ct.top);
            runge_draw(e.clientX - canvas_rect.left, e.clientY - canvas_rect.top, false); // double work
           }
    }, false);

    runge.addEventListener('mousedown', function(e){
        var canvas_rect = runge.getBoundingClientRect();
        runge_xs[runge_i] = client_to_x(e.clientX - canvas_rect.left);
        runge_ys[runge_i] = client_to_y(e.clientY - canvas_rect.top);
        runge_draw(e.clientX - canvas_rect.left, e.clientY - canvas_rect.top, false);
    }, false);

    runge.addEve