主要思想：
首先要准备一张有连续帧的图片，然后利用HTML5 Canvas的draw方法在不同的时间间隔绘制不同的帧，这样看起来就像动画在播放。
关键技术点：
JavaScript 函数setTimeout()有两个参数，第一个是参数可以传递一个JavaScript方法，
另外一个参数代表间隔时间，单位为毫秒数。代码示例：
setTimeout( update, 1000/30)
Canvas的API-drawImage()方法，需要指定全部9个参数：
ctx.drawImage(myImage, offw, offh, width,height, x2, y2, width, height)
其中offw, offh是指源图像的起始坐标点，width, height表示源图像的宽与高，x2,y2表
示源图像在目标Canvas上的起始坐标点。
<!DOCTYPE html><html>
<head>
<meta http-equiv="X-UA-Compatible" content="chrome=IE8">
<meta http-equiv="Content-type" content="text/htmlcharset=UTF-8">
<title>Canvas Mouse Event Demo</title>
<link href="default.css" rel="stylesheet" />
<script>
var ctx = null // global variable 2d context
var started = false
var mText_canvas = null
var x = 0, y =0
var frame = 0 // 22 5*5 + 2
var imageReady = false
var myImage = null
var px = 300
var py = 300
var x2 = 300
var y2 = 0
window.onload = function() {
var canvas = document.getElementById("animation_canvas")
console.log(canvas.parentNode.clientWidth)
canvas.width = canvas.parentNode.clientWidth
canvas.height = canvas.parentNode.clientHeight
if (!canvas.getContext) {
console.log("Canvas not supported. Please install a HTML5 compatible browser.")
return
}
// get 2D context of canvas and draw rectangel
ctx = canvas.getContext("2d")
ctx.fillStyle="black"
ctx.fillRect(0, 0, canvas.width, canvas.height)
myImage = document.createElement('img')
myImage.src = "../robin.png"
myImage.onload = loaded()
}
function loaded() {
imageReady = true
setTimeout( update, 1000/30)
}
function redraw() {
ctx.clearRect(0, 0, 460, 460)
ctx.fillStyle="black"
ctx.fillRect(0, 0, 460, 460)
// find the index of frames in image
var height = myImage.naturalHeight/5
var width = myImage.naturalWidth/5
var row = Math.floor(frame / 5)
var col = frame - row * 5
var offw = col * width
var offh = row * height
// first robin
px = px - 5
py = py - 5
if(px < -50) {
px = 300
}
if(py < -50) {
py = 300
}
//var rate = (frame+1) /22
//var rw = Math.floor(rate * width)
//var rh = Math.floor(rate * height)
ctx.drawImage(myImage, offw, offh, width, height, px, py, width, height)
// second robin
x2 = x2 - 5
y2 = y2 + 5
if(x2 < -50) {
x2 = 300
y2 = 0
}
ctx.drawImage(myImage, offw, offh, width, height, x2, y2, width, height)
}
function update() {
redraw()
frame++
if (frame >= 22) frame = 0
setTimeout( update, 1000/30)
}
</script>
</head>
<body>
<h1>HTML Canvas Animations Demo - By Gloomy Fish</h1>
<pre>Play Animations</pre>
<div id="my_painter">
<canvas id="animation_canvas"></canvas>
</div>
</body>
</html>
可以设置cookie（可以加载一个cookie.min.js，使用起来非常方便）。就是当第一次进入页面的时候，先去读取该cookie，如果存在，说明之前已经做了更改，把cookie值稍作处理就可以完成初始化了（记得当初始化完成后删除该cookie），如果cookie不存在说明还没有做过更改。欢迎分享，转载请注明来源：内存溢出
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