// Arrange the Adorners. protected override Size ArrangeOverride(Size finalSize) { Rect rcExterior = new Rect(0, 0, AdornedElement.RenderSize.Width, AdornedElement.RenderSize.Height); _prCropMask.RectExterior = rcExterior; Rect rcInterior = _prCropMask.RectInterior; _prCropMask.Arrange(rcExterior); SetThumbs(rcInterior); _cnvThumbs.Arrange(rcExterior); return(finalSize); }