window.onload = function () {
    let bgm = document.getElementById('bgm');
    let div = document.getElementById('subtitle');
    let tips = document.getElementById('tips');
    let height = div.clientHeight;
    div.style.transform = `rotateX(80deg) translateY(${height/2+200}px)`;
    let reqid = requestAnimationFrame(scroll);
    function scroll() {
        div.style.transform = `rotateX(90deg) translateY(${height/2+200 - reqid*0.3}px)`;
        reqid = requestAnimationFrame(scroll);
        if(height - reqid*0.3 < -height/2) cancelAnimationFrame(reqid);
    }
    function play(){
        let flag = true;
        return function () {
            if(flag){
                flag = false;
                bgm.play();
                bgm.volume = 0.5;
                tips.innerHTML = '<br>';
            }
        }
    }
    document.addEventListener('click', play());
};