1

这是我第一次在 javascript 中做键盘事件，但我知道动画确实有效。这个想法很简单：当用户按下回车时播放一个矩形移动的动画。下面是我的代码。

//Event listeners
window.addEventListener("keydown", onKeyDown, false);

function onKeyDown(event){
    var keyCode = event.keyCode;
    switch(keyCode){
        case 13  //enter
            drawStuff();
        break;
    }
}

//code to be executed onKeyDown
function drawStuff(){
var x = document.getElementById("myCanvas");
var canvas = x.getContext('2d');

var i = 0;

function animate(){
    if(i < 451){
        canvas.clearRect(0,0,500,500);
        canvas.fillStyle="red";
        canvas.fillRect(30,i,50,50);
        i++;
    }
    else{}
}

window.setInterval(animate, 1);
}

任何建议如何解决这个问题？

4

1 回答 1

0

看看 Paul Irish 的requestAnimationFrame垫片；rAF 比 setInterval 方法有很多优点；主要是它是为做到这一点而构建的，而且它只在浏览器准备好时才请求帧，所以当你的网站在后台时它会暂停发生的事情。当我切换时，我还注意到性能更流畅。

我会说这样的事情应该有效：

var animationHasTriggered = false;
var x = document.getElementById("myCanvas");
var canvas = x.getContext('2d');
var keysDown = {};

var i = 0;

window.addEventListener('load', function()
{
    addEventListener("keydown", function(e)
    {
        keysDown[e.keyCode] = true;
    }, false);

    addEventListener("keyup", function(e)
    {
        delete keysDown[e.keyCode];
    }, false);

    updateAll();

}, false);

function updateAll()
{
    if (13 in keysDown || animationHasTriggered)
    {
        animationHasTriggered = true;
        animate();
    }
    requestAnimationFrame(updateAll);
}

function animate()
{
    if (i < 451)
    {
        canvas.clearRect(0,0,500,500);
        canvas.fillStyle="red";
        canvas.fillRect(30,i,50,50);
        i++;
    }
    else
    {
        animationHasTriggered = false;
    }
}
(function()
{
    // http://paulirish.com/2011/requestanimationframe-for-smart-animating/
    var lastTime = 0;
    var vendors = ['ms', 'moz', 'webkit', 'o'];
    for(var x = 0; x < vendors.length && !window.requestAnimationFrame; ++x)
    {
        window.requestAnimationFrame = window[vendors[x]+'RequestAnimationFrame'];
        window.cancelAnimationFrame = window[vendors[x]+'CancelAnimationFrame'] || window[vendors[x]+'CancelRequestAnimationFrame'];
    }

    if (!window.requestAnimationFrame) window.requestAnimationFrame = function(callback, element)
    {
        var currTime = new Date().getTime();
        var timeToCall = Math.max(0, 16 - (currTime - lastTime));
        var id = window.setTimeout(function()
        {
            callback(currTime + timeToCall);
        }, timeToCall);
        lastTime = currTime + timeToCall;
        return id;
    };

    if (!window.cancelAnimationFrame) window.cancelAnimationFrame = function(id)
    {
        clearTimeout(id);
    };
}());
于 2013-01-16T13:16:54.913 回答