New Grease Pencil object for 2D animation

This commit merge the full development done in greasepencil-object branch and include mainly the following features.

- New grease pencil object.
- New drawing engine.
- New grease pencil modes Draw/Sculpt/Edit and Weight Paint.
- New brushes for grease pencil.
- New modifiers for grease pencil.
- New shaders FX.
- New material system (replace old palettes and colors).
- Split of annotations (old grease pencil) and new grease pencil object.
- UI adapted to blender 2.8.

You can get more info here:

https://code.blender.org/2017/12/drawing-2d-animation-in-blender-2-8/
https://code.blender.org/2018/07/grease-pencil-status-update/

This is the result of nearly two years of development and I want thanks firstly the other members of the grease pencil team: Daniel M. Lara, Matias Mendiola and Joshua Leung for their support, ideas and to keep working in the project all the time, without them this project had been impossible.

Also, I want thanks other Blender developers for their help, advices and to be there always to help me, and specially to Clément Foucault, Dalai Felinto, Pablo Vázquez and Campbell Barton.

1 files changed, 2382 insertions, 0 deletions

diff --git a/source/blender/editors/gpencil/annotate_paint.c b/source/blender/editors/gpencil/annotate_paint.c
new file mode 100644
index 00000000000..6325052fccd
--- /dev/null
+++ b/source/blender/editors/gpencil/annotate_paint.c
@@ -0,0 +1,2382 @@
+/*
+ * ***** BEGIN GPL LICENSE BLOCK *****
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ *
+ * The Original Code is Copyright (C) 2008/2018, Blender Foundation
+ * This is a new part of Blender
+ *
+ * Contributor(s): Joshua Leung
+ *
+ * ***** END GPL LICENSE BLOCK *****
+ */
+
+/** \file blender/editors/gpencil/annotate_paint.c
+ *  \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_math_geom.h"
+
+#include "BLT_translation.h"
+
+#include "PIL_time.h"
+
+#include "BKE_colortools.h"
+#include "BKE_context.h"
+#include "BKE_global.h"
+#include "BKE_gpencil.h"
+#include "BKE_main.h"
+#include "BKE_report.h"
+#include "BKE_screen.h"
+#include "BKE_tracking.h"
+
+#include "DNA_object_types.h"
+#include "DNA_scene_types.h"
+#include "DNA_gpencil_types.h"
+#include "DNA_windowmanager_types.h"
+
+#include "UI_view2d.h"
+
+#include "ED_gpencil.h"
+#include "ED_screen.h"
+#include "ED_view3d.h"
+#include "ED_clip.h"
+
+#include "BIF_glutil.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 "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_V3D_ERASER_DEPTH = (1 << 2),
+	GP_PAINTFLAG_SELECTMASK     = (1 << 3),
+} eGPencil_PaintFlags;
+
+
+/* Temporary 'Stroke' Operation data
+ *   "p" = op->customdata
+ */
+typedef struct tGPsdata {
+	Main *bmain;
+	Scene *scene;       /* current scene from context */
+	struct Depsgraph *depsgraph;
+
+	wmWindow *win;      /* window where painting originated */
+	ScrArea *sa;        /* area where painting originated */
+	ARegion *ar;        /* region where painting originated */
+	View2D *v2d;        /* needed for GP_STROKE_2DSPACE */
+	rctf *subrect;      /* for using the camera rect within the 3d view */
+	rctf subrect_data;
+
+	GP_SpaceConversion gsc; /* settings to pass to gp_points_to_xy() */
+
+	PointerRNA ownerPtr; /* pointer to owner of gp-datablock */
+	bGPdata *gpd;       /* gp-datablock layer comes from */
+	bGPDlayer *gpl;     /* layer we're working on */
+	bGPDframe *gpf;     /* frame we're working on */
+
+	char *align_flag;   /* projection-mode flags (toolsettings - eGPencil_Placement_Flags) */
+
+	eGPencil_PaintStatus status;     /* current status of painting */
+	eGPencil_PaintModes  paintmode;  /* mode for painting */
+	eGPencil_PaintFlags  flags;      /* flags that can get set during runtime (eGPencil_PaintFlags) */
+
+	short radius;       /* radius of influence for eraser */
+
+	int mval[2];        /* current mouse-position */
+	int mvalo[2];       /* previous recorded mouse-position */
+
+	float pressure;     /* current stylus pressure */
+	float opressure;    /* previous stylus pressure */
+
+	/* 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.
+	 */
+	double inittime;    /* Used when converting to path */
+	double curtime;     /* Used when converting to path */
+	double ocurtime;    /* Used when converting to path */
+
+	float imat[4][4];   /* inverted transformation matrix applying when converting coords from screen-space
+	                     * to region space */
+	float mat[4][4];
+
+	float custom_color[4]; /* custom color - hack for enforcing a particular color for track/mask editing */
+
+	void *erasercursor; /* radial cursor data for drawing eraser */
+
+	short straight[2];   /* 1: line horizontal, 2: line vertical, other: not defined, second element position */
+	int lock_axis;       /* lock drawing to one axis */
+
+	short keymodifier;   /* key used for invoking the operator */
+} tGPsdata;
+
+/* ------ */
+
+/* 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 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;
+}
+
+/* ------ */
+/* 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)) {
+		/* check if current context can support GPencil data */
+		if (ED_gpencil_data_get_pointers(C, NULL) != NULL) {
+			/* check if Grease Pencil isn't already running */
+			if (ED_gpencil_session_active() == 0)
+				return 1;
+			else
+				CTX_wm_operator_poll_msg_set(C, "Annotation operator is already active");
+		}
+		else {
+			CTX_wm_operator_poll_msg_set(C, "Failed to find Grease Pencil data to draw into");
+		}
+	}
+	else {
+		CTX_wm_operator_poll_msg_set(C, "Active region not set");
+	}
+
+	return 0;
+}
+
+/* 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])
+{
+	View3D *v3d = p->sa->spacedata.first;
+	const float *fp = ED_view3d_cursor3d_get(p->scene, v3d)->location;
+
+	/* use 3D-cursor */
+	copy_v3_v3(vec, fp);
+}
+
+/* Stroke Editing ---------------------------- */
+
+/* check if the current mouse position is suitable for adding a new point */
+static bool gp_stroke_filtermval(tGPsdata *p, const int mval[2], int pmval[2])
+{
+	int dx = abs(mval[0] - pmval[0]);
+	int dy = abs(mval[1] - pmval[1]);
+
+	/* 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;
+
+	/* 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 the points of the stroke to a plane locked to axis to avoid stroke offset */
+static void gp_project_points_to_plane(RegionView3D *rv3d, bGPDstroke *gps, const float origin[3], const int axis)
+{
+	float plane_normal[3];
+	float vn[3];
+
+	float ray[3];
+	float rpoint[3];
+
+	/* normal vector for a plane locked to axis */
+	zero_v3(plane_normal);
+	plane_normal[axis] = 1.0f;
+
+	/* Reproject the points in the plane */
+	for (int i = 0; i < gps->totpoints; i++) {
+		bGPDspoint *pt = &gps->points[i];
+
+		/* get a vector from the point with the current view direction of the viewport */
+		ED_view3d_global_to_vector(rv3d, &pt->x, vn);
+
+		/* calculate line extrem point to create a ray that cross the plane */
+		mul_v3_fl(vn, -50.0f);
+		add_v3_v3v3(ray, &pt->x, vn);
+
+		/* if the line never intersect, the point is not changed */
+		if (isect_line_plane_v3(rpoint, &pt->x, ray, origin, plane_normal)) {
+			copy_v3_v3(&pt->x, rpoint);
+		}
+	}
+}
+
+/* reproject stroke to plane locked to axis in 3d cursor location */
+static void gp_reproject_toplane(tGPsdata *p, bGPDstroke *gps)
+{
+	bGPdata *gpd = p->gpd;
+	float origin[3];
+	float cursor[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 3d cursor and set origin for locked axis only. Uses axis-1 because the enum for XYZ start with 1 */
+	gp_get_3d_reference(p, cursor);
+	zero_v3(origin);
+	origin[p->lock_axis - 1] = cursor[p->lock_axis - 1];
+
+	gp_project_points_to_plane(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 int 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) {
+		if (gpencil_project_check(p) && (ED_view3d_autodist_simple(p->ar, mval, out, 0, depth))) {
+			/* projecting onto 3D-Geometry
+			 *	- nothing more needs to be done here, since view_autodist_simple() has already done it
+			 */
+		}
+		else {
+			float mval_prj[2];
+			float rvec[3], dvec[3];
+			float mval_f[2] = {UNPACK2(mval)};
+			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.
+			 *
+			 * TODO:
+			 *	- investigate using nearest point(s) on a previous stroke as
+			 *	  reference point instead or as offset, for easier stroke matching
+			 */
+
+			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_f);
+				ED_view3d_win_to_delta(p->ar, mval_f, dvec, zfac);
+				sub_v3_v3v3(out, rvec, dvec);
+			}
+			else {
+				zero_v3(out);
+			}
+		}
+	}
+
+	/* 2d - on 'canvas' (assume that p->v2d is set) */
+	else if ((gpd->runtime.sbuffer_sflag & GP_STROKE_2DSPACE) && (p->v2d)) {
+		UI_view2d_region_to_view(p->v2d, mval[0], mval[1], &out[0], &out[1]);
+		mul_v3_m4v3(out, p->imat, out);
+	}
+
+	/* 2d - relative to screen (viewport area) */
+	else {
+		if (p->subrect == NULL) { /* normal 3D view */
+			out[0] = (float)(mval[0]) / (float)(p->ar->winx) * 100;
+			out[1] = (float)(mval[1]) / (float)(p->ar->winy) * 100;
+		}
+		else { /* camera view, use subrect */
+			out[0] = ((mval[0] - p->subrect->xmin) / BLI_rctf_size_x(p->subrect)) * 100;
+			out[1] = ((mval[1] - p->subrect->ymin) / BLI_rctf_size_y(p->subrect)) * 100;
+		}
+	}
+}
+
+/* add current stroke-point to buffer (returns whether point was successfully added) */
+static short gp_stroke_addpoint(
+        tGPsdata *p, const int mval[2], float pressure, double curtime)
+{
+	bGPdata *gpd = p->gpd;
+	tGPspoint *pt;
+	ToolSettings *ts = p->scene->toolsettings;
+
+	/* 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_int(&pt->x, mval);
+			pt->pressure = 1.0f; /* T44932 - Pressure vals are unreliable, so ignore for now */
+			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_int(&pt->x, mval);
+			pt->pressure = 1.0f; /* T44932 - Pressure vals are unreliable, so ignore for now */
+			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 */
+		copy_v2_v2_int(&pt->x, mval);
+		pt->pressure = pressure;
+		pt->strength = 1.0f;  /* unused for annotations, but initialise for easier conversions to GP Object */
+
+		/* point time */
+		pt->time = (float)(curtime - p->inittime);
+
+		/* increment counters */
+		gpd->runtime.sbuffer_size++;
+
+		/* 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) {
+		/* get pointer to destination point */
+		pt = (tGPspoint *)(gpd->runtime.sbuffer);
+
+		/* store settings */
+		copy_v2_v2_int(&pt->x, mval);
+		pt->pressure = 1.0f; /* T44932 - Pressure vals are unreliable, so ignore for now */
+		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;
+
+			/* 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));
+				gps->totpoints++;
+			}
+
+			pts = &gps->points[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 *v3d = p->sa->spacedata.first;
+
+				view3d_region_operator_needs_opengl(p->win, p->ar);
+				ED_view3d_autodist_init(
+				        p->depsgraph, p->ar, v3d, (ts->annotate_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);
+			/* if axis locked, reproject to plane locked (only in 3d space) */
+			if (p->lock_axis > GP_LOCKAXIS_NONE) {
+				gp_reproject_toplane(p, gps);
+			}
+
+			/* copy pressure and time */
+			pts->pressure = pt->pressure;
+			pts->strength = pt->strength;
+			pts->time = pt->time;
+
+			/* force fill recalc */
+			gps->flag |= GP_STROKE_RECALC_CACHES;
+		}
+
+		/* 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;
+}
+
+/* simplify a stroke (in buffer) before storing it
+ *	- applies a reverse Chaikin filter
+ *	- code adapted from etch-a-ton branch
+ */
+static void gp_stroke_simplify(tGPsdata *p)
+{
+	bGPdata *gpd = p->gpd;
+	tGPspoint *old_points = (tGPspoint *)gpd->runtime.sbuffer;
+	short num_points = gpd->runtime.sbuffer_size;
+	short flag = gpd->runtime.sbuffer_sflag;
+	short i, j;
+
+	/* only simplify if simplification is enabled, and we're not doing a straight line */
+	if (!(U.gp_settings & GP_PAINT_DOSIMPLIFY) || (p->paintmode == GP_PAINTMODE_DRAW_STRAIGHT))
+		return;
+
+	/* don't simplify if less than 4 points in buffer */
+	if ((num_points <= 4) || (old_points == NULL))
+		return;
+
+	/* clear buffer (but don't free mem yet) so that we can write to it
+	 *	- firstly set sbuffer to NULL, so a new one is allocated
+	 *	- secondly, reset flag after, as it gets cleared auto
+	 */
+	gpd->runtime.sbuffer = NULL;
+	gp_session_validatebuffer(p);
+	gpd->runtime.sbuffer_sflag = flag;
+
+/* macro used in loop to get position of new point
+ *	- used due to the mixture of datatypes in use here
+ */
+#define GP_SIMPLIFY_AVPOINT(offs, sfac) \
+	{ \
+		co[0] += (float)(old_points[offs].x * sfac); \
+		co[1] += (float)(old_points[offs].y * sfac); \
+		pressure += old_points[offs].pressure * sfac; \
+		time += old_points[offs].time * sfac; \
+	} (void)0
+
+	/* XXX Here too, do not lose start and end points! */
+	gp_stroke_addpoint(p, &old_points->x, old_points->pressure, p->inittime + (double)old_points->time);
+	for (i = 0, j = 0; i < num_points; i++) {
+		if (i - j == 3) {
+			float co[2], pressure, time;
+			int mco[2];
+
+			/* initialize values */
+			co[0] = 0.0f;
+			co[1] = 0.0f;
+			pressure = 0.0f;
+			time = 0.0f;
+
+			/* using macro, calculate new point */
+			GP_SIMPLIFY_AVPOINT(j, -0.25f);
+			GP_SIMPLIFY_AVPOINT(j + 1, 0.75f);
+			GP_SIMPLIFY_AVPOINT(j + 2, 0.75f);
+			GP_SIMPLIFY_AVPOINT(j + 3, -0.25f);
+
+			/* set values for adding */
+			mco[0] = (int)co[0];
+			mco[1] = (int)co[1];
+
+			/* ignore return values on this... assume to be ok for now */
+			gp_stroke_addpoint(p, mco, pressure, p->inittime + (double)time);
+
+			j += 2;
+		}
+	}
+	gp_stroke_addpoint(p, &old_points[num_points - 1].x, old_points[num_points - 1].pressure,
+	                   p->inittime + (double)old_points[num_points - 1].time);
+
+	/* free old buffer */
+	MEM_freeN(old_points);
+}
+
+/* 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;
+	ToolSettings *ts = p->scene->toolsettings;
+
+	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->annotate_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) {
+		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 = gpl->thickness;
+	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_CACHES;
+
+	/* allocate enough memory for a continuous array for storage points */
+	gps->points = MEM_callocN(sizeof(bGPDspoint) * gps->totpoints, "gp_stroke_points");
+	gps->tot_triangles = 0;
+
+	/* set pointer to first non-initialized point */
+	pt = gps->points + (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);
+			/* if axis locked, reproject to plane locked (only in 3d space) */
+			if (p->lock_axis > GP_LOCKAXIS_NONE) {
+				gp_reproject_toplane(p, 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;
+
+			pt++;
+		}
+
+		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);
+			/* if axis locked, reproject to plane locked (only in 3d space) */
+			if (p->lock_axis > GP_LOCKAXIS_NONE) {
+				gp_reproject_toplane(p, 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;
+		}
+	}
+	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);
+		/* if axis locked, reproject to plane locked (only in 3d space) */
+		if (p->lock_axis > GP_LOCKAXIS_NONE) {
+			gp_reproject_toplane(p, gps);
+		}
+		/* copy pressure and time */
+		pt->pressure = ptc->pressure;
+		pt->strength = ptc->strength;
+		pt->time = ptc->time;
+	}
+	else {
+		float *depth_arr = NULL;
+
+		/* get an array of depths, far depths are blended */
+		if (gpencil_project_check(p)) {
+			int mval[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++) {
+				copy_v2_v2_int(mval, &ptc->x);
+
+				if ((ED_view3d_autodist_depth(p->ar, mval, depth_margin, depth_arr + i) == 0) &&
+				    (i && (ED_view3d_autodist_depth_seg(p->ar, mval, mval_prev, depth_margin + 1, depth_arr + i) == 0)))
+				{
+					interp_depth = true;
+				}
+				else {
+					found_depth = true;
+				}
+
+				copy_v2_v2_int(mval_prev, mval);
+			}
+
+			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->annotate_v3d_align & GP_PROJECT_DEPTH_STROKE_ENDPOINTS) {
+					/* remove all info between the valid endpoints */
+					int first_valid = 0;
+					int last_valid = 0;
+
+					for (i = 0; i < gpd->runtime.sbuffer_size; i++) {
+						if (depth_arr[i] != FLT_MAX)
+							break;
+					}
+					first_valid = i;
+
+					for (i = gpd->runtime.sbuffer_size - 1; i >= 0; i--) {
+						if (depth_arr[i] != FLT_MAX)
+							break;
+					}
+					last_valid = i;
+
+					/* invalidate non-endpoints, so only blend between first and last */
+					for (i = first_valid + 1; i < last_valid; i++)
+						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;
+
+		/* 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;
+		}
+
+		/* if axis locked, reproject to plane locked (only in 3d space) */
+		if (p->lock_axis > GP_LOCKAXIS_NONE) {
+			gp_reproject_toplane(p, gps);
+		}
+
+		if (depth_arr)
+			MEM_freeN(depth_arr);
+	}
+
+	/* add stroke to frame */
+	BLI_addtail(&p->gpf->strokes, gps);
+	gp_stroke_added_enable(p);
+}
+
+/* --- 'Eraser' for 'Paint' Tool ------ */
+
+/* helper to free a stroke
+ * NOTE: gps->dvert and gps->triangles should be NULL, but check anyway for good measure
+ */
+static void gp_free_stroke(bGPdata *UNUSED(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);
+}
+
+
+/* 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 (3d view) */
+static bool gp_stroke_eraser_is_occluded(tGPsdata *p, const bGPDspoint *pt, const int x, const int y)
+{
+	if ((p->sa->spacetype == SPACE_VIEW3D) &&
+	    (p->flags & GP_PAINTFLAG_V3D_ERASER_DEPTH))
+	{
+		RegionView3D *rv3d = p->ar->regiondata;
+		const int mval[2] = {x, y};
+		float mval_3d[3];
+
+		if (ED_view3d_autodist_simple(p->ar, mval, mval_3d, 0, NULL)) {
+			const float depth_mval = view3d_point_depth(rv3d, mval_3d);
+			const float depth_pt   = view3d_point_depth(rv3d, &pt->x);
+
+			if (depth_pt > depth_mval) {
+				return true;
+			}
+		}
+	}
+	return false;
+}
+
+/* eraser tool - evaluation per stroke */
+/* TODO: this could really do with some optimization (KD-Tree/BVH?) */
+static void gp_stroke_eraser_dostroke(tGPsdata *p,
+                                      bGPDframe *gpf, bGPDstroke *gps,
+                                      const int mval[2], const int mvalo[2],
+                                      const int radius, const rcti *rect)
+{
+	bGPDspoint *pt1, *pt2;
+	int pc1[2] = {0};
+	int pc2[2] = {0};
+	int i;
+
+	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)) {
+			gp_point_to_xy(&p->gsc, gps, gps->points, &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, pc1) <= radius) {
+					/* free stroke */
+					gp_free_stroke(p->gpd, gpf, gps);
+				}
+			}
+		}
+	}
+	else {
+		/* 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 */
+			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;
+
+			gp_point_to_xy(&p->gsc, gps, pt1, &pc1[0], &pc1[1]);
+			gp_point_to_xy(&p->gsc, gps, pt2, &pc2[0], &pc2[1]);
+
+			/* Check that point segment of the boundbox of the eraser stroke */
+			if (((!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, pc1[0], pc1[1], pc2[0], pc2[1])) {
+					if ((gp_stroke_eraser_is_occluded(p, pt1, pc1[0], pc1[1]) == false) ||
+					    (gp_stroke_eraser_is_occluded(p, pt2, pc2[0], pc2[1]) == false))
+					{
+						/* Edge is affected - Check individual points now */
+						if (len_v2v2_int(mval, pc1) <= radius) {
+							pt1->flag |= GP_SPOINT_TAG;
+						}
+						if (len_v2v2_int(mval, pc2) <= radius) {
+							pt2->flag |= GP_SPOINT_TAG;
+						}
+						do_cull = true;
+					}
+				}
+			}
+		}
+
+		/* Second Pass: Remove any points that are tagged */
+		if (do_cull) {
+			gp_stroke_delete_tagged_points(gpf, gps, gps->next, GP_SPOINT_TAG, false);
+		}
+	}
+}
+
+/* erase strokes which fall under the eraser strokes */
+static void gp_stroke_doeraser(tGPsdata *p)
+{
+	bGPDframe *gpf = p->gpf;
+	bGPDstroke *gps, *gpn;
+	rcti rect;
+
+	/* rect is rectangle of eraser */
+	rect.xmin = p->mval[0] - p->radius;
+	rect.ymin = p->mval[1] - p->radius;
+	rect.xmax = p->mval[0] + p->radius;
+	rect.ymax = p->mval[1] + p->radius;
+
+	if (p->sa->spacetype == SPACE_VIEW3D) {
+		if (p->flags & GP_PAINTFLAG_V3D_ERASER_DEPTH) {
+			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 strokes of active layer only (session init already took care of ensuring validity),
+	 * checking segments for intersections to remove
+	 */
+	for (gps = gpf->strokes.first; gps; gps = gpn) {
+		gpn = gps->next;
+		/* 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, gpf, gps, p->mval, p->mvalo, p->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;
+
+	/* 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;
+}
+
+/* (re)init new painting data */
+static bool gp_session_initdata(bContext *C, 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);
+
+	/* 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->bmain = CTX_data_main(C);
+	p->scene = CTX_data_scene(C);
+	p->depsgraph = CTX_data_depsgraph(C);
+	p->win = CTX_wm_window(C);
+
+	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->annotate_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;
+			}
+			break;
+		}
+		case SPACE_NODE:
+		{
+			/* SpaceNode *snode = curarea->spacedata.first; */
+
+			/* set current area */
+			p->sa = curarea;
+			p->ar = ar;
+			p->v2d = &ar->v2d;
+			p->align_flag = &ts->gpencil_v2d_align;
+			break;
+		}
+		case SPACE_SEQ:
+		{
+			SpaceSeq *sseq = curarea->spacedata.first;
+
+			/* set current area */
+			p->sa = curarea;
+			p->ar = ar;
+			p->v2d = &ar->v2d;
+			p->align_flag = &ts->gpencil_seq_align;
+
+			/* check that gpencil data is allowed to be drawn */
+			if (sseq->mainb == SEQ_DRAW_SEQUENCE) {
+				p->status = GP_STATUS_ERROR;
+				if (G.debug & G_DEBUG)
+					printf("Error: In active view (sequencer), active mode doesn't support Grease Pencil\n");
+				return 0;
+			}
+			break;
+		}
+		case SPACE_IMAGE:
+		{
+			/* SpaceImage *sima = curarea->spacedata.first; */
+
+			/* set the current area */
+			p->sa = curarea;
+			p->ar = ar;
+			p->v2d = &ar->v2d;
+			p->align_flag = &ts->gpencil_ima_align;
+			break;
+		}
+		case SPACE_CLIP:
+		{
+			SpaceClip *sc = curarea->spacedata.first;
+			MovieClip *clip = ED_space_clip_get_clip(sc);
+
+			if (clip == NULL) {
+				p->status = GP_STATUS_ERROR;
+				return false;
+			}
+
+			/* set the current area */
+			p->sa = curarea;
+			p->ar = ar;
+			p->v2d = &ar->v2d;
+			p->align_flag = &ts->gpencil_v2d_align;
+
+			invert_m4_m4(p->imat, sc->unistabmat);
+
+			/* custom color for new layer */
+			p->custom_color[0] = 1.0f;
+			p->custom_color[1] = 0.0f;
+			p->custom_color[2] = 0.5f;
+			p->custom_color[3] = 0.9f;
+
+			if (sc->gpencil_src == SC_GPENCIL_SRC_TRACK) {
+				int framenr = ED_space_clip_get_clip_frame_number(sc);
+				MovieTrackingTrack *track = BKE_tracking_track_get_active(&clip->tracking);
+				MovieTrackingMarker *marker = track ? BKE_tracking_marker_get(track, framenr) : NULL;
+
+				if (marker) {
+					p->imat[3][0] -= marker->pos[0];
+					p->imat[3][1] -= marker->pos[1];
+				}
+				else {
+					p->status = GP_STATUS_ERROR;
+					return false;
+				}
+			}
+
+			invert_m4_m4(p->mat, p->imat);
+			copy_m4_m4(p->gsc.mat, p->mat);
+			break;
+		}
+		/* unsupported views */
+		default:
+		{
+			p->status = GP_STATUS_ERROR;
+			if (G.debug & G_DEBUG)
+				printf("Error: Annotations are not supported in this editor\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 Annotation data\n");
+		return 0;
+	}
+	else {
+		/* if no existing GPencil block exists, add one */
+		if (*gpd_ptr == NULL) {
+			bGPdata *gpd = BKE_gpencil_data_addnew(bmain, "Annotations");
+			*gpd_ptr = gpd;
+
+			/* mark datablock as being used for annotations */
+			gpd->flag |= GP_DATA_ANNOTATIONS;
+
+			/* annotations always in front of all objects */
+			gpd->xray_mode = GP_XRAY_FRONT;
+		}
+		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);
+
+	/* lock axis */
+	p->lock_axis = ts->gp_sculpt.lock_axis;
+
+	return 1;
+}
+
+/* init new painting session */
+static tGPsdata *gp_session_initpaint(bContext *C)
+{
+	tGPsdata *p = NULL;
+
+	/* create new context data */
+	p = MEM_callocN(sizeof(tGPsdata), "Annotation Drawing Data");
+
+	gp_session_initdata(C, p);
+
+	/* radius for eraser circle is defined in userprefs now */
+	/* NOTE: we do this here, so that if we exit immediately,
+	 *       erase size won't get lost
+	 */
+	p->radius = U.gp_eraser;
+
+	/* 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_freeN(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)
+{
+	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;
+
+	/* 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_("Note"), true);
+
+		if (p->custom_color[3])
+			copy_v3_v3(p->gpl->color, p->custom_color);
+	}
+	if (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) Only allow erasing on the active layer (unlike for 3d-art Grease Pencil),
+		 *    since we won't be exposing layer locking in the UI
+		 * 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;
+
+		if (gpencil_layer_is_editable(p->gpl)) {
+			/* Ensure that there's stuff to erase here (not including selection mask below)... */
+			if (p->gpl->actframe && p->gpl->actframe->strokes.first) {
+				has_layer_to_erase = true;
+			}
+		}
+
+		/* Ensure active frame is set correctly... */
+		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_BRUSHEDIT_FLAG_SELECT_MASK) {
+				p->flags |= GP_PAINTFLAG_SELECTMASK;
+			}
+		}
+
+		if (has_layer_to_erase == false) {
+			p->status = GP_STATUS_ERROR;
+			//if (G.debug & G_DEBUG)
+				printf("Error: Eraser will not be affecting anything (gpencil_paint_init)\n");
+			return;
+		}
+	}
+	else {
+		/* Drawing Modes - Add a new frame if needed on the active layer */
+		short add_frame_mode = GP_GETFRAME_ADD_NEW;
+
+		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, add_frame_mode);
+
+		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;
+
+		/* check if we should respect depth while erasing */
+		if (p->sa->spacetype == SPACE_VIEW3D) {
+			if (p->gpl->flag & GP_LAYER_NO_XRAY) {
+				p->flags |= GP_PAINTFLAG_V3D_ERASER_DEPTH;
+			}
+		}
+	}
+	else {
+		/* disable eraser flags - so that we can switch modes during a session */
+		p->gpd->runtime.sbuffer_sflag &= ~GP_STROKE_ERASER;
+
+		if (p->sa->spacetype == SPACE_VIEW3D) {
+			if (p->gpl->flag & GP_LAYER_NO_XRAY) {
+				p->flags &= ~GP_PAINTFLAG_V3D_ERASER_DEPTH;
+			}
+		}
+	}
+
+	/* 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) {
+				ED_view3d_calc_camera_border(p->scene, depsgraph, p->ar, v3d, rv3d, &p->subrect_data, true); /* no shift */
+				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;
+			}
+			case SPACE_NODE:
+			{
+				p->gpd->runtime.sbuffer_sflag |= GP_STROKE_2DSPACE;
+				break;
+			}
+			case SPACE_SEQ:
+			{
+				p->gpd->runtime.sbuffer_sflag |= GP_STROKE_2DSPACE;
+				break;
+			}
+			case SPACE_IMAGE:
+			{
+				SpaceImage *sima = (SpaceImage *)p->sa->spacedata.first;
+
+				/* only set these flags if the image editor doesn't have an image active,
+				 * otherwise user will be confused by strokes not appearing after they're drawn
+				 *
+				 * Admittedly, this is a bit hacky, but it works much nicer from an ergonomic standpoint!
+				 */
+				if (ELEM(NULL, sima, sima->image)) {
+					/* make strokes be drawn in screen space */
+					p->gpd->runtime.sbuffer_sflag &= ~GP_STROKE_2DSPACE;
+					*(p->align_flag) &= ~GP_PROJECT_VIEWSPACE;
+				}
+				else {
+					p->gpd->runtime.sbuffer_sflag |= GP_STROKE_2DSPACE;
+				}
+				break;
+			}
+			case SPACE_CLIP:
+			{
+				p->gpd->runtime.sbuffer_sflag |= GP_STROKE_2DSPACE;
+				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->annotate_v3d_align & GP_PROJECT_DEPTH_STROKE) ? 1 : 0);
+	}
+
+	/* check if doing eraser or not */
+	if ((p->gpd->runtime.sbuffer_sflag & GP_STROKE_ERASER) == 0) {
+		/* simplify stroke before transferring? */
+		gp_stroke_simplify(p);
+
+		/* 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) {
+		/* enable cursor */
+		p->erasercursor = WM_paint_cursor_activate(CTX_wm_manager(C),
+		                                           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;
+
+	/* clear undo stack */
+	gpencil_undo_finish();
+
+	/* restore cursor to indicate end of drawing */
+	WM_cursor_modal_restore(CTX_wm_window(C));
+
+	/* 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.
+		 */
+		U.gp_eraser = p->radius;
+
+		/* cleanup */
+		gp_paint_cleanup(p);
+		gp_session_cleanup(p);
+		gp_session_free(p);
+	}
+
+	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");
+
+	/* check context */
+	p = op->customdata = gp_session_initpaint(C);
+	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;
+	}
+
+	/* everything is now setup ok */
+	return 1;
+}
+
+
+/* ------------------------------- */
+
+/* ensure that the correct cursor icon is set */
+static void gpencil_draw_cursor_set(tGPsdata *p)
+{
+	if (p->paintmode == GP_PAINTMODE_ERASER)
+		WM_cursor_modal_set(p->win, BC_CROSSCURSOR);  /* XXX need a better cursor */
+	else
+		WM_cursor_modal_set(p->win, BC_PAINTBRUSHCURSOR);
+}
+
+/* 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_PAINTING:
+			switch (p->paintmode) {
+				case GP_PAINTMODE_DRAW_POLY:
+					/* Provide usage tips, since this is modal, and unintuitive without hints */
+					ED_workspace_status_text(C, IFACE_("Annotation Create Poly: LMB click to place next stroke vertex | "
+					                                  "ESC/Enter to end  (or click outside this area)"));
+					break;
+				default:
+					/* Do nothing - the others are self explanatory, exit quickly once the mouse is released
+					 * Showing any text would just be annoying as it would flicker.
+					 */
+					break;
+			}
+			break;
+
+		case GP_STATUS_IDLING:
+			/* print status info */
+			switch (p->paintmode) {
+				case GP_PAINTMODE_ERASER:
+					ED_workspace_status_text(C, IFACE_("Annotation Eraser: 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_("Annotation Line Draw: Hold and drag LMB to draw | "
+					                                  "ESC/Enter to end  (or click outside this area)"));
+					break;
+				case GP_PAINTMODE_DRAW:
+					ED_workspace_status_text(C, IFACE_("Annotation Freehand Draw: Hold and drag LMB to draw | "
+					                                  "E/ESC/Enter to end  (or click outside this area)"));
+					break;
+				case GP_PAINTMODE_DRAW_POLY:
+					ED_workspace_status_text(C, IFACE_("Annotation Create Poly: LMB click to place next stroke vertex | "
+					                                  "ESC/Enter to end  (or click outside this area)"));
+					break;
+
+				default: /* unhandled future cases */
+					ED_workspace_status_text(C, IFACE_("Annotation 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;
+	}
+}
+
+/* ------------------------------- */
+
+/* create a new stroke point at the point indicated by the painting context */
+static void gpencil_draw_apply(wmOperator *op, tGPsdata *p, Depsgraph *depsgraph)
+{
+	/* handle drawing/erasing -> test for erasing first */
+	if (p->paintmode == GP_PAINTMODE_ERASER) {
+		/* do 'live' erasing now */
+		gp_stroke_doeraser(p);
+
+		/* store used values */
+		p->mvalo[0] = p->mval[0];
+		p->mvalo[1] = p->mval[1];
+		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)) {
+		/* 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 */
+		p->mvalo[0] = p->mval[0];
+		p->mvalo[1] = p->mval[1];
+		p->opressure = p->pressure;
+		p->ocurtime = p->curtime;
+	}
+}
+
+/* handle draw event */
+static void gpencil_draw_apply_event(wmOperator *op, const wmEvent *event, Depsgraph *depsgraph)
+{
+	tGPsdata *p = op->customdata;
+	PointerRNA itemptr;
+	float mousef[2];
+	int tablet = 0;
+
+	/* convert from window-space to area-space mouse coordinates
+	 * NOTE: float to ints conversions, +1 factor is probably used to ensure a bit more accurate rounding...
+	 */
+	p->mval[0] = event->mval[0] + 1;
+	p->mval[1] = event->mval[1] + 1;
+
+	/* verify key status for straight lines */
+	if ((event->ctrl > 0) || (event->alt > 0)) {
+		if (p->straight[0] == 0) {
+			int dx = abs(p->mval[0] - p->mvalo[0]);
+			int dy = abs(p->mval[1] - p->mvalo[1]);
+			if ((dx > 0) || (dy > 0)) {
+				/* check mouse direction to replace the other coordinate with previous values */
+				if (dx >= dy) {
+					/* horizontal */
+					p->straight[0] = 1;
+					p->straight[1] = p->mval[1]; /* save y */
+				}
+				else {
+					/* vertical */
+					p->straight[0] = 2;
+					p->straight[1] = p->mval[0]; /* save x */
+				}
+			}
+		}
+	}
+	else {
+		p->straight[0] = 0;
+	}
+
+	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 exception for start of strokes (i.e. maybe for just a dot) */
+	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->inittime = p->ocurtime = p->curtime;
+		p->straight[0] = 0;
+		p->straight[1] = 0;
+
+		/* 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;
+	}
+
+	/* check if alt key is pressed and limit to straight lines */
+	if (p->straight[0] != 0) {
+		if (p->straight[0] == 1) {
+			/* horizontal */
+			p->mval[1] = p->straight[1]; /* replace y */
+		}
+		else {
+			/* vertical */
+			p->mval[0] = p->straight[1]; /* 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(op, p, depsgraph);
+
+	/* force refresh */
+	ED_region_tag_redraw(p->ar); /* just active area for now, since doing whole screen is too slow */
+}
+
+/* ------------------------------- */
+
+/* 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)) {
+		if (op->customdata) MEM_freeN(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] = (int)mousef[0];
+		p->mval[1] = (int)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(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;
+}
+
+/* ------------------------------- */
+
+/* start of interactive drawing part of operator */
+static int gpencil_draw_invoke(bContext *C, wmOperator *op, const wmEvent *event)
+{
+	Object *ob = CTX_data_active_object(C);
+	tGPsdata *p = NULL;
+
+	/* GPXX Need a better solution */
+	if ((ob != NULL) && (ob->type == OB_GPENCIL)) {
+		BKE_report(op->reports, RPT_ERROR, "Cannot draw annotation with a Grease Pencil object active");
+		return OPERATOR_CANCELLED;
+	}
+
+	if (G.debug & G_DEBUG)
+		printf("GPencil - Starting Drawing\n");
+
+	/* 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);
+	}
+	/* 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(op, event, CTX_data_depsgraph(C));
+		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;
+	}
+
+	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, 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;
+}
+
+/* events handling during interactive drawing part of operator */
+static int gpencil_draw_modal(bContext *C, wmOperator *op, const wmEvent *event)
+{
+	tGPsdata *p = op->customdata;
+	int estate = OPERATOR_PASS_THROUGH; /* default exit state - pass through to support MMB view nav, etc. */
+
+	/* 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;
+	}
+
+	/* 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 {
+			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 (ELEM(event->type, RETKEY, PADENTER, ESCKEY, SPACEKEY, EKEY)) {
+		/* exit() ends the current stroke before cleaning up */
+		/* printf("\t\tGP - end of paint op + end of stroke\n"); */
+		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"); */
+				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)
+				 */
+				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;
+		}
+	}
+
+	/* 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"); */
+			gpencil_draw_apply_event(op, event, CTX_data_depsgraph(C));
+
+			/* 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 */
+			ED_region_tag_redraw(p->ar); /* just active area for now, since doing whole screen is too slow */
+
+			/* 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:
+			/* 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 Annotation strokes"},
+	{0, NULL, 0, NULL, NULL}
+};
+
+void GPENCIL_OT_annotate(wmOperatorType *ot)
+{
+	PropertyRNA *prop;
+
+	/* identifiers */
+	ot->name = "Annotation Draw";
+	ot->idname = "GPENCIL_OT_annotate";
+	ot->description = "Make annotations on the active data";
+
+	/* 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_SKIP_SAVE);
+}