/*
 * 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 <stdio.h>
#include <stddef.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>

#include "MEM_guardedalloc.h"

#include "BLI_blenlib.h"
#include "BLI_math.h"
#include "BLI_utildefines.h"
#include "BLI_rand.h"
#include "BLI_math_geom.h"

#include "BLT_translation.h"

#include "PIL_time.h"

#include "DNA_meshdata_types.h"
#include "DNA_object_types.h"
#include "DNA_scene_types.h"
#include "DNA_gpencil_types.h"
#include "DNA_material_types.h"
#include "DNA_brush_types.h"
#include "DNA_windowmanager_types.h"

#include "BKE_colortools.h"
#include "BKE_main.h"
#include "BKE_brush.h"
#include "BKE_paint.h"
#include "BKE_context.h"
#include "BKE_deform.h"
#include "BKE_global.h"
#include "BKE_gpencil.h"
#include "BKE_report.h"
#include "BKE_layer.h"
#include "BKE_material.h"
#include "BKE_screen.h"
#include "BKE_tracking.h"

#include "UI_view2d.h"

#include "ED_gpencil.h"
#include "ED_screen.h"
#include "ED_object.h"
#include "ED_view3d.h"
#include "ED_clip.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 '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;
	/** window where painting originated. */
	wmWindow *win;
	/** area where painting originated. */
	ScrArea *sa;
	/** region where painting originated. */
	ARegion *ar;
	/** 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];

	/** 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 */
	/** guide spacing */
	float guide_spacing;
	/** half guide spacing */
	float half_spacing;
	/** origin */
	float origin[2];

	ReportList *reports;
} 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_manhattendist)
/* minimum length of new segment before new point can be added */
#define MIN_EUCLIDEAN_PX    (U.gp_euclideandist)

static void gp_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 bool gp_stroke_added_check(tGPsdata *p)
{
	return (p->gpf && p->gpf->strokes.last && p->flags & GP_PAINTFLAG_STROKEADDED);
}

static void gp_stroke_added_enable(tGPsdata *p)
{
	BLI_assert(p->gpf->strokes.last != NULL);
	p->flags |= GP_PAINTFLAG_STROKEADDED;

	/* drawing batch cache is dirty now */
	gp_update_cache(p->gpd);
}

/* ------ */
/* Forward defines for some functions... */

static void gp_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 *sa = CTX_wm_area(C);
		/* 3D Viewport */
		if (sa->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;
	}
	else {
		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 gp_get_3d_reference(tGPsdata *p, float vec[3])
{
	Object *ob = NULL;
	if (p->ownerPtr.type == &RNA_Object) {
		ob = (Object *)p->ownerPtr.data;
	}
	ED_gp_get_drawing_reference(p->scene, ob, p->gpl, *p->align_flag, vec);
}

/* Stroke Editing ---------------------------- */
/* check if the current mouse position is suitable for adding a new point */
static bool gp_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_size == 0) {
		return true;
	}
	/* if lazy mouse, check minimum distance */
	else 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;
		}
		else {
			/* 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
	 */
	else 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
	 */
	else if ((dx * dx + dy * dy) > MIN_EUCLIDEAN_PX * MIN_EUCLIDEAN_PX)
		return true;

	/* mouse 'didn't move' */
	else
		return false;
}

/* reproject stroke to plane locked to axis in 3d cursor location */
static void gp_reproject_toplane(tGPsdata *p, bGPDstroke *gps)
{
	bGPdata *gpd = p->gpd;
	Object *obact = (Object *)p->ownerPtr.data;

	float origin[3];
	RegionView3D *rv3d = p->ar->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 */
	gp_get_3d_reference(p, origin);
	ED_gp_project_stroke_to_plane(
	        p->scene, obact, rv3d, gps,
	        origin, p->lock_axis - 1);
}

/* convert screen-coordinates to buffer-coordinates */
/* XXX this method needs a total overhaul! */
static void gp_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);
		}

		int mval_i[2];
		round_v2i_v2fl(mval_i, mval);

		if (gpencil_project_check(p) && (ED_view3d_autodist_simple(p->ar, 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. */

		gp_get_3d_reference(p, rvec);
		zfac = ED_view3d_calc_zfac(p->ar->regiondata, rvec, NULL);

		if (ED_view3d_project_float_global(p->ar, 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->ar, mval_f, dvec, zfac);
			sub_v3_v3v3(out, rvec, dvec);
		}
		else {
			zero_v3(out);
		}
	}
}

/* apply jitter to stroke */
static void gp_brush_jitter(
        bGPdata *gpd, Brush *brush, tGPspoint *pt, const float mval[2],
        const float pressure, float r_mval[2], RNG *rng)
{
	float tmp_pressure = pressure;
	if (brush->gpencil_settings->draw_jitter > 0.0f) {
		float curvef = curvemapping_evaluateF(brush->gpencil_settings->curve_jitter, 0, pressure);
		tmp_pressure = curvef * brush->gpencil_settings->draw_sensitivity;
	}
	/* exponential value */
	const float exfactor = (brush->gpencil_settings->draw_jitter + 2.0f) * (brush->gpencil_settings->draw_jitter + 2.0f);
	const float fac = BLI_rng_get_float(rng) * exfactor * tmp_pressure;
	/* Jitter is applied perpendicular to the mouse movement vector (2D space) */
	float mvec[2], svec[2];
	/* mouse movement in ints -> floats */
	if (gpd->runtime.sbuffer_size > 1) {
		mvec[0] = (mval[0] - (pt - 1)->x);
		mvec[1] = (mval[1] - (pt - 1)->y);
		normalize_v2(mvec);
	}
	else {
		mvec[0] = 0.0f;
		mvec[1] = 0.0f;
	}
	/* rotate mvec by 90 degrees... */
	svec[0] = -mvec[1];
	svec[1] = mvec[0];
	/* scale the displacement by the random, and apply */
	if (BLI_rng_get_float(rng) > 0.5f) {
		mul_v2_fl(svec, -fac);
	}
	else {
		mul_v2_fl(svec, fac);
	}

	r_mval[0] = mval[0] + svec[0];
	r_mval[1] = mval[1] + svec[1];

}

/* apply pressure change depending of the angle of the stroke to simulate a pen with shape */
static void gp_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;
	float mpressure;

	/* 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_size == 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_size >= 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 */
		mpressure = interpf(pt->pressure - (sen * fac), (pt - 1)->pressure, 0.3f);
		pt->pressure = mpressure;

		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 gp_smooth_buffer(tGPsdata *p, float inf, int idx)
{
	bGPdata *gpd = p->gpd;
	short num_points = gpd->runtime.sbuffer_size;

	/* 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;
	float steps = 4.0f;
	if (idx < 4) {
		steps--;
	}

	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];
	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);
	}
	if (ptb) {
		copy_v2_v2(b, &ptb->x);
		madd_v2_v2fl(sco, b, average_fac);
	}
	if (ptc) {
		copy_v2_v2(c, &ptc->x);
		madd_v2_v2fl(sco, c, average_fac);
	}
	if (ptd) {
		copy_v2_v2(d, &ptd->x);
		madd_v2_v2fl(sco, d, average_fac);
	}

	/* Based on influence factor, blend between original and optimal smoothed coordinate */
	interp_v2_v2v2(c, c, sco, inf);
	copy_v2_v2(&ptc->x, c);
}

/* add current stroke-point to buffer (returns whether point was successfully added) */
static short gp_stroke_addpoint(
	tGPsdata *p, const float mval[2], float pressure, double curtime)
{
	bGPdata *gpd = p->gpd;
	Brush *brush = p->brush;
	tGPspoint *pt;
	ToolSettings *ts = p->scene->toolsettings;
	Object *obact = (Object *)p->ownerPtr.data;
	Depsgraph *depsgraph = p->depsgraph;
	RegionView3D *rv3d = p->ar->regiondata;
	View3D *v3d = p->sa->spacedata.first;
	MaterialGPencilStyle *gp_style = p->material->gp_style;
	const int def_nr = obact->actdef - 1;
	const bool have_weight = (bool)BLI_findlink(&obact->defbase, def_nr);

	/* 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_size == 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_size++;
		}
		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_size = 2;
		}

		/* can keep carrying on this way :) */
		return GP_STROKEADD_NORMAL;
	}
	else if (p->paintmode == GP_PAINTMODE_DRAW) { /* normal drawing */
		/* check if still room in buffer */
		if (gpd->runtime.sbuffer_size >= GP_STROKE_BUFFER_MAX)
			return GP_STROKEADD_OVERFLOW;

		/* get pointer to destination point */
		pt = ((tGPspoint *)(gpd->runtime.sbuffer) + gpd->runtime.sbuffer_size);

		/* store settings */
		/* pressure */
		if (brush->gpencil_settings->flag & GP_BRUSH_USE_PRESSURE) {
			float curvef = curvemapping_evaluateF(brush->gpencil_settings->curve_sensitivity, 0, pressure);
			pt->pressure = curvef * brush->gpencil_settings->draw_sensitivity;
		}
		else {
			pt->pressure = 1.0f;
		}

		/* Apply jitter to position */
		if ((brush->gpencil_settings->flag & GP_BRUSH_GROUP_RANDOM) &&
		    (brush->gpencil_settings->draw_jitter > 0.0f))
		{
			float r_mval[2];
			const float jitpress = (brush->gpencil_settings->flag & GP_BRUSH_USE_JITTER_PRESSURE) ? pressure : 1.0f;
			gp_brush_jitter(gpd, brush, pt, mval, jitpress, r_mval, p->rng);
			copy_v2_v2(&pt->x, r_mval);
		}
		else {
			copy_v2_v2(&pt->x, mval);
		}
		/* apply randomness to pressure */
		if ((brush->gpencil_settings->flag & GP_BRUSH_GROUP_RANDOM) &&
		    (brush->gpencil_settings->draw_random_press > 0.0f))
		{
			float curvef = curvemapping_evaluateF(brush->gpencil_settings->curve_sensitivity, 0, pressure);
			float tmp_pressure = curvef * brush->gpencil_settings->draw_sensitivity;
			if (BLI_rng_get_float(p->rng) > 0.5f) {
				pt->pressure -= tmp_pressure * brush->gpencil_settings->draw_random_press * BLI_rng_get_float(p->rng);
			}
			else {
				pt->pressure += tmp_pressure * brush->gpencil_settings->draw_random_press * BLI_rng_get_float(p->rng);
			}
			CLAMP(pt->pressure, GPENCIL_STRENGTH_MIN, 1.0f);
		}

		/* apply randomness to uv texture rotation */
		if ((brush->gpencil_settings->flag & GP_BRUSH_GROUP_RANDOM) && (brush->gpencil_settings->uv_random > 0.0f)) {
			if (BLI_rng_get_float(p->rng) > 0.5f) {
				pt->uv_rot = (BLI_rng_get_float(p->rng) * M_PI * -1) * brush->gpencil_settings->uv_random;
			}
			else {
				pt->uv_rot = (BLI_rng_get_float(p->rng) * M_PI) * brush->gpencil_settings->uv_random;
			}
			CLAMP(pt->uv_rot, -M_PI_2, M_PI_2);
		}
		else {
			pt->uv_rot = 0.0f;
		}

		/* apply angle of stroke to brush size */
		if (brush->gpencil_settings->draw_angle_factor != 0.0f) {
			gp_brush_angle(gpd, brush, pt, mval);
		}

		/* color strength */
		if (brush->gpencil_settings->flag & GP_BRUSH_USE_STENGTH_PRESSURE) {
			float curvef = curvemapping_evaluateF(brush->gpencil_settings->curve_strength, 0, pressure);
			float tmp_pressure = curvef * brush->gpencil_settings->draw_sensitivity;

			pt->strength = tmp_pressure * brush->gpencil_settings->draw_strength;
		}
		else {
			pt->strength = brush->gpencil_settings->draw_strength;
		}
		CLAMP(pt->strength, GPENCIL_STRENGTH_MIN, 1.0f);

		/* apply randomness to color strength */
		if ((brush->gpencil_settings->flag & GP_BRUSH_GROUP_RANDOM) &&
		    (brush->gpencil_settings->draw_random_strength > 0.0f))
		{
			if (BLI_rng_get_float(p->rng) > 0.5f) {
				pt->strength -= pt->strength * brush->gpencil_settings->draw_random_strength * BLI_rng_get_float(p->rng);
			}
			else {
				pt->strength += pt->strength * brush->gpencil_settings->draw_random_strength * BLI_rng_get_float(p->rng);
			}
			CLAMP(pt->strength, GPENCIL_STRENGTH_MIN, 1.0f);
		}

		/* point time */
		pt->time = (float)(curtime - p->inittime);

		/* point uv (only 3d view) */
		if ((p->sa->spacetype == SPACE_VIEW3D) && (gpd->runtime.sbuffer_size > 0)) {
			float pixsize = gp_style->texture_pixsize / 1000000.0f;
			tGPspoint *ptb = (tGPspoint *)gpd->runtime.sbuffer + gpd->runtime.sbuffer_size - 1;
			bGPDspoint spt, spt2;

			/* get origin to reproject point */
			float origin[3];
			gp_get_3d_reference(p, origin);
			/* reproject current */
			ED_gpencil_tpoint_to_point(p->ar, origin, pt, &spt);
			ED_gp_project_point_to_plane(p->scene, obact, rv3d, origin, p->lock_axis - 1, &spt);

			/* reproject previous */
			ED_gpencil_tpoint_to_point(p->ar, origin, ptb, &spt2);
			ED_gp_project_point_to_plane(p->scene, obact, rv3d, origin, p->lock_axis - 1, &spt2);
			p->totpixlen += len_v3v3(&spt.x, &spt2.x) / pixsize;
			pt->uv_fac = p->totpixlen;
			if ((gp_style) && (gp_style->sima)) {
				pt->uv_fac /= gp_style->sima->gen_x;
			}
		}
		else {
			p->totpixlen = 0.0f;
			pt->uv_fac = 0.0f;
		}

		/* increment counters */
		gpd->runtime.sbuffer_size++;

		/* 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++) {
				gp_smooth_buffer(p, brush->gpencil_settings->active_smooth * ((3.0f - s) / 3.0f), gpd->runtime.sbuffer_size - s);
			}
		}

		/* check if another operation can still occur */
		if (gpd->runtime.sbuffer_size == GP_STROKE_BUFFER_MAX)
			return GP_STROKEADD_FULL;
		else
			return GP_STROKEADD_NORMAL;
	}
	else if (p->paintmode == GP_PAINTMODE_DRAW_POLY) {

		/* enable special flag for drawing engine */
		gpd->flag |= GP_DATA_STROKE_POLYGON;

		bGPDlayer *gpl = BKE_gpencil_layer_getactive(gpd);
		/* get pointer to destination 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);

		/* if there's stroke for this poly line session add (or replace last) point
		 * to stroke. This allows to draw lines more interactively (see new segment
		 * during mouse slide, e.g.)
		 */
		if (gp_stroke_added_check(p)) {
			bGPDstroke *gps = p->gpf->strokes.last;
			bGPDspoint *pts;
			MDeformVert *dvert = NULL;

			/* first time point is adding to temporary buffer -- need to allocate new point in stroke */
			if (gpd->runtime.sbuffer_size == 0) {
				gps->points = MEM_reallocN(gps->points, sizeof(bGPDspoint) * (gps->totpoints + 1));
				if (gps->dvert != NULL) {
					gps->dvert = MEM_reallocN(gps->dvert, sizeof(MDeformVert) * (gps->totpoints + 1));
				}
				gps->totpoints++;
			}

			pts = &gps->points[gps->totpoints - 1];
			if (gps->dvert != NULL) {
				dvert = &gps->dvert[gps->totpoints - 1];
			}
			/* special case for poly lines: normally,
			 * depth is needed only when creating new stroke from buffer,
			 * but poly lines are converting to stroke instantly,
			 * so initialize depth buffer before converting coordinates
			 */
			if (gpencil_project_check(p)) {
				view3d_region_operator_needs_opengl(p->win, p->ar);
				ED_view3d_autodist_init(
				        p->depsgraph, p->ar, v3d, (ts->gpencil_v3d_align & GP_PROJECT_DEPTH_STROKE) ? 1 : 0);
			}

			/* convert screen-coordinates to appropriate coordinates (and store them) */
			gp_stroke_convertcoords(p, &pt->x, &pts->x, NULL);
			/* reproject to plane (only in 3d space) */
			gp_reproject_toplane(p, gps);
			/* if parented change position relative to parent object */
			gp_apply_parent_point(depsgraph, obact, gpd, gpl, pts);
			/* copy pressure and time */
			pts->pressure = pt->pressure;
			pts->strength = pt->strength;
			pts->time = pt->time;
			pts->uv_fac = pt->uv_fac;
			pts->uv_rot = pt->uv_rot;

			if ((ts->gpencil_flags & GP_TOOL_FLAG_CREATE_WEIGHTS) && (have_weight)) {
				BKE_gpencil_dvert_ensure(gps);
				MDeformWeight *dw = defvert_verify_index(dvert, def_nr);
				if (dw) {
					dw->weight = ts->vgroup_weight;
				}
			}
			else {
				if (dvert != NULL) {
					dvert->totweight = 0;
					dvert->dw = NULL;
				}
			}

			/* force fill recalc */
			gps->flag |= GP_STROKE_RECALC_GEOMETRY;
			/* drawing batch cache is dirty now */
			gp_update_cache(p->gpd);
		}

		/* increment counters */
		if (gpd->runtime.sbuffer_size == 0)
			gpd->runtime.sbuffer_size++;

		return GP_STROKEADD_NORMAL;
	}

	/* return invalid state for now... */
	return GP_STROKEADD_INVALID;
}

/* make a new stroke from the buffer data */
static void gp_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->ar->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;

	/* 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_size >= 2) ? 2 : gpd->runtime.sbuffer_size;
	else
		totelem = gpd->runtime.sbuffer_size;

	/* 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_size);
		return;
	}

	/* special case for poly line -- for already added stroke during session
	 * coordinates are getting added to stroke immediately to allow more
	 * interactive behavior
	 */
	if (p->paintmode == GP_PAINTMODE_DRAW_POLY) {
		/* be sure to hide any lazy cursor */
		ED_gpencil_toggle_brush_cursor(p->C, true, NULL);

		if (gp_stroke_added_check(p)) {
			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->flag = gpd->runtime.sbuffer_sflag;
	gps->inittime = p->inittime;

	/* enable recalculation flag by default (only used if hq fill) */
	gps->flag |= GP_STROKE_RECALC_GEOMETRY;

	/* 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");

	/* initialize triangle memory to dummy data */
	gps->triangles = MEM_callocN(sizeof(bGPDtriangle), "GP Stroke triangulation");
	gps->flag |= GP_STROKE_RECALC_GEOMETRY;
	gps->tot_triangles = 0;
	/* drawing batch cache is dirty now */
	gp_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);
	}

	/* 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) */
			gp_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;
			pt++;

			if ((ts->gpencil_flags & GP_TOOL_FLAG_CREATE_WEIGHTS) && (have_weight)) {
				BKE_gpencil_dvert_ensure(gps);
				MDeformWeight *dw = defvert_verify_index(dvert, def_nr);
				if (dw) {
					dw->weight = ts->vgroup_weight;
				}
				dvert++;
			}
			else {
				if (dvert != NULL) {
					dvert->totweight = 0;
					dvert->dw = NULL;
					dvert++;
				}
			}
		}

		if (totelem == 2) {
			/* last point if applicable */
			ptc = ((tGPspoint *)gpd->runtime.sbuffer) + (gpd->runtime.sbuffer_size - 1);

			/* convert screen-coordinates to appropriate coordinates (and store them) */
			gp_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;

			if ((ts->gpencil_flags & GP_TOOL_FLAG_CREATE_WEIGHTS) && (have_weight)) {
				BKE_gpencil_dvert_ensure(gps);
				MDeformWeight *dw = defvert_verify_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) */
		gp_reproject_toplane(p, gps);
		pt = gps->points;
		for (i = 0; i < gps->totpoints; i++, pt++) {
			/* if parented change position relative to parent object */
			gp_apply_parent_point(depsgraph, obact, gpd, 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 if (p->paintmode == GP_PAINTMODE_DRAW_POLY) {
		/* first point */
		ptc = gpd->runtime.sbuffer;

		/* convert screen-coordinates to appropriate coordinates (and store them) */
		gp_stroke_convertcoords(p, &ptc->x, &pt->x, NULL);
		/* reproject to plane (only in 3d space) */
		gp_reproject_toplane(p, gps);
		/* if parented change position relative to parent object */
		gp_apply_parent_point(depsgraph, obact, gpd, 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);
		}
		/* copy pressure and time */
		pt->pressure = ptc->pressure;
		pt->strength = ptc->strength;
		CLAMP(pt->strength, GPENCIL_STRENGTH_MIN, 1.0f);
		pt->time = ptc->time;

		if ((ts->gpencil_flags & GP_TOOL_FLAG_CREATE_WEIGHTS) && (have_weight)) {
			BKE_gpencil_dvert_ensure(gps);
			MDeformWeight *dw = defvert_verify_index(dvert, def_nr);
			if (dw) {
				dw->weight = ts->vgroup_weight;
			}
		}
		else {
			if (dvert != NULL) {
				dvert->totweight = 0;
				dvert->dw = NULL;
			}
		}

	}
	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_size, "depth_points");

			for (i = 0, ptc = gpd->runtime.sbuffer; i < gpd->runtime.sbuffer_size; i++, ptc++, pt++) {

				round_v2i_v2fl(mval_i, &ptc->x);

				if ((ED_view3d_autodist_depth(p->ar, mval_i, depth_margin, depth_arr + i) == 0) &&
				    (i && (ED_view3d_autodist_depth_seg(p->ar, 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_size - 1; i >= 0; i--)
					depth_arr[i] = 0.9999f;
			}
			else {
				if ((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_size; 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_size - 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_size; 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_size, FLT_MAX);
				}
			}
		}

		pt = gps->points;
		dvert = gps->dvert;

		/* convert all points (normal behavior) */
		for (i = 0, ptc = gpd->runtime.sbuffer; i < gpd->runtime.sbuffer_size && ptc; i++, ptc++, pt++) {
			/* convert screen-coordinates to appropriate coordinates (and store them) */
			gp_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);
			pt->time = ptc->time;
			pt->uv_fac = ptc->uv_fac;
			pt->uv_rot = ptc->uv_rot;

			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)) {
			gp_subdivide_stroke(gps, subdivide);
		}
		/* apply randomness to stroke */
		if ((brush->gpencil_settings->flag & GP_BRUSH_GROUP_RANDOM) &&
		    (brush->gpencil_settings->draw_random_sub > 0.0f))
		{
			gp_randomize_stroke(gps, brush, p->rng);
		}

		/* 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_smooth_stroke(gps, i, brush->gpencil_settings->draw_smoothfac - reduce);
					BKE_gpencil_smooth_stroke_strength(gps, i, brush->gpencil_settings->draw_smoothfac);
				}
				reduce += 0.25f;  // reduce the factor
			}
		}
		/* smooth thickness */
		if ((brush->gpencil_settings->flag & GP_BRUSH_GROUP_SETTINGS) &&
		    (brush->gpencil_settings->thick_smoothfac > 0.0f))
		{
			for (int r = 0; r < brush->gpencil_settings->thick_smoothlvl * 2; r++) {
				for (i = 0; i < gps->totpoints - 1; i++) {
					BKE_gpencil_smooth_stroke_thickness(gps, i, brush->gpencil_settings->thick_smoothfac);
				}
			}
		}

		/* reproject to plane (only in 3d space) */
		gp_reproject_toplane(p, gps);
		/* change position relative to parent object */
		gp_apply_parent(depsgraph, obact, gpd, 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_get_material_index_for_brush(p->ob, p->brush);

	/* calculate UVs along the stroke */
	ED_gpencil_calc_stroke_uv(obact, gps);

	/* 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) && (p->paintmode != GP_PAINTMODE_DRAW_POLY)) {
		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 = defvert_verify_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_trim_stroke(gps);
	}

	gp_stroke_added_enable(p);
}

/* --- 'Eraser' for 'Paint' Tool ------ */

/* which which point is infront (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);
	}
	else {
		return -dot_v3v3(rv3d->viewinv[2], co);
	}
}

/* only erase stroke points that are visible */
static bool gp_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->sa->spacetype == SPACE_VIEW3D) &&
	    (gp_settings->flag & GP_BRUSH_OCCLUDE_ERASER))
	{
		RegionView3D *rv3d = p->ar->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 */
		ED_gpencil_parent_location(p->depsgraph, obact, p->gpd, gpl, diff_mat);

		if (ED_view3d_autodist_simple(p->ar, 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 gp_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 gp_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);
	gp_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 gp_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 */
/* TODO: this could really do with some optimization (KD-Tree/BVH?) */
static void gp_stroke_eraser_dostroke(tGPsdata *p,
	bGPDlayer *gpl, bGPDframe *gpf, bGPDstroke *gps,
	const float mval[2], const float mvalo[2],
	const int radius, const rcti *rect)
{
	Depsgraph *depsgraph = p->depsgraph;
	Object *obact = (Object *)p->ownerPtr.data;
	Brush *eraser = p->eraser;
	bGPDspoint *pt0, *pt1, *pt2;
	int pc0[2] = {0};
	int pc1[2] = {0};
	int pc2[2] = {0};
	int i;
	float diff_mat[4][4];
	int mval_i[2];
	round_v2i_v2fl(mval_i, mval);

	/* calculate difference matrix */
	ED_gpencil_parent_location(depsgraph, obact, p->gpd, gpl, diff_mat);

	if (gps->totpoints == 0) {
		/* just free stroke */
		gp_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;
			gp_point_to_parent_space(gps->points, diff_mat, &pt_temp);
			gp_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 */
					gp_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;
			gp_point_to_parent_space(pt1, diff_mat, &npt);
			gp_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 */
					gp_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) {
				gp_point_to_parent_space(pt0, diff_mat, &npt);
				gp_point_to_xy(&p->gsc, gps, &npt, &pc0[0], &pc0[1]);
			}
			else {
				/* avoid null values */
				copy_v2_v2_int(pc0, pc1);
			}

			gp_point_to_parent_space(pt1, diff_mat, &npt);
			gp_point_to_xy(&p->gsc, gps, &npt, &pc1[0], &pc1[1]);

			gp_point_to_parent_space(pt2, diff_mat, &npt);
			gp_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 (gp_stroke_inside_circle(mval, mvalo, radius, pc0[0], pc0[1], pc2[0], pc2[1])) {
					if ((gp_stroke_eraser_is_occluded(p, pt0, pc0[0], pc0[1]) == false) ||
					    (gp_stroke_eraser_is_occluded(p, pt1, pc1[0], pc1[1]) == false) ||
					    (gp_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 = gp_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 = gp_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 = gp_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 -= gp_stroke_eraser_calc_influence(p, mval, radius, pc1) * strength;
							pt2->pressure -= gp_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) {
				gp_stroke_soft_refine(gps);
			}

			gp_stroke_delete_tagged_points(gpf, gps, gps->next, GP_SPOINT_TAG, false, 0);
		}
		gp_update_cache(p->gpd);
	}
}

/* erase strokes which fall under the eraser strokes */
static void gp_stroke_doeraser(tGPsdata *p)
{
	bGPDlayer *gpl;
	bGPDstroke *gps, *gpn;
	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->sa->spacetype == SPACE_VIEW3D) {
		if ((gp_settings != NULL) && (gp_settings->flag & GP_BRUSH_OCCLUDE_ERASER)) {
			View3D *v3d = p->sa->spacedata.first;
			view3d_region_operator_needs_opengl(p->win, p->ar);
			ED_view3d_autodist_init(p->depsgraph, p->ar, 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...
	 */
	for (gpl = p->gpd->layers.first; gpl; gpl = gpl->next) {
		bGPDframe *gpf = gpl->actframe;

		/* only affect layer if it's editable (and visible) */
		if (gpencil_layer_is_editable(gpl) == false) {
			continue;
		}
		else if (gpf == NULL) {
			continue;
		}

		/* loop over strokes, checking segments for intersections */
		for (gps = gpf->strokes.first; gps; gps = gpn) {
			gpn = gps->next;
			/* check if the color is editable */
			if (ED_gpencil_stroke_color_use(p->ob, gpl, gps) == false) {
				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->sa, gps)) {
				gp_stroke_eraser_dostroke(p, gpl, gpf, gps, p->mval, p->mvalo, calc_radius, &rect);
			}
		}
	}
}

/* ******************************************* */
/* Sketching Operator */

/* clear the session buffers (call this before AND after a paint operation) */
static void gp_session_validatebuffer(tGPsdata *p)
{
	bGPdata *gpd = p->gpd;
	Brush *brush = p->brush;

	/* clear memory of buffer (or allocate it if starting a new session) */
	if (gpd->runtime.sbuffer) {
		/* printf("\t\tGP - reset sbuffer\n"); */
		memset(gpd->runtime.sbuffer, 0, sizeof(tGPspoint) * GP_STROKE_BUFFER_MAX);
	}
	else {
		/* printf("\t\tGP - allocate sbuffer\n"); */
		gpd->runtime.sbuffer = MEM_callocN(sizeof(tGPspoint) * GP_STROKE_BUFFER_MAX, "gp_session_strokebuffer");
	}

	/* reset indices */
	gpd->runtime.sbuffer_size = 0;

	/* 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 *gp_get_default_eraser(Main *bmain, ToolSettings *ts)
{
	Brush *brush_dft = NULL;
	Paint *paint = &ts->gp_paint->paint;
	Brush *brush_old = paint->brush;
	for (Brush *brush = bmain->brushes.first; brush; brush = brush->id.next) {
		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 */
	else {
		brush_dft = BKE_brush_add_gpencil(bmain, ts, "Soft Eraser");
		brush_dft->size = 30.0f;
		brush_dft->gpencil_settings->flag |= (GP_BRUSH_ENABLE_CURSOR | 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_old);

		return brush_dft;
	}
}

/* helper to set default eraser and disable others */
static void gp_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 gp_init_drawing_brush(bContext *C, tGPsdata *p)
{
	Scene *scene = CTX_data_scene(C);
	ToolSettings *ts = CTX_data_tool_settings(C);

	Paint *paint = &ts->gp_paint->paint;

	/* if not exist, create a new one */
	if (paint->brush == NULL) {
		/* create new brushes */
		BKE_brush_gpencil_presets(C);
	}
	/* be sure curves are initializated */
	curvemapping_initialize(paint->brush->gpencil_settings->curve_sensitivity);
	curvemapping_initialize(paint->brush->gpencil_settings->curve_strength);
	curvemapping_initialize(paint->brush->gpencil_settings->curve_jitter);

	/* assign to temp tGPsdata */
	p->brush = paint->brush;
	if (paint->brush->gpencil_tool != GPAINT_TOOL_ERASE) {
		p->eraser = gp_get_default_eraser(p->bmain, ts);
	}
	else {
		p->eraser = paint->brush;
	}
	/* set new eraser as default */
	gp_set_default_eraser(p->bmain, p->eraser);

	/* use radius of eraser */
	p->radius = (short)p->eraser->size;

	/* GPXX: Need this update to synchronize brush with draw manager.
	 * Maybe this update can be removed when the new tool system
	 * will be in place, but while, we need this to keep drawing working.
	 */
	DEG_id_tag_update(&scene->id, ID_RECALC_COPY_ON_WRITE);
}


/* initialize a paint brush and a default color if not exist */
static void gp_init_colors(tGPsdata *p)
{
	bGPdata *gpd = p->gpd;
	Brush *brush = p->brush;

	MaterialGPencilStyle *gp_style = NULL;

	/* use brush material */
	p->material = BKE_gpencil_current_input_brush_material(p->bmain, p->ob, brush);

	/* assign color information to temp tGPsdata */
	gp_style = p->material->gp_style;
	if (gp_style) {

		/* set colors */
		if (gp_style->flag & GP_STYLE_STROKE_SHOW) {
			copy_v4_v4(gpd->runtime.scolor, gp_style->stroke_rgba);
		}
		else {
			/* if no stroke, use fill */
			copy_v4_v4(gpd->runtime.scolor, gp_style->fill_rgba);
		}
		copy_v4_v4(gpd->runtime.sfill, gp_style->fill_rgba);
		/* add some alpha to make easy the filling without hide strokes */
		if (gpd->runtime.sfill[3] > 0.8f) {
			gpd->runtime.sfill[3] = 0.8f;
		}

		gpd->runtime.mode = (short)gp_style->mode;
		gpd->runtime.bstroke_style = gp_style->stroke_style;
		gpd->runtime.bfill_style = gp_style->fill_style;
	}
}

/* (re)init new painting data */
static bool gp_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 *ar = 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_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:
		{
			/* View3D *v3d = curarea->spacedata.first; */
			/* RegionView3D *rv3d = ar->regiondata; */

			/* 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->sa = curarea;
			p->ar = ar;
			p->align_flag = &ts->gpencil_v3d_align;

			if (ar->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->sa->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, p->scene, cur, local_view_bits);
			}
			/* assign object after all checks to be sure we have one active */
			p->ob = obact;

			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;
	}
	else {
		/* if no existing GPencil block exists, add one */
		if (*gpd_ptr == NULL)
			*gpd_ptr = BKE_gpencil_data_addnew(bmain, "GPencil");
		p->gpd = *gpd_ptr;
	}

	if (ED_gpencil_session_active() == 0) {
		/* initialize undo stack,
		 * also, existing undo stack would make buffer drawn
		 */
		gpencil_undo_init(p->gpd);
	}

	/* clear out buffer (stored in gp-data), in case something contaminated it */
	gp_session_validatebuffer(p);

	/* set brush and create a new one if null */
	gp_init_drawing_brush(C, p);

	/* setup active color */
	if (curarea->spacetype == SPACE_VIEW3D) {
		/* NOTE: This is only done for 3D view, as Materials aren't used for
		 *       annotations in 2D editors
		 */
		int totcol = p->ob->totcol;

		gp_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;
	}

	/* region where paint was originated */
	p->gpd->runtime.ar = CTX_wm_region(C);

	return 1;
}

/* init new painting session */
static tGPsdata *gp_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 (gp_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 gp_session_cleanup(tGPsdata *p)
{
	bGPdata *gpd = (p) ? p->gpd : NULL;

	/* error checking */
	if (gpd == NULL)
		return;

	/* free stroke buffer */
	if (gpd->runtime.sbuffer) {
		/* printf("\t\tGP - free sbuffer\n"); */
		MEM_SAFE_FREE(gpd->runtime.sbuffer);
		gpd->runtime.sbuffer = NULL;
	}

	/* clear flags */
	gpd->runtime.sbuffer_size = 0;
	gpd->runtime.sbuffer_sflag = 0;
	p->inittime = 0.0;
}

static void gp_session_free(tGPsdata *p)
{
	if (p->rng != NULL) {
		BLI_rng_free(p->rng);
	}

	MEM_freeN(p);
}

/* init new stroke */
static void gp_paint_initstroke(tGPsdata *p, eGPencil_PaintModes paintmode, Depsgraph *depsgraph)
{
	Scene *scene = p->scene;
	ToolSettings *ts = scene->toolsettings;
	int cfra_eval = (int)DEG_get_ctime(p->depsgraph);

	/* get active layer (or add a new one if non-existent) */
	p->gpl = BKE_gpencil_layer_getactive(p->gpd);
	if (p->gpl == NULL) {
		p->gpl = BKE_gpencil_layer_addnew(p->gpd, DATA_("GP_Layer"), 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;
	}

	/* get active frame (add a new one if not matching frame) */
	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)
		 */
		bool has_layer_to_erase = false;

		for (bGPDlayer *gpl = p->gpd->layers.first; gpl; gpl = gpl->next) {
			/* Skip if layer not editable */
			if (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) {
				gpl->actframe = BKE_gpencil_layer_getframe(gpl, cfra_eval, GP_GETFRAME_ADD_COPY);
				has_layer_to_erase = true;
			}

			/* XXX: we omit GP_FRAME_PAINT here for now,
			 * as it is only really useful for doing
			 * paintbuffer drawing
			 */
		}

		/* Ensure this gets set... */
		p->gpf = p->gpl->actframe;

		/* Restrict eraser to only affecting selected strokes, if the "selection mask" is on
		 * (though this is only available in editmode)
		 */
		if (p->gpd->flag & GP_DATA_STROKE_EDITMODE) {
			if (ts->gp_sculpt.flag & GP_SCULPT_SETT_FLAG_SELECT_MASK) {
				p->flags |= GP_PAINTFLAG_SELECTMASK;
			}
		}

		if (has_layer_to_erase == false) {
			p->status = GP_STATUS_ERROR;
			return;
		}
	}
	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;

		p->gpf = BKE_gpencil_layer_getframe(p->gpl, cfra_eval, add_frame_mode);
		/* set as dirty draw manager cache */
		gp_update_cache(p->gpd);

		if (p->gpf == NULL) {
			p->status = GP_STATUS_ERROR;
			if (G.debug & G_DEBUG)
				printf("Error: No frame created (gpencil_paint_init)\n");
			return;
		}
		else {
			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;
		/* replace stroke color with fill color */
		copy_v4_v4(p->gpd->runtime.scolor, p->gpd->runtime.sfill);
	}

	/* 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->sa->spacetype == SPACE_VIEW3D) {
			View3D *v3d = p->sa->spacedata.first;
			RegionView3D *rv3d = p->ar->regiondata;

			/* for camera view set the subrect */
			if (rv3d->persp == RV3D_CAMOB) {
				/* no shift */
				ED_view3d_calc_camera_border(p->scene, depsgraph, p->ar, 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.sa = p->sa;
	p->gsc.ar = p->ar;
	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->sa->spacetype) {
			case SPACE_VIEW3D:
			{
				p->gpd->runtime.sbuffer_sflag |= GP_STROKE_3DSPACE;
				break;
			}
		}
	}
}

/* finish off a stroke (clears buffer, but doesn't finish the paint operation) */
static void gp_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->sa->spacedata.first;

		/* need to restore the original projection settings before packing up */
		view3d_region_operator_needs_opengl(p->win, p->ar);
		ED_view3d_autodist_init(p->depsgraph, p->ar, 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 */
		gp_stroke_newfrombuffer(p);
	}

	/* clean up buffer now */
	gp_session_validatebuffer(p);
}

/* finish off stroke painting operation */
static void gp_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 */
		gp_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(bContext *C, tGPsdata *p, short enable)
{
	if (p->erasercursor && !enable) {
		/* clear cursor */
		WM_paint_cursor_end(CTX_wm_manager(C), 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(
		        CTX_wm_manager(C),
		        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)
{
	if (event->tablet_data) {
		const wmTabletData *wmtab = event->tablet_data;
		return (wmtab->Active == EVT_TABLET_ERASER);
	}

	return false;
}

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

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(C, 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->sa->spacetype != SPACE_VIEW3D) {
			WM_cursor_modal_restore(CTX_wm_window(C));
		}
		else {
			/* or restore paint if 3D view */
			if ((p) && (p->paintmode == GP_PAINTMODE_ERASER)) {
				WM_cursor_modal_set(p->win, CURSOR_STD);
			}

			/* drawing batch cache is dirty now */
			bGPdata *gpd = CTX_data_gpencil_data(C);
			if (gpd) {
				gpd->flag &= ~GP_DATA_STROKE_POLYGON;
				gp_update_cache(gpd);
			}
		}

		/* clear undo stack */
		gpencil_undo_finish();

		/* cleanup */
		WM_cursor_modal_set(p->win, CURSOR_STD);

		gp_paint_cleanup(p);
		gp_session_cleanup(p);
		ED_gpencil_toggle_brush_cursor(C, true, NULL);

		/* finally, free the temp data */
		gp_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 = gp_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 */
	gp_paint_initstroke(p, paintmode, CTX_data_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;
}


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

/* ensure that the correct cursor icon is set */
static void gpencil_draw_cursor_set(tGPsdata *p)
{
	Brush *brush = p->brush;
	if ((p->paintmode == GP_PAINTMODE_ERASER) ||
	    (brush->gpencil_tool == GPAINT_TOOL_ERASE))
	{
		WM_cursor_modal_set(p->win, BC_CROSSCURSOR);  /* XXX need a better cursor */
	}
	else {
		WM_cursor_modal_set(p->win,	CURSOR_NONE);
	}
}

/* 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, IFACE_("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, IFACE_("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, IFACE_("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, IFACE_("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, IFACE_("Grease Pencil Freehand Session: Hold and drag LMB to draw"));
					}
					break;
				}
				case GP_PAINTMODE_DRAW_POLY:
				{
					ED_workspace_status_text(C, IFACE_("Grease Pencil Poly Session: LMB click to place next stroke vertex | "
						"Release Shift/ESC/Enter to end  (or click outside this area)"));
					break;
				}
				default: /* unhandled future cases */
				{
					ED_workspace_status_text(C, IFACE_("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;
	}
}

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

/* 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 */
		gp_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 (gp_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);
		}

		/* try to add point */
		short ok = gp_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 */
			gp_paint_strokeend(p);
			/* And start a new one!!! Else, projection errors! */
			gp_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;
				gp_stroke_addpoint(p, p->mvalo, p->opressure, p->ocurtime);
			}
			else {
				p->inittime = p->curtime;
			}
			gp_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_size - 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_size > 0))
	{
		pt = (tGPspoint *)gpd->runtime.sbuffer + gpd->runtime.sbuffer_size - 1;
		if (p->paintmode != GP_PAINTMODE_ERASER) {
			ED_gpencil_toggle_brush_cursor(C, true, &pt->x);
		}
	}
}

/* Helper to rotate point around origin */
static void gp_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 gp_snap_to_grid_fl(float v, const float offset, const float spacing)
{
	if (spacing > 0.0f) {
		return roundf(v / spacing) * spacing + fmodf(offset, spacing);
	}
	else {
		return v;
	}
}

static void UNUSED_FUNCTION(gp_snap_to_grid_v2)(float v[2], const float offset[2], const float spacing)
{
	v[0] = gp_snap_to_grid_fl(v[0], offset[0], spacing);
	v[1] = gp_snap_to_grid_fl(v[1], offset[1], spacing);
}

/* get reference point - screen coords to buffer coords */
static void gp_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);
	gp_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 gp_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;
	gp_point_3d_to_xy(gsc, p->gpd->runtime.sbuffer_sflag, location, origin);
}

/* handle draw event */
static void gpencil_draw_apply_event(bContext *C, wmOperator *op, const wmEvent *event, Depsgraph *depsgraph, float x, float y)
{
	tGPsdata *p = op->customdata;
	GP_Sculpt_Guide *guide = &p->scene->toolsettings->gp_sculpt.guide;
	PointerRNA itemptr;
	float mousef[2];
	int tablet = 0;

	/* convert from window-space to area-space mouse coordinates
	 * add any x,y override position for fake events
	 */
	p->mval[0] = (float)event->mval[0] - x;
	p->mval[1] = (float)event->mval[1] - y;
	p->shift = event->shift;

	/* verify direction for straight lines */
	if ((guide->use_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;
				}
			}
		}
	}

	p->curtime = PIL_check_seconds_timer();

	/* handle pressure sensitivity (which is supplied by tablets) */
	if (event->tablet_data) {
		const wmTabletData *wmtab = event->tablet_data;

		tablet = (wmtab->Active != EVT_TABLET_NONE);
		p->pressure = wmtab->Pressure;

		/* 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 ((wmtab->Active != EVT_TABLET_ERASER) && (p->pressure < 0.001f)) {
				p->pressure = 1.0f;
			}
		}
	}
	else {
		/* No tablet data -> No pressure info is available */
		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) {
		p->flags &= ~GP_PAINTFLAG_FIRSTRUN;

		/* set values */
		copy_v2_v2(p->mvalo, p->mval);
		p->opressure = p->pressure;
		p->inittime = p->ocurtime = p->curtime;
		p->straight = 0;

		/* save initial mouse */
		copy_v2_v2(p->mvali, p->mval);

		/* calculate once and store snapping distance and origin */
		RegionView3D * rv3d = p->ar->regiondata;
		float scale = 1.0f;
		if (rv3d->is_persp) {
			float vec[3];
			gp_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->half_spacing = p->guide_spacing * 0.5f;
		gp_origin_get(p, p->origin);

		/* special exception here for too high pressure values on first touch in
		 * windows for some tablets, then we just skip first touch...
		 */
		if (tablet && (p->pressure >= 0.99f)) {
			return;
		}

		/* special exception for grid snapping
		 * it requires direction which needs at least two points
		 */
		if (!ELEM(p->paintmode, GP_PAINTMODE_ERASER, GP_PAINTMODE_SET_CP) &&
		    guide->use_guide &&
		    guide->use_snapping &&
		    (guide->type == GP_GUIDE_GRID))
		{
			p->flags |= GP_PAINTFLAG_REQ_VECTOR;
		}
	}

	/* wait for vector then add initial point */
	if (p->flags & GP_PAINTFLAG_REQ_VECTOR) {
		if (p->straight == 0) {
			return;
		}

		p->flags &= ~GP_PAINTFLAG_REQ_VECTOR;

		/* create fake events */
		float tmp[2];
		float pt[2];
		copy_v2_v2(tmp, p->mval);
		sub_v2_v2v2(pt, p->mval, p->mvali);
		gpencil_draw_apply_event(C, op, event, CTX_data_depsgraph(C), pt[0], pt[1]);
		if (len_v2v2(p->mval, p->mvalo)) {
			sub_v2_v2v2(pt, p->mval, p->mvalo);
			gpencil_draw_apply_event(C, op, event, CTX_data_depsgraph(C), pt[0], pt[1]);
		}
		copy_v2_v2(p->mval, tmp);
	}

	/* check if stroke is straight or guided */
	if ((p->paintmode != GP_PAINTMODE_ERASER) &&
	    ((p->straight) || (guide->use_guide)))
	{
		/* guided stroke */
		if (guide->use_guide) {
			switch (guide->type) {
				default:
				case GP_GUIDE_CIRCULAR:
				{
					float distance;
					distance = len_v2v2(p->mvali, p->origin);

					if (guide->use_snapping && (guide->spacing > 0.0f)) {
						distance = gp_snap_to_grid_fl(distance, 0.0f, p->guide_spacing);
					}

					dist_ensure_v2_v2fl(p->mval, p->origin, distance);
					break;
				}
				case GP_GUIDE_RADIAL:
				{
					if (guide->use_snapping && (guide->angle_snap > 0.0f)) {
						float point[2];
						float xy[2];
						float angle;
						float half_angle = guide->angle_snap * 0.5f;
						sub_v2_v2v2(xy, p->mvali, p->origin);
						angle = atan2f(xy[1], xy[0]);
						angle += (M_PI * 2.0f);
						angle = fmodf(angle + half_angle, guide->angle_snap);
						angle -= half_angle;
						gp_rotate_v2_v2v2fl(point, p->mvali, p->origin, -angle);
						closest_to_line_v2(p->mval, p->mval, point, p->origin);
					}
					else {
						closest_to_line_v2(p->mval, p->mval, p->mvali, p->origin);
					}
					break;
				}
				case GP_GUIDE_PARALLEL:
				{
					float point[2];
					float unit[2];
					copy_v2_v2(unit, p->mvali);
					unit[0] += 1.0f; /* start from horizontal */
					gp_rotate_v2_v2v2fl(point, unit, p->mvali, guide->angle);
					closest_to_line_v2(p->mval, p->mval, p->mvali, point);

					if (guide->use_snapping && (guide->spacing > 0.0f)) {
						gp_rotate_v2_v2v2fl(p->mval, p->mval, p->origin, -guide->angle);
						p->mval[1] = gp_snap_to_grid_fl(p->mval[1] - p->half_spacing, p->origin[1], p->guide_spacing);
						gp_rotate_v2_v2v2fl(p->mval, p->mval, p->origin, guide->angle);
					}
					break;
				}
				case GP_GUIDE_GRID:
				{
					if (guide->use_snapping && (guide->spacing > 0.0f)) {
						float point[2];
						float unit[2];
						float angle;
						copy_v2_v2(unit, p->mvali);
						unit[0] += 1.0f; /* start from horizontal */
						angle = (p->straight == STROKE_VERTICAL) ? M_PI_2 : 0.0f;
						gp_rotate_v2_v2v2fl(point, unit, p->mvali, angle);
						closest_to_line_v2(p->mval, p->mval, p->mvali, point);

						if (p->straight == STROKE_HORIZONTAL) {
							p->mval[1] = gp_snap_to_grid_fl(p->mval[1] - p->half_spacing, p->origin[1], p->guide_spacing);
						}
						else {
							p->mval[0] = gp_snap_to_grid_fl(p->mval[0] - p->half_spacing, p->origin[0], p->guide_spacing);
						}
					}
					else if (p->straight == STROKE_HORIZONTAL) {
						p->mval[1] = p->mvali[1]; /* replace y */
					}
					else {
						p->mval[0] = p->mvali[0]; /* replace x */
					}
					break;
				}
			}
		}
		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->ar);
}

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

/* 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_depsgraph(C);

	/* printf("GPencil - Starting Re-Drawing\n"); */

	/* try to initialize context data needed while drawing */
	if (!gpencil_draw_init(C, op, NULL)) {
		MEM_SAFE_FREE(op->customdata);
		/* printf("\tGP - no valid data\n"); */
		return OPERATOR_CANCELLED;
	}
	else
		p = op->customdata;

	/* printf("\tGP - Start redrawing stroke\n"); */

	/* 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];

		/* printf("\t\tGP - stroke elem\n"); */

		/* 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 */
				gp_paint_strokeend(p);
				gp_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;

	/* printf("\tGP - done\n"); */

	/* 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 == OKEY) && (event->val == KM_RELEASE)) {
		if (p->paintmode == GP_PAINTMODE_DRAW && 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 == VKEY) && (event->val == KM_RELEASE)) {
		guide->use_guide = false;
		add_notifier = true;
	}
	/* Alternate or flip direction */
	else if ((event->type == 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 == 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 == 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, JKEY, 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 == 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 hide");
			return OPERATOR_CANCELLED;
		}
	}
	else {
		/* don't erase empty frames */
		bool has_layer_to_erase = false;
		for (bGPDlayer *gpl = gpd->layers.first; gpl; gpl = gpl->next) {
			/* Skip if layer not editable */
			if (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;
	}
	else
		p = op->customdata;

	/* TODO: set any additional settings that we can take from the events?
	 * TODO? if tablet is erasing, force eraser to be on? */

	 /* TODO: move cursor setting stuff to stroke-start so that paintmode can be changed midway... */

	 /* if eraser is on, draw radial aid */
	if (p->paintmode == GP_PAINTMODE_ERASER) {
		gpencil_draw_toggle_eraser_cursor(C, p, true);
	}
	else {
		ED_gpencil_toggle_brush_cursor(C, true, NULL);
	}
	/* set cursor
	 * NOTE: This may change later (i.e. intentionally via brush toggle,
	 *       or unintentionally if the user scrolls outside the area)...
	 */
	gpencil_draw_cursor_set(p);

	/* 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 */
		/* printf("\tGP - set first spot\n"); */
		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_depsgraph(C), 0.0f, 0.0f);
		op->flag |= OP_IS_MODAL_CURSOR_REGION;
	}
	else {
		/* toolbar invoked - don't start drawing yet... */
		/* printf("\tGP - hotkey invoked... waiting for click-drag\n"); */
		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 *sa_test)
{
	bScreen *sc = CTX_wm_screen(C);
	return (BLI_findindex(&sc->areabase, sa_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->sa) {
		printf("\t\t\tGP - wrong area execution abort!\n");
		p->status = GP_STATUS_ERROR;
	}

	/* printf("\t\tGP - start stroke\n"); */

	/* we may need to set up paint env again if we're resuming */
	/* XXX: watch it with the paintmode! in future,
	 *      it'd be nice to allow changing paint-mode when in sketching-sessions */

	if (gp_session_initdata(C, op, p))
		gp_paint_initstroke(p, p->paintmode, CTX_data_depsgraph(C));

	if (p->status != GP_STATUS_ERROR) {
		p->status = GP_STATUS_PAINTING;
		op->flag &= ~OP_IS_MODAL_CURSOR_REGION;
	}

	return op->customdata;
}

static void gpencil_stroke_end(wmOperator *op)
{
	tGPsdata *p = op->customdata;

	gp_paint_cleanup(p);

	gpencil_undo_push(p->gpd);

	gp_session_cleanup(p);

	p->status = GP_STATUS_IDLING;
	op->flag |= OP_IS_MODAL_CURSOR_REGION;

	p->gpd = NULL;
	p->gpl = NULL;
	p->gpf = NULL;
}

/* Move last stroke in the listbase to the head to be drawn below all previous strokes in the layer */
static void gpencil_move_last_stroke_to_back(bContext *C)
{
	/* move last stroke (the polygon) to head of the listbase stroke to draw on back of all previous strokes */
	bGPdata *gpd = ED_gpencil_data_get_active(C);
	bGPDlayer *gpl = BKE_gpencil_layer_getactive(gpd);

	/* sanity checks */
	if (ELEM(NULL, gpd, gpl, gpl->actframe)) {
		return;
	}

	bGPDframe *gpf = gpl->actframe;
	bGPDstroke *gps = gpf->strokes.last;
	if (ELEM(NULL, gps)) {
		return;
	}

	BLI_remlink(&gpf->strokes, gps);
	BLI_insertlinkbefore(&gpf->strokes, gpf->strokes.first, gps);
}

/* add events for missing mouse movements when the artist draw very fast */
static void gpencil_add_missing_events(bContext *C, wmOperator *op, const wmEvent *event, tGPsdata *p)
{
	Brush *brush = p->brush;
	GP_Sculpt_Guide *guide = &p->scene->toolsettings->gp_sculpt.guide;
	int input_samples = brush->gpencil_settings->input_samples;

	/* ensure sampling when using circular guide */
	if (guide->use_guide && (guide->type == GP_GUIDE_CIRCULAR)) {
		input_samples = GP_MAX_INPUT_SAMPLES;
	}

	if (input_samples == 0) {
		return;
	}

	RegionView3D *rv3d = p->ar->regiondata;
	float defaultpixsize = rv3d->pixsize * 1000.0f;
	int samples = (GP_MAX_INPUT_SAMPLES - input_samples + 1);
	float thickness = (float)brush->size;

	float pt[2], a[2], b[2];
	float vec[3];
	float scale = 1.0f;

	/* get pixel scale */
	gp_get_3d_reference(p, vec);
	mul_m4_v3(rv3d->persmat, vec);
	if (rv3d->is_persp) {
		scale = vec[2] * defaultpixsize;
	}
	else {
		scale = defaultpixsize;
	}

	/* The thickness of the brush is reduced of thickness to get overlap dots */
	float dot_factor = 0.50f;
	if (samples < 2) {
		dot_factor = 0.05f;
	}
	else if (samples < 4) {
		dot_factor = 0.10f;
	}
	else if (samples < 7) {
		dot_factor = 0.3f;
	}
	else if (samples < 10) {
		dot_factor = 0.4f;
	}
	float factor = ((thickness * dot_factor) / scale) * samples;

	copy_v2_v2(a, p->mvalo);
	b[0] = (float)event->mval[0] + 1.0f;
	b[1] = (float)event->mval[1] + 1.0f;

	/* get distance in pixels */
	float dist = len_v2v2(a, b);

	/* for very small distances, add a half way point */
	if (dist <= 2.0f) {
		interp_v2_v2v2(pt, a, b, 0.5f);
		sub_v2_v2v2(pt, b, pt);
		/* create fake event */
		gpencil_draw_apply_event(C, op, event, CTX_data_depsgraph(C), pt[0], pt[1]);
	}
	else if (dist >= factor) {
		int slices = 2 + (int)((dist - 1.0) / factor);
		float n = 1.0f / slices;
		for (int i = 1; i < slices; i++) {
			interp_v2_v2v2(pt, a, b, n * i);
			sub_v2_v2v2(pt, b, pt);
			/* create fake event */
			gpencil_draw_apply_event(
			        C, op, event, CTX_data_depsgraph(C),
			        pt[0], pt[1]);
		}
	}
}

/* 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 *ar = CTX_wm_region(C);
		p->ar = ar;
	}

	/* special mode for editing control points */
	if (p->paintmode == GP_PAINTMODE_SET_CP) {
		wmWindow *win = p->win;
		WM_cursor_modal_set(win, BC_NSEW_SCROLLCURSOR);
		bool drawmode = false;

		switch (event->type) {
			/* cancel */
			case ESCKEY:
			case RIGHTMOUSE:
			{
				if (ELEM(event->val, KM_RELEASE)) {
					drawmode = true;
				}
				break;
			}
			/* set */
			case LEFTMOUSE:
			{
				if (ELEM(event->val, KM_RELEASE)) {
					gp_origin_set(op, event->mval);
					drawmode = true;
				}
				break;
			}
		}
		if (drawmode) {
			p->status = GP_STATUS_IDLING;
			p->paintmode = GP_PAINTMODE_DRAW;
			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, LEFTARROWKEY, DOWNARROWKEY, RIGHTARROWKEY, UPARROWKEY, ZKEY)) {
			/* allow some keys:
			 *   - for frame changing [#33412]
			 *   - for undo (during sketching sessions)
			 */
		}
		else if (ELEM(event->type, PAD0, PAD1, PAD2, PAD3, PAD4, PAD5, PAD6, PAD7, PAD8, 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 == 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;
		}
	}

	//printf("\tGP - handle modal event...\n");

	/* exit painting mode (and/or end current stroke)
	 * NOTE: cannot do RIGHTMOUSE (as is standard for canceling) as that would break polyline [#32647]
	 */
	 /* if polyline and release shift must cancel */
	if ((ELEM(event->type, RETKEY, PADENTER, ESCKEY, SPACEKEY, EKEY)) ||
	    ((p->paintmode == GP_PAINTMODE_DRAW_POLY) && (event->shift == 0)))
	{
		/* exit() ends the current stroke before cleaning up */
		/* printf("\t\tGP - end of paint op + end of stroke\n"); */
		/* if drawing polygon and enable on back, must move stroke */
		if (ts) {
			if ((ts->gpencil_flags & GP_TOOL_FLAG_PAINT_ONBACK) && (p->paintmode == GP_PAINTMODE_DRAW_POLY)) {
				if (p->flags & GP_PAINTFLAG_STROKEADDED) {
					gpencil_move_last_stroke_to_back(C);
				}
			}
		}

		p->status = GP_STATUS_DONE;
		estate = OPERATOR_FINISHED;
	}

	/* toggle painting mode upon mouse-button movement
	 * - LEFTMOUSE  = standard drawing (all) / straight line drawing (all) / polyline (toolbox only)
	 * - RIGHTMOUSE = polyline (hotkey) / 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) {
			int sketch = 0;

			/* basically, this should be mouse-button up = end stroke
			 * BUT, polyline drawing is an exception -- all knots should be added during one session
			 */
			sketch |= (p->paintmode == GP_PAINTMODE_DRAW_POLY);

			if (sketch) {
				/* end stroke only, and then wait to resume painting soon */
				/* printf("\t\tGP - end stroke only\n"); */
				gpencil_stroke_end(op);

				/* If eraser mode is on, turn it off after the stroke finishes
				 * NOTE: This just makes it nicer to work with drawing sessions
				 */
				if (p->paintmode == GP_PAINTMODE_ERASER) {
					p->paintmode = RNA_enum_get(op->ptr, "mode");

					/* if the original mode was *still* eraser,
					 * we'll let it say for now, since this gives
					 * users an opportunity to have visual feedback
					 * when adjusting eraser size
					 */
					if (p->paintmode != GP_PAINTMODE_ERASER) {
						/* turn off cursor...
						 * NOTE: this should be enough for now
						 *       Just hiding this makes it seem like
						 *       you can paint again...
						 */
						gpencil_draw_toggle_eraser_cursor(C, p, false);
					}
				}

				/* we've just entered idling state, so this event was processed (but no others yet) */
				estate = OPERATOR_RUNNING_MODAL;

				/* stroke could be smoothed, send notifier to refresh screen */
				WM_event_add_notifier(C, NC_GPENCIL | NA_EDITED, NULL);
			}
			else {
				/* printf("\t\tGP - end of stroke + op\n"); */
				/* if drawing polygon and enable on back, must move stroke */
				if (ts) {
					if ((ts->gpencil_flags & GP_TOOL_FLAG_PAINT_ONBACK) && (p->paintmode == GP_PAINTMODE_DRAW_POLY)) {
						if (p->flags & GP_PAINTFLAG_STROKEADDED) {
							gpencil_move_last_stroke_to_back(C);
						}
					}
				}
				/* drawing batch cache is dirty now */
				gp_update_cache(p->gpd);

				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->ar) && (p->ar->regiontype == RGN_TYPE_TOOLS)) {
				/* Change to whatever region is now under the mouse */
				ARegion *current_region = BKE_area_find_region_xy(p->sa, RGN_TYPE_ANY, event->x, event->y);

				if (G.debug & G_DEBUG) {
					printf("found alternative region %p (old was %p) - at %d %d (sa: %d %d -> %d %d)\n",
					       current_region, p->ar, event->x, event->y,
					       p->sa->totrct.xmin, p->sa->totrct.ymin, p->sa->totrct.xmax, p->sa->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->ar = 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->ar) {
				rcti region_rect;

				/* Perform bounds check using  */
				ED_region_visible_rect(p->ar, &region_rect);
				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(C, 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)
				 */
				 /* if drawing polygon and enable on back, must move stroke */
				if (ts) {
					if ((ts->gpencil_flags & GP_TOOL_FLAG_PAINT_ONBACK) && (p->paintmode == GP_PAINTMODE_DRAW_POLY)) {
						if (p->flags & GP_PAINTFLAG_STROKEADDED) {
							gpencil_move_last_stroke_to_back(C);
						}
					}
				}
				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->ar);
		}
	}

	/* 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 */
			/* printf("\t\tGP - add point\n"); */

			if (((p->flags & GP_PAINTFLAG_FIRSTRUN) == 0) || (guide->use_guide)) {
				gpencil_add_missing_events(C, op, event, p);
			}

			gpencil_draw_apply_event(C, op, event, CTX_data_depsgraph(C), 0.0f, 0.0f);

			/* 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 */
				/* printf("\t\t\t\tGP - add point handled!\n"); */
				estate = OPERATOR_RUNNING_MODAL;
			}
		}
		/* eraser size */
		else if ((p->paintmode == GP_PAINTMODE_ERASER) &&
		         ELEM(event->type, WHEELUPMOUSE, WHEELDOWNMOUSE, PADPLUSKEY, PADMINUS))
		{
			/* just resize the brush (local version)
			 * TODO: fix the hardcoded size jumps (set to make a visible difference) and hardcoded keys
			 */
			 /* printf("\t\tGP - resize eraser\n"); */
			switch (event->type) {
				case WHEELDOWNMOUSE: /* larger */
				case PADPLUSKEY:
					p->radius += 5;
					break;

				case WHEELUPMOUSE: /* smaller */
				case 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->ar);

			/* 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->sa))
		estate = OPERATOR_CANCELLED;
	else {
		/* update status indicators - cursor, header, etc. */
		gpencil_draw_status_indicators(C, p);
		gpencil_draw_cursor_set(p); /* cursor may have changed outside our control - T44084 */
	}

	/* 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 */
#if 0
			printf("unhandled event -> %d (mmb? = %d | mmv? = %d)\n",
			       event->type, event->type == MIDDLEMOUSE, event->type == MOUSEMOVE);
#endif
			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_DRAW_POLY, "DRAW_POLY", 0, "Draw Poly Line", "Click to place endpoints of straight line segments (connected)"},
	{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 a 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);
}