public void OnDeserialization(object sender)
        {
            region = PdnRegion.CreateEmpty();

            Rectangle[] rects = new Rectangle[placedSurfaces.Count];

            for (int i = 0; i < placedSurfaces.Count; ++i)
            {
                rects[i] = ((PlacedSurface)placedSurfaces[i]).Bounds;
            }

            region = Utility.RectanglesToRegion(rects);
        }