Rectangle rect = new Rectangle(p.x, p.y, 1, 1);
Viewport port = ((IHTMLGraphicalViewer) viewer).getViewport();
Point viewLocation = port.getViewLocation();
Point lastLocation = viewLocation.getCopy();
new ExposeHelper((IHTMLGraphicalViewer) viewer).exposeArea(rect);
viewLocation = port.getViewLocation();
Dimension offset = lastLocation.getDifference(viewLocation);
p.translate(offset.width, offset.height);
EditPart part = viewer.findObjectAt(p);