为什么我应该使用requestAnimationFrame而不是setTimeout或setInterval?
这个自问自答的问题是一个文档示例。
为什么我应该使用requestAnimationFrame而不是setTimeout或setInterval?
这个自问自答的问题是一个文档示例。
简单来说,使用requestAnimationFrame
可以产生更高质量的动画效果,完全消除了使用setTimeout
或setInterval
时可能出现的闪烁和剪切,并减少或完全消除帧跳过的情况。
是指在显示扫描的中途向显示缓冲区呈现新的画布缓冲区,导致由于动画位置不匹配而引起的错位线。
闪烁是由于在画布完全渲染之前将画布缓冲区呈现给显示缓冲区造成的。
帧跳过是由于渲染帧之间的时间与显示硬件不精确同步引起的。每隔一段时间就会跳过一个帧,导致动画不连贯。(有方法可以减少这种情况,但我个人认为这些方法的总体效果更差)大多数设备使用60帧每秒(或其倍数),每16.666...毫秒产生一个新帧,计时器setTimeout
和setInterval
使用整数值,它们永远无法完全匹配帧速率(如果你有interval = 1000/60
,则会四舍五入为17ms)。
更新问题的答案requestAnimationFrame loop not correct fps显示setTimeout的帧时间不一致,并将其与requestAnimationFrame进行比较。
演示了一个简单的动画(条纹在屏幕上移动),单击鼠标按钮将切换使用的渲染更新方法。
使用了几种更新方法。具体的动画伪像外观取决于您运行的硬件设置。您将寻找条纹移动中的小抖动。
注意。您可能已关闭显示同步或关闭硬件加速,这将影响所有计时方法的质量。低端设备可能也无法处理动画。
双定时器,使用两个定时器,一个每1000/60调用清除,另一个用于渲染。
2019年10月更新,定时器呈现内容的方式有所变化。为了表明setInterval
不能正确地与显示刷新同步,我已更改了双定时器示例,以表明使用多个setInterval
仍然可能会导致严重的闪烁。这种闪烁的程度取决于硬件设置。
RAF定时动画,使用requestAnimationFrame,但使用帧经过的时间进行动画。这种技术在动画中非常常见。我认为它有缺陷,但我将其留给观众自行决定。
/** SimpleFullCanvasMouse.js begin **/
var backBuff;
var bctx;
const STRIPE_WIDTH = 250;
var textWidth;
const helpText = "Click mouse to change render update method.";
var onResize = function(){
if(backBuff === undefined){
backBuff = document.createElement("canvas") ;
bctx = backBuff.getContext("2d");
}
backBuff.width = canvas.width;
backBuff.height = canvas.height;
bctx.fillStyle = "White"
bctx.fillRect(0,0,w,h);
bctx.fillStyle = "Black";
for(var i = 0; i < w; i += STRIPE_WIDTH){
bctx.fillRect(i,0,STRIPE_WIDTH/2,h) ;
}
ctx.font = "20px arial";
ctx.textAlign = "center";
ctx.font = "20px arial";
textWidth = ctx.measureText(helpText).width;
};
var tick = 0;
var displayMethod = 0;
var methods = "Timer,RAF Best Quality,Dual Timers,RAF with timed animation,Timer with timed animation".split(",");
var dualTimersActive = false;
var hdl1, hdl2
function display(timeAdvance){ // put code in here
tick += timeAdvance;
tick %= w;
ctx.drawImage(backBuff,tick-w,0);
ctx.drawImage(backBuff,tick,0);
if(textWidth !== undefined){
ctx.fillStyle = "rgba(255,255,255,0.7)";
ctx.fillRect(w /2 - textWidth/2, 0,textWidth,40);
ctx.fillStyle = "black";
ctx.fillText(helpText,w/2, 14);
ctx.fillText("Display method : " + methods[displayMethod],w/2, 34);
}
if(mouse.buttonRaw&1){
displayMethod += 1;
displayMethod %= methods.length;
mouse.buttonRaw = 0;
lastTime = null;
tick = 0;
if(dualTimersActive) {
dualTimersActive = false;
clearInterval(hdl1);
clearInterval(hdl2);
updateMethods[displayMethod]()
}
}
}
//==================================================================================================
// The following code is support code that provides me with a standard interface to various forums.
// It provides a mouse interface, a full screen canvas, and some global often used variable
// like canvas, ctx, mouse, w, h (width and height), globalTime
// This code is not intended to be part of the answer unless specified and has been formated to reduce
// display size. It should not be used as an example of how to write a canvas interface.
// By Blindman67
const U = undefined;const RESIZE_DEBOUNCE_TIME = 100;
var w,h,cw,ch,canvas,ctx,mouse,createCanvas,resizeCanvas,setGlobals,globalTime=0,resizeCount = 0;
var L = typeof log === "function" ? log : function(d){ console.log(d); }
createCanvas = function () { var c,cs; cs = (c = document.createElement("canvas")).style; cs.position = "absolute"; cs.top = cs.left = "0px"; cs.zIndex = 1000; document.body.appendChild(c); return c;}
resizeCanvas = function () {
if (canvas === U) { canvas = createCanvas(); } canvas.width = window.innerWidth; canvas.height = window.innerHeight; ctx = canvas.getContext("2d");
if (typeof setGlobals === "function") { setGlobals(); } if (typeof onResize === "function"){ resizeCount += 1; setTimeout(debounceResize,RESIZE_DEBOUNCE_TIME);}
}
function debounceResize(){ resizeCount -= 1; if(resizeCount <= 0){ onResize();}}
setGlobals = function(){ cw = (w = canvas.width) / 2; ch = (h = canvas.height) / 2; mouse.updateBounds(); }
mouse = (function(){
function preventDefault(e) { e.preventDefault(); }
var mouse = {
x : 0, y : 0, w : 0, alt : false, shift : false, ctrl : false, buttonRaw : 0, over : false, bm : [1, 2, 4, 6, 5, 3],
active : false,bounds : null, crashRecover : null, mouseEvents : "mousemove,mousedown,mouseup,mouseout,mouseover,mousewheel,DOMMouseScroll".split(",")
};
var m = mouse;
function mouseMove(e) {
var t = e.type;
m.x = e.clientX - m.bounds.left; m.y = e.clientY - m.bounds.top;
m.alt = e.altKey; m.shift = e.shiftKey; m.ctrl = e.ctrlKey;
if (t === "mousedown") { m.buttonRaw |= m.bm[e.which-1]; }
else if (t === "mouseup") { m.buttonRaw &= m.bm[e.which + 2]; }
else if (t === "mouseout") { m.buttonRaw = 0; m.over = false; }
else if (t === "mouseover") { m.over = true; }
else if (t === "mousewheel") { m.w = e.wheelDelta; }
else if (t === "DOMMouseScroll") { m.w = -e.detail; }
if (m.callbacks) { m.callbacks.forEach(c => c(e)); }
if((m.buttonRaw & 2) && m.crashRecover !== null){ if(typeof m.crashRecover === "function"){ setTimeout(m.crashRecover,0);}}
e.preventDefault();
}
m.updateBounds = function(){
if(m.active){
m.bounds = m.element.getBoundingClientRect();
}
}
m.addCallback = function (callback) {
if (typeof callback === "function") {
if (m.callbacks === U) { m.callbacks = [callback]; }
else { m.callbacks.push(callback); }
} else { throw new TypeError("mouse.addCallback argument must be a function"); }
}
m.start = function (element, blockContextMenu) {
if (m.element !== U) { m.removeMouse(); }
m.element = element === U ? document : element;
m.blockContextMenu = blockContextMenu === U ? false : blockContextMenu;
m.mouseEvents.forEach( n => { m.element.addEventListener(n, mouseMove); } );
if (m.blockContextMenu === true) { m.element.addEventListener("contextmenu", preventDefault, false); }
m.active = true;
m.updateBounds();
}
m.remove = function () {
if (m.element !== U) {
m.mouseEvents.forEach(n => { m.element.removeEventListener(n, mouseMove); } );
if (m.contextMenuBlocked === true) { m.element.removeEventListener("contextmenu", preventDefault);}
m.element = m.callbacks = m.contextMenuBlocked = U;
m.active = false;
}
}
return mouse;
})();
resizeCanvas();
mouse.start(canvas,true);
onResize()
var lastTime = null;
window.addEventListener("resize",resizeCanvas);
function clearCTX(){
ctx.setTransform(1,0,0,1,0,0); // reset transform
ctx.globalAlpha = 1; // reset alpha
ctx.clearRect(0,0,w,h); // though not needed this is here to be fair across methods and demonstrat flicker
}
function dualUpdate(){
if(!dualTimersActive) {
dualTimersActive = true;
hdl1 = setInterval( clearCTX, 1000/60);
hdl2 = setInterval(() => display(10), 1000/60);
}
}
function timerUpdate(){
timer = performance.now();
if(!lastTime){
lastTime = timer;
}
var time = (timer-lastTime) / (1000/60);
lastTime = timer;
setTimeout(updateMethods[displayMethod],1000/60);
clearCTX();
display(10*time);
}
function updateRAF(){
clearCTX();
requestAnimationFrame(updateMethods[displayMethod]);
display(10);
}
function updateRAFTimer(timer){ // Main update loop
clearCTX();
requestAnimationFrame(updateMethods[displayMethod]);
if(!timer){
timer = 0;
}
if(!lastTime){
lastTime = timer;
}
var time = (timer-lastTime) / (1000/60);
display(10 * time);
lastTime = timer;
}
displayMethod = 1;
var updateMethods = [timerUpdate,updateRAF,dualUpdate,updateRAFTimer,timerUpdate]
updateMethods[displayMethod]();
/** SimpleFullCanvasMouse.js end **/
requestAnimationFrames
的回调是特殊的,当退出时,后备缓冲区会保持直到Vsync(没有像素移动到显示器)。这可以防止剪切和闪烁。 - Blindman67
requestIdleCallback
: https://developer.chrome.com/blog/using-requestidlecallback/ - undefined