我刚刚开始 HTML 5 javascript 游戏开发,我了解到最好使用 requestAnimationFrame polyfill。
我了解该功能,但我不了解其背后的数学原理。
准确地说:
(function() {
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);
};
}());
我不明白的数学线是:
var timeToCall = Math.max(0, 16 - (currTime - lastTime));
如果有人能给我简短解释那行代码是如何工作的,那就太好了。
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