如何获得javascript中“window.requestAnimationFrame”回调之间的时差的最佳方法是什么?
我试过了:
// create the best .requestAnimationFrame callback for each browser
window.FPS = (function() {
return window.requestAnimationFrame || window.webkitRequestAnimationFrame || window.mozRequestAnimationFrame || window.oRequestAnimationFrame || window.msRequestAnimationFrame ||
function(callback) {window.setTimeout(callback, 1000 / 60);};
})();
// start animation loop
var dt, stamp = (new Date()).getTime();
function loop() {
window.FPS(loop);
var now = (new Date()).getTime();
var dt = now - stamp;
stamp = now;
}
// has "dt" the best accuracy?
最佳答案
大多数现代浏览器会自动将高精度时间戳作为参数发送到每个requestAnimation回调循环中:http://caniuse.com/#search=performance
因此,您只需从当前时间戳中减去最后一个时间戳,即可获得自上次运行循环以来耗时。
这是示例代码和演示:
var canvas=document.getElementById("canvas");
var ctx=canvas.getContext("2d");
var cw=canvas.width;
var ch=canvas.height;
var startingTime;
var lastTime;
var totalElapsedTime;
var elapsedSinceLastLoop;
var $total=$('#total');
var $loop=$('#loop');
requestAnimationFrame(loop);
function loop(currentTime){
if(!startingTime){startingTime=currentTime;}
if(!lastTime){lastTime=currentTime;}
totalElapsedTime=(currentTime-startingTime);
elapsedSinceLastLoop=(currentTime-lastTime);
lastTime=currentTime;
$total.text('Since start: '+totalElapsedTime+' ms');
$loop.text('Since last loop: '+elapsedSinceLastLoop+' ms');
requestAnimationFrame(loop);
}
body{ background-color: ivory; }
#canvas{border:1px solid red;}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js"></script>
<p id=total>T1</p>
<p id=loop>T2</p>
<canvas id="canvas" width=300 height=300></canvas>
对于不支持
Performance
的两种浏览器,您将不得不在循环内使用Date.now()
而不是currentTime
,因为这些浏览器不会自动将时间戳发送到循环中。