<mx:Script>
          <![CDATA[
  
 blog.flexexamples.com/2008/09/09/rounding-the-corners-of-an-image-control-in-flex-using-a-mask


              import mx.events.ResizeEvent;
  
              private var roundedMask:Sprite;
  
              private function init():void {
                  roundedMask = new Sprite();
                  canvas.rawChildren.addChild(roundedMask);
              }