GraphicalViewer viewer = getGraphicalViewer();

KeyHandler keyHandler = new KeyHandler();


viewer.setProperty(MouseWheelHandler.KeyGenerator.getKey(SWT.MOD2),
		new MouseWheelHandler() {
			final int DELTA = 20;

			@Override
			public void handleMouseWheel(Event event,
					EditPartViewer viewer) {
				ScalableFreeformRootEditPart rootEditPart_;
				rootEditPart_ = (ScalableFreeformRootEditPart) viewer
						.getRootEditPart();
				Viewport viewport = rootEditPart_.getZoomManager()
						.getViewport();
				if (viewport != null) {
					viewport.setViewLocation(viewport.getViewLocation()
							.translate(DELTA * event.count, 0));
					event.doit = false;
				}
			}
		});