void updateWidth (GC gc) {
	String oldDisplayText = displayText;
	computeDisplayText (gc);
	/* the header must be damaged if the display text has changed or if the alignment is not LEFT */
	if (parent.getHeaderVisible ()) {
		if ((getStyle () & SWT.LEFT) == 0 || !oldDisplayText.equals (displayText)) {
			int padding = parent.getHeaderPadding ();
			parent.header.redraw (getX () + padding, 0, width - padding, parent.getHeaderHeight (), false);
		}
	}
}