Improve grease pencil stroke quality

Improve the quality of current grease pencil strokes adding a new dynamic smooth and subdivision. The level of smooth and subdivide can be adjusted using UI parameters. These options are disabled by default in order to keep the grease pencil stroke compatible with any existing add-on.

Both parameters are defined at layer level.

Reviewers: aligorith

Differential Revision: https://developer.blender.org/D1866

release/scripts/startup/bl_ui/properties_grease_pencil_common.py

@@ -622,6 +622,14 @@ class GreasePencilDataPanel:
         row.prop(gpl, "after_color", text="")
         sub.prop(gpl, "ghost_after_range", text="After")
 
+        # Smooth and subdivide new strokes
+        layout.separator()
+        col = layout.column(align=True)
+        col.label(text="New Stroke Quality:")
+        split = col.split()
+        split.prop(gpl, "smooth_drawfac")
+        split.prop(gpl, "subdivision")
+
 
 class GreasePencilToolsPanel:
     # subclass must set

source/blender/editors/gpencil/gpencil_brush.c

@@ -223,70 +223,9 @@ static bool gp_brush_smooth_apply(tGP_BrushEditData *gso, bGPDstroke *gps, int i
 	GP_EditBrush_Data *brush = gso->brush;
 	bGPDspoint *pt = &gps->points[i];
 	float inf = gp_brush_influence_calc(gso, radius, co);
-	float pressure = 0.0f;
-	float sco[3] = {0.0f};
 	
-	/* Do nothing if not enough points to smooth out */
+	/* perform smoothing */
-	if (gps->totpoints <= 2) {
+	return gp_smooth_stroke(gps, i, inf);
-		return false;
-	}
-	
-	/* Only affect endpoints by a fraction of the normal strength,
-	 * to prevent the stroke from shrinking too much
-	 */
-	if ((i == 0) || (i == gps->totpoints - 1)) {
-		inf *= 0.1f;
-	}
-	
-	/* Compute smoothed coordinate by taking the ones nearby */
-	/* XXX: This is potentially slow, and suffers from accumulation error as earlier points are handled before later ones */
-	{	
-		// XXX: this is hardcoded to look at 2 points on either side of the current one (i.e. 5 items total)
-		const int   steps = 2;
-		const float average_fac = 1.0f / (float)(steps * 2 + 1);
-		int step;
-		
-		/* add the point itself */
-		madd_v3_v3fl(sco, &pt->x, average_fac);
-		
-		if (brush->flag & GP_EDITBRUSH_FLAG_SMOOTH_PRESSURE) {
-			pressure += pt->pressure * average_fac;
-		}
-		
-		/* n-steps before/after current point */
-		// XXX: review how the endpoints are treated by this algorithm
-		// XXX: falloff measures should also introduce some weighting variations, so that further-out points get less weight
-		for (step = 1; step <= steps; step++) {
-			bGPDspoint *pt1, *pt2;
-			int before = i - step;
-			int after  = i + step;
-			
-			CLAMP_MIN(before, 0);
-			CLAMP_MAX(after, gps->totpoints - 1);
-			
-			pt1 = &gps->points[before];
-			pt2 = &gps->points[after];
-			
-			/* add both these points to the average-sum (s += p[i]/n) */
-			madd_v3_v3fl(sco, &pt1->x, average_fac);
-			madd_v3_v3fl(sco, &pt2->x, average_fac);
-			
-			/* do pressure too? */
-			if (brush->flag & GP_EDITBRUSH_FLAG_SMOOTH_PRESSURE) {
-				pressure += pt1->pressure * average_fac;
-				pressure += pt2->pressure * average_fac;
-			}
-		}
-	}
-	
-	/* Based on influence factor, blend between original and optimal smoothed coordinate */
-	interp_v3_v3v3(&pt->x, &pt->x, sco, inf);
-	
-	if (brush->flag & GP_EDITBRUSH_FLAG_SMOOTH_PRESSURE) {
-		pt->pressure = pressure;
-	}
-	
-	return true;
 }
 
 /* ----------------------------------------------- */

source/blender/editors/gpencil/gpencil_intern.h

@@ -208,6 +208,21 @@ void gpencil_undo_init(struct bGPdata *gpd);
 void gpencil_undo_push(struct bGPdata *gpd);
 void gpencil_undo_finish(void);
 
+/**
+* Apply smooth to stroke
+*
+* gps  Stroke to smooth
+* i    Point index
+* inf  Smooth factor
+*/
+bool gp_smooth_stroke(bGPDstroke *gps, int i, float inf);
+
+/* subdivide a stroke
+* gps           Stroke data
+* new_totpoints Total number of points
+*/
+void gp_subdivide_stroke(bGPDstroke *gps, const int new_totpoints);
+
 /******************************************************* */
 /* FILTERED ACTION DATA - TYPES  ---> XXX DEPRECEATED OLD ANIM SYSTEM CODE! */
 

source/blender/editors/gpencil/gpencil_paint.c

@@ -571,6 +571,8 @@ static void gp_stroke_newfrombuffer(tGPsdata *p)
 	bGPDstroke *gps;
 	bGPDspoint *pt;
 	tGPspoint *ptc;
+	bGPDlayer *layer = gpencil_layer_getactive(p->gpd);
+
 	int i, totelem;
 	/* since strokes are so fine, when using their depth we need a margin otherwise they might get missed */
 	int depth_margin = (p->gpd->flag & GP_DATA_DEPTH_STROKE) ? 4 : 0;
@@ -610,8 +612,20 @@ static void gp_stroke_newfrombuffer(tGPsdata *p)
 	gps->inittime = p->inittime;
 	
 	/* allocate enough memory for a continuous array for storage points */
-	gps->points = MEM_callocN(sizeof(bGPDspoint) * gps->totpoints, "gp_stroke_points");
+	int sublevel = layer->sublevel;
-	
+	int new_totpoints = gps->totpoints;
+	for (i = 0; i < sublevel; ++i)
+	{
+		// Avoid error if subdivide is too big (assume totpoints is right)
+		if (new_totpoints + (new_totpoints - 1) > GP_STROKE_BUFFER_MAX)
+		{
+			sublevel = i;  // reduce sublevel
+			break;
+		}
+		new_totpoints += new_totpoints - 1;
+	}
+	gps->points = MEM_callocN(sizeof(bGPDspoint) * new_totpoints, "gp_stroke_points");
+
 	/* set pointer to first non-initialized point */
 	pt = gps->points + (gps->totpoints - totelem);
 	
@@ -730,10 +744,29 @@ static void gp_stroke_newfrombuffer(tGPsdata *p)
 			pt->time = ptc->time;
 		}
 		
+		/* subdivide the stroke */
+		if (sublevel > 0)
+		{
+			int sub = gps->totpoints;
+			for (i = 0; i < sublevel; ++i)
+			{
+				sub += sub - 1;
+				gp_subdivide_stroke(gps, sub);
+			}
+		}
+		/* smooth stroke */
+		if (layer->smooth_drawfac > 0.0f)  // only if something to do
+		{
+			for (i = 0; i < gps->totpoints; i++)
+			{
+				gp_smooth_stroke(gps, i, layer->smooth_drawfac);
+			}
+		}
+
 		if (depth_arr)
 			MEM_freeN(depth_arr);
 	}
-	
+
 	/* add stroke to frame */
 	BLI_addtail(&p->gpf->strokes, gps);
 	gp_stroke_added_enable(p);

source/blender/editors/gpencil/gpencil_utils.c

@@ -533,4 +533,102 @@ bool gp_point_xy_to_3d(GP_SpaceConversion *gsc, Scene *scene, const float screen
 	}
 }
 
+/* Apply smooth to stroke point 
+* gps  Stroke to smooth
+* i    Point index
+* inf  Smooth factor
+*/
+bool gp_smooth_stroke(bGPDstroke *gps, int i, float inf)
+{
+	bGPDspoint *pt = &gps->points[i];
+	float sco[3] = { 0.0f };
+
+	/* Do nothing if not enough points to smooth out */
+	if (gps->totpoints <= 2) {
+		return false;
+	}
+
+	/* Only affect endpoints by a fraction of the normal strength,
+	* to prevent the stroke from shrinking too much
+	*/
+	if ((i == 0) || (i == gps->totpoints - 1)) {
+		inf *= 0.1f;
+	}
+
+	/* Compute smoothed coordinate by taking the ones nearby */
+	/* XXX: This is potentially slow, and suffers from accumulation error as earlier points are handled before later ones */
+	{
+		// XXX: this is hardcoded to look at 2 points on either side of the current one (i.e. 5 items total)
+		const int   steps = 2;
+		const float average_fac = 1.0f / (float)(steps * 2 + 1);
+		int step;
+
+		/* add the point itself */
+		madd_v3_v3fl(sco, &pt->x, average_fac);
+
+		/* n-steps before/after current point */
+		// XXX: review how the endpoints are treated by this algorithm
+		// XXX: falloff measures should also introduce some weighting variations, so that further-out points get less weight
+		for (step = 1; step <= steps; step++) {
+			bGPDspoint *pt1, *pt2;
+			int before = i - step;
+			int after = i + step;
+
+			CLAMP_MIN(before, 0);
+			CLAMP_MAX(after, gps->totpoints - 1);
+
+			pt1 = &gps->points[before];
+			pt2 = &gps->points[after];
+
+			/* add both these points to the average-sum (s += p[i]/n) */
+			madd_v3_v3fl(sco, &pt1->x, average_fac);
+			madd_v3_v3fl(sco, &pt2->x, average_fac);
+
+		}
+	}
+
+	/* Based on influence factor, blend between original and optimal smoothed coordinate */
+	interp_v3_v3v3(&pt->x, &pt->x, sco, inf);
+
+	return true;
+}
+
+/* subdivide a stroke 
+* gps           Stroke data
+* new_totpoints Total number of points
+*/
+void gp_subdivide_stroke(bGPDstroke *gps, const int new_totpoints)
+{
+	int i;
+	// Subdivide stroke adding a point half way existing points
+	bGPDspoint *pt_a;
+	bGPDspoint *pt_b;
+	bGPDspoint *pt_n;
+
+	/* Move points to insert subdivision */
+	int y = 1;
+	for (i = gps->totpoints - 1; i > 0; --i)
+	{
+		pt_n = &gps->points[i];
+		gps->points[new_totpoints - y] = *pt_n;
+		y = y + 2;
+	}
+	/* Create interpolated points */
+	for (i = 0; i < new_totpoints - 1; ++i)
+	{
+		pt_a = &gps->points[i];
+		pt_n = &gps->points[i + 1];
+		pt_b = &gps->points[i + 2];
+		// Interpolate all values
+		interp_v3_v3v3(&pt_n->x, &pt_a->x, &pt_b->x, 0.5f);
+		pt_n->pressure = interpf(pt_a->pressure, pt_b->pressure, 0.5f);
+		pt_n->time = interpf(pt_a->time, pt_b->time, 0.5f);
+
+		++i; // add to loop to jump next pair
+	}
+
+	gps->totpoints = new_totpoints;  // Increase number of points
+
+}
+
 /* ******************************************************** */

source/blender/makesdna/DNA_gpencil_types.h

@@ -130,6 +130,10 @@ typedef struct bGPDlayer {
 	
 	char info[128];			/* optional reference info about this layer (i.e. "director's comments, 12/3")
 							 * this is used for the name of the layer  too and kept unique. */
+	
+	float smooth_drawfac;   /* factor used for dynamic smooth of strokes */
+	short sublevel;         /* subdivision level */
+	short pad[5];           /* padding for compiler error */
 } bGPDlayer;
 
 /* bGPDlayer->flag */

source/blender/makesrna/intern/rna_gpencil.c

@@ -796,7 +796,21 @@ static void rna_def_gpencil_layer(BlenderRNA *brna)
 	RNA_def_property_range(prop, 0.0f, 1.0f);
 	RNA_def_property_ui_text(prop, "After Color", "Base color for ghosts after the active frame");
 	RNA_def_property_update(prop, NC_GPENCIL | ND_DATA, "rna_GPencil_update");
-	
+
+	/* dynamic smooth factor */
+	prop = RNA_def_property(srna, "smooth_drawfac", PROP_FLOAT, PROP_NONE);
+	RNA_def_property_float_sdna(prop, NULL, "smooth_drawfac");
+	RNA_def_property_range(prop, 0.0, 2.0f);
+	RNA_def_property_ui_text(prop, "Smooth", "Amount of smoothing to apply to newly created strokes, to reduce jitter/noise");
+	RNA_def_property_update(prop, NC_GPENCIL | ND_DATA, "rna_GPencil_update");
+
+	/* Subdivision level */
+	prop = RNA_def_property(srna, "subdivision", PROP_INT, PROP_NONE);
+	RNA_def_property_int_sdna(prop, NULL, "sublevel");
+	RNA_def_property_range(prop, 0, 3);
+	RNA_def_property_ui_text(prop, "Subdivide", "Number of times to subdivide newly created strokes, for less jagged strokes");
+	RNA_def_property_update(prop, NC_GPENCIL | ND_DATA, "rna_GPencil_update");
+
 	/* Flags */
 	prop = RNA_def_property(srna, "hide", PROP_BOOLEAN, PROP_NONE);
 	RNA_def_property_boolean_sdna(prop, NULL, "flag", GP_LAYER_HIDE);