ie6下png图片背景不透明的解决办法使用js实现

我们时常在使用png图片的时候，在ie6下发生背景不透明的问题，下面给大家介绍下一个js解决的方式。
首先我们要用到一个js，代码如下：

/** 
* DD_belatedPNG: Adds IE6 support: PNG images for CSS background-image and HTML <IMG/>. 
* Author: Drew Diller 
* Email: [e-mail] 
* URL: http://www.dillerdesign.com/experiment/DD_belatedPNG/ 
* Version: 0.0.8a 
* Licensed under the MIT License: http://dillerdesign.com/experiment/DD_belatedPNG/#license 
* 
* Example usage: 
* DD_belatedPNG.fix('.png_bg'); // argument is a CSS selector 
* DD_belatedPNG.fixPng( someNode ); // argument is an HTMLDomElement 
**/ 
/* 
PLEASE READ: 
Absolutely everything in this script is SILLY. I know this. IE's rendering of certain pixels doesn't make sense, so neither does this code! 
*/ 
/** rewrite by waitingbar 2012.1.12 
为了解决IE6下透明的png图片缩小时不能完全显示问题 
el.vml.image.fill.type = 'tile'; 改为： 
el.vml.image.fill.type = 'frame'; 
*/ var DD_belatedPNG = { 
ns: 'DD_belatedPNG', 
imgSize: {}, 
delay: 10, 
nodesFixed: 0, 
createVmlNameSpace: function () { /* enable VML */ 
if (document.namespaces && !document.namespaces[this.ns]) { 
document.namespaces.add(this.ns, 'urn:schemas-microsoft-com:vml'); 
} 
}, 
createVmlStyleSheet: function () { /* style VML, enable behaviors */ 
/* 
Just in case lots of other developers have added 
lots of other stylesheets using document.createStyleSheet 
and hit the 31-limit mark, let's not use that method! 
further reading: http://msdn.microsoft.com/en-us/library/ms531194(VS.85).aspx 
*/ 
var screenStyleSheet, printStyleSheet; 
screenStyleSheet = document.createElement('style'); 
screenStyleSheet.setAttribute('media', 'screen'); 
document.documentElement.firstChild.insertBefore(screenStyleSheet, document.documentElement.firstChild.firstChild); 
if (screenStyleSheet.styleSheet) { 
screenStyleSheet = screenStyleSheet.styleSheet; 
screenStyleSheet.addRule(this.ns + '\\:*', '{behavior:url(#default#VML)}'); 
screenStyleSheet.addRule(this.ns + '\\:shape', 'position:absolute;'); 
screenStyleSheet.addRule('img.' + this.ns + '_sizeFinder', 'behavior:none; border:none; position:absolute; z-index:-1; top:-10000px; visibility:hidden;'); /* large negative top value for avoiding vertical scrollbars for large images, suggested by James O'Brien, http://www.thanatopsic.org/hendrik/ */ 
this.screenStyleSheet = screenStyleSheet; 
/* Add a print-media stylesheet, for preventing VML artifacts from showing up in print (including preview). */ 
/* Thanks to R?i Pr?ost for automating this! */ 
printStyleSheet = document.createElement('style'); 
printStyleSheet.setAttribute('media', 'print'); 
document.documentElement.firstChild.insertBefore(printStyleSheet, document.documentElement.firstChild.firstChild); 
printStyleSheet = printStyleSheet.styleSheet; 
printStyleSheet.addRule(this.ns + '\\:*', '{display: none !important;}'); 
printStyleSheet.addRule('img.' + this.ns + '_sizeFinder', '{display: none !important;}'); 
} 
}, 
readPropertyChange: function () { 
var el, display, v; 
el = event.srcElement; 
if (!el.vmlInitiated) { 
return; 
} 
if (event.propertyName.search('background') != -1 || event.propertyName.search('border') != -1) { 
DD_belatedPNG.applyVML(el); 
} 
if (event.propertyName == 'style.display') { 
display = (el.currentStyle.display == 'none') ? 'none' : 'block'; 
for (v in el.vml) { 
if (el.vml.hasOwnProperty(v)) { 
el.vml[v].shape.style.display = display; 
} 
} 
} 
if (event.propertyName.search('filter') != -1) { 
DD_belatedPNG.vmlOpacity(el); 
} 
}, 
vmlOpacity: function (el) { 
if (el.currentStyle.filter.search('lpha') != -1) { 
var trans = el.currentStyle.filter; 
trans = parseInt(trans.substring(trans.lastIndexOf('=')+1, trans.lastIndexOf(')')), 10)/100; 
el.vml.color.shape.style.filter = el.currentStyle.filter; /* complete guesswork */ 
el.vml.image.fill.opacity = trans; /* complete guesswork */ 
} 
}, 
handlePseudoHover: function (el) { 
setTimeout(function () { /* wouldn't work as intended without setTimeout */ 
DD_belatedPNG.applyVML(el); 
}, 1); 
}, 
/** 
* This is the method to use in a document. 
* @param {String} selector - REQUIRED - a CSS selector, such as '#doc .container' 
**/ 
fix: function (selector) { 
if (this.screenStyleSheet) { 
var selectors, i; 
selectors = selector.split(','); /* multiple selectors supported, no need for multiple calls to this anymore */ 
for (i=0; i<selectors.length; i++) { 
this.screenStyleSheet.addRule(selectors[i], 'behavior:expression(DD_belatedPNG.fixPng(this))'); /* seems to execute the function without adding it to the stylesheet - interesting... */ 
} 
} 
}, 
applyVML: function (el) { 
el.runtimeStyle.cssText = ''; 
this.vmlFill(el); 
this.vmlOffsets(el); 
this.vmlOpacity(el); 
if (el.isImg) { 
this.copyImageBorders(el); 
} 
}, 
attachHandlers: function (el) { 
var self, handlers, handler, moreForAs, a, h; 
self = this; 
handlers = {resize: 'vmlOffsets', move: 'vmlOffsets'}; 
if (el.nodeName == 'A') { 
moreForAs = {mouseleave: 'handlePseudoHover', mouseenter: 'handlePseudoHover', focus: 'handlePseudoHover', blur: 'handlePseudoHover'}; 
for (a in moreForAs) { 
if (moreForAs.hasOwnProperty(a)) { 
handlers[a] = moreForAs[a]; 
} 
} 
} 
for (h in handlers) { 
if (handlers.hasOwnProperty(h)) { 
handler = function () { 
self[handlers[h]](el); 
}; 
el.attachEvent('on' + h, handler); 
} 
} 
el.attachEvent('onpropertychange', this.readPropertyChange); 
}, 
giveLayout: function (el) { 
el.style.zoom = 1; 
if (el.currentStyle.position == 'static') { 
el.style.position = 'relative'; 
} 
}, 
copyImageBorders: function (el) { 
var styles, s; 
styles = {'borderStyle':true, 'borderWidth':true, 'borderColor':true}; 
for (s in styles) { 
if (styles.hasOwnProperty(s)) { 
el.vml.color.shape.style[s] = el.currentStyle[s]; 
} 
} 
}, 
vmlFill: function (el) { 
if (!el.currentStyle) { 
return; 
} else { 
var elStyle, noImg, lib, v, img, imgLoaded; 
elStyle = el.currentStyle; 
} 
for (v in el.vml) { 
if (el.vml.hasOwnProperty(v)) { 
el.vml[v].shape.style.zIndex = elStyle.zIndex; 
} 
} 
el.runtimeStyle.backgroundColor = ''; 
el.runtimeStyle.backgroundImage = ''; 
noImg = true; 
if (elStyle.backgroundImage != 'none' || el.isImg) { 
if (!el.isImg) { 
el.vmlBg = elStyle.backgroundImage; 
el.vmlBg = el.vmlBg.substr(5, el.vmlBg.lastIndexOf('")')-5); 
} 
else { 
el.vmlBg = el.src; 
} 
lib = this; 
if (!lib.imgSize[el.vmlBg]) { /* determine size of loaded image */ 
img = document.createElement('img'); 
lib.imgSize[el.vmlBg] = img; 
img.className = lib.ns + '_sizeFinder'; 
img.runtimeStyle.cssText = 'behavior:none; position:absolute; left:-10000px; top:-10000px; border:none; margin:0; padding:0;'; /* make sure to set behavior to none to prevent accidental matching of the helper elements! */ 
imgLoaded = function () { 
this.width = this.offsetWidth; /* weird cache-busting requirement! */ 
this.height = this.offsetHeight; 
lib.vmlOffsets(el); 
}; 
img.attachEvent('onload', imgLoaded); 
img.src = el.vmlBg; 
img.removeAttribute('width'); 
img.removeAttribute('height'); 
document.body.insertBefore(img, document.body.firstChild); 
} 
el.vml.image.fill.src = el.vmlBg; 
noImg = false; 
} 
el.vml.image.fill.on = !noImg; 
el.vml.image.fill.color = 'none'; 
el.vml.color.shape.style.backgroundColor = elStyle.backgroundColor; 
el.runtimeStyle.backgroundImage = 'none'; 
el.runtimeStyle.backgroundColor = 'transparent'; 
}, 
/* IE can't figure out what do when the offsetLeft and the clientLeft add up to 1, and the VML ends up getting fuzzy... so we have to push/enlarge things by 1 pixel and then clip off the excess */ 
vmlOffsets: function (el) { 
var thisStyle, size, fudge, makeVisible, bg, bgR, dC, altC, b, c, v; 
thisStyle = el.currentStyle; 
size = {'W':el.clientWidth+1, 'H':el.clientHeight+1, 'w':this.imgSize[el.vmlBg].width, 'h':this.imgSize[el.vmlBg].height, 'L':el.offsetLeft, 'T':el.offsetTop, 'bLW':el.clientLeft, 'bTW':el.clientTop}; 
fudge = (size.L + size.bLW == 1) ? 1 : 0; 
/* vml shape, left, top, width, height, origin */ 
makeVisible = function (vml, l, t, w, h, o) { 
vml.coordsize = w+','+h; 
vml.coordorigin = o+','+o; 
vml.path = 'm0,0l'+w+',0l'+w+','+h+'l0,'+h+' xe'; 
vml.style.width = w + 'px'; 
vml.style.height = h + 'px'; 
vml.style.left = l + 'px'; 
vml.style.top = t + 'px'; 
}; 
makeVisible(el.vml.color.shape, (size.L + (el.isImg ? 0 : size.bLW)), (size.T + (el.isImg ? 0 : size.bTW)), (size.W-1), (size.H-1), 0); 
makeVisible(el.vml.image.shape, (size.L + size.bLW), (size.T + size.bTW), (size.W), (size.H), 1 ); 
bg = {'X':0, 'Y':0}; 
if (el.isImg) { 
bg.X = parseInt(thisStyle.paddingLeft, 10) + 1; 
bg.Y = parseInt(thisStyle.paddingTop, 10) + 1; 
} 
else { 
for (b in bg) { 
if (bg.hasOwnProperty(b)) { 
this.figurePercentage(bg, size, b, thisStyle['backgroundPosition'+b]); 
} 
} 
} 
el.vml.image.fill.position = (bg.X/size.W) + ',' + (bg.Y/size.H); 
bgR = thisStyle.backgroundRepeat; 
dC = {'T':1, 'R':size.W+fudge, 'B':size.H, 'L':1+fudge}; /* these are defaults for repeat of any kind */ 
altC = { 'X': {'b1': 'L', 'b2': 'R', 'd': 'W'}, 'Y': {'b1': 'T', 'b2': 'B', 'd': 'H'} }; 
if (bgR != 'repeat' || el.isImg) { 
c = {'T':(bg.Y), 'R':(bg.X+size.w), 'B':(bg.Y+size.h), 'L':(bg.X)}; /* these are defaults for no-repeat - clips down to the image location */ 
if (bgR.search('repeat-') != -1) { /* now let's revert to dC for repeat-x or repeat-y */ 
v = bgR.split('repeat-')[1].toUpperCase(); 
c[altC[v].b1] = 1; 
c[altC[v].b2] = size[altC[v].d]; 
} 
if (c.B > size.H) { 
c.B = size.H; 
} 
el.vml.image.shape.style.clip = 'rect('+c.T+'px '+(c.R+fudge)+'px '+c.B+'px '+(c.L+fudge)+'px)'; 
} 
else { 
el.vml.image.shape.style.clip = 'rect('+dC.T+'px '+dC.R+'px '+dC.B+'px '+dC.L+'px)'; 
} 
}, 
figurePercentage: function (bg, size, axis, position) { 
var horizontal, fraction; 
fraction = true; 
horizontal = (axis == 'X'); 
switch(position) { 
case 'left': 
case 'top': 
bg[axis] = 0; 
break; 
case 'center': 
bg[axis] = 0.5; 
break; 
case 'right': 
case 'bottom': 
bg[axis] = 1; 
break; 
default: 
if (position.search('%') != -1) { 
bg[axis] = parseInt(position, 10) / 100; 
} 
else { 
fraction = false; 
} 
} 
bg[axis] = Math.ceil( fraction ? ( (size[horizontal?'W': 'H'] * bg[axis]) - (size[horizontal?'w': 'h'] * bg[axis]) ) : parseInt(position, 10) ); 
if (bg[axis] % 2 === 0) { 
bg[axis]++; 
} 
return bg[axis]; 
}, 
fixPng: function (el) { 
el.style.behavior = 'none'; 
var lib, els, nodeStr, v, e; 
if (el.nodeName == 'BODY' || el.nodeName == 'TD' || el.nodeName == 'TR') { /* elements not supported yet */ 
return; 
} 
el.isImg = false; 
if (el.nodeName == 'IMG') { 
if(el.src.toLowerCase().search(/\.png$/) != -1) { 
el.isImg = true; 
el.style.visibility = 'hidden'; 
} 
else { 
return; 
} 
} 
else if (el.currentStyle.backgroundImage.toLowerCase().search('.png') == -1) { 
return; 
} 
lib = DD_belatedPNG; 
el.vml = {color: {}, image: {}}; 
els = {shape: {}, fill: {}}; 
for (v in el.vml) { 
if (el.vml.hasOwnProperty(v)) { 
for (e in els) { 
if (els.hasOwnProperty(e)) { 
nodeStr = lib.ns + ':' + e; 
el.vml[v][e] = document.createElement(nodeStr); 
} 
} 
el.vml[v].shape.stroked = false; 
el.vml[v].shape.appendChild(el.vml[v].fill); 
el.parentNode.insertBefore(el.vml[v].shape, el); 
} 
} 
el.vml.image.shape.fillcolor = 'none'; /* Don't show blank white shapeangle when waiting for image to load. */ 
//el.vml.image.fill.type = 'tile'; /* Makes image show up. */ 
el.vml.image.fill.type = 'frame'; /* 2012.1.12 */ 
el.vml.color.fill.on = false; /* Actually going to apply vml element's style.backgroundColor, so hide the whiteness. */ 
lib.attachHandlers(el); 
lib.giveLayout(el); 
lib.giveLayout(el.offsetParent); 
el.vmlInitiated = true; 
lib.applyVML(el); /* Render! */ 
} 
}; 
try { 
document.execCommand("BackgroundImageCache", false, true); /* TredoSoft Multiple IE doesn't like this, so try{} it */ 
} catch(r) {} 
DD_belatedPNG.createVmlNameSpace(); 
DD_belatedPNG.createVmlStyleSheet();

下面我们来看怎么使用这个js：
DD_belatedPNG是一款完美解决IE6下的PNG透明JS插件，DD_belatedPNG使用了微软的VML语言对PNG图片进行重新绘制，以达到半透明的效果，并且能支持background-position和background-repeat属性，支持伪类。在众多的ie6下png透明问题上，DD_belatedPNG是最好的解决方案，其它的都有很多负作用。

使用方法：

< !--[if IE 6]><script src="DD_belatedPNG.js"></script><script> DD_belatedPNG.fix('.png_bg');</script><![endif]-->

引用函数是DD_belatedPNG.fix()，括号里的 *表示所有css选择器.png_bg 改成你的css选择器名称。