void dispose(){
  if (popup != null) {
    popup.removeAll();
  }
  popup=null;
  for (  RayTrack ray : rayList) {
    ray.dispose();
  }
}

void dispose ( ) { if ( popup != null ) { popup . removeAll ( ) ; } popup = null ; for ( RayTrack ray : rayList ) { ray . dispose ( ) ; } }
clean up when this object is no longer needed . should not be called while the object is still displayed ; see remove ( )
