gsc, gps, &npt, &pc2[0], &pc2[1]);
  
        /* Check that point segment of the boundbox of the eraser stroke */
        if (((!ELEM(V2D_IS_CLIPPED, pc0[0], pc0[1])) && BLI_rcti_isect_pt(rect, pc0[0], pc0[1])) ||
            ((!ELEM(V2D_IS_CLIPPED, pc1[0], pc1[1])) && BLI_rcti_isect_pt(rect, pc1[0], pc1[1])) ||
            ((!ELEM(V2D_IS_CLIPPED, pc2[0], pc2[1])) && BLI_rcti_isect_pt(rect, pc2[0], pc2[1]))) {
          /* Check if point segment of stroke had anything to do with
           * eraser region  (either within stroke painted, or on its lines)
           * - this assumes that linewidth is irrelevant
           */
          if (gpencil_stroke_inside_circle(mval, radius, pc0[0], pc0[1], pc2[0], pc2[1])) {
            if ((gpencil_stroke_eraser_is_occluded(p, pt0, pc0[0], pc0[1]) == false) ||
                (gpencil_stroke_eraser_is_occluded(p, pt1, pc1[0], pc1[1]) == false) ||
                (gpencil_stroke_eraser_is_occluded(p, pt2, pc2[0], pc2[1]) == false)) {
              /* Point is affected: */
              /* Adjust thickness
               *  - Influence of eraser falls off with distance from the middle of the eraser
               *  - Second point gets less influence, as it might get hit again in the next segment
               */
  
              /* Adjust strength if the eraser is soft */
              if (eraser->gpencil_settings->eraser_mode == GP_BRUSH_ERASER_SOFT) {
                float f_strength = eraser->gpencil_settings->era_strength_f / 100.0f;
                float f_thickness = eraser->gpencil_settings->era_thickness_f / 100.0f;
                float influence = 0.0f;
  
                if (pt0) {
                  influence = gpencil_stroke_eraser_calc_influence(p, mval, radius, pc0);
                  pt0->strength -= influence * strength * f_strength * 0.5f;
                  CLAMP_MIN(pt0->strength, 0.0f);
                  pt0->pressure -= influence * strength * f_thickness * 0.5f;
                }
  
                influence = gpencil_stroke_eraser_calc_influence(p, mval, radius, pc1);
                pt1->strength -= influence * strength * f_strength;
                CLAMP_MIN(pt1->strength, 0.0f);
                pt1->pressure -= influence * strength * f_thickness;
  
                influence = gpencil_stroke_eraser_calc_influence(p, mval, radius, pc2);
                pt2->strength -= influence * strength * f_strength * 0.5f;
                CLAMP_MIN(pt2->strength, 0.0f);
                pt2->pressure -= influence * strength * f_thickness * 0.5f;
  
                /* if invisible, delete point */
                if ((pt0) && ((pt0->strength <= GPENCIL_ALPHA_OPACITY_THRESH) ||
                              (pt0->pressure < cull_thresh))) {
                  pt0->flag |= GP_SPOINT_TAG;
                  do_cull = true;
                }
                if ((pt1->strength <= GPENCIL_ALPHA_OPACITY_THRESH) ||
                    (pt1->pressure < cull_thresh)) {
                  pt1->flag |= GP_SPOINT_TAG;
                  do_cull = true;
                }
                if ((pt2->strength <= GPENCIL_ALPHA_OPACITY_THRESH) ||
                    (pt2->pressure < cull_thresh)) {
                  pt2->flag |= GP_SPOINT_TAG;
                  do_cull = true;
                }
              }
              else {
                pt1->pressure -= gpencil_stroke_eraser_calc_influence(p, mval, radius, pc1) *
                                 strength;
                pt2->pressure -= gpencil_stroke_eraser_calc_influence(p, mval, radius, pc2) *
                                 strength * 0.5f;
              }
  
              /* 2) Tag any point with overly low influence for removal in the next pass */
              if ((pt1->pressure < cull_thresh) || (p->flags & GP_PAINTFLAG_HARD_ERASER) ||
                  (eraser->gpencil_settings->eraser_mode == GP_BRUSH_ERASER_HARD)) {
                pt1->flag |= GP_SPOINT_TAG;
                do_cull = true;
              }
              if ((pt2->pressure < cull_thresh) || (p->flags & GP_PAINTFLAG_HARD_ERASER) ||
                  (eraser->gpencil_settings->eraser_mode == GP_BRUSH_ERASER_HARD)) {
                pt2->flag |= GP_SPOINT_TAG;
                do_cull = true;
              }
            }
          }
        }
      }
  
      /* Second Pass: Remove any points that are tagged */
      if (do_cull) {
        /* if soft eraser, must analyze points to be sure the stroke ends
         * don't get rounded */
        if (eraser->gpencil_settings->eraser_mode == GP_BRUSH_ERASER_SOFT) {
          gpencil_stroke_soft_refine(gps);
        }
  
        gpencil_stroke_delete_tagged_points(gpf, gps, gps->next, GP_SPOINT_TAG, false, 0);
      }
      gpencil_update_cache(p->gpd);
    }
  }
  
  /* erase strokes which fall under the eraser strokes */
  static void gpencil_stroke_doeraser(tGPsdata *p)
  {
    rcti rect;
    Brush *brush = p->brush;
    Brush *eraser = p->eraser;
    bool use_pressure = false;
    float press = 1.0f;
    BrushGpencilSettings *gp_settings = NULL;
  
    /* detect if use pressure in eraser */
    if (brush->gpencil_tool == GPAINT_TOOL_ERASE) {
      use_pressure = (bool)(brush->gpencil_settings->flag & GP_BRUSH_USE_PRESSURE);
      gp_settings = brush->gpencil_settings;
    }
    else if ((eraser != NULL) & (eraser->gpencil_tool == GPAINT_TOOL_ERASE)) {
      use_pressure = (bool)(eraser->gpencil_settings->flag & GP_BRUSH_USE_PRESSURE);
      gp_settings = eraser->gpencil_settings;
    }
    if (use_pressure) {
      press = p->pressure;
      CLAMP(press, 0.01f, 1.0f);
    }
    /* rect is rectangle of eraser */
    const int calc_radius = (int)p->radius * press;
    rect.xmin = p->mval[0] - calc_radius;
    rect.ymin = p->mval[1] - calc_radius;
    rect.xmax = p->mval[0] + calc_radius;
    rect.ymax = p->mval[1] + calc_radius;
  
    if (p->area->spacetype == SPACE_VIEW3D) {
      if ((gp_settings != NULL) && (gp_settings->flag & GP_BRUSH_OCCLUDE_ERASER)) {
        View3D *v3d = p->area->spacedata.first;
        view3d_region_operator_needs_opengl(p->win, p->region);
        ED_view3d_autodist_init(p->depsgraph, p->region, v3d, 0);
      }
    }
  
    /* loop over all layers too, since while it's easy to restrict editing to
     * only a subset of layers, it is harder to perform the same erase operation
     * on multiple layers...
     */
    LISTBASE_FOREACH (bGPDlayer *, gpl, &p->gpd->layers) {
      bGPDframe *gpf = gpl->actframe;
  
      /* only affect layer if it's editable (and visible) */
      if (BKE_gpencil_layer_is_editable(gpl) == false) {
        continue;
      }
      if (gpf == NULL) {
        continue;
      }
      /* calculate difference matrix */
      BKE_gpencil_parent_matrix_get(p->depsgraph, p->ob, gpl, p->diff_mat);
  
      /* loop over strokes, checking segments for intersections */
      LISTBASE_FOREACH_MUTABLE (bGPDstroke *, gps, &gpf->strokes) {
        /* check if the color is editable */
        if (ED_gpencil_stroke_color_use(p->ob, gpl, gps) == false) {
          continue;
        }
  
        /* Check if the stroke collide with mouse. */
        if (!ED_gpencil_stroke_check_collision(&p->gsc, gps, p->mval, calc_radius, p->diff_mat)) {
          continue;
        }
  
        /* Not all strokes in the datablock may be valid in the current editor/context
         * (e.g. 2D space strokes in the 3D view, if the same datablock is shared)
         */
        if (ED_gpencil_stroke_can_use_direct(p->area, gps)) {
          gpencil_stroke_eraser_dostroke(p, gpf, gps, p->mval, calc_radius, &rect);
        }
      }
    }
  }
  
  /* ******************************************* */
  /* Sketching Operator */
  
  /* clear the session buffers (call this before AND after a paint operation) */
  static void gpencil_session_validatebuffer(tGPsdata *p)
  {
    bGPdata *gpd = p->gpd;
    Brush *brush = p->brush;
  
    /* clear memory of buffer (or allocate it if starting a new session) */
    gpd->runtime.sbuffer = ED_gpencil_sbuffer_ensure(
        gpd->runtime.sbuffer, &gpd->runtime.sbuffer_size, &gpd->runtime.sbuffer_used, true);
  
    /* reset flags */
    gpd->runtime.sbuffer_sflag = 0;
  
    /* reset inittime */
    p->inittime = 0.0;
  
    /* reset lazy */
    if (brush) {
      brush->gpencil_settings->flag &= ~GP_BRUSH_STABILIZE_MOUSE_TEMP;
    }
  }
  
  /* helper to get default eraser and create one if no eraser brush */
  static Brush *gpencil_get_default_eraser(Main *bmain, ToolSettings *ts)
  {
    Brush *brush_dft = NULL;
    Paint *paint = &ts->gp_paint->paint;
    Brush *brush_prev = paint->brush;
    for (Brush *brush = bmain->brushes.first; brush; brush = brush->id.next) {
      if (brush->gpencil_settings == NULL) {
        continue;
      }
      if ((brush->ob_mode == OB_MODE_PAINT_GPENCIL) && (brush->gpencil_tool == GPAINT_TOOL_ERASE)) {
        /* save first eraser to use later if no default */
        if (brush_dft == NULL) {
          brush_dft = brush;
        }
        /* found default */
        if (brush->gpencil_settings->flag & GP_BRUSH_DEFAULT_ERASER) {
          return brush;
        }
      }
    }
    /* if no default, but exist eraser brush, return this and set as default */
    if (brush_dft) {
      brush_dft->gpencil_settings->flag |= GP_BRUSH_DEFAULT_ERASER;
      return brush_dft;
    }
    /* create a new soft eraser brush */
  
    brush_dft = BKE_brush_add_gpencil(bmain, ts, "Soft Eraser", OB_MODE_PAINT_GPENCIL);
    brush_dft->size = 30.0f;
    brush_dft->gpencil_settings->flag |= GP_BRUSH_DEFAULT_ERASER;
    brush_dft->gpencil_settings->icon_id = GP_BRUSH_ICON_ERASE_SOFT;
    brush_dft->gpencil_tool = GPAINT_TOOL_ERASE;
    brush_dft->gpencil_settings->eraser_mode = GP_BRUSH_ERASER_SOFT;
  
    /* reset current brush */
    BKE_paint_brush_set(paint, brush_prev);
  
    return brush_dft;
  }
  
  /* helper to set default eraser and disable others */
  static void gpencil_set_default_eraser(Main *bmain, Brush *brush_dft)
  {
    if (brush_dft == NULL) {
      return;
    }
  
    for (Brush *brush = bmain->brushes.first; brush; brush = brush->id.next) {
      if ((brush->gpencil_settings) && (brush->gpencil_tool == GPAINT_TOOL_ERASE)) {
        if (brush == brush_dft) {
          brush->gpencil_settings->flag |= GP_BRUSH_DEFAULT_ERASER;
        }
        else if (brush->gpencil_settings->flag & GP_BRUSH_DEFAULT_ERASER) {
          brush->gpencil_settings->flag &= ~GP_BRUSH_DEFAULT_ERASER;
        }
      }
    }
  }
  
  /* initialize a drawing brush */
  static void gpencil_init_drawing_brush(bContext *C, tGPsdata *p)
  {
    Main *bmain = CTX_data_main(C);
    Scene *scene = CTX_data_scene(C);
    ToolSettings *ts = CTX_data_tool_settings(C);
  
    Paint *paint = &ts->gp_paint->paint;
    bool changed = false;
    /* if not exist, create a new one */
    if ((paint->brush == NULL) || (paint->brush->gpencil_settings == NULL)) {
      /* create new brushes */
      BKE_brush_gpencil_paint_presets(bmain, ts, true);
      changed = true;
    }
    /* Be sure curves are initializated. */
    BKE_curvemapping_init(paint->brush->gpencil_settings->curve_sensitivity);
    BKE_curvemapping_init(paint->brush->gpencil_settings->curve_strength);
    BKE_curvemapping_init(paint->brush->gpencil_settings->curve_jitter);
    BKE_curvemapping_init(paint->brush->gpencil_settings->curve_rand_pressure);
    BKE_curvemapping_init(paint->brush->gpencil_settings->curve_rand_strength);
    BKE_curvemapping_init(paint->brush->gpencil_settings->curve_rand_uv);
    BKE_curvemapping_init(paint->brush->gpencil_settings->curve_rand_hue);
    BKE_curvemapping_init(paint->brush->gpencil_settings->curve_rand_saturation);
    BKE_curvemapping_init(paint->brush->gpencil_settings->curve_rand_value);
  
    /* assign to temp tGPsdata */
    p->brush = paint->brush;
    if (paint->brush->gpencil_tool != GPAINT_TOOL_ERASE) {
      p->eraser = gpencil_get_default_eraser(p->bmain, ts);
    }
    else {
      p->eraser = paint->brush;
    }
    /* set new eraser as default */
    gpencil_set_default_eraser(p->bmain, p->eraser);
  
    /* use radius of eraser */
    p->radius = (short)p->eraser->size;
  
    /* Need this update to synchronize brush with draw manager. */
    if (changed) {
      DEG_id_tag_update(&scene->id, ID_RECALC_COPY_ON_WRITE);
    }
  }
  
  /* initialize a paint brush and a default color if not exist */
  static void gpencil_init_colors(tGPsdata *p)
  {
    bGPdata *gpd = p->gpd;
    Brush *brush = p->brush;
  
    /* use brush material */
    p->material = BKE_gpencil_object_material_ensure_from_active_input_brush(p->bmain, p->ob, brush);
  
    gpd->runtime.matid = BKE_object_material_slot_find_index(p->ob, p->material);
    gpd->runtime.sbuffer_brush = brush;
  }
  
  /* (re)init new painting data */
  static bool gpencil_session_initdata(bContext *C, wmOperator *op, tGPsdata *p)
  {
    Main *bmain = CTX_data_main(C);
    bGPdata **gpd_ptr = NULL;
    ScrArea *curarea = CTX_wm_area(C);
    ARegion *region = CTX_wm_region(C);
    ToolSettings *ts = CTX_data_tool_settings(C);
    Object *obact = CTX_data_active_object(C);
  
    /* make sure the active view (at the starting time) is a 3d-view */
    if (curarea == NULL) {
      p->status = GP_STATUS_ERROR;
      if (G.debug & G_DEBUG) {
        printf("Error: No active view for painting\n");
      }
      return 0;
    }
  
    /* pass on current scene and window */
    p->C = C;
    p->bmain = CTX_data_main(C);
    p->scene = CTX_data_scene(C);
    p->depsgraph = CTX_data_ensure_evaluated_depsgraph(C);
    p->win = CTX_wm_window(C);
    p->disable_fill = RNA_boolean_get(op->ptr, "disable_fill");
  
    unit_m4(p->imat);
    unit_m4(p->mat);
  
    switch (curarea->spacetype) {
      /* supported views first */
      case SPACE_VIEW3D: {
        /* set current area
         * - must verify that region data is 3D-view (and not something else)
         */
        /* CAUTION: If this is the "toolbar", then this will change on the first stroke */
        p->area = curarea;
        p->region = region;
        p->align_flag = &ts->gpencil_v3d_align;
  
        if (region->regiondata == NULL) {
          p->status = GP_STATUS_ERROR;
          if (G.debug & G_DEBUG) {
            printf(
                "Error: 3D-View active region doesn't have any region data, so cannot be "
                "drawable\n");
          }
          return 0;
        }
  
        if ((!obact) || (obact->type != OB_GPENCIL)) {
          View3D *v3d = p->area->spacedata.first;
          /* if active object doesn't exist or isn't a GP Object, create one */
          const float *cur = p->scene->cursor.location;
  
          ushort local_view_bits = 0;
          if (v3d->localvd) {
            local_view_bits = v3d->local_view_uuid;
          }
          /* create new default object */
          obact = ED_gpencil_add_object(C, cur, local_view_bits);
        }
        /* assign object after all checks to be sure we have one active */
        p->ob = obact;
        p->ob_eval = (Object *)DEG_get_evaluated_object(p->depsgraph, p->ob);
  
        break;
      }
  
      /* unsupported views */
      default: {
        p->status = GP_STATUS_ERROR;
        if (G.debug & G_DEBUG) {
          printf("Error: Active view not appropriate for Grease Pencil drawing\n");
        }
        return 0;
      }
    }
  
    /* get gp-data */
    gpd_ptr = ED_gpencil_data_get_pointers(C, &p->ownerPtr);
    if ((gpd_ptr == NULL) || ED_gpencil_data_owner_is_annotation(&p->ownerPtr)) {
      p->status = GP_STATUS_ERROR;
      if (G.debug & G_DEBUG) {
        printf("Error: Current context doesn't allow for any Grease Pencil data\n");
      }
      return 0;
    }
  
    /* if no existing GPencil block exists, add one */
    if (*gpd_ptr == NULL) {
      *gpd_ptr = BKE_gpencil_data_addnew(bmain, "GPencil");
    }
    p->gpd = *gpd_ptr;
  
    /* clear out buffer (stored in gp-data), in case something contaminated it */
    gpencil_session_validatebuffer(p);
  
    /* set brush and create a new one if null */
    gpencil_init_drawing_brush(C, p);
  
    /* setup active color */
    /* region where paint was originated */
    int totcol = p->ob->totcol;
    gpencil_init_colors(p);
  
    /* check whether the material was newly added */
    if (totcol != p->ob->totcol) {
      WM_event_add_notifier(C, NC_SPACE | ND_SPACE_PROPERTIES, NULL);
    }
  
    /* lock axis (in some modes, disable) */
    if (((*p->align_flag & GP_PROJECT_DEPTH_VIEW) == 0) &&
        ((*p->align_flag & GP_PROJECT_DEPTH_STROKE) == 0)) {
      p->lock_axis = ts->gp_sculpt.lock_axis;
    }
    else {
      p->lock_axis = 0;
    }
  
    return 1;
  }
  
  /* init new painting session */
  static tGPsdata *gpencil_session_initpaint(bContext *C, wmOperator *op)
  {
    tGPsdata *p = NULL;
  
    /* Create new context data */
    p = MEM_callocN(sizeof(tGPsdata), "GPencil Drawing Data");
  
    /* Try to initialize context data
     * WARNING: This may not always succeed (e.g. using GP in an annotation-only context)
     */
    if (gpencil_session_initdata(C, op, p) == 0) {
      /* Invalid state - Exit
       * NOTE: It should be safe to just free the data, since failing context checks should
       * only happen when no data has been allocated.
       */
      MEM_freeN(p);
      return NULL;
    }
  
    /* Random generator, only init once. */
    uint rng_seed = (uint)(PIL_check_seconds_timer_i() & UINT_MAX);
    rng_seed ^= POINTER_AS_UINT(p);
    p->rng = BLI_rng_new(rng_seed);
  
    /* return context data for running paint operator */
    return p;
  }
  
  /* cleanup after a painting session */
  static void gpencil_session_cleanup(tGPsdata *p)
  {
    bGPdata *gpd = (p) ? p->gpd : NULL;
  
    /* error checking */
    if (gpd == NULL) {
      return;
    }
  
    /* free stroke buffer */
    if (gpd->runtime.sbuffer) {
      MEM_SAFE_FREE(gpd->runtime.sbuffer);
      gpd->runtime.sbuffer = NULL;
    }
  
    /* clear flags */
    gpd->runtime.sbuffer_used = 0;
    gpd->runtime.sbuffer_size = 0;
    gpd->runtime.sbuffer_sflag = 0;
    p->inittime = 0.0;
  }
  
  static void gpencil_session_free(tGPsdata *p)
  {
    if (p->rng != NULL) {
      BLI_rng_free(p->rng);
    }
  
    MEM_freeN(p);
  }
  
  /* init new stroke */
  static void gpencil_paint_initstroke(tGPsdata *p,
                                       eGPencil_PaintModes paintmode,
                                       Depsgraph *depsgraph)
  {
    Scene *scene = p->scene;
    ToolSettings *ts = scene->toolsettings;
    bool changed = false;
  
    /* get active layer (or add a new one if non-existent) */
    p->gpl = BKE_gpencil_layer_active_get(p->gpd);
    if (p->gpl == NULL) {
      p->gpl = BKE_gpencil_layer_addnew(p->gpd, DATA_("GP_Layer"), true);
      changed = true;
      if (p->custom_color[3]) {
        copy_v3_v3(p->gpl->color, p->custom_color);
      }
    }
    if ((paintmode != GP_PAINTMODE_ERASER) && (p->gpl->flag & GP_LAYER_LOCKED)) {
      p->status = GP_STATUS_ERROR;
      if (G.debug & G_DEBUG) {
        printf("Error: Cannot paint on locked layer\n");
      }
      return;
    }
  
    /* Eraser mode: If no active strokes, add one or just return. */
    if (paintmode == GP_PAINTMODE_ERASER) {
      /* Eraser mode:
       * 1) Add new frames to all frames that we might touch,
       * 2) Ensure that p->gpf refers to the frame used for the active layer
       *    (to avoid problems with other tools which expect it to exist)
       *
       * This is done only if additive drawing is enabled.
       */
      bool has_layer_to_erase = false;
  
      LISTBASE_FOREACH (bGPDlayer *, gpl, &p->gpd->layers) {
        /* Skip if layer not editable */
        if (BKE_gpencil_layer_is_editable(gpl) == false) {
          continue;
        }
  
        /* Add a new frame if needed (and based off the active frame,
         * as we need some existing strokes to erase)
         *
         * Note: We don't add a new frame if there's nothing there now, so
         *       -> If there are no frames at all, don't add one
         *       -> If there are no strokes in that frame, don't add a new empty frame
         */
        if (gpl->actframe && gpl->actframe->strokes.first) {
          if (ts->gpencil_flags & GP_TOOL_FLAG_RETAIN_LAST) {
            gpl->actframe = BKE_gpencil_layer_frame_get(gpl, CFRA, GP_GETFRAME_ADD_COPY);
          }
          has_layer_to_erase = true;
          break;
        }
      }
  
      /* Ensure this gets set. */
      if (ts->gpencil_flags & GP_TOOL_FLAG_RETAIN_LAST) {
        p->gpf = p->gpl->actframe;
      }
  
      if (has_layer_to_erase == false) {
        p->status = GP_STATUS_ERROR;
        return;
      }
      /* Ensure this gets set... */
      p->gpf = p->gpl->actframe;
    }
    else {
      /* Drawing Modes - Add a new frame if needed on the active layer */
      short add_frame_mode;
  
      if (ts->gpencil_flags & GP_TOOL_FLAG_RETAIN_LAST) {
        add_frame_mode = GP_GETFRAME_ADD_COPY;
      }
      else {
        add_frame_mode = GP_GETFRAME_ADD_NEW;
      }
  
      bool need_tag = p->gpl->actframe == NULL;
      p->gpf = BKE_gpencil_layer_frame_get(p->gpl, CFRA, add_frame_mode);
      /* Only if there wasn't an active frame, need update. */
      if (need_tag) {
        DEG_id_tag_update(&p->gpd->id, ID_RECALC_TRANSFORM | ID_RECALC_GEOMETRY);
      }
  
      if (p->gpf == NULL) {
        p->status = GP_STATUS_ERROR;
        if (G.debug & G_DEBUG) {
          printf("Error: No frame created (gpencil_paint_init)\n");
        }
        return;
      }
      p->gpf->flag |= GP_FRAME_PAINT;
    }
  
    /* set 'eraser' for this stroke if using eraser */
    p->paintmode = paintmode;
    if (p->paintmode == GP_PAINTMODE_ERASER) {
      p->gpd->runtime.sbuffer_sflag |= GP_STROKE_ERASER;
    }
    else {
      /* disable eraser flags - so that we can switch modes during a session */
      p->gpd->runtime.sbuffer_sflag &= ~GP_STROKE_ERASER;
    }
  
    /* set special fill stroke mode */
    if (p->disable_fill == true) {
      p->gpd->runtime.sbuffer_sflag |= GP_STROKE_NOFILL;
    }
  
    /* set 'initial run' flag, which is only used to denote when a new stroke is starting */
    p->flags |= GP_PAINTFLAG_FIRSTRUN;
  
    /* when drawing in the camera view, in 2D space, set the subrect */
    p->subrect = NULL;
    if ((*p->align_flag & GP_PROJECT_VIEWSPACE) == 0) {
      if (p->area->spacetype == SPACE_VIEW3D) {
        View3D *v3d = p->area->spacedata.first;
        RegionView3D *rv3d = p->region->regiondata;
  
        /* for camera view set the subrect */
        if (rv3d->persp == RV3D_CAMOB) {
          /* no shift */
          ED_view3d_calc_camera_border(
              p->scene, depsgraph, p->region, v3d, rv3d, &p->subrect_data, true);
          p->subrect = &p->subrect_data;
        }
      }
    }
  
    /* init stroke point space-conversion settings... */
    p->gsc.gpd = p->gpd;
    p->gsc.gpl = p->gpl;
  
    p->gsc.area = p->area;
    p->gsc.region = p->region;
    p->gsc.v2d = p->v2d;
  
    p->gsc.subrect_data = p->subrect_data;
    p->gsc.subrect = p->subrect;
  
    copy_m4_m4(p->gsc.mat, p->mat);
  
    /* check if points will need to be made in view-aligned space */
    if (*p->align_flag & GP_PROJECT_VIEWSPACE) {
      switch (p->area->spacetype) {
        case SPACE_VIEW3D: {
          p->gpd->runtime.sbuffer_sflag |= GP_STROKE_3DSPACE;
          break;
        }
      }
    }
    if (!changed) {
      /* Copy the brush to avoid a full tag (very slow). */
      bGPdata *gpd_eval = (bGPdata *)p->ob_eval->data;
      gpd_eval->runtime.sbuffer_brush = p->gpd->runtime.sbuffer_brush;
    }
    else {
      gpencil_update_cache(p->gpd);
    }
  }
  
  /* finish off a stroke (clears buffer, but doesn't finish the paint operation) */
  static void gpencil_paint_strokeend(tGPsdata *p)
  {
    ToolSettings *ts = p->scene->toolsettings;
    /* for surface sketching, need to set the right OpenGL context stuff so that
     * the conversions will project the values correctly...
     */
    if (gpencil_project_check(p)) {
      View3D *v3d = p->area->spacedata.first;
  
      /* need to restore the original projection settings before packing up */
      view3d_region_operator_needs_opengl(p->win, p->region);
      ED_view3d_autodist_init(
          p->depsgraph, p->region, v3d, (ts->gpencil_v3d_align & GP_PROJECT_DEPTH_STROKE) ? 1 : 0);
    }
  
    /* check if doing eraser or not */
    if ((p->gpd->runtime.sbuffer_sflag & GP_STROKE_ERASER) == 0) {
      /* transfer stroke to frame */
      gpencil_stroke_newfrombuffer(p);
    }
  
    /* clean up buffer now */
    gpencil_session_validatebuffer(p);
  }
  
  /* finish off stroke painting operation */
  static void gpencil_paint_cleanup(tGPsdata *p)
  {
    /* p->gpd==NULL happens when stroke failed to initialize,
     * for example when GP is hidden in current space (sergey)
     */
    if (p->gpd) {
      /* finish off a stroke */
      gpencil_paint_strokeend(p);
    }
  
    /* "unlock" frame */
    if (p->gpf) {
      p->gpf->flag &= ~GP_FRAME_PAINT;
    }
  }
  /* ------------------------------- */
  
  /* Helper callback for drawing the cursor itself */
  static void gpencil_draw_eraser(bContext *UNUSED(C), int x, int y, void *p_ptr)
  {
    tGPsdata *p = (tGPsdata *)p_ptr;
  
    if (p->paintmode == GP_PAINTMODE_ERASER) {
      GPUVertFormat *format = immVertexFormat();
      const uint shdr_pos = GPU_vertformat_attr_add(format, "pos", GPU_COMP_F32, 2, GPU_FETCH_FLOAT);
      immBindBuiltinProgram(GPU_SHADER_2D_UNIFORM_COLOR);
  
      GPU_line_smooth(true);
      GPU_blend(true);
      GPU_blend_set_func_separate(
          GPU_SRC_ALPHA, GPU_ONE_MINUS_SRC_ALPHA, GPU_ONE, GPU_ONE_MINUS_SRC_ALPHA);
  
      immUniformColor4ub(255, 100, 100, 20);
      imm_draw_circle_fill_2d(shdr_pos, x, y, p->radius, 40);
  
      immUnbindProgram();
  
      immBindBuiltinProgram(GPU_SHADER_2D_LINE_DASHED_UNIFORM_COLOR);
  
      float viewport_size[4];
      GPU_viewport_size_get_f(viewport_size);
      immUniform2f("viewport_size", viewport_size[2], viewport_size[3]);
  
      immUniformColor4f(1.0f, 0.39f, 0.39f, 0.78f);
      immUniform1i("colors_len", 0); /* "simple" mode */
      immUniform1f("dash_width", 12.0f);
      immUniform1f("dash_factor", 0.5f);
  
      imm_draw_circle_wire_2d(shdr_pos,
                              x,
                              y,
                              p->radius,
                              /* XXX Dashed shader gives bad results with sets of small segments
                               * currently, temp hack around the issue. :( */
                              max_ii(8, p->radius / 2)); /* was fixed 40 */
  
      immUnbindProgram();
  
      GPU_blend(false);
      GPU_line_smooth(false);
    }
  }
  
  /* Turn brush cursor in 3D view on/off */
  static void gpencil_draw_toggle_eraser_cursor(tGPsdata *p, short enable)
  {
    if (p->erasercursor && !enable) {
      /* clear cursor */
      WM_paint_cursor_end(p->erasercursor);
      p->erasercursor = NULL;
    }
    else if (enable && !p->erasercursor) {
      ED_gpencil_toggle_brush_cursor(p->C, false, NULL);
      /* enable cursor */
      p->erasercursor = WM_paint_cursor_activate(SPACE_TYPE_ANY,
                                                 RGN_TYPE_ANY,
                                                 NULL, /* XXX */
                                                 gpencil_draw_eraser,
                                                 p);
    }
  }
  
  /* Check if tablet eraser is being used (when processing events) */
  static bool gpencil_is_tablet_eraser_active(const wmEvent *event)
  {
    return (event->tablet.active == EVT_TABLET_ERASER);
  }
  
  /* ------------------------------- */
  
  static void gpencil_draw_exit(bContext *C, wmOperator *op)
  {
    tGPsdata *p = op->customdata;
  
    /* don't assume that operator data exists at all */
    if (p) {
      /* check size of buffer before cleanup, to determine if anything happened here */
      if (p->paintmode == GP_PAINTMODE_ERASER) {
        /* turn off radial brush cursor */
        gpencil_draw_toggle_eraser_cursor(p, false);
      }
  
      /* always store the new eraser size to be used again next time
       * NOTE: Do this even when not in eraser mode, as eraser may
       *       have been toggled at some point.
       */
      if (p->eraser) {
        p->eraser->size = p->radius;
      }
  
      /* restore cursor to indicate end of drawing */
      if (p->area->spacetype != SPACE_VIEW3D) {
        WM_cursor_modal_restore(CTX_wm_window(C));
      }
      else {
        /* drawing batch cache is dirty now */
        bGPdata *gpd = CTX_data_gpencil_data(C);
        gpencil_update_cache(gpd);
      }
  
      /* clear undo stack */
      gpencil_undo_finish();
  
      /* cleanup */
      gpencil_paint_cleanup(p);
      gpencil_session_cleanup(p);
      ED_gpencil_toggle_brush_cursor(C, true, NULL);
  
      /* finally, free the temp data */
      gpencil_session_free(p);
      p = NULL;
    }
  
    op->customdata = NULL;
  }
  
  static void gpencil_draw_cancel(bContext *C, wmOperator *op)
  {
    /* this is just a wrapper around exit() */
    gpencil_draw_exit(C, op);
  }
  
  /* ------------------------------- */
  
  static int gpencil_draw_init(bContext *C, wmOperator *op, const wmEvent *event)
  {
    tGPsdata *p;
    eGPencil_PaintModes paintmode = RNA_enum_get(op->ptr, "mode");
    ToolSettings *ts = CTX_data_tool_settings(C);
    Brush *brush = BKE_paint_brush(&ts->gp_paint->paint);
  
    /* if mode is draw and the brush is eraser, cancel */
    if (paintmode != GP_PAINTMODE_ERASER) {
      if ((brush) && (brush->gpencil_tool == GPAINT_TOOL_ERASE)) {
        return 0;
      }
    }
  
    /* check context */
    p = op->customdata = gpencil_session_initpaint(C, op);
    if ((p == NULL) || (p->status == GP_STATUS_ERROR)) {
      /* something wasn't set correctly in context */
      gpencil_draw_exit(C, op);
      return 0;
    }
  
    /* init painting data */
    gpencil_paint_initstroke(p, paintmode, CTX_data_ensure_evaluated_depsgraph(C));
    if (p->status == GP_STATUS_ERROR) {
      gpencil_draw_exit(C, op);
      return 0;
    }
  
    if (event != NULL) {
      p->keymodifier = event->keymodifier;
    }
    else {
      p->keymodifier = -1;
    }
  
    p->reports = op->reports;
  
    /* everything is now setup ok */
    return 1;
  }
  
  /* ------------------------------- */
  
  /* update UI indicators of status, including cursor and header prints */
  static void gpencil_draw_status_indicators(bContext *C, tGPsdata *p)
  {
    /* header prints */
    switch (p->status) {
      case GP_STATUS_IDLING: {
        /* print status info */
        switch (p->paintmode) {
          case GP_PAINTMODE_ERASER: {
            ED_workspace_status_text(
                C,
                TIP_("Grease Pencil Erase Session: Hold and drag LMB or RMB to erase | "
                     "ESC/Enter to end  (or click outside this area)"));
            break;
          }
          case GP_PAINTMODE_DRAW_STRAIGHT: {
            ED_workspace_status_text(C,
                                     TIP_("Grease Pencil Line Session: Hold and drag LMB to draw | "
                                          "ESC/Enter to end  (or click outside this area)"));
            break;
          }
          case GP_PAINTMODE_SET_CP: {
            ED_workspace_status_text(
                C,
                TIP_("Grease Pencil Guides: LMB click and release to place reference point | "
                     "Esc/RMB to cancel"));
            break;
          }
          case GP_PAINTMODE_DRAW: {
            GP_Sculpt_Guide *guide = &p->scene->toolsettings->gp_sculpt.guide;
            if (guide->use_guide) {
              ED_workspace_status_text(
                  C,
                  TIP_("Grease Pencil Freehand Session: Hold and drag LMB to draw | "
                       "M key to flip guide | O key to move reference point"));
            }
            else {
              ED_workspace_status_text(
                  C, TIP_("Grease Pencil Freehand Session: Hold and drag LMB to draw"));
            }
            break;
          }
          default: /* unhandled future cases */
          {
            ED_workspace_status_text(
                C, TIP_("Grease Pencil Session: ESC/Enter to end (or click outside this area)"));
            break;
          }
        }
        break;
      }
      case GP_STATUS_ERROR:
      case GP_STATUS_DONE: {
        /* clear status string */
        ED_workspace_status_text(C, NULL);
        break;
      }
      case GP_STATUS_PAINTING:
        break;
    }
  }
  
  /* ------------------------------- */
  
  /* Helper to rotate point around origin */
  static void gpencil_rotate_v2_v2v2fl(float v[2],
                                       const float p[2],
                                       const float origin[2],
                                       const float angle)
  {
    float pt[2];
    float r[2];
    sub_v2_v2v2(pt, p, origin);
    rotate_v2_v2fl(r, pt, angle);
    add_v2_v2v2(v, r, origin);
  }
  
  /* Helper to snap value to grid */
  static float gpencil_snap_to_grid_fl(float v, const float offset, const float spacing)
  {
    if (spacing > 0.0f) {
      v -= spacing * 0.5f;
      v -= offset;
      v = roundf((v + spacing * 0.5f) / spacing) * spacing;
      v += offset;
    }
    return v;
  }
  
  /* Helper to snap value to grid */
  static void gpencil_snap_to_rotated_grid_fl(float v[2],
                                              const float origin[2],
                                              const float spacing,
                                              const float angle)
  {
    gpencil_rotate_v2_v2v2fl(v, v, origin, -angle);
    v[1] = gpencil_snap_to_grid_fl(v[1], origin[1], spacing);
    gpencil_rotate_v2_v2v2fl(v, v, origin, angle);
  }
  
  /* get reference point - screen coords to buffer coords */
  static void gpencil_origin_set(wmOperator *op, const int mval[2])
  {
    tGPsdata *p = op->customdata;
    GP_Sculpt_Guide *guide = &p->scene->toolsettings->gp_sculpt.guide;
    float origin[2];
    float point[3];
    copy_v2fl_v2i(origin, mval);
    gpencil_stroke_convertcoords(p, origin, point, NULL);
    if (guide->reference_point == GP_GUIDE_REF_CUSTOM) {
      copy_v3_v3(guide->location, point);
    }
    else if (guide->reference_point == GP_GUIDE_REF_CURSOR) {
      copy_v3_v3(p->scene->cursor.location, point);
    }
  }
  
  /* get reference point - buffer coords to screen coords */
  static void gpencil_origin_get(tGPsdata *p, float origin[2])
  {
    GP_Sculpt_Guide *guide = &p->scene->toolsettings->gp_sculpt.guide;
    float location[3];
    if (guide->reference_point == GP_GUIDE_REF_CUSTOM) {
      copy_v3_v3(location, guide->location);
    }
    else if (guide->reference_point == GP_GUIDE_REF_OBJECT && guide->reference_object != NULL) {
      copy_v3_v3(location, guide->reference_object->loc);
    }
    else {
      copy_v3_v3(location, p->scene->cursor.location);
    }
    GP_SpaceConversion *gsc = &p->gsc;
    gpencil_point_3d_to_xy(gsc, p->gpd->runtime.sbuffer_sflag, location, origin);
  }
  
  /* speed guide initial values */
  static void gpencil_speed_guide_init(tGPsdata *p, GP_Sculpt_Guide *guide)
  {
    /* calculate initial guide values */
    RegionView3D *rv3d = p->region->regiondata;
    float scale = 1.0f;
    if (rv3d->is_persp) {
      float vec[3];
      gpencil_get_3d_reference(p, vec);
      mul_m4_v3(rv3d->persmat, vec);
      scale = vec[2] * rv3d->pixsize;
    }
    else {
      scale = rv3d->pixsize;
    }
    p->guide.spacing = guide->spacing / scale;
    p->guide.half_spacing = p->guide.spacing * 0.5f;
    gpencil_origin_get(p, p->guide.origin);
  
    /* reference for angled snap */
    copy_v2_v2(p->guide.unit, p->mvali);
    p->guide.unit[0] += 1.0f;
  
    float xy[2];
    sub_v2_v2v2(xy, p->mvali, p->guide.origin);
    p->guide.origin_angle = atan2f(xy[1], xy[0]) + (M_PI * 2.0f);
  
    p->guide.origin_distance = len_v2v2(p->mvali, p->guide.origin);
    if (guide->use_snapping && (guide->spacing > 0.0f)) {
      p->guide.origin_distance = gpencil_snap_to_grid_fl(
          p->guide.origin_distance, 0.0f, p->guide.spacing);
    }
  
    if (ELEM(guide->type, GP_GUIDE_RADIAL)) {
      float angle;
      float half_angle = guide->angle_snap * 0.5f;
      angle = p->guide.origin_angle + guide->angle;
      angle = fmodf(angle + half_angle, guide->angle_snap);
      angle -= half_angle;
      gpencil_rotate_v2_v2v2fl(p->guide.rot_point, p->mvali, p->guide.origin, -angle);
    }
    else {
      gpencil_rotate_v2_v2v2fl(p->guide.rot_point, p->guide.unit, p->mvali, guide->angle);
    }
  }
  
  /* apply speed guide */
  static void gpencil_snap_to_guide(const tGPsdata *p, const GP_Sculpt_Guide *guide, float point[2])
  {
    switch (guide->type) {
      default:
      case GP_GUIDE_CIRCULAR: {
        dist_ensure_v2_v2fl(point, p->guide.origin, p->guide.origin_distance);
        break;
      }
      case GP_GUIDE_RADIAL: {
        if (guide->use_snapping && (guide->angle_snap > 0.0f)) {
          closest_to_line_v2(point, point, p->guide.rot_point, p->guide.origin);
        }
        else {
          closest_to_line_v2(point, point, p->mvali, p->guide.origin);
        }
        break;
      }
      case GP_GUIDE_PARALLEL: {
        closest_to_line_v2(point, point, p->mvali, p->guide.rot_point);
        if (guide->use_snapping && (guide->spacing > 0.0f)) {
          gpencil_snap_to_rotated_grid_fl(point, p->guide.origin, p->guide.spacing, guide->angle);
        }
        break;
      }
      case GP_GUIDE_ISO: {
        closest_to_line_v2(point, point, p->mvali, p->guide.rot_point);
        if (guide->use_snapping && (guide->spacing > 0.0f)) {
          gpencil_snap_to_rotated_grid_fl(
              point, p->guide.origin, p->guide.spacing, p->guide.rot_angle);
        }
        break;
      }
      case GP_GUIDE_GRID: {
        if (guide->use_snapping && (guide->spacing > 0.0f)) {
          closest_to_line_v2(point, point, p->mvali, p->guide.rot_point);
          if (p->straight == STROKE_HORIZONTAL) {
            point[1] = gpencil_snap_to_grid_fl(point[1], p->guide.origin[1], p->guide.spacing);
          }
          else {
            point[0] = gpencil_snap_to_grid_fl(point[0], p->guide.origin[0], p->guide.spacing);
          }
        }
        else if (p->straight == STROKE_HORIZONTAL) {
          point[1] = p->mvali[1]; /* replace y */
        }
        else {
          point[0] = p->mvali[0]; /* replace x */
        }
        break;
      }
    }
  }
  
  /* create a new stroke point at the point indicated by the painting context */
  static void gpencil_draw_apply(bContext *C, wmOperator *op, tGPsdata *p, Depsgraph *depsgraph)
  {
    bGPdata *gpd = p->gpd;
    tGPspoint *pt = NULL;
  
    /* handle drawing/erasing -> test for erasing first */
    if (p->paintmode == GP_PAINTMODE_ERASER) {
      /* do 'live' erasing now */
      gpencil_stroke_doeraser(p);
  
      /* store used values */
      copy_v2_v2(p->mvalo, p->mval);
      p->opressure = p->pressure;
    }
    /* Only add current point to buffer if mouse moved
     * (even though we got an event, it might be just noise). */
    else if (gpencil_stroke_filtermval(p, p->mval, p->mvalo)) {
  
      /* if lazy mouse, interpolate the last and current mouse positions */
      if (GPENCIL_LAZY_MODE(p->brush, p->shift)) {
        float now_mouse[2];
        float last_mouse[2];
        copy_v2_v2(now_mouse, p->mval);
        copy_v2_v2(last_mouse, p->mvalo);
        interp_v2_v2v2(now_mouse, now_mouse, last_mouse, p->brush->smooth_stroke_factor);
        copy_v2_v2(p->mval, now_mouse);
  
        GP_Sculpt_Guide *guide = &p->scene->toolsettings->gp_sculpt.guide;
        bool is_speed_guide = ((guide->use_guide) &&
                               (p->brush && (p->brush->gpencil_tool == GPAINT_TOOL_DRAW)));
        if (is_speed_guide) {
          gpencil_snap_to_guide(p, guide, p->mval);
        }
      }
  
      /* try to add point */
      short ok = gpencil_stroke_addpoint(p, p->mval, p->pressure, p->curtime);
  
      /* handle errors while adding point */
      if ((ok == GP_STROKEADD_FULL) || (ok == GP_STROKEADD_OVERFLOW)) {
        /* finish off old stroke */
        gpencil_paint_strokeend(p);
        /* And start a new one!!! Else, projection errors! */
        gpencil_paint_initstroke(p, p->paintmode, depsgraph);
  
        /* start a new stroke, starting from previous point */
        /* XXX Must manually reset inittime... */
        /* XXX We only need to reuse previous point if overflow! */
        if (ok == GP_STROKEADD_OVERFLOW) {
          p->inittime = p->ocurtime;
          gpencil_stroke_addpoint(p, p->mvalo, p->opressure, p->ocurtime);
        }
        else {
          p->inittime = p->curtime;
        }
        gpencil_stroke_addpoint(p, p->mval, p->pressure, p->curtime);
      }
      else if (ok == GP_STROKEADD_INVALID) {
        /* the painting operation cannot continue... */
        BKE_report(op->reports, RPT_ERROR, "Cannot paint stroke");
        p->status = GP_STATUS_ERROR;
  
        if (G.debug & G_DEBUG) {
          printf("Error: Grease-Pencil Paint - Add Point Invalid\n");
        }
        return;
      }
  
      /* store used values */
      copy_v2_v2(p->mvalo, p->mval);
      p->opressure = p->pressure;
      p->ocurtime = p->curtime;
  
      pt = (tGPspoint *)gpd->runtime.sbuffer + gpd->runtime.sbuffer_used - 1;
      if (p->paintmode != GP_PAINTMODE_ERASER) {
        ED_gpencil_toggle_brush_cursor(C, true, &pt->x);
      }
    }
    else if ((p->brush->gpencil_settings->flag & GP_BRUSH_STABILIZE_MOUSE_TEMP) &&
             (gpd->runtime.sbuffer_used > 0)) {
      pt = (tGPspoint *)gpd->runtime.sbuffer + gpd->runtime.sbuffer_used - 1;
      if (p->paintmode != GP_PAINTMODE_ERASER) {
        ED_gpencil_toggle_brush_cursor(C, true, &pt->x);
      }
    }
  }
  
  /* handle draw event */
  static void gpencil_draw_apply_event(bContext *C,
                                       wmOperator *op,
                                       const wmEvent *event,
                                       Depsgraph *depsgraph)
  {
    tGPsdata *p = op->customdata;
    GP_Sculpt_Guide *guide = &p->scene->toolsettings->gp_sculpt.guide;
    PointerRNA itemptr;
    float mousef[2];
    bool is_speed_guide = ((guide->use_guide) &&
                           (p->brush && (p->brush->gpencil_tool == GPAINT_TOOL_DRAW)));
  
    /* convert from window-space to area-space mouse coordinates
     * add any x,y override position
     */
    copy_v2fl_v2i(p->mval, event->mval);
    p->shift = event->shift;
  
    /* verify direction for straight lines and guides */
    if ((is_speed_guide) ||
        ((event->alt > 0) && (RNA_boolean_get(op->ptr, "disable_straight") == false))) {
      if (p->straight == 0) {
        int dx = (int)fabsf(p->mval[0] - p->mvali[0]);
        int dy = (int)fabsf(p->mval[1] - p->mvali[1]);
        if ((dx > 0) || (dy > 0)) {
          /* store mouse direction */
          if (dx > dy) {
            p->straight = STROKE_HORIZONTAL;
          }
          else if (dx < dy) {
            p->straight = STROKE_VERTICAL;
          }
        }
        /* reset if a stroke angle is required */
        if ((p->flags & GP_PAINTFLAG_REQ_VECTOR) && ((dx == 0) || (dy == 0))) {
          p->straight = 0;
        }
      }
    }
  
    p->curtime = PIL_check_seconds_timer();
  
    /* handle pressure sensitivity (which is supplied by tablets or otherwise 1.0) */
    p->pressure = event->tablet.pressure;
    /* By default use pen pressure for random curves but attenuated. */
    p->random_settings.pen_press = pow(p->pressure, 3.0f);
  
    /* Hack for pressure sensitive eraser on D+RMB when using a tablet:
     * The pen has to float over the tablet surface, resulting in
     * zero pressure (T47101). Ignore pressure values if floating
     * (i.e. "effectively zero" pressure), and only when the "active"
     * end is the stylus (i.e. the default when not eraser)
     */
    if (p->paintmode == GP_PAINTMODE_ERASER) {
      if ((event->tablet.active != EVT_TABLET_ERASER) && (p->pressure < 0.001f)) {
        p->pressure = 1.0f;
      }
    }
  
    /* special eraser modes */
    if (p->paintmode == GP_PAINTMODE_ERASER) {
      if (event->shift > 0) {
        p->flags |= GP_PAINTFLAG_HARD_ERASER;
      }
      else {
        p->flags &= ~GP_PAINTFLAG_HARD_ERASER;
      }
      if (event->alt > 0) {
        p->flags |= GP_PAINTFLAG_STROKE_ERASER;
      }
      else {
        p->flags &= ~GP_PAINTFLAG_STROKE_ERASER;
      }
    }
  
    /* special exception for start of strokes (i.e. maybe for just a dot) */
    if (p->flags & GP_PAINTFLAG_FIRSTRUN) {
  
      /* special exception here for too high pressure values on first touch in
       * windows for some tablets, then we just skip first touch...
       */
      if ((event->tablet.active != EVT_TABLET_NONE) && (p->pressure >= 0.99f)) {
        return;
      }
  
      p->flags &= ~GP_PAINTFLAG_FIRSTRUN;
  
      /* set values */
      p->opressure = p->pressure;
      p->inittime = p->ocurtime = p->curtime;
      p->straight = 0;
  
      /* save initial mouse */
      copy_v2_v2(p->mvalo, p->mval);
      copy_v2_v2(p->mvali, p->mval);
  
      if (is_speed_guide && !ELEM(p->paintmode, GP_PAINTMODE_ERASER, GP_PAINTMODE_SET_CP) &&
          ((guide->use_snapping && (guide->type == GP_GUIDE_GRID)) ||
           (guide->type == GP_GUIDE_ISO))) {
        p->flags |= GP_PAINTFLAG_REQ_VECTOR;
      }
  
      /* calculate initial guide values */
      if (is_speed_guide) {
        gpencil_speed_guide_init(p, guide);
      }
    }
  
    /* wait for vector then add initial point */
    if (is_speed_guide && (p->flags & GP_PAINTFLAG_REQ_VECTOR)) {
      if (p->straight == 0) {
        return;
      }
  
      p->flags &= ~GP_PAINTFLAG_REQ_VECTOR;
  
      /* get initial point */
      float pt[2];
      sub_v2_v2v2(pt, p->mval, p->mvali);
  
      /* get stroke angle for grids */
      if (ELEM(guide->type, GP_GUIDE_ISO)) {
        p->guide.stroke_angle = atan2f(pt[1], pt[0]);
        /* determine iso angle, less weight is given for vertical strokes */
        if (((p->guide.stroke_angle >= 0.0f) && (p->guide.stroke_angle < DEG2RAD(75))) ||
            (p->guide.stroke_angle < DEG2RAD(-105))) {
          p->guide.rot_angle = guide->angle;
        }
        else if (((p->guide.stroke_angle < 0.0f) && (p->guide.stroke_angle > DEG2RAD(-75))) ||
                 (p->guide.stroke_angle > DEG2RAD(105))) {
          p->guide.rot_angle = -guide->angle;
        }
        else {
          p->guide.rot_angle = DEG2RAD(90);
        }
        gpencil_rotate_v2_v2v2fl(p->guide.rot_point, p->guide.unit, p->mvali, p->guide.rot_angle);
      }
      else if (ELEM(guide->type, GP_GUIDE_GRID)) {
        gpencil_rotate_v2_v2v2fl(p->guide.rot_point,
                                 p->guide.unit,
                                 p->mvali,
                                 (p->straight == STROKE_VERTICAL) ? M_PI_2 : 0.0f);
      }
    }
  
    /* check if stroke is straight or guided */
    if ((p->paintmode != GP_PAINTMODE_ERASER) && ((p->straight) || (is_speed_guide))) {
      /* guided stroke */
      if (is_speed_guide) {
        gpencil_snap_to_guide(p, guide, p->mval);
      }
      else if (p->straight == STROKE_HORIZONTAL) {
        p->mval[1] = p->mvali[1]; /* replace y */
      }
      else {
        p->mval[0] = p->mvali[0]; /* replace x */
      }
    }
  
    /* fill in stroke data (not actually used directly by gpencil_draw_apply) */
    RNA_collection_add(op->ptr, "stroke", &itemptr);
  
    mousef[0] = p->mval[0];
    mousef[1] = p->mval[1];
    RNA_float_set_array(&itemptr, "mouse", mousef);
    RNA_float_set(&itemptr, "pressure", p->pressure);
    RNA_boolean_set(&itemptr, "is_start", (p->flags & GP_PAINTFLAG_FIRSTRUN) != 0);
  
    RNA_float_set(&itemptr, "time", p->curtime - p->inittime);
  
    /* apply the current latest drawing point */
    gpencil_draw_apply(C, op, p, depsgraph);
  
    /* force refresh */
    /* just active area for now, since doing whole screen is too slow */
    ED_region_tag_redraw(p->region);
  }
  
  /* ------------------------------- */
  
  /* operator 'redo' (i.e. after changing some properties, but also for repeat last) */
  static int gpencil_draw_exec(bContext *C, wmOperator *op)
  {
    tGPsdata *p = NULL;
    Depsgraph *depsgraph = CTX_data_ensure_evaluated_depsgraph(C);
  
    /* try to initialize context data needed while drawing */
    if (!gpencil_draw_init(C, op, NULL)) {
      MEM_SAFE_FREE(op->customdata);
      return OPERATOR_CANCELLED;
    }
  
    p = op->customdata;
  
    /* loop over the stroke RNA elements recorded (i.e. progress of mouse movement),
     * setting the relevant values in context at each step, then applying
     */
    RNA_BEGIN (op->ptr, itemptr, "stroke") {
      float mousef[2];
  
      /* get relevant data for this point from stroke */
      RNA_float_get_array(&itemptr, "mouse", mousef);
      p->mval[0] = mousef[0];
      p->mval[1] = mousef[1];
      p->pressure = RNA_float_get(&itemptr, "pressure");
      p->curtime = (double)RNA_float_get(&itemptr, "time") + p->inittime;
  
      if (RNA_boolean_get(&itemptr, "is_start")) {
        /* if first-run flag isn't set already (i.e. not true first stroke),
         * then we must terminate the previous one first before continuing
         */
        if ((p->flags & GP_PAINTFLAG_FIRSTRUN) == 0) {
          /* TODO: both of these ops can set error-status, but we probably don't need to worry */
          gpencil_paint_strokeend(p);
          gpencil_paint_initstroke(p, p->paintmode, depsgraph);
        }
      }
  
      /* if first run, set previous data too */
      if (p->flags & GP_PAINTFLAG_FIRSTRUN) {
        p->flags &= ~GP_PAINTFLAG_FIRSTRUN;
  
        p->mvalo[0] = p->mval[0];
        p->mvalo[1] = p->mval[1];
        p->opressure = p->pressure;
        p->ocurtime = p->curtime;
      }
  
      /* apply this data as necessary now (as per usual) */
      gpencil_draw_apply(C, op, p, depsgraph);
    }
    RNA_END;
  
    /* cleanup */
    gpencil_draw_exit(C, op);
  
    /* refreshes */
    WM_event_add_notifier(C, NC_GPENCIL | NA_EDITED, NULL);
  
    /* done */
    return OPERATOR_FINISHED;
  }
  
  /* ------------------------------- */
  
  /* handle events for guides */
  static void gpencil_guide_event_handling(bContext *C,
                                           wmOperator *op,
                                           const wmEvent *event,
                                           tGPsdata *p)
  {
    bool add_notifier = false;
    GP_Sculpt_Guide *guide = &p->scene->toolsettings->gp_sculpt.guide;
  
    /* Enter or exit set center point mode */
    if ((event->type == EVT_OKEY) && (event->val == KM_RELEASE)) {
      if ((p->paintmode == GP_PAINTMODE_DRAW) && guide->use_guide &&
          (guide->reference_point != GP_GUIDE_REF_OBJECT)) {
        add_notifier = true;
        p->paintmode = GP_PAINTMODE_SET_CP;
        ED_gpencil_toggle_brush_cursor(C, false, NULL);
      }
    }
    /* Freehand mode, turn off speed guide */
    else if ((event->type == EVT_VKEY) && (event->val == KM_RELEASE)) {
      guide->use_guide = false;
      add_notifier = true;
    }
    /* Alternate or flip direction */
    else if ((event->type == EVT_MKEY) && (event->val == KM_RELEASE)) {
      if (guide->type == GP_GUIDE_CIRCULAR) {
        add_notifier = true;
        guide->type = GP_GUIDE_RADIAL;
      }
      else if (guide->type == GP_GUIDE_RADIAL) {
        add_notifier = true;
        guide->type = GP_GUIDE_CIRCULAR;
      }
      else if (guide->type == GP_GUIDE_PARALLEL) {
        add_notifier = true;
        guide->angle += M_PI_2;
        guide->angle = angle_compat_rad(guide->angle, M_PI);
      }
      else {
        add_notifier = false;
      }
    }
    /* Line guides */
    else if ((event->type == EVT_LKEY) && (event->val == KM_RELEASE)) {
      add_notifier = true;
      guide->use_guide = true;
      if (event->ctrl) {
        guide->angle = 0.0f;
        guide->type = GP_GUIDE_PARALLEL;
      }
      else if (event->alt) {
        guide->type = GP_GUIDE_PARALLEL;
        guide->angle = RNA_float_get(op->ptr, "guide_last_angle");
      }
      else {
        guide->type = GP_GUIDE_PARALLEL;
      }
    }
    /* Point guide */
    else if ((event->type == EVT_CKEY) && (event->val == KM_RELEASE)) {
      add_notifier = true;
      if (!guide->use_guide) {
        guide->use_guide = true;
        guide->type = GP_GUIDE_CIRCULAR;
      }
      else if (guide->type == GP_GUIDE_CIRCULAR) {
        guide->type = GP_GUIDE_RADIAL;
      }
      else if (guide->type == GP_GUIDE_RADIAL) {
        guide->type = GP_GUIDE_CIRCULAR;
      }
      else {
        guide->type = GP_GUIDE_CIRCULAR;
      }
    }
    /* Change line angle  */
    else if (ELEM(event->type, EVT_JKEY, EVT_KKEY) && (event->val == KM_RELEASE)) {
      add_notifier = true;
      float angle = guide->angle;
      float adjust = (float)M_PI / 180.0f;
      if (event->alt) {
        adjust *= 45.0f;
      }
      else if (!event->shift) {
        adjust *= 15.0f;
      }
      angle += (event->type == EVT_JKEY) ? adjust : -adjust;
      angle = angle_compat_rad(angle, M_PI);
      guide->angle = angle;
    }
  
    if (add_notifier) {
      WM_event_add_notifier(C, NC_SCENE | ND_TOOLSETTINGS | NC_GPENCIL | NA_EDITED, NULL);
    }
  }
  
  /* start of interactive drawing part of operator */
  static int gpencil_draw_invoke(bContext *C, wmOperator *op, const wmEvent *event)
  {
    tGPsdata *p = NULL;
    Object *ob = CTX_data_active_object(C);
    bGPdata *gpd = (bGPdata *)ob->data;
  
    if (G.debug & G_DEBUG) {
      printf("GPencil - Starting Drawing\n");
    }
  
    /* support for tablets eraser pen */
    if (gpencil_is_tablet_eraser_active(event)) {
      RNA_enum_set(op->ptr, "mode", GP_PAINTMODE_ERASER);
    }
  
    /* do not draw in locked or invisible layers */
    eGPencil_PaintModes paintmode = RNA_enum_get(op->ptr, "mode");
    if (paintmode != GP_PAINTMODE_ERASER) {
      bGPDlayer *gpl = CTX_data_active_gpencil_layer(C);
      if ((gpl) && ((gpl->flag & GP_LAYER_LOCKED) || (gpl->flag & GP_LAYER_HIDE))) {
        BKE_report(op->reports, RPT_ERROR, "Active layer is locked or hidden");
        return OPERATOR_CANCELLED;
      }
    }
    else {
      /* don't erase empty frames */
      bool has_layer_to_erase = false;
      LISTBASE_FOREACH (bGPDlayer *, gpl, &gpd->layers) {
        /* Skip if layer not editable */
        if (BKE_gpencil_layer_is_editable(gpl)) {
          if (gpl->actframe && gpl->actframe->strokes.first) {
            has_layer_to_erase = true;
            break;
          }
        }
      }
      if (!has_layer_to_erase) {
        BKE_report(op->reports, RPT_ERROR, "Nothing to erase or all layers locked");
        return OPERATOR_FINISHED;
      }
    }
  
    /* try to initialize context data needed while drawing */
    if (!gpencil_draw_init(C, op, event)) {
      if (op->customdata) {
        MEM_freeN(op->customdata);
      }
      if (G.debug & G_DEBUG) {
        printf("\tGP - no valid data\n");
      }
      return OPERATOR_CANCELLED;
    }
  
    p = op->customdata;
  
    /* Init random settings. */
    ED_gpencil_init_random_settings(p->brush, event->mval, &p->random_settings);
  
    /* TODO: set any additional settings that we can take from the events?
     * if eraser is on, draw radial aid */
    if (p->paintmode == GP_PAINTMODE_ERASER) {
      gpencil_draw_toggle_eraser_cursor(p, true);
    }
    else {
      ED_gpencil_toggle_brush_cursor(C, true, NULL);
    }
  
    /* only start drawing immediately if we're allowed to do so... */
    if (RNA_boolean_get(op->ptr, "wait_for_input") == false) {
      /* hotkey invoked - start drawing */
      p->status = GP_STATUS_PAINTING;
  
      /* handle the initial drawing - i.e. for just doing a simple dot */
      gpencil_draw_apply_event(C, op, event, CTX_data_ensure_evaluated_depsgraph(C));
      op->flag |= OP_IS_MODAL_CURSOR_REGION;
    }
    else {
      /* toolbar invoked - don't start drawing yet... */
      op->flag |= OP_IS_MODAL_CURSOR_REGION;
    }
  
    /* enable paint mode */
    /* handle speed guide events before drawing inside view3d */
    if (!ELEM(p->paintmode, GP_PAINTMODE_ERASER, GP_PAINTMODE_SET_CP)) {
      gpencil_guide_event_handling(C, op, event, p);
    }
  
    if (ob && (ob->type == OB_GPENCIL) && ((p->gpd->flag & GP_DATA_STROKE_PAINTMODE) == 0)) {
      /* FIXME: use the mode switching operator, this misses notifiers, messages. */
      /* Just set paintmode flag... */
      p->gpd->flag |= GP_DATA_STROKE_PAINTMODE;
      /* disable other GP modes */
      p->gpd->flag &= ~GP_DATA_STROKE_EDITMODE;
      p->gpd->flag &= ~GP_DATA_STROKE_SCULPTMODE;
      p->gpd->flag &= ~GP_DATA_STROKE_WEIGHTMODE;
      /* set workspace mode */
      ob->restore_mode = ob->mode;
      ob->mode = OB_MODE_PAINT_GPENCIL;
      /* redraw mode on screen */
      WM_event_add_notifier(C, NC_SCENE | ND_MODE, NULL);
    }
  
    WM_event_add_notifier(C, NC_GPENCIL | NA_EDITED, NULL);
  
    /* add a modal handler for this operator, so that we can then draw continuous strokes */
    WM_event_add_modal_handler(C, op);
  
    return OPERATOR_RUNNING_MODAL;
  }
  
  /* gpencil modal operator stores area, which can be removed while using it (like fullscreen) */
  static bool gpencil_area_exists(bContext *C, ScrArea *area_test)
  {
    bScreen *screen = CTX_wm_screen(C);
    return (BLI_findindex(&screen->areabase, area_test) != -1);
  }
  
  static tGPsdata *gpencil_stroke_begin(bContext *C, wmOperator *op)
  {
    tGPsdata *p = op->customdata;
  
    /* we must check that we're still within the area that we're set up to work from
     * otherwise we could crash (see bug #20586)
     */
    if (CTX_wm_area(C) != p->area) {
      printf("\t\t\tGP - wrong area execution abort!\n");
      p->status = GP_STATUS_ERROR;
    }
  
    /* we may need to set up paint env again if we're resuming */
    if (gpencil_session_initdata(C, op, p)) {
      gpencil_paint_initstroke(p, p->paintmode, CTX_data_depsgraph_pointer(C));
    }
  
    if (p->status != GP_STATUS_ERROR) {
      p->status = GP_STATUS_PAINTING;
      op->flag &= ~OP_IS_MODAL_CURSOR_REGION;
    }
  
    return op->customdata;
  }
  
  /* Apply pressure change depending of the angle of the stroke for a segment. */
  static void gpencil_brush_angle_segment(tGPsdata *p, tGPspoint *pt_prev, tGPspoint *pt)
  {
    Brush *brush = p->brush;
    /* Sensitivity. */
    const float sen = brush->gpencil_settings->draw_angle_factor;
    /* Default angle of brush in radians */
    const float angle = brush->gpencil_settings->draw_angle;
  
    float mvec[2];
    float fac;
  
    /* angle vector of the brush with full thickness */
    float v0[2] = {cos(angle), sin(angle)};
  
    mvec[0] = pt->x - pt_prev->x;
    mvec[1] = pt->y - pt_prev->y;
    normalize_v2(mvec);
    fac = 1.0f - fabs(dot_v2v2(v0, mvec)); /* 0.0 to 1.0 */
    /* interpolate with previous point for smoother transitions */
    pt->pressure = interpf(pt->pressure - (sen * fac), pt_prev->pressure, 0.3f);
    CLAMP(pt->pressure, GPENCIL_ALPHA_OPACITY_THRESH, 1.0f);
  }
  
  /* Add arc points between two mouse events using the previous segment to determine the vertice of
   * the arc.
   *        /+ CTL
   *       / |
   *      /  |
   * PtA +...|...+ PtB
   *    /
   *   /
   *  + PtA - 1
   * /
   * CTL is the vertice of the triangle created between PtA and PtB */
  static void gpencil_add_arc_points(tGPsdata *p, float mval[2], int segments)
  {
    bGPdata *gpd = p->gpd;
    BrushGpencilSettings *brush_settings = p->brush->gpencil_settings;
  
    if (gpd->runtime.sbuffer_used < 3) {
      tGPspoint *points = (tGPspoint *)gpd->runtime.sbuffer;
      /* Apply other randomness to first points. */
      for (int i = 0; i < gpd->runtime.sbuffer_used; i++) {
        tGPspoint *pt = &points[i];
        gpencil_apply_randomness(p, brush_settings, pt, false, false, true);
      }
      return;
    }
    int idx_prev = gpd->runtime.sbuffer_used;
  
    /* Add space for new arc points. */
    gpd->runtime.sbuffer_used += segments - 1;
  
    /* Check if still room in buffer or add more. */
    gpd->runtime.sbuffer = ED_gpencil_sbuffer_ensure(
        gpd->runtime.sbuffer, &gpd->runtime.sbuffer_size, &gpd->runtime.sbuffer_used, false);
  
    tGPspoint *points = (tGPspoint *)gpd->runtime.sbuffer;
    tGPspoint *pt = NULL;
    tGPspoint *pt_before = &points[idx_prev - 1]; /* current - 2 */
    tGPspoint *pt_prev = &points[idx_prev - 2];   /* previous */
  
    /* Create two vectors, previous and half way of the actual to get the vertex of the triangle
     * for arc curve.
     */
    float v_prev[2], v_cur[2], v_half[2];
    sub_v2_v2v2(v_cur, mval, &pt_prev->x);
  
    sub_v2_v2v2(v_prev, &pt_prev->x, &pt_before->x);
    interp_v2_v2v2(v_half, &pt_prev->x, mval, 0.5f);
    sub_v2_v2(v_half, &pt_prev->x);
  
    /* If angle is too sharp undo all changes and return. */
    const float min_angle = DEG2RADF(120.0f);
    float angle = angle_v2v2(v_prev, v_half);
    if (angle < min_angle) {
      gpd->runtime.sbuffer_used -= segments - 1;
      return;
    }
  
    /* Project the half vector to the previous vector and calculate the mid projected point. */
    float dot = dot_v2v2(v_prev, v_half);
    float l = len_squared_v2(v_prev);
    if (l > 0.0f) {
      mul_v2_fl(v_prev, dot / l);
    }
  
    /* Calc the position of the control point. */
    float ctl[2];
    add_v2_v2v2(ctl, &pt_prev->x, v_prev);
  
    float step = M_PI_2 / (float)(segments + 1);
    float a = step;
  
    float midpoint[2], start[2], end[2], cp1[2], corner[2];
    mid_v2_v2v2(midpoint, &pt_prev->x, mval);
    copy_v2_v2(start, &pt_prev->x);
    copy_v2_v2(end, mval);
    copy_v2_v2(cp1, ctl);
  
    corner[0] = midpoint[0] - (cp1[0] - midpoint[0]);
    corner[1] = midpoint[1] - (cp1[1] - midpoint[1]);
    float stepcolor = 1.0f / segments;
  
    tGPspoint *pt_step = pt_prev;
    for (int i = 0; i < segments; i++) {
      pt = &points[idx_prev + i - 1];
      pt->x = corner[0] + (end[0] - corner[0]) * sinf(a) + (start[0] - corner[0]) * cosf(a);
      pt->y = corner[1] + (end[1] - corner[1]) * sinf(a) + (start[1] - corner[1]) * cosf(a);
  
      /* Set pressure and strength equals to previous. It will be smoothed later. */
      pt->pressure = pt_prev->pressure;
      pt->strength = pt_prev->strength;
      /* Interpolate vertex color. */
      interp_v4_v4v4(
          pt->vert_color, pt_before->vert_color, pt_prev->vert_color, stepcolor * (i + 1));
  
      /* Apply angle of stroke to brush size to interpolated points but slightly attenuated.. */
      if (brush_settings->draw_angle_factor != 0.0f) {
        gpencil_brush_angle_segment(p, pt_step, pt);
        CLAMP(pt->pressure, pt_prev->pressure * 0.5f, 1.0f);
        /* Use the previous interpolated point for next segment. */
        pt_step = pt;
      }
  
      /* Apply other randomness. */
      gpencil_apply_randomness(p, brush_settings, pt, false, false, true);
  
      a += step;
    }
  }
  
  static void gpencil_add_guide_points(const tGPsdata *p,
                                       const GP_Sculpt_Guide *guide,
                                       const float start[2],
                                       const float end[2],
                                       int segments)
  {
    bGPdata *gpd = p->gpd;
    if (gpd->runtime.sbuffer_used == 0) {
      return;
    }
  
    int idx_prev = gpd->runtime.sbuffer_used;
  
    /* Add space for new points. */
    gpd->runtime.sbuffer_used += segments - 1;
  
    /* Check if still room in buffer or add more. */
    gpd->runtime.sbuffer = ED_gpencil_sbuffer_ensure(
        gpd->runtime.sbuffer, &gpd->runtime.sbuffer_size, &gpd->runtime.sbuffer_used, false);
  
    tGPspoint *points = (tGPspoint *)gpd->runtime.sbuffer;
    tGPspoint *pt = NULL;
    tGPspoint *pt_before = &points[idx_prev - 1];
  
    /* Use arc sampling for circular guide */
    if (guide->type == GP_GUIDE_CIRCULAR) {
      float cw = cross_tri_v2(start, p->guide.origin, end);
      float angle = angle_v2v2v2(start, p->guide.origin, end);
  
      float step = angle / (float)(segments + 1);
      if (cw < 0.0f) {
        step = -step;
      }
  
      float a = step;
  
      for (int i = 0; i < segments; i++) {
        pt = &points[idx_prev + i - 1];
  
        gpencil_rotate_v2_v2v2fl(&pt->x, start, p->guide.origin, -a);
        gpencil_snap_to_guide(p, guide, &pt->x);
        a += step;
  
        /* Set pressure and strength equals to previous. It will be smoothed later. */
        pt->pressure = pt_before->pressure;
        pt->strength = pt_before->strength;
        copy_v4_v4(pt->vert_color, pt_before->vert_color);
      }
    }
    else {
      float step = 1.0f / (float)(segments + 1);
      float a = step;
  
      for (int i = 0; i < segments; i++) {
        pt = &points[idx_prev + i - 1];
  
        interp_v2_v2v2(&pt->x, start, end, a);
        gpencil_snap_to_guide(p, guide, &pt->x);
        a += step;
  
        /* Set pressure and strength equals to previous. It will be smoothed later. */
        pt->pressure = pt_before->pressure;
        pt->strength = pt_before->strength;
        copy_v4_v4(pt->vert_color, pt_before->vert_color);
      }
    }
  }
  
  /**
   * Add fake points for missing mouse movements when the artist draw very fast creating an arc
   * with the vertex in the middle of the segment and using the angle of the previous segment.
   */
  static void gpencil_add_fake_points(const wmEvent *event, tGPsdata *p)
  {
    Brush *brush = p->brush;
    /* Lazy mode do not use fake events. */
    if (GPENCIL_LAZY_MODE(brush, p->shift)) {
      return;
    }
  
    GP_Sculpt_Guide *guide = &p->scene->toolsettings->gp_sculpt.guide;
    int input_samples = brush->gpencil_settings->input_samples;
    bool is_speed_guide = ((guide->use_guide) &&
                           (p->brush && (p->brush->gpencil_tool == GPAINT_TOOL_DRAW)));
  
    /* TODO: ensure sampling enough points when using circular guide,
    but the arc must be around the center. (see if above to check other guides only)
    */
    if (is_speed_guide && (guide->type == GP_GUIDE_CIRCULAR)) {
      input_samples = GP_MAX_INPUT_SAMPLES;
    }
  
    if (input_samples == 0) {
      return;
    }
  
    int samples = GP_MAX_INPUT_SAMPLES - input_samples + 1;
  
    float mouse_prv[2], mouse_cur[2];
    float min_dist = 4.0f * samples;
  
    copy_v2_v2(mouse_prv, p->mvalo);
    copy_v2fl_v2i(mouse_cur, event->mval);
  
    /* get distance in pixels */
    float dist = len_v2v2(mouse_prv, mouse_cur);
  
    /* get distance for circular guide */
    if (is_speed_guide && (guide->type == GP_GUIDE_CIRCULAR)) {
      float middle[2];
      gpencil_snap_to_guide(p, guide, mouse_prv);
      gpencil_snap_to_guide(p, guide, mouse_cur);
      mid_v2_v2v2(middle, mouse_cur, mouse_prv);
      gpencil_snap_to_guide(p, guide, middle);
      dist = len_v2v2(mouse_prv, middle) + len_v2v2(middle, mouse_cur);
    }
  
    if ((dist > 3.0f) && (dist > min_dist)) {
      int slices = (dist / min_dist) + 1;
  
      if (is_speed_guide) {
        gpencil_add_guide_points(p, guide, mouse_prv, mouse_cur, slices);
      }
      else {
        gpencil_add_arc_points(p, mouse_cur, slices);
      }
    }
  }
  
  /* events handling during interactive drawing part of operator */
  static int gpencil_draw_modal(bContext *C, wmOperator *op, const wmEvent *event)
  {
    tGPsdata *p = op->customdata;
    // ToolSettings *ts = CTX_data_tool_settings(C);
    GP_Sculpt_Guide *guide = &p->scene->toolsettings->gp_sculpt.guide;
  
    /* default exit state - pass through to support MMB view nav, etc. */
    int estate = OPERATOR_PASS_THROUGH;
  
    /* if (event->type == NDOF_MOTION)
     *    return OPERATOR_PASS_THROUGH;
     * -------------------------------
     * [mce] Not quite what I was looking
     * for, but a good start! GP continues to
     * draw on the screen while the 3D mouse
     * moves the viewpoint. Problem is that
     * the stroke is converted to 3D only after
     * it is finished. This approach should work
     * better in tools that immediately apply
     * in 3D space.
     */
  
    if (p->status == GP_STATUS_IDLING) {
      ARegion *region = CTX_wm_region(C);
      p->region = region;
    }
  
    /* special mode for editing control points */
    if (p->paintmode == GP_PAINTMODE_SET_CP) {
      wmWindow *win = p->win;
      WM_cursor_modal_set(win, WM_CURSOR_NSEW_SCROLL);
      bool drawmode = false;
  
      switch (event->type) {
        /* cancel */
        case EVT_ESCKEY:
        case RIGHTMOUSE: {
          if (ELEM(event->val, KM_RELEASE)) {
            drawmode = true;
          }
          break;
        }
        /* set */
        case LEFTMOUSE: {
          if (ELEM(event->val, KM_RELEASE)) {
            gpencil_origin_set(op, event->mval);
            drawmode = true;
          }
          break;
        }
      }
      if (drawmode) {
        p->status = GP_STATUS_IDLING;
        p->paintmode = GP_PAINTMODE_DRAW;
        WM_cursor_modal_restore(p->win);
        ED_gpencil_toggle_brush_cursor(C, true, NULL);
        DEG_id_tag_update(&p->scene->id, ID_RECALC_COPY_ON_WRITE);
      }
      else {
        return OPERATOR_RUNNING_MODAL;
      }
    }
  
    /* We don't pass on key events, GP is used with key-modifiers -
     * prevents Dkey to insert drivers. */
    if (ISKEYBOARD(event->type)) {
      if (ELEM(event->type, EVT_LEFTARROWKEY, EVT_DOWNARROWKEY, EVT_RIGHTARROWKEY, EVT_UPARROWKEY)) {
        /* allow some keys:
         *   - for frame changing [#33412]
         *   - for undo (during sketching sessions)
         */
      }
      else if (event->type == EVT_ZKEY) {
        if (event->ctrl) {
          p->status = GP_STATUS_DONE;
          estate = OPERATOR_FINISHED;
        }
      }
      else if (ELEM(event->type,
                    EVT_PAD0,
                    EVT_PAD1,
                    EVT_PAD2,
                    EVT_PAD3,
                    EVT_PAD4,
                    EVT_PAD5,
                    EVT_PAD6,
                    EVT_PAD7,
                    EVT_PAD8,
                    EVT_PAD9)) {
        /* allow numpad keys so that camera/view manipulations can still take place
         * - PAD0 in particular is really important for Grease Pencil drawing,
         *   as animators may be working "to camera", so having this working
         *   is essential for ensuring that they can quickly return to that view
         */
      }
      else if ((event->type == EVT_BKEY) && (event->val == KM_RELEASE)) {
        /* Add Blank Frame
         * - Since this operator is non-modal, we can just call it here, and keep going...
         * - This operator is especially useful when animating
         */
        WM_operator_name_call(C, "GPENCIL_OT_blank_frame_add", WM_OP_EXEC_DEFAULT, NULL);
        estate = OPERATOR_RUNNING_MODAL;
      }
      else if ((!ELEM(p->paintmode, GP_PAINTMODE_ERASER, GP_PAINTMODE_SET_CP))) {
        gpencil_guide_event_handling(C, op, event, p);
        estate = OPERATOR_RUNNING_MODAL;
      }
      else {
        estate = OPERATOR_RUNNING_MODAL;
      }
    }
  
    /* Exit painting mode (and/or end current stroke).
     *
     */
    if (ELEM(event->type, EVT_RETKEY, EVT_PADENTER, EVT_ESCKEY, EVT_SPACEKEY, EVT_EKEY)) {
  
      p->status = GP_STATUS_DONE;
      estate = OPERATOR_FINISHED;
    }
  
    /* toggle painting mode upon mouse-button movement
     * - LEFTMOUSE  = standard drawing (all) / straight line drawing (all)
     * - RIGHTMOUSE = eraser (all)
     *   (Disabling RIGHTMOUSE case here results in bugs like [#32647])
     * also making sure we have a valid event value, to not exit too early
     */
    if (ELEM(event->type, LEFTMOUSE, RIGHTMOUSE) && (ELEM(event->val, KM_PRESS, KM_RELEASE))) {
      /* if painting, end stroke */
      if (p->status == GP_STATUS_PAINTING) {
        p->status = GP_STATUS_DONE;
        estate = OPERATOR_FINISHED;
      }
      else if (event->val == KM_PRESS) {
        bool in_bounds = false;
  
        /* Check if we're outside the bounds of the active region
         * NOTE: An exception here is that if launched from the toolbar,
         *       whatever region we're now in should become the new region
         */
        if ((p->region) && (p->region->regiontype == RGN_TYPE_TOOLS)) {
          /* Change to whatever region is now under the mouse */
          ARegion *current_region = BKE_area_find_region_xy(
              p->area, RGN_TYPE_ANY, event->x, event->y);
  
          if (G.debug & G_DEBUG) {
            printf("found alternative region %p (old was %p) - at %d %d (area: %d %d -> %d %d)\n",
                   current_region,
                   p->region,
                   event->x,
                   event->y,
                   p->area->totrct.xmin,
                   p->area->totrct.ymin,
                   p->area->totrct.xmax,
                   p->area->totrct.ymax);
          }
  
          if (current_region) {
            /* Assume that since we found the cursor in here, it is in bounds
             * and that this should be the region that we begin drawing in
             */
            p->region = current_region;
            in_bounds = true;
          }
          else {
            /* Out of bounds, or invalid in some other way */
            p->status = GP_STATUS_ERROR;
            estate = OPERATOR_CANCELLED;
  
            if (G.debug & G_DEBUG) {
              printf("%s: Region under cursor is out of bounds, so cannot be drawn on\n", __func__);
            }
          }
        }
        else if (p->region) {
          /* Perform bounds check using  */
          const rcti *region_rect = ED_region_visible_rect(p->region);
          in_bounds = BLI_rcti_isect_pt_v(region_rect, event->mval);
        }
        else {
          /* No region */
          p->status = GP_STATUS_ERROR;
          estate = OPERATOR_CANCELLED;
  
          if (G.debug & G_DEBUG) {
            printf("%s: No active region found in GP Paint session data\n", __func__);
          }
        }
  
        if (in_bounds) {
          /* Switch paintmode (temporarily if need be) based on which button was used
           * NOTE: This is to make it more convenient to erase strokes when using drawing sessions
           */
          if ((event->type == RIGHTMOUSE) || gpencil_is_tablet_eraser_active(event)) {
            /* turn on eraser */
            p->paintmode = GP_PAINTMODE_ERASER;
          }
          else if (event->type == LEFTMOUSE) {
            /* restore drawmode to default */
            p->paintmode = RNA_enum_get(op->ptr, "mode");
          }
  
          gpencil_draw_toggle_eraser_cursor(p, p->paintmode == GP_PAINTMODE_ERASER);
  
          /* not painting, so start stroke (this should be mouse-button down) */
          p = gpencil_stroke_begin(C, op);
  
          if (p->status == GP_STATUS_ERROR) {
            estate = OPERATOR_CANCELLED;
          }
        }
        else if (p->status != GP_STATUS_ERROR) {
          /* User clicked outside bounds of window while idling, so exit paintmode
           * NOTE: Don't enter this case if an error occurred while finding the
           *       region (as above)
           */
          p->status = GP_STATUS_DONE;
          estate = OPERATOR_FINISHED;
        }
      }
      else if (event->val == KM_RELEASE) {
        p->status = GP_STATUS_IDLING;
        op->flag |= OP_IS_MODAL_CURSOR_REGION;
        ED_region_tag_redraw(p->region);
      }
    }
  
    /* handle mode-specific events */
    if (p->status == GP_STATUS_PAINTING) {
      /* handle painting mouse-movements? */
      if (ELEM(event->type, MOUSEMOVE, INBETWEEN_MOUSEMOVE) || (p->flags & GP_PAINTFLAG_FIRSTRUN)) {
        /* handle drawing event */
        bool is_speed_guide = ((guide->use_guide) &&
                               (p->brush && (p->brush->gpencil_tool == GPAINT_TOOL_DRAW)));
  
        int size_before = p->gpd->runtime.sbuffer_used;
        if (((p->flags & GP_PAINTFLAG_FIRSTRUN) == 0) && (p->paintmode != GP_PAINTMODE_ERASER) &&
            !(is_speed_guide && (p->flags & GP_PAINTFLAG_REQ_VECTOR))) {
          gpencil_add_fake_points(event, p);
        }
  
        gpencil_draw_apply_event(C, op, event, CTX_data_depsgraph_pointer(C));
        int size_after = p->gpd->runtime.sbuffer_used;
  
        /* Smooth segments if some fake points were added (need loop to get cumulative smooth).
         * the 0.15 value gets a good result in Windows and Linux. */
        if (!is_speed_guide && (size_after - size_before > 1)) {
          for (int r = 0; r < 5; r++) {
            gpencil_smooth_segment(p->gpd, 0.15f, size_before - 1, size_after - 1);
          }
        }
  
        /* finish painting operation if anything went wrong just now */
        if (p->status == GP_STATUS_ERROR) {
          printf("\t\t\t\tGP - add error done!\n");
          estate = OPERATOR_CANCELLED;
        }
        else {
          /* event handled, so just tag as running modal */
          estate = OPERATOR_RUNNING_MODAL;
        }
      }
      /* eraser size */
      else if ((p->paintmode == GP_PAINTMODE_ERASER) &&
               ELEM(event->type, WHEELUPMOUSE, WHEELDOWNMOUSE, EVT_PADPLUSKEY, EVT_PADMINUS)) {
        /* Just resize the brush (local version). */
        switch (event->type) {
          case WHEELDOWNMOUSE: /* larger */
          case EVT_PADPLUSKEY:
            p->radius += 5;
            break;
  
          case WHEELUPMOUSE: /* smaller */
          case EVT_PADMINUS:
            p->radius -= 5;
  
            if (p->radius <= 0) {
              p->radius = 1;
            }
            break;
        }
  
        /* force refresh */
        /* just active area for now, since doing whole screen is too slow */
        ED_region_tag_redraw(p->region);
  
        /* event handled, so just tag as running modal */
        estate = OPERATOR_RUNNING_MODAL;
      }
      /* there shouldn't be any other events, but just in case there are, let's swallow them
       * (i.e. to prevent problems with undo)
       */
      else {
        /* swallow event to save ourselves trouble */
        estate = OPERATOR_RUNNING_MODAL;
      }
    }
  
    /* gpencil modal operator stores area, which can be removed while using it (like fullscreen) */
    if (0 == gpencil_area_exists(C, p->area)) {
      estate = OPERATOR_CANCELLED;
    }
    else {
      /* update status indicators - cursor, header, etc. */
      gpencil_draw_status_indicators(C, p);
    }
  
    /* process last operations before exiting */
    switch (estate) {
      case OPERATOR_FINISHED:
        /* store stroke angle for parallel guide */
        if ((p->straight == 0) || (guide->use_guide && (guide->type == GP_GUIDE_CIRCULAR))) {
          float xy[2];
          sub_v2_v2v2(xy, p->mval, p->mvali);
          float angle = atan2f(xy[1], xy[0]);
          RNA_float_set(op->ptr, "guide_last_angle", angle);
        }
        /* one last flush before we're done */
        gpencil_draw_exit(C, op);
        WM_event_add_notifier(C, NC_GPENCIL | NA_EDITED, NULL);
        break;
  
      case OPERATOR_CANCELLED:
        gpencil_draw_exit(C, op);
        break;
  
      case OPERATOR_RUNNING_MODAL | OPERATOR_PASS_THROUGH:
        /* event doesn't need to be handled */
        break;
    }
  
    /* return status code */
    return estate;
  }
  
  /* ------------------------------- */
  
  static const EnumPropertyItem prop_gpencil_drawmodes[] = {
      {GP_PAINTMODE_DRAW, "DRAW", 0, "Draw Freehand", "Draw freehand stroke(s)"},
      {GP_PAINTMODE_DRAW_STRAIGHT,
       "DRAW_STRAIGHT",
       0,
       "Draw Straight Lines",
       "Draw straight line segment(s)"},
      {GP_PAINTMODE_ERASER, "ERASER", 0, "Eraser", "Erase Grease Pencil strokes"},
      {0, NULL, 0, NULL, NULL},
  };
  
  void GPENCIL_OT_draw(wmOperatorType *ot)
  {
    PropertyRNA *prop;
  
    /* identifiers */
    ot->name = "Grease Pencil Draw";
    ot->idname = "GPENCIL_OT_draw";
    ot->description = "Draw mouse_prv new stroke in the active Grease Pencil Object";
  
    /* api callbacks */
    ot->exec = gpencil_draw_exec;
    ot->invoke = gpencil_draw_invoke;
    ot->modal = gpencil_draw_modal;
    ot->cancel = gpencil_draw_cancel;
    ot->poll = gpencil_draw_poll;
  
    /* flags */
    ot->flag = OPTYPE_UNDO | OPTYPE_BLOCKING;
  
    /* settings for drawing */
    ot->prop = RNA_def_enum(
        ot->srna, "mode", prop_gpencil_drawmodes, 0, "Mode", "Way to interpret mouse movements");
  
    prop = RNA_def_collection_runtime(ot->srna, "stroke", &RNA_OperatorStrokeElement, "Stroke", "");
    RNA_def_property_flag(prop, PROP_HIDDEN | PROP_SKIP_SAVE);
  
    /* NOTE: wait for input is enabled by default,
     * so that all UI code can work properly without needing users to know about this */
    prop = RNA_def_boolean(ot->srna,
                           "wait_for_input",
                           true,
                           "Wait for Input",
                           "Wait for first click instead of painting immediately");
    RNA_def_property_flag(prop, PROP_HIDDEN | PROP_SKIP_SAVE);
  
    prop = RNA_def_boolean(
        ot->srna, "disable_straight", false, "No Straight lines", "Disable key for straight lines");
    RNA_def_property_flag(prop, PROP_SKIP_SAVE);
  
    prop = RNA_def_boolean(ot->srna,
                           "disable_fill",
                           false,
                           "No Fill Areas",
                           "Disable fill to use stroke as fill boundary");
    RNA_def_property_flag(prop, PROP_SKIP_SAVE);
  
    /* guides */
    prop = RNA_def_float(ot->srna,
                         "guide_last_angle",
                         0.0f,
                         -10000.0f,
                         10000.0f,
                         "Angle",
                         "Speed guide angle",
                         -10000.0f,
                         10000.0f);
  }
  
  /* additional OPs */
  
  static int gpencil_guide_rotate(bContext *C, wmOperator *op)
  {
    ToolSettings *ts = CTX_data_tool_settings(C);
    GP_Sculpt_Guide *guide = &ts->gp_sculpt.guide;
    float angle = RNA_float_get(op->ptr, "angle");
    bool increment = RNA_boolean_get(op->ptr, "increment");
    if (increment) {
      float oldangle = guide->angle;
      oldangle += angle;
      guide->angle = angle_compat_rad(oldangle, M_PI);
    }
    else {
      guide->angle = angle_compat_rad(angle, M_PI);
    }
  
    return OPERATOR_FINISHED;
  }
  
  void GPENCIL_OT_guide_rotate(wmOperatorType *ot)
  {
    /* identifiers */
    ot->name = "Rotate Guide Angle";
    ot->idname = "GPENCIL_OT_guide_rotate";
    ot->description = "Rotate guide angle";
  
    /* api callbacks */
    ot->exec = gpencil_guide_rotate;
  
    /* flags */
    ot->flag = OPTYPE_REGISTER | OPTYPE_UNDO;
  
    PropertyRNA *prop;
  
    prop = RNA_def_boolean(ot->srna, "increment", true, "Increment", "Increment angle");
    RNA_def_property_flag(prop, PROP_HIDDEN | PROP_SKIP_SAVE);
    prop = RNA_def_float(
        ot->srna, "angle", 0.0f, -10000.0f, 10000.0f, "Angle", "Guide angle", -10000.0f, 10000.0f);
    RNA_def_property_flag(prop, PROP_HIDDEN);
  }
  