PNGHandler-借助JS让PNG图在IE下实现透明（包括背景图）

PNG.JS代码：
// PNGHandler: Object-Oriented Javascript-based PNG wrapper
// --------------------------------------------------------
// Version 1.1.20031218
// Code by Scott Schiller - www.schillmania.com
// --------------------------------------------------------
// Description:
// Provides gracefully-degrading PNG functionality where
// PNG is supported natively or via filters （Damn you, IE！）
// Should work with PNGs as images and DIV background images.

function PNGHandler（） {
var self = this;

this.na = navigator.appName.toLowerCase（）;
this.nv = navigator.appVersion.toLowerCase（）;
this.isIE = this.na.indexOf（"internet explorer"）+1？1:0;
this.isWin = this.nv.indexOf（"windows"）+1？1:0;
this.ver = this.isIE？parseFloat（this.nv.split（"msie "）[1]）:parseFloat（this.nv）;
this.isMac = this.nv.indexOf（"mac"）+1？1:0;
this.isOpera = （navigator.userAgent.toLowerCase（）.indexOf（"opera "）+1 || navigator.userAgent.toLowerCase（）.indexOf（"opera/"）+1）;
if （this.isOpera） this.isIE = false; // Opera filter catch （which is sneaky, pretending to be IE by default）

this.transform = null;

this.getElementsByClassName = function（className,oParent） {
doc = （oParent||document）;
matches = [];
nodes = doc.all||doc.getElementsByTagName（"*"）;
for （i=0; i<nodes.length; i++） {
if （nodes[i].className == className || nodes[i].className.indexOf（className）+1 || nodes[i].className.indexOf（className+" "）+1 || nodes[i].className.indexOf（" "+className）+1） {
matches[matches.length] = nodes[i];
}
}
return matches; // kids, don"t play with fire. ;）
}

this.filterMethod = function（oOld） {
// IE 5.5+ proprietary filter garbage （boo！）
// Create new element based on old one. Doesn"t seem to render properly otherwise （due to filter？）
// use proprietary "currentStyle" object, so rules inherited via CSS are picked up.

var o = document.createElement（"div"）; // oOld.nodeName
var filterID = "DXImageTransform.Microsoft.AlphaImageLoader";
// o.style.width = oOld.currentStyle.width;
// o.style.height = oOld.currentStyle.height;

if （oOld.nodeName == "DIV"） {
var b = oOld.currentStyle.backgroundImage.toString（）; // parse out background image URL
oOld.style.backgroundImage = "none";
// Parse out background image URL from currentStyle object.
var i1 = b.indexOf（"url（""）+5;
var newSrc = b.substr（i1,b.length-i1-2）.replace（".gif",".png"）; // find first instance of "） after （", chop from string
o = oOld;
o.style.writingMode = "lr-tb"; // Has to be applied so filter "has layout" and is displayed. Seriously. Refer to http://msdn.microsoft.com/workshop/author/filter/reference/filters/alphaimageloader.asp？frame=true
o.style.filter = "progid:"+filterID+"（src=""+newSrc+"",sizingMethod="crop"）";
// Replace the old （existing） with the new （just created） element.
// oOld.parentNode.replaceChild（o,oOld）;
} else if （oOld.nodeName == "IMG"） {
var newSrc = oOld.getAttribute（"src"）.replace（".gif",".png"）;
// apply filter
oOld.src = "none.gif"; // get rid of image
oOld.style.filter = "progid:"+filterID+"（src=""+newSrc+"",sizingMethod="crop"）";
oOld.style.writingMode = "lr-tb"; // Has to be applied so filter "has layout" and is displayed. Seriously. Refer to http://msdn.microsoft.com/workshop/author/filter/reference/filters/alphaimageloader.asp？frame=true
}
}

this.pngMethod = function（o） {
// Native transparency support. Easy to implement. （woo！）
bgImage = this.getBackgroundImage（o）;
if （bgImage） {
// set background image, replacing .gif
o.style.backgroundImage = "url（"+bgImage.replace（".gif",".png"）+"）";
} else if （o.nodeName == "IMG"） {
o.src = o.src.replace（".gif",".png"）;
} else if （！this.isMac） {
// window.status = "PNGHandler.applyPNG（）: Node is not a DIV or IMG.";
}
}

this.getBackgroundImage = function（o） {
var b, i1; // background-related variables
var bgUrl = null;

if （o.nodeName == "DIV" && ！（this.isIE && this.isMac）） { // ie:mac PNG support broken for DIVs with PNG backgrounds
if （document.defaultView） {
if （document.defaultView.getComputedStyle） {
b = document.defaultView.getComputedStyle（o,""）.getPropertyValue（"background-image"）;
i1 = b.indexOf（"url（"）+4;
bgUrl = b.substr（i1,b.length-i1-1）;
} else {
// no computed style
}
} else {
// no default view
}
}
return bgUrl;
}

this.supportTest = function（） {
// Determine method to use.
// IE 5.5+/win32: filter

if （this.isIE && this.isWin && this.ver >= 5.5） {
// IE proprietary filter method （via DXFilter）
self.transform = self.filterMethod;
} else if （！this.isIE && this.ver < 5） {
self.transform = null;
// No PNG support or broken support
// Leave existing content as-is
} else if （！this.isIE && this.ver >= 5 || （this.isIE && this.isMac && this.ver >= 5）） { // version 5+ browser （not IE）, or IE:mac 5+
self.transform = self.pngMethod;
} else {
// Presumably no PNG support. GIF used instead.
self.transform = null;
return false;
}
return true;
}

this.init = function（） {
if （this.supportTest（）） {
this.elements = this.getElementsByClassName（"png"）;
for （var i=0; i<this.elements.length; i++） {
this.transform（this.elements[i]）;
}
}
}

}

// Instantiate and initialize PNG Handler

var pngHandler = new PNGHandler（）;

DEMO页HTML代码：
<html>
<head>
<title>Schillmania！ | png.js demo</title>
<script type="text/javascript" src="png.js"></script>
</head>

<body>

<！--

Don"t copy this part here, this is just for your information.

// Required under the <head> tag:

<script type="text/javascript" src="png.js"></script>

// Required in the <body> tag:

<img src="your-image.gif" class="png" style="width:XXXpx;height:YYYpx" />

// ..Where XXX and YYY are the width/height of your image. Without width/height the PNG won"t work under IE:win32.

// Required before the </body> tag （but after all of your content）:

<script type="text/javascript">
pngHandler.init（）;
</script>

// This javascript block should be put at the bottom of your page, inside the <body> and before </body>.
// It calls the library and replaces the GIF images （if applicable） before the page has loaded （and before the GIF has loaded, So the user doesn"t load 2 images for each PNG you want to replace.）
// If you don"t put it after all of your content, it may do strange things and miss some images.

-->

<h1>PNG （img）</h1>

<img src="foo.gif" alt="" class="png" style="width:220px;height:100px" />

<h1>PNG （div with background image）</h1>

<div class="png" style="width:220px;height:100px;background-image:url（foo.gif）;background-repeat:no-repeat">

</div>

<script type="text/javascript">
pngHandler.init（）;
</script>

</body>
</html>

源码及DEMO打包下载：
本地下载