spline_context.beginPath();
    for(var i = 0; i < spline_n; ++i){
        spline_context.moveTo(x_to_client(spline_xs[i])-5.5, y_to_client(spline_ys[i])+5.5);
        spline_context.lineTo(x_to_client(spline_xs[i])+5.5, y_to_client(spline_ys[i])-5.5);
        spline_context.moveTo(x_to_client(spline_xs[i])+5.5, y_to_client(spline_ys[i])+5.5);
        spline_context.lineTo(x_to_client(spline_xs[i])-5.5, y_to_client(spline_ys[i])-5.5);
    }
    spline_context.strokeStyle="#AA3311";
    spline_context.stroke