public Point2D convertWindowToReference(Point2D apt){
  if (scrollBackReferenceRect == null)   return null;
 else   return new Point2D.Double((apt.getX() - scrollBackReferenceRect.getX()) / scrollBackReferenceRect.getWidth(),(apt.getY() - scrollBackReferenceRect.getY()) / scrollBackReferenceRect.getHeight());
}

public Point2D convertWindowToReference ( Point2D apt ) { if ( scrollBackReferenceRect == null ) return null ; else return new Point2D . Double ( ( apt . getX ( ) - scrollBackReferenceRect . getX ( ) ) / scrollBackReferenceRect . getWidth ( ) , ( apt . getY ( ) - scrollBackReferenceRect . getY ( ) ) / scrollBackReferenceRect . getHeight ( ) ) ; }
converts a point from window coordinates to reference coordinates
