requestAnimationFrame与setInterval,setTimeout

自打学习canvas动画以来,都说requestAnimationFrame好,就一直用,也没觉得有什么太过于特殊的地方,直到刚才,在写完前面的"小球碰撞墙壁----干掉误差"之后,,突然想去看看如果这里改回setInterval,会是个什么样,差距究竟有多大?

结果....一看吓一跳,差距太大了,说难听点,setInterval...简直像屎一样

具体结果,只需要将前面那篇里面的gamleLoop方法和该方法前面的那句gameLoop()  替换成下面的代码,一看就知道了.

function gameLoop(){

    ctx.clearRect(0,0,CANVAS_WIDTH,CANVAS_HEIGHT);
    ball.draw(ctx);
    ball.update();
}    

setInterval(gameLoop,30)

不亲自做实践,就没法取得进步,果真是这样.

requestAnimationFrame简易可兼容的方法

window.requestAnimFrame = (function() {
    return window.requestAnimationFrame || window.webkitRequestAnimationFrame || window.mozRequestAnimationFrame || window.oRequestAnimationFrame || window.msRequestAnimationFrame ||
        function( /* function FrameRequestCallback */ callback, /* DOMElement Element */ element) {
            return window.setTimeout(callback, 1000 / 60);
        };
})();

较为完整的方法

(function() {
    var lastTime = 0;
    var vendors = ['webkit', 'moz'];
    for(var x = 0; x < vendors.length && !window.requestAnimationFrame; ++x) {
        window.requestAnimationFrame = window[vendors[x] + 'RequestAnimationFrame'];
        window.cancelAnimationFrame = window[vendors[x] + 'CancelAnimationFrame'] ||    // Webkit中此取消方法的名字变了
                                      window[vendors[x] + 'CancelRequestAnimationFrame'];
    }

    if (!window.requestAnimationFrame) {
        window.requestAnimationFrame = function(callback, element) {
            var currTime = new Date().getTime();
            var timeToCall = Math.max(0, 16.7 - (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);
        };
    }
}());