material: Path.addPath => Path.shift

Runtime/rendering/proxy_box.cs

             return base.hitTest(result, position: position);
         }
 
-        //todo:xingwei.zhu: implementation shadow + compositeLayer + Path.shift
+        //todo:xingwei.zhu: implementation shadow + compositeLayer
-                //Path offsetPath = this._clip.shift(offset);
-                Path offsetPath = this._clip;
+                Path offsetPath = new Path();
+                offsetPath.addPath(this._clip, offset);
 
                 Canvas canvas = context.canvas;
 //                if (this.elevation != 0.0 && paintShadows) {