<!DOCTYPE html>
<html>
<head>
<title></title>
<style type="text/css">
#div1 {
width: 800px;
height: 600px;
background-color: #ff0;
position: absolute;
}
.imgRotate {
width: 100px;
height: 80px;
position: absolute;
top: 50%;
left: 50%;
margin: -40px 0 0 -50px;
}
</style>
</head>
<body>
<div id="div1">
<img id="img1" class="imgRotate" src="http://www.baidu.com/img/logo-yy.gif" />
<input id="input2" type="button" value="btn2"></input>
</div>
</body>
<script type="text/javascript" src="jquery.min.js"></script>
<script type="text/javascript" src="jQueryRotate.js"></script>
<script type="text/javascript">
var num = 0;
$("#input2").click(function(){
num ++;
$("#img1").rotate(90*num);
});
</script>
</html>
测试结果：chrome下效果正常，旋转后img对象仍为img对象；ie8下效果正常，但旋转后img对象变为下面对象，由于对象变化，若旋转后仍按原来方法获取img对象，则会报js错误。欲获取image对象，可根据class获取。如果图像旋转后，不进行其它操作，则可用此方法。若进行其它操作，如放大、缩小图像，则此方法实现较复杂。
<!DOCTYPE html>
<html>
<head>
<title></title>
<style type="text/css">
#div1 {
width: 800px;
height: 600px;
background-color: #ff0;
position: absolute;
}
.imgRotate {
width: 100px;
height: 100px;
position: absolute;
top: 50%;
left: 50%;
margin: -50px 0 0 -50px;
}
#imgRotate {
width: 100px;
height: 100px;
position: absolute;
top: 50%;
left: 50%;
margin: -50px 0 0 -50px;
}
</style>
</head>
<body>
<div id="div1">
<img id="img1" class="imgRotate" src="http://www.baidu.com/img/logo-yy.gif" />
<input id="input1" type="button" value="btn1"></input>
</div>
</body>
<script type="text/javascript" src="jquery.min.js"></script>
<script type="text/javascript">
function rotate(id,angle,whence) {
var p = document.getElementById(id);
// we store the angle inside the image tag for persistence
if (!whence) {
p.angle = ((p.angle==undefined?0:p.angle) + angle) % 360;
} else {
p.angle = angle;
}
if (p.angle >= 0) {
var rotation = Math.PI * p.angle / 180;
} else {
var rotation = Math.PI * (360+p.angle) / 180;
}
var costheta = Math.cos(rotation);
var sintheta = Math.sin(rotation);
if (document.all && !window.opera) {
var canvas = document.createElement('img');
canvas.src = p.src;
canvas.height = p.height;
canvas.width = p.width;
canvas.style.filter = "progid:DXImageTransform.Microsoft.Matrix(M11="+costheta+",M12="+(-sintheta)+",M21="+sintheta+",M22="+costheta+",SizingMethod='auto expand')";
} else {
var canvas = document.createElement('canvas');
if (!p.oImage) {
canvas.oImage = new Image();
canvas.oImage.src = p.src;
} else {
canvas.oImage = p.oImage;
}
canvas.style.width = canvas.width = Math.abs(costheta*canvas.oImage.width) + Math.abs(sintheta*canvas.oImage.height);
canvas.style.height = canvas.height = Math.abs(costheta*canvas.oImage.height) + Math.abs(sintheta*canvas.oImage.width);
var context = canvas.getContext('2d');
context.save();
if (rotation <= Math.PI/2) {
context.translate(sintheta*canvas.oImage.height,0);
} else if (rotation <= Math.PI) {
context.translate(canvas.width,-costheta*canvas.oImage.height);
} else if (rotation <= 1.5*Math.PI) {
context.translate(-costheta*canvas.oImage.width,canvas.height);
} else {
context.translate(0,-sintheta*canvas.oImage.width);
}
context.rotate(rotation);
context.drawImage(canvas.oImage, 0, 0, canvas.oImage.width, canvas.oImage.height);
context.restore();
}
canvas.id = p.id;
canvas.angle = p.angle;
p.parentNode.replaceChild(canvas, p);
}
function rotateRight(id,angle) {
rotate(id,angle==undefined?90:angle);
}
function rotateLeft(id,angle) {
rotate(id,angle==undefined?-90:-angle);
}
$("#input1").click(function(){
$("img.imgRotate").attr("id","imgRotate");
rotateLeft("imgRotate",90);
$("#imgRotate").attr("top","50%");
$("#imgRotate").attr("left","50%");
$("#imgRotate").attr("margin","-50px 0 0 -50px");
});
</script>
</html>
测试结果：chrome下效果正常，但旋转后img对象变为canvas对象；ie8下效果正常，旋转后img对象仍为img对象。Matrix()参数较多，使用时需较多计算。
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
</head>
<body>
<img id="image" src="http://www.baidu.com/img/logo-yy.gif" />
<input id="input2" type="button" value="btn2"></input>
</body>
<script type="text/javascript" src="jquery.min.js"></script>
<script type="text/javascript">
var num = 0;
$("#input2").click(function(){
num = (num + 1) % 4;
document.getElementById('image').style.filter = 'progid:DXImageTransform.Microsoft.BasicImage(rotation='+num+')';
});
</script>
</html>
查看这三种方法的代码会发现，本质上是一种解决方案：chrome下使用canvas对象实现，ie8下使用VML或者Matrix()或BasicImage()实现。本人近期改造一个组件：其中涉及到旋转、放大图片，由于jQueryRotate.js在ie8下会生成一个新的对象，导致放大图片前选择图片时，需要进行特殊处理。后决定对chrome、ie8分开处理，chrome下使用jQueryRotate实现，ie8下使用BasicImage()实现，保证了代码的简洁性和可读性。
