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：
复制代码代码如下:
/**
* DD_belatedPNG: Adds IE6 support: PNG images for CSS background-image and HTML <IMG/>.
* Author: Drew Diller
* Email: drew.diller@gmail.com
* 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閙i Pr関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：
复制代码代码如下:
< ！--[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。