void setSortDirection (int value) {
	if (value == sort) return;
	boolean widthChange = value == SWT.NONE || sort == SWT.NONE;
	sort = value;
	if (widthChange) {
		/* 
		 * adding/removing the sort arrow decreases/increases the width that is
		 * available for the column's header text, so recompute the display text
		 */
		GC gc = new GC (parent);
		computeDisplayText (gc);
		gc.dispose ();
	}
	if (parent.drawCount <= 0 && parent.getHeaderVisible ()) {
		/* don't damage the header's drawn borders */
		parent.header.redraw (getX (), 1, width - 2, parent.getHeaderHeight () - 3, false);
	}
}