       spline_ys[spline_i] = client_to_y(e.clientY - canvas_rect.top);
        spline_draw(e.clientX - canvas_rect.left, e.clientY - canvas_rect.top, false);
    }, false);

    spline.addEventListener('mouseleave', function(e){
        spline_draw(0, 0, false);
    }, false);
}

function spline_draw(client_x, client_y, do_guides){
    spline = document.getElementById("spline");
    var spline_context = spline.getContext("2d");
    spline_context.font = "16px sans-serif";
    // background
    spline_contex