public void choosePoints(Vertex v, MouseEvent e)
    {
        if (v == null)  return;
        if (v.getClass() != Point.class)    return;
        Point p = (Point)v;
        if (leftPoint == null)  leftPoint = p;
        else
        {
            rightPoint = p;
            if (e.getButton() == MouseEvent.BUTTON3)
            {
                removePointsInBetween();
                leftPoint = null;
                rightPoint = null;
            }
        }
    }