Add simplify brush for sculpt mode

source/blender/editors/sculpt_paint/sculpt.c

@@ -2981,7 +2981,9 @@ static void sculpt_topology_update(Sculpt *sd, Object *ob, Brush *brush)
 	if (totnode) {
 		PBVHTopologyUpdateMode mode = PBVH_Subdivide;
 
-		if (sd->flags & SCULPT_DYNTOPO_COLLAPSE) {
+		if ((sd->flags & SCULPT_DYNTOPO_COLLAPSE) ||
+			(brush->sculpt_tool == SCULPT_TOOL_SIMPLIFY))
+		{
 			mode |= PBVH_Collapse;
 		}
 
@@ -3539,6 +3541,8 @@ static const char *sculpt_tool_name(Sculpt *sd)
 			return "Rotate Brush";
 		case SCULPT_TOOL_MASK:
 			return "Mask Brush";
+		case SCULPT_TOOL_SIMPLIFY:
+			return "Simplify Brush";
 	}
 
 	return "Sculpting";
@@ -4262,7 +4266,8 @@ static void sculpt_stroke_update_step(bContext *C, struct PaintStroke *stroke, P
 		do_symmetrical_brush_actions(sd, ob, sculpt_topology_update);
 	}
 
-	do_symmetrical_brush_actions(sd, ob, do_brush_action);
+	if (paint_brush(&sd->paint)->sculpt_tool != SCULPT_TOOL_SIMPLIFY)
+		do_symmetrical_brush_actions(sd, ob, do_brush_action);
 
 	sculpt_combine_proxies(sd, ob);
 

source/blender/makesdna/DNA_brush_types.h

@@ -156,10 +156,7 @@ typedef enum BrushSculptTool {
 	SCULPT_TOOL_THUMB = 12,
 	SCULPT_TOOL_SNAKE_HOOK = 13,
 	SCULPT_TOOL_ROTATE = 14,
-	
-	/* slot 15 is free for use */
-	/* SCULPT_TOOL_ = 15, */
-	
+	SCULPT_TOOL_SIMPLIFY = 15,
 	SCULPT_TOOL_CREASE = 16,
 	SCULPT_TOOL_BLOB = 17,
 	SCULPT_TOOL_CLAY_STRIPS = 18,

source/blender/makesrna/intern/rna_brush.c

@@ -65,6 +65,7 @@ EnumPropertyItem brush_sculpt_tool_items[] = {
 	{SCULPT_TOOL_PINCH, "PINCH", ICON_BRUSH_PINCH, "Pinch", ""},
 	{SCULPT_TOOL_ROTATE, "ROTATE", ICON_BRUSH_ROTATE, "Rotate", ""},
 	{SCULPT_TOOL_SCRAPE, "SCRAPE", ICON_BRUSH_SCRAPE, "Scrape", ""},
+	{SCULPT_TOOL_SIMPLIFY, "SIMPLIFY", ICON_BRUSH_SUBTRACT /* icon TODO */, "Simplify", ""},
 	{SCULPT_TOOL_SMOOTH, "SMOOTH", ICON_BRUSH_SMOOTH, "Smooth", ""},
 	{SCULPT_TOOL_SNAKE_HOOK, "SNAKE_HOOK", ICON_BRUSH_SNAKE_HOOK, "Snake Hook", ""},
 	{SCULPT_TOOL_THUMB, "THUMB", ICON_BRUSH_THUMB, "Thumb", ""},