* Shows the margin.
*/
private void showMargin() {
if (fMarginPainter == null) {
if (fSourceViewer instanceof ITextViewerExtension2) {
fMarginPainter= new MarginPainter(fSourceViewer);
fMarginPainter.setMarginRulerColor(getColor(fMarginPainterColorKey));
if (fPreferenceStore != null)
fMarginPainter.setMarginRulerColumn(fPreferenceStore.getInt(fMarginPainterColumnKey));
ITextViewerExtension2 extension= (ITextViewerExtension2) fSourceViewer;
extension.addPainter(fMarginPainter);