New freehand curve drawing tool

- Access with Shift-LMB or from the 'Create' toolbar tab.
- Uses curve fitting for bezier curves, with error and corner angle options.
- Optional tablet pressure to curve radius mapping.
- Depth can use the cursor or optionally draw onto the surface,
  for the entire stroke or using the stroke start.
- Stroke plane can optionally be perpendicular to, or aligned to the surface normal.
- Optional radius tapering and for start/end points.
- Supports operator redo and calling from Python.

4 files changed, 1164 insertions, 1 deletions

diff --git a/source/blender/editors/curve/CMakeLists.txt b/source/blender/editors/curve/CMakeLists.txt
index 83346e9550c..ebdf6bb43ff 100644
--- a/source/blender/editors/curve/CMakeLists.txt
+++ b/source/blender/editors/curve/CMakeLists.txt
@@ -23,20 +23,24 @@ set(INC
 	../../blenkernel
 	../../blenlib
 	../../blentranslation
+	../../gpu
 	../../makesdna
 	../../makesrna
 	../../windowmanager
 	../../../../intern/guardedalloc
+	../../../../intern/glew-mx
+	../../../../extern/curve_fit_nd
 )
 
 set(INC_SYS
-
+	${GLEW_INCLUDE_PATH}
 )
 
 set(SRC
 	curve_ops.c
 	editcurve.c
 	editcurve_add.c
+	editcurve_paint.c
 	editcurve_select.c
 	editfont.c
 
@@ -47,4 +51,6 @@ if(WITH_INTERNATIONAL)
 	add_definitions(-DWITH_INTERNATIONAL)
 endif()
 
+add_definitions(${GL_DEFINITIONS})
+
 blender_add_lib(bf_editor_curve "${SRC}" "${INC}" "${INC_SYS}")
diff --git a/source/blender/editors/curve/curve_intern.h b/source/blender/editors/curve/curve_intern.h
index 1af0b49bd86..d63616e4f43 100644
--- a/source/blender/editors/curve/curve_intern.h
+++ b/source/blender/editors/curve/curve_intern.h
@@ -166,4 +166,7 @@ void SURFACE_OT_primitive_nurbs_surface_cylinder_add(struct wmOperatorType *ot);
 void SURFACE_OT_primitive_nurbs_surface_sphere_add(struct wmOperatorType *ot);
 void SURFACE_OT_primitive_nurbs_surface_torus_add(struct wmOperatorType *ot);
 
+/* editcurve_paint.c */
+void CURVE_OT_draw(struct wmOperatorType *ot);
+
 #endif /* __CURVE_INTERN_H__ */
diff --git a/source/blender/editors/curve/curve_ops.c b/source/blender/editors/curve/curve_ops.c
index 967187e66c9..d1994c8fc15 100644
--- a/source/blender/editors/curve/curve_ops.c
+++ b/source/blender/editors/curve/curve_ops.c
@@ -135,6 +135,7 @@ void ED_operatortypes_curve(void)
 	WM_operatortype_append(CURVE_OT_make_segment);
 	WM_operatortype_append(CURVE_OT_spin);
 	WM_operatortype_append(CURVE_OT_vertex_add);
+	WM_operatortype_append(CURVE_OT_draw);
 	WM_operatortype_append(CURVE_OT_extrude);
 	WM_operatortype_append(CURVE_OT_cyclic_toggle);
 
@@ -234,6 +235,9 @@ void ED_keymap_curve(wmKeyConfig *keyconf)
 
 	WM_keymap_add_item(keymap, "CURVE_OT_vertex_add", ACTIONMOUSE, KM_CLICK, KM_CTRL, 0);
 
+	kmi = WM_keymap_add_item(keymap, "CURVE_OT_draw", ACTIONMOUSE, KM_PRESS, KM_SHIFT, 0);
+	RNA_boolean_set(kmi->ptr, "wait_for_input", false);
+
 	kmi = WM_keymap_add_item(keymap, "CURVE_OT_select_all", AKEY, KM_PRESS, 0, 0);
 	RNA_enum_set(kmi->ptr, "action", SEL_TOGGLE);
 	kmi = WM_keymap_add_item(keymap, "CURVE_OT_select_all", IKEY, KM_PRESS, KM_CTRL, 0);
diff --git a/source/blender/editors/curve/editcurve_paint.c b/source/blender/editors/curve/editcurve_paint.c
new file mode 100644
index 00000000000..4af123c0f51
--- /dev/null
+++ b/source/blender/editors/curve/editcurve_paint.c
@@ -0,0 +1,1150 @@
+/*
+ * ***** 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.
+ *
+ * ***** END GPL LICENSE BLOCK *****
+ */
+
+/** \file blender/editors/curve/editcurve_paint.c
+ *  \ingroup edcurve
+ */
+
+#include "DNA_object_types.h"
+#include "DNA_scene_types.h"
+
+#include "MEM_guardedalloc.h"
+
+#include "BLI_blenlib.h"
+#include "BLI_math.h"
+#include "BLI_mempool.h"
+
+#include "BKE_context.h"
+#include "BKE_curve.h"
+#include "BKE_depsgraph.h"
+#include "BKE_fcurve.h"
+#include "BKE_report.h"
+
+#include "WM_api.h"
+#include "WM_types.h"
+
+#include "ED_space_api.h"
+#include "ED_screen.h"
+#include "ED_view3d.h"
+#include "ED_curve.h"
+
+#include "BIF_gl.h"
+#include "BIF_glutil.h"
+
+#include "curve_intern.h"
+
+#include "UI_resources.h"
+
+#include "RNA_access.h"
+#include "RNA_define.h"
+
+#define USE_SPLINE_FIT
+
+#ifdef USE_SPLINE_FIT
+#include "curve_fit_nd.h"
+#endif
+
+/* Distance between input samples */
+#define STROKE_SAMPLE_DIST_MIN_PX 3
+#define STROKE_SAMPLE_DIST_MAX_PX 6
+
+
+/* -------------------------------------------------------------------- */
+
+/** \name Depth Utilities
+ * \{ */
+
+
+static float depth_read_zbuf(const ViewContext *vc, int x, int y)
+{
+	ViewDepths *vd = vc->rv3d->depths;
+
+	if (vd && vd->depths && x > 0 && y > 0 && x < vd->w && y < vd->h)
+		return vd->depths[y * vd->w + x];
+	else
+		return -1.0f;
+}
+
+static bool depth_unproject(
+        const ARegion *ar, const bglMats *mats,
+        const int mval[2], const float depth,
+        float r_location_world[3])
+{
+	double p[3];
+	if (gluUnProject(
+	        (double)ar->winrct.xmin + mval[0] + 0.5,
+	        (double)ar->winrct.ymin + mval[1] + 0.5,
+	        depth, mats->modelview, mats->projection, (const GLint *)mats->viewport,
+	        &p[0], &p[1], &p[2]))
+	{
+		copy_v3fl_v3db(r_location_world, p);
+		return true;
+	}
+	return false;
+}
+
+static bool depth_read_normal(
+        const ViewContext *vc, const bglMats *mats, const int mval[2],
+        float r_normal[3])
+{
+	/* pixels surrounding */
+	bool  depths_valid[9] = {false};
+	float coords[9][3] = {{0}};
+
+	ARegion *ar = vc->ar;
+	const ViewDepths *depths = vc->rv3d->depths;
+
+	for (int x = 0, i = 0; x < 2; x++) {
+		for (int y = 0; y < 2; y++) {
+			const int mval_ofs[2] = {mval[0] + (x - 1), mval[1] + (y - 1)};
+
+			float depth = depth_read_zbuf(vc, mval_ofs[0], mval_ofs[1]);
+			if ((depth > depths->depth_range[0]) && (depth < depths->depth_range[1])) {
+				if (depth_unproject(ar, mats, mval_ofs, depth, coords[i])) {
+					depths_valid[i] = true;
+				}
+			}
+			i++;
+		}
+	}
+
+	const int edges[2][6][2] = {
+	    /* x edges */
+	    {{0, 1}, {1, 2},
+	     {3, 4}, {4, 5},
+	     {6, 7}, {7, 8}},
+	    /* y edges */
+	    {{0, 3}, {3, 6},
+	     {1, 4}, {4, 7},
+	     {2, 5}, {5, 8}},
+	};
+
+	float cross[2][3] = {{0.0f}};
+
+	for (int i = 0; i < 6; i++) {
+		for (int axis = 0; axis < 2; axis++) {
+			if (depths_valid[edges[axis][i][0]] && depths_valid[edges[axis][i][1]]) {
+				float delta[3];
+				sub_v3_v3v3(delta, coords[edges[axis][i][0]], coords[edges[axis][i][1]]);
+				add_v3_v3(cross[axis], delta);
+			}
+		}
+	}
+
+	cross_v3_v3v3(r_normal, cross[0], cross[1]);
+
+	if (normalize_v3(r_normal) != 0.0f) {
+		return true;
+	}
+	else {
+		return false;
+	}
+}
+
+/** \} */
+
+
+/* -------------------------------------------------------------------- */
+
+/** \name StrokeElem / #RNA_OperatorStrokeElement Conversion Functions
+ * \{ */
+
+struct StrokeElem {
+	float mval[2];
+	float location_world[3];
+	float location_local[3];
+	float pressure;
+};
+
+struct CurveDrawData {
+	short init_event_type;
+	short curve_type;
+
+	/* projecting 2D into 3D space */
+	struct {
+		/* use a plane or project to the surface */
+		bool use_plane;
+		float    plane[4];
+
+		/* use 'rv3d->depths', note that this will become 'damaged' while drawing, but thats OK. */
+		bool use_depth;
+	} project;
+
+	/* cursor sampling */
+	struct {
+		/* use substeps, needed for nicely interpolating depth */
+		bool use_substeps;
+	} sample;
+
+	struct {
+		float min, max, range;
+		float offset;
+	} radius;
+
+	struct {
+		float mouse[2];
+		/* used incase we can't calculate the depth */
+		float location_world[3];
+
+		float location_world_valid[3];
+
+		const struct StrokeElem *selem;
+	} prev;
+
+	ViewContext vc;
+	bglMats mats;
+	enum {
+		CURVE_DRAW_IDLE = 0,
+		CURVE_DRAW_PAINTING = 1,
+	} state;
+
+	/* StrokeElem */
+	BLI_mempool *stroke_elem_pool;
+
+	void *draw_handle_view;
+};
+
+static float stroke_elem_radius(const struct CurveDrawData *cdd, const struct StrokeElem *selem)
+{
+	const Curve *cu = cdd->vc.obedit->data;
+	return ((selem->pressure * cdd->radius.range) + cdd->radius.min) * cu->ext2;
+}
+
+static void stroke_elem_interp(
+        struct StrokeElem *selem_out,
+        const struct StrokeElem *selem_a,  const struct StrokeElem *selem_b, float t)
+{
+	interp_v2_v2v2(selem_out->mval, selem_a->mval, selem_b->mval, t);
+	interp_v3_v3v3(selem_out->location_world, selem_a->location_world, selem_b->location_world, t);
+	interp_v3_v3v3(selem_out->location_local, selem_a->location_local, selem_b->location_local, t);
+	selem_out->pressure = interpf(selem_a->pressure, selem_b->pressure, t);
+}
+
+
+/**
+ * Sets the depth from #StrokeElem.mval
+ */
+static bool stroke_elem_project(
+        const struct CurveDrawData *cdd,
+        const int mval_i[2], const float mval_fl[2],
+        const float radius_offset, const float radius,
+        float r_location_world[3])
+{
+	View3D *v3d = cdd->vc.v3d;
+	ARegion *ar = cdd->vc.ar;
+	RegionView3D *rv3d = cdd->vc.rv3d;
+
+	bool is_location_world_set = false;
+
+	/* project to 'location_world' */
+	if (cdd->project.use_plane) {
+		/* get the view vector to 'location' */
+		float ray_origin[3], ray_direction[3];
+		ED_view3d_win_to_ray(cdd->vc.ar, v3d, mval_fl, ray_origin, ray_direction, false);
+
+		float lambda;
+		if (isect_ray_plane_v3(ray_origin, ray_direction, cdd->project.plane, &lambda, true)) {
+			madd_v3_v3v3fl(r_location_world, ray_origin, ray_direction, lambda);
+			is_location_world_set = true;
+		}
+	}
+	else {
+		const ViewDepths *depths = rv3d->depths;
+		if (depths &&
+		    ((unsigned int)mval_i[0] < depths->w) &&
+		    ((unsigned int)mval_i[1] < depths->h))
+		{
+			float depth = depth_read_zbuf(&cdd->vc, mval_i[0], mval_i[1]);
+			if ((depth > depths->depth_range[0]) && (depth < depths->depth_range[1])) {
+				if (depth_unproject(ar, &cdd->mats, mval_i, depth, r_location_world)) {
+					is_location_world_set = true;
+
+					if (radius_offset != 0.0f) {
+						float normal[3];
+						if (depth_read_normal(&cdd->vc, &cdd->mats, mval_i, normal)) {
+							madd_v3_v3fl(r_location_world, normal, radius_offset * radius);
+						}
+					}
+				}
+			}
+		}
+	}
+
+	return is_location_world_set;
+}
+
+static bool stroke_elem_project_fallback(
+        const struct CurveDrawData *cdd,
+        const int mval_i[2], const float mval_fl[2],
+        const float radius_offset, const float radius,
+        const float location_fallback_depth[3],
+        float r_location_world[3], float r_location_local[3])
+{
+	bool is_depth_found = stroke_elem_project(
+	        cdd, mval_i, mval_fl,
+	        radius_offset, radius,
+	        r_location_world);
+	if (is_depth_found == false) {
+		ED_view3d_win_to_3d(cdd->vc.ar, location_fallback_depth, mval_fl, r_location_world);
+	}
+	mul_v3_m4v3(r_location_local, cdd->vc.obedit->imat, r_location_world);
+
+	return is_depth_found;
+}
+
+/**
+ * \note #StrokeElem.mval & #StrokeElem.pressure must be set first.
+ */
+static bool stroke_elem_project_fallback_elem(
+        const struct CurveDrawData *cdd,
+        const float location_fallback_depth[3],
+        struct StrokeElem *selem)
+{
+	const int mval_i[2] = {UNPACK2(selem->mval)};
+	const float radius = stroke_elem_radius(cdd, selem);
+	return stroke_elem_project_fallback(
+	        cdd, mval_i, selem->mval,
+	        cdd->radius.offset, radius,
+	        location_fallback_depth,
+	        selem->location_world, selem->location_local);
+}
+
+/** \} */
+
+
+/* -------------------------------------------------------------------- */
+
+/** \name Operator/Stroke Conversion
+ * \{ */
+
+static void curve_draw_stroke_to_operator_elem(
+        wmOperator *op, const struct StrokeElem *selem)
+{
+	PointerRNA itemptr;
+	RNA_collection_add(op->ptr, "stroke", &itemptr);
+
+	RNA_float_set_array(&itemptr, "mouse", selem->mval);
+	RNA_float_set_array(&itemptr, "location", selem->location_world);
+	RNA_float_set(&itemptr, "pressure", selem->pressure);
+}
+
+static void curve_draw_stroke_from_operator_elem(
+        wmOperator *op, PointerRNA *itemptr)
+{
+	struct CurveDrawData *cdd = op->customdata;
+
+	struct StrokeElem *selem = BLI_mempool_calloc(cdd->stroke_elem_pool);
+
+	RNA_float_get_array(itemptr, "mouse", selem->mval);
+	RNA_float_get_array(itemptr, "location", selem->location_world);
+	mul_v3_m4v3(selem->location_local, cdd->vc.obedit->imat, selem->location_world);
+	selem->pressure = RNA_float_get(itemptr, "pressure");
+}
+
+static void curve_draw_stroke_to_operator(wmOperator *op)
+{
+	struct CurveDrawData *cdd = op->customdata;
+
+	BLI_mempool_iter iter;
+	const struct StrokeElem *selem;
+
+	BLI_mempool_iternew(cdd->stroke_elem_pool, &iter);
+	for (selem = BLI_mempool_iterstep(&iter); selem; selem = BLI_mempool_iterstep(&iter)) {
+		curve_draw_stroke_to_operator_elem(op, selem);
+	}
+}
+
+static void curve_draw_stroke_from_operator(wmOperator *op)
+{
+	RNA_BEGIN (op->ptr, itemptr, "stroke")
+	{
+		curve_draw_stroke_from_operator_elem(op, &itemptr);
+	}
+	RNA_END;
+}
+
+/** \} */
+
+
+/* -------------------------------------------------------------------- */
+
+/** \name Operator Callbacks & Helpers
+ * \{ */
+
+static void curve_draw_stroke_3d(const struct bContext *UNUSED(C), ARegion *UNUSED(ar), void *arg)
+{
+	wmOperator *op = arg;
+	struct CurveDrawData *cdd = op->customdata;
+
+	const int stroke_len = BLI_mempool_count(cdd->stroke_elem_pool);
+
+	if (stroke_len == 0) {
+		return;
+	}
+
+	View3D *v3d = cdd->vc.v3d;
+	Object *obedit = cdd->vc.obedit;
+	Curve *cu = obedit->data;
+
+	UI_ThemeColor(TH_WIRE);
+
+	if (cu->ext2 > 0.0f) {
+		GLUquadricObj *qobj = gluNewQuadric();
+
+		gluQuadricDrawStyle(qobj, GLU_FILL);
+
+		BLI_mempool_iter iter;
+		const struct StrokeElem *selem;
+
+		const float  location_zero[3] = {0};
+		const float *location_prev = location_zero;
+
+		/* scale to edit-mode space */
+		glPushMatrix();
+		glMultMatrixf(obedit->obmat);
+
+		BLI_mempool_iternew(cdd->stroke_elem_pool, &iter);
+		for (selem = BLI_mempool_iterstep(&iter); selem; selem = BLI_mempool_iterstep(&iter)) {
+			glTranslatef(
+			        selem->location_local[0] - location_prev[0],
+			        selem->location_local[1] - location_prev[1],
+			        selem->location_local[2] - location_prev[2]);
+			location_prev = selem->location_local;
+			const float radius = stroke_elem_radius(cdd, selem);
+			gluSphere(qobj, radius , 12, 8);
+
+			location_prev = selem->location_local;
+		}
+
+		glPopMatrix();
+
+		gluDeleteQuadric(qobj);
+	}
+
+	if (stroke_len > 1) {
+		float (*coord_array)[3] = MEM_mallocN(sizeof(*coord_array) * stroke_len, __func__);
+
+		{
+			BLI_mempool_iter iter;
+			const struct StrokeElem *selem;
+			int i;
+			BLI_mempool_iternew(cdd->stroke_elem_pool, &iter);
+			for (selem = BLI_mempool_iterstep(&iter), i = 0; selem; selem = BLI_mempool_iterstep(&iter), i++) {
+				copy_v3_v3(coord_array[i], selem->location_world);
+			}
+		}
+
+		{
+			glEnable(GL_BLEND);
+			glEnable(GL_LINE_SMOOTH);
+
+			glEnableClientState(GL_VERTEX_ARRAY);
+			glVertexPointer(3, GL_FLOAT, 0, coord_array);
+
+			cpack(0x0);
+			glLineWidth(3.0f);
+			glDrawArrays(GL_LINE_STRIP, 0, stroke_len);
+
+			if (v3d->zbuf)
+				glDisable(GL_DEPTH_TEST);
+
+			cpack(0xffffffff);
+			glLineWidth(1.0f);
+			glDrawArrays(GL_LINE_STRIP, 0, stroke_len);
+
+			if (v3d->zbuf)
+				glEnable(GL_DEPTH_TEST);
+
+			glDisableClientState(GL_VERTEX_ARRAY);
+
+			glDisable(GL_BLEND);
+			glDisable(GL_LINE_SMOOTH);
+		}
+
+		MEM_freeN(coord_array);
+	}
+}
+
+static void curve_draw_event_add(wmOperator *op, const wmEvent *event)
+{
+	struct CurveDrawData *cdd = op->customdata;
+	Object *obedit = cdd->vc.obedit;
+
+	invert_m4_m4(obedit->imat, obedit->obmat);
+
+	struct StrokeElem *selem = BLI_mempool_calloc(cdd->stroke_elem_pool);
+
+	ARRAY_SET_ITEMS(selem->mval, event->mval[0], event->mval[1]);
+
+	/* handle pressure sensitivity (which is supplied by tablets) */
+	if (event->tablet_data) {
+		const wmTabletData *wmtab = event->tablet_data;
+		selem->pressure = wmtab->Pressure;
+	}
+	else {
+		selem->pressure = 1.0f;
+	}
+
+	bool is_depth_found = stroke_elem_project_fallback_elem(
+	        cdd, cdd->prev.location_world_valid, selem);
+
+	if (is_depth_found) {
+		/* use the depth if a fallback wasn't used */
+		copy_v3_v3(cdd->prev.location_world_valid, selem->location_world);
+	}
+	copy_v3_v3(cdd->prev.location_world, selem->location_world);
+
+	float len_sq = len_squared_v2v2(cdd->prev.mouse, selem->mval);
+	copy_v2_v2(cdd->prev.mouse, selem->mval);
+
+	if (cdd->sample.use_substeps && cdd->prev.selem) {
+		const struct StrokeElem selem_target = *selem;
+		struct StrokeElem *selem_new_last = selem;
+		if (len_sq >= SQUARE(STROKE_SAMPLE_DIST_MAX_PX)) {
+			int n = (int)ceil(sqrt((double)len_sq)) / STROKE_SAMPLE_DIST_MAX_PX ;
+
+			for (int i = 1; i < n; i++) {
+				struct StrokeElem *selem_new = selem_new_last;
+				stroke_elem_interp(selem_new, cdd->prev.selem, &selem_target, (float)i / n);
+
+				const bool is_depth_found_substep = stroke_elem_project_fallback_elem(
+				        cdd, cdd->prev.location_world_valid, selem_new);
+				if (is_depth_found == false) {
+					if (is_depth_found_substep) {
+						copy_v3_v3(cdd->prev.location_world_valid, selem_new->location_world);
+					}
+				}
+
+				selem_new_last = BLI_mempool_calloc(cdd->stroke_elem_pool);
+			}
+		}
+		selem = selem_new_last;
+		*selem_new_last = selem_target;
+	}
+
+	cdd->prev.selem = selem;
+
+	ED_region_tag_redraw(cdd->vc.ar);
+}
+
+static void curve_draw_event_add_first(wmOperator *op, const wmEvent *event)
+{
+	struct CurveDrawData *cdd = op->customdata;
+	const CurvePaintSettings *cps = &cdd->vc.scene->toolsettings->curve_paint_settings;
+
+	/* add first point */
+	curve_draw_event_add(op, event);
+
+	if ((cps->depth_mode == CURVE_PAINT_PROJECT_SURFACE) && cdd->project.use_depth &&
+	    (cps->flag & CURVE_PAINT_FLAG_DEPTH_STROKE_ENDPOINTS))
+	{
+		RegionView3D *rv3d = cdd->vc.rv3d;
+
+		cdd->project.use_depth = false;
+		cdd->project.use_plane = true;
+
+		float normal[3] = {0.0f};
+		if (ELEM(cps->surface_plane,
+		         CURVE_PAINT_SURFACE_PLANE_NORMAL_VIEW,
+		         CURVE_PAINT_SURFACE_PLANE_NORMAL_SURFACE))
+		{
+			if (depth_read_normal(&cdd->vc, &cdd->mats, event->mval, normal)) {
+				if (cps->surface_plane == CURVE_PAINT_SURFACE_PLANE_NORMAL_VIEW) {
+					float cross_a[3], cross_b[3];
+					cross_v3_v3v3(cross_a, rv3d->viewinv[2], normal);
+					cross_v3_v3v3(cross_b, normal, cross_a);
+					copy_v3_v3(normal, cross_b);
+				}
+			}
+		}
+
+		/* CURVE_PAINT_SURFACE_PLANE_VIEW or fallback */
+		if (is_zero_v3(normal)) {
+			copy_v3_v3(normal, rv3d->viewinv[2]);
+		}
+
+		normalize_v3_v3(cdd->project.plane, normal);
+		cdd->project.plane[3] = -dot_v3v3(cdd->project.plane, cdd->prev.location_world_valid);
+	}
+
+	cdd->init_event_type = event->type;
+	cdd->state = CURVE_DRAW_PAINTING;
+}
+
+static bool curve_draw_init(bContext *C, wmOperator *op, bool is_invoke)
+{
+	BLI_assert(op->customdata == NULL);
+
+	struct CurveDrawData *cdd = MEM_callocN(sizeof(*cdd), __func__);
+
+	if (is_invoke) {
+		view3d_set_viewcontext(C, &cdd->vc);
+		if (ELEM(NULL, cdd->vc.ar, cdd->vc.rv3d, cdd->vc.v3d, cdd->vc.win, cdd->vc.scene)) {
+			MEM_freeN(cdd);
+			BKE_report(op->reports, RPT_ERROR, "Unable to access 3D viewport.");
+			return false;
+		}
+	}
+	else {
+		cdd->vc.scene = CTX_data_scene(C);
+		cdd->vc.obedit = CTX_data_edit_object(C);
+	}
+
+	op->customdata = cdd;
+
+	const CurvePaintSettings *cps = &cdd->vc.scene->toolsettings->curve_paint_settings;
+
+	cdd->curve_type = cps->curve_type;
+
+	cdd->radius.min = cps->radius_min;
+	cdd->radius.max = cps->radius_max;
+	cdd->radius.range = cps->radius_max - cps->radius_min;
+	cdd->radius.offset = cps->radius_offset;
+
+	cdd->stroke_elem_pool = BLI_mempool_create(
+	        sizeof(struct StrokeElem), 0, 512, BLI_MEMPOOL_ALLOW_ITER);
+
+	return true;
+}
+
+
+static void curve_draw_exit(wmOperator *op)
+{
+	struct CurveDrawData *cdd = op->customdata;
+	if (cdd) {
+		if (cdd->draw_handle_view) {
+			ED_region_draw_cb_exit(cdd->vc.ar->type, cdd->draw_handle_view);
+			WM_cursor_modal_restore(cdd->vc.win);
+		}
+
+		if (cdd->stroke_elem_pool) {
+			BLI_mempool_destroy(cdd->stroke_elem_pool);
+		}
+
+		MEM_freeN(cdd);
+		op->customdata = NULL;
+	}
+}
+
+/**
+ * Initialize values before calling 'exec' (when running interactively).
+ */
+static void curve_draw_exec_precalc(wmOperator *op)
+{
+	struct CurveDrawData *cdd = op->customdata;
+	const CurvePaintSettings *cps = &cdd->vc.scene->toolsettings->curve_paint_settings;
+	PropertyRNA *prop;
+
+	prop = RNA_struct_find_property(op->ptr, "corner_angle");
+	if (!RNA_property_is_set(op->ptr, prop)) {
+		const float corner_angle = (cps->flag & CURVE_PAINT_FLAG_CORNERS_DETECT) ? cps->corner_angle : M_PI;
+		RNA_property_float_set(op->ptr, prop, corner_angle);
+	}
+
+	prop = RNA_struct_find_property(op->ptr, "error_threshold");
+	if (!RNA_property_is_set(op->ptr, prop)) {
+
+		/* error isnt set so we'll have to calculate it from the pixel values */
+		BLI_mempool_iter iter;
+		const struct StrokeElem *selem, *selem_prev;
+
+		float len_3d = 0.0f, len_2d = 0.0f;
+		float scale_px;  /* pixel to local space scale */
+
+		int i = 0;
+		BLI_mempool_iternew(cdd->stroke_elem_pool, &iter);
+		selem_prev = BLI_mempool_iterstep(&iter);
+		for (selem = BLI_mempool_iterstep(&iter); selem; selem = BLI_mempool_iterstep(&iter), i++) {
+			len_3d += len_v3v3(selem->location_local, selem_prev->location_local);
+			len_2d += len_v2v2(selem->mval, selem_prev->mval);
+			selem_prev = selem;
+		}
+		scale_px = ((len_3d > 0.0f) && (len_2d > 0.0f)) ?  (len_3d / len_2d) : 0.0f;
+		float error_threshold = (cps->error_threshold * U.pixelsize) * scale_px;
+		RNA_property_float_set(op->ptr, prop, error_threshold);
+	}
+
+	if ((cps->radius_taper_start != 0.0f) ||
+	    (cps->radius_taper_end   != 0.0f))
+	{
+		/* note, we could try to de-duplicate the length calculations above */
+		const int stroke_len = BLI_mempool_count(cdd->stroke_elem_pool);
+
+		BLI_mempool_iter iter;
+		struct StrokeElem *selem, *selem_prev;
+
+		float *lengths = MEM_mallocN(sizeof(float) * stroke_len, __func__);
+		struct StrokeElem **selem_array = MEM_mallocN(sizeof(*selem_array) * stroke_len, __func__);
+		lengths[0] = 0.0f;
+
+		float len_3d = 0.0f;
+
+		int i = 1;
+		BLI_mempool_iternew(cdd->stroke_elem_pool, &iter);
+		selem_prev = BLI_mempool_iterstep(&iter);
+		selem_array[0] = selem_prev;
+		for (selem = BLI_mempool_iterstep(&iter); selem; selem = BLI_mempool_iterstep(&iter), i++) {
+			const float len_3d_segment = len_v3v3(selem->location_local, selem_prev->location_local);
+			len_3d += len_3d_segment;
+			lengths[i] = len_3d;
+			selem_array[i] = selem;
+			selem_prev = selem;
+		}
+
+		if (cps->radius_taper_start != 0.0) {
+			selem_array[0]->pressure = 0.0f;
+			const float len_taper_max = cps->radius_taper_start * len_3d;
+			for (i = 1; i < stroke_len && lengths[i] < len_taper_max; i++) {
+				selem_array[i]->pressure *=   lengths[i] / len_taper_max;
+			}
+		}
+
+		if (cps->radius_taper_end != 0.0) {
+			selem_array[stroke_len - 1]->pressure = 0.0f;
+			const float len_taper_max = cps->radius_taper_end * len_3d;
+			const float len_taper_min = len_3d - len_taper_max;
+			for (i = stroke_len - 2; i > 0 && lengths[i] > len_taper_min; i--) {
+				selem_array[i]->pressure *= (len_3d - lengths[i]) / len_taper_max;
+			}
+		}
+
+		MEM_freeN(lengths);
+		MEM_freeN(selem_array);
+	}
+}
+
+static int curve_draw_exec(bContext *C, wmOperator *op)
+{
+	if (op->customdata == NULL) {
+		if (!curve_draw_init(C, op, false)) {
+			return OPERATOR_CANCELLED;
+		}
+	}
+
+	struct CurveDrawData *cdd = op->customdata;
+
+	const CurvePaintSettings *cps = &cdd->vc.scene->toolsettings->curve_paint_settings;
+	Object *obedit = cdd->vc.scene->obedit;
+	Curve *cu = obedit->data;
+	ListBase *nurblist = object_editcurve_get(obedit);
+
+	int stroke_len = BLI_mempool_count(cdd->stroke_elem_pool);
+
+	const bool is_3d = (cu->flag & CU_3D) != 0;
+	invert_m4_m4(obedit->imat, obedit->obmat);
+
+	if (BLI_mempool_count(cdd->stroke_elem_pool) == 0) {
+		curve_draw_stroke_from_operator(op);
+		stroke_len = BLI_mempool_count(cdd->stroke_elem_pool);
+	}
+
+	ED_curve_deselect_all(cu->editnurb);
+
+	const double radius_min = cps->radius_min;
+	const double radius_max = cps->radius_max;
+	const double radius_range = cps->radius_max - cps->radius_min;
+
+	Nurb *nu = MEM_callocN(sizeof(Nurb), __func__);
+	nu->pntsv = 1;
+	nu->resolu = cu->resolu;
+	nu->resolv = cu->resolv;
+	nu->flag |= CU_SMOOTH;
+
+	const bool use_pressure_radius =
+	        (cps->flag & CURVE_PAINT_FLAG_PRESSURE_RADIUS) ||
+	        ((cps->radius_taper_start != 0.0f) ||
+	         (cps->radius_taper_end   != 0.0f));
+
+	if (cdd->curve_type == CU_BEZIER) {
+		nu->type = CU_BEZIER;
+
+#ifdef USE_SPLINE_FIT
+
+		/* Allow to interpolate multiple channels */
+		int dims = 3;
+		struct {
+			int radius;
+		} coords_indices;
+		coords_indices.radius = use_pressure_radius ? dims++ : -1;
+
+		float *coords = MEM_mallocN(sizeof(*coords) * stroke_len * dims, __func__);
+
+		float       *cubic_spline = NULL;
+		unsigned int cubic_spline_len = 0;
+
+		/* error in object local space */
+		const float error_threshold = RNA_float_get(op->ptr, "error_threshold");
+		const float corner_angle = RNA_float_get(op->ptr, "corner_angle");
+
+		{
+			BLI_mempool_iter iter;
+			const struct StrokeElem *selem;
+			float *co = coords;
+
+			BLI_mempool_iternew(cdd->stroke_elem_pool, &iter);
+			for (selem = BLI_mempool_iterstep(&iter); selem; selem = BLI_mempool_iterstep(&iter), co += dims) {
+				copy_v3_v3(co, selem->location_local);
+				if (coords_indices.radius != -1) {
+					co[coords_indices.radius] = selem->pressure;
+				}
+			}
+		}
+
+		unsigned int *corners = NULL;
+		unsigned int  corners_len = 0;
+
+		if (corner_angle < M_PI) {
+			/* this could be configurable... */
+			const float corner_radius_min = error_threshold / 8;
+			const float corner_radius_max = error_threshold * 2;
+			const unsigned int samples_max = 16;
+
+			curve_fit_corners_detect_fl(
+			        (const float *)coords, stroke_len, dims,
+			        corner_radius_min, corner_radius_max,
+			        samples_max, corner_angle,
+			        &corners, &corners_len);
+		}
+
+		unsigned int *corners_index = NULL;
+		unsigned int  corners_index_len = 0;
+
+		const int result = curve_fit_cubic_to_points_fl(
+		        coords, stroke_len, dims, error_threshold,
+		        corners, corners_len,
+		        &cubic_spline, &cubic_spline_len,
+		        NULL,
+		        &corners_index, &corners_index_len);
+
+		MEM_freeN(coords);
+		if (corners) {
+			free(corners);
+		}
+
+		if (result == 0) {
+			nu->pntsu = cubic_spline_len;
+			nu->bezt = MEM_callocN(sizeof(BezTriple) * nu->pntsu, __func__);
+
+			float *co = cubic_spline;
+			BezTriple *bezt = nu->bezt;
+			for (int j = 0; j < cubic_spline_len; j++, bezt++, co += (dims * 3)) {
+				const float *handle_l = co + (dims * 0);
+				const float *pt       = co + (dims * 1);
+				const float *handle_r = co + (dims * 2);
+
+				copy_v3_v3(bezt->vec[0], handle_l);
+				copy_v3_v3(bezt->vec[1], pt);
+				copy_v3_v3(bezt->vec[2], handle_r);
+
+				if (coords_indices.radius != -1) {
+					bezt->radius = (pt[coords_indices.radius] * cdd->radius.range) + cdd->radius.min;
+				}
+				else {
+					bezt->radius = radius_max;
+				}
+
+				bezt->h1 = bezt->h2 = HD_ALIGN;  /* will set to free in second pass */
+				bezt->f1 = bezt->f2 = bezt->f3 = SELECT;
+			}
+
+			if (corners_index) {
+				/* ignore the first and last */
+				for (unsigned int i = 1; i < corners_index_len - 1; i++) {
+					bezt = &nu->bezt[corners_index[i]];
+					bezt->h1 = bezt->h2 = HD_FREE;
+				}
+			}
+		}
+
+		if (corners_index) {
+			free(corners_index);
+		}
+
+		if (cubic_spline) {
+			free(cubic_spline);
+		}
+
+#else
+		nu->pntsu = stroke_len;
+		nu->bezt = MEM_callocN(nu->pntsu * sizeof(BezTriple), __func__);
+
+		BezTriple *bezt = nu->bezt;
+
+		{
+			BLI_mempool_iter iter;
+			const struct StrokeElem *selem;
+
+			BLI_mempool_iternew(cdd->stroke_elem_pool, &iter);
+			for (selem = BLI_mempool_iterstep(&iter); selem; selem = BLI_mempool_iterstep(&iter)) {
+				copy_v3_v3(bezt->vec[1], selem->location_local);
+				if (!is_3d) {
+					bezt->vec[1][2] = 0.0f;
+				}
+
+				if (use_pressure_radius) {
+					bezt->radius = selem->pressure;
+				}
+				else {
+					bezt->radius = radius_max;
+				}
+
+				bezt->h1 = bezt->h2 = HD_AUTO;
+
+				bezt->f1 |= SELECT;
+				bezt->f2 |= SELECT;
+				bezt->f3 |= SELECT;
+
+				bezt++;
+			}
+		}
+#endif
+
+		BKE_nurb_handles_calc(nu);
+	}
+	else {  /* CU_POLY */
+		BLI_mempool_iter iter;
+		const struct StrokeElem *selem;
+
+		nu->pntsu = stroke_len;
+		nu->type = CU_POLY;
+		nu->bp = MEM_callocN(nu->pntsu * sizeof(BPoint), __func__);
+
+		BPoint *bp = nu->bp;
+
+		BLI_mempool_iternew(cdd->stroke_elem_pool, &iter);
+		for (selem = BLI_mempool_iterstep(&iter); selem; selem = BLI_mempool_iterstep(&iter)) {
+			copy_v3_v3(bp->vec, selem->location_local);
+			if (!is_3d) {
+				bp->vec[2] = 0.0f;
+			}
+
+			if (use_pressure_radius) {
+				bp->radius = (selem->pressure * radius_range) + radius_min;
+			}
+			else {
+				bp->radius = cps->radius_max;
+			}
+			bp->f1 = SELECT;
+			bp->vec[3] = 1.0f;
+
+			bp++;
+		}
+
+		BKE_nurb_knot_calc_u(nu);
+	}
+
+	BLI_addtail(nurblist, nu);
+
+	BKE_curve_nurb_active_set(cu, nu);
+	cu->actvert = nu->pntsu - 1;
+
+	WM_event_add_notifier(C, NC_GEOM | ND_DATA, obedit->data);
+	DAG_id_tag_update(obedit->data, 0);
+
+	curve_draw_exit(op);
+
+	return OPERATOR_FINISHED;
+}
+
+static int curve_draw_invoke(bContext *C, wmOperator *op, const wmEvent *event)
+{
+	if (RNA_struct_property_is_set(op->ptr, "stroke")) {
+		return curve_draw_exec(C, op);
+	}
+
+	if (!curve_draw_init(C, op, true)) {
+		return OPERATOR_CANCELLED;
+	}
+
+	struct CurveDrawData *cdd = op->customdata;
+
+	const CurvePaintSettings *cps = &cdd->vc.scene->toolsettings->curve_paint_settings;
+
+	const bool is_modal = RNA_boolean_get(op->ptr, "wait_for_input");
+
+	/* fallback (incase we can't find the depth on first test) */
+	{
+		const float mval_fl[2] = {UNPACK2(event->mval)};
+		float center[3];
+		negate_v3_v3(center, cdd->vc.rv3d->ofs);
+		ED_view3d_win_to_3d(cdd->vc.ar, center, mval_fl, cdd->prev.location_world);
+		copy_v3_v3(cdd->prev.location_world_valid, cdd->prev.location_world);
+	}
+
+	cdd->draw_handle_view = ED_region_draw_cb_activate(
+	        cdd->vc.ar->type, curve_draw_stroke_3d, op, REGION_DRAW_POST_VIEW);
+	WM_cursor_modal_set(cdd->vc.win, BC_PAINTBRUSHCURSOR);
+
+	{
+		View3D *v3d = cdd->vc.v3d;
+		RegionView3D *rv3d = cdd->vc.rv3d;
+		Object *obedit = cdd->vc.obedit;
+		Curve *cu = obedit->data;
+
+		const float *plane_no = NULL;
+		const float *plane_co = NULL;
+
+		if ((cu->flag & CU_3D) == 0) {
+			/* 2D overrides other options */
+			plane_co = obedit->obmat[3];
+			plane_no = obedit->obmat[2];
+			cdd->project.use_plane = true;
+		}
+		else {
+			if ((cps->depth_mode == CURVE_PAINT_PROJECT_SURFACE) &&
+			    (v3d->drawtype > OB_WIRE))
+			{
+				view3d_get_transformation(cdd->vc.ar, cdd->vc.rv3d, NULL, &cdd->mats);
+
+				/* needed or else the draw matrix can be incorrect */
+				view3d_operator_needs_opengl(C);
+
+				ED_view3d_autodist_init(cdd->vc.scene, cdd->vc.ar, cdd->vc.v3d, 0);
+
+				if (cdd->vc.rv3d->depths) {
+					cdd->vc.rv3d->depths->damaged = true;
+				}
+
+				ED_view3d_depth_update(cdd->vc.ar);
+
+				if (cdd->vc.rv3d->depths != NULL) {
+					cdd->project.use_depth = true;
+				}
+				else {
+					BKE_report(op->reports, RPT_WARNING, "Unable to access depth buffer, using view plane.");
+					cdd->project.use_depth = false;
+				}
+			}
+
+			/* use view plane (when set or as fallback when surface can't be found) */
+			if (cdd->project.use_depth == false) {
+				plane_co = ED_view3d_cursor3d_get(cdd->vc.scene, v3d);;
+				plane_no = rv3d->viewinv[2];
+				cdd->project.use_plane = true;
+			}
+
+			if (cdd->project.use_depth && (cdd->curve_type != CU_POLY)) {
+				cdd->sample.use_substeps = true;
+			}
+		}
+
+		if (cdd->project.use_plane) {
+			normalize_v3_v3(cdd->project.plane, plane_no);
+			cdd->project.plane[3] = -dot_v3v3(cdd->project.plane, plane_co);
+		}
+	}
+
+	if (is_modal == false) {
+		curve_draw_event_add_first(op, event);
+	}
+
+	/* add temp handler */
+	WM_event_add_modal_handler(C, op);
+
+	return OPERATOR_RUNNING_MODAL;
+}
+
+static void curve_draw_cancel(bContext *UNUSED(C), wmOperator *op)
+{
+	curve_draw_exit(op);
+}
+
+
+/* Modal event handling of frame changing */
+static int curve_draw_modal(bContext *C, wmOperator *op, const wmEvent *event)
+{
+	int ret = OPERATOR_RUNNING_MODAL;
+	struct CurveDrawData *cdd = op->customdata;
+
+	UNUSED_VARS(C, op);
+
+	if (event->type == cdd->init_event_type) {
+		if (event->val == KM_RELEASE) {
+			ED_region_tag_redraw(cdd->vc.ar);
+
+			curve_draw_exec_precalc(op);
+
+			curve_draw_stroke_to_operator(op);
+
+			curve_draw_exec(C, op);
+
+			return OPERATOR_FINISHED;
+		}
+	}
+	else if (ELEM(event->type, ESCKEY, RIGHTMOUSE)) {
+		ED_region_tag_redraw(cdd->vc.ar);
+		curve_draw_cancel(C, op);
+		return OPERATOR_CANCELLED;
+	}
+	else if (ELEM(event->type, LEFTMOUSE)) {
+		if (event->val == KM_PRESS) {
+			curve_draw_event_add_first(op, event);
+		}
+	}
+	else if (ELEM(event->type, MOUSEMOVE, INBETWEEN_MOUSEMOVE)) {
+		if (cdd->state == CURVE_DRAW_PAINTING) {
+			const float mval_fl[2] = {UNPACK2(event->mval)};
+			if (len_squared_v2v2(mval_fl, cdd->prev.location_world) > SQUARE(STROKE_SAMPLE_DIST_MIN_PX)) {
+				curve_draw_event_add(op, event);
+			}
+		}
+	}
+
+	return ret;
+}
+
+void CURVE_OT_draw(wmOperatorType *ot)
+{
+	/* identifiers */
+	ot->name = "Draw Curve";
+	ot->idname = "CURVE_OT_draw";
+	ot->description = "Draw a freehand spline";
+
+	/* api callbacks */
+	ot->exec = curve_draw_exec;
+	ot->invoke = curve_draw_invoke;
+	ot->cancel = curve_draw_cancel;
+	ot->modal = curve_draw_modal;
+	ot->poll = ED_operator_editcurve;
+
+	/* flags */
+	ot->flag = OPTYPE_REGISTER | OPTYPE_UNDO;
+
+	/* properties */
+	PropertyRNA *prop;
+
+	prop = RNA_def_float_distance(
+	        ot->srna, "error_threshold", 0.0f, 0.0f, 10.0f, "Error",
+	        "Error distance threshold (in object units)",
+	        0.0001f, 10.0f);
+	RNA_def_property_ui_range(prop, 0.0, 10, 1, 4);
+
+	prop = RNA_def_float_distance(
+	        ot->srna, "corner_angle", DEG2RADF(70.0f), 0.0f, M_PI, "Corner Angle", "", 0.0f, M_PI);
+	RNA_def_property_subtype(prop, PROP_ANGLE);
+
+	prop = RNA_def_collection_runtime(ot->srna, "stroke", &RNA_OperatorStrokeElement, "Stroke", "");
+	RNA_def_property_flag(prop, PROP_SKIP_SAVE);
+
+	prop = RNA_def_boolean(ot->srna, "wait_for_input", true, "Wait for Input", "");
+	RNA_def_property_flag(prop, PROP_HIDDEN | PROP_SKIP_SAVE);
+}
+
+/** \} */