IGraphicalEditPart p1 = getGraphicalPart(d1);
 IGraphicalEditPart p2 = getGraphicalPart(d2);

      if (p1 != null && p2 != null) {

          IFigure f1 = p1.getFigure();
          IFigure f2 = p2.getFigure();
          
          PolylineConnectionEx conn = new PolylineConnectionEx() {
            public void paint(Graphics graphics) {
              setLineWidth(3);
              setForegroundColor(ColorConstants.red);
              super.paint(graphics);
            }
          };
 
          conn.setSourceAnchor(new ChopboxAnchor(f1));
          conn.setTargetAnchor(new ChopboxAnchor(f2));

          LayerManager manager = (LayerManager) viewer.getEditPartRegistry()
              .get(LayerManager.ID);
          ConnectionLayer layer = (ConnectionLayer) manager.getLayer(LayerConstants.CONNECTION_LAYER);
          layer.add(conn);