使用DD_belatedPNG完美解决png在ie6下不透明的bug

解决IE6下图片透明的方法有很多很多，可以把图片保存成为gif格式、png8格式 alpha下透明，但是图片会严重失真，有毛边等等，这都不是最好的方法。目前最流行的也是国内大型网站使用最多的方法就是使用DD_belatedPNG插件来解决png透明。

 火狐浏览器下结果：

IE6下的结果：




DD_belatedPNG.js插件代码：

/**
* 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: 0.0.7a
* 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!
*/

var DD_belatedPNG = {

    ns: 'DD_belatedPNG',
    imgSize: {},
    
    createVmlNameSpace: function() { /* enable VML */
        if (document.namespaces && !document.namespaces[this.ns]) {
          document.namespaces.add(this.ns, 'urn:schemas-microsoft-com:vml');
        }
        if (window.attachEvent) {
            window.attachEvent('onbeforeunload', function() {
                DD_belatedPNG = null;
            });
        }
    },
    
    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 style = document.createElement('style');
        document.documentElement.firstChild.insertBefore(style, document.documentElement.firstChild.firstChild);
        var styleSheet = style.styleSheet;
        styleSheet.addRule(this.ns + '\\:*', '{behavior:url(#default#VML)}');
        styleSheet.addRule(this.ns + '\\:shape', 'position:absolute;');
        styleSheet.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.styleSheet = styleSheet;
    },
    
    readPropertyChange: function() {
        var el = event.srcElement;
        if (event.propertyName.search('background') != -1 || event.propertyName.search('border') != -1) {
            DD_belatedPNG.applyVML(el);
        }
        if (event.propertyName == 'style.display') {
            var display = (el.currentStyle.display == 'none') ? 'none' : 'block';
            for (var v in el.vml) {
                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) {
        var selectors = selector.split(','); /* multiple selectors supported, no need for multiple calls to this anymore */
        for (var i=0; i<selectors.length; i++) {
            this.styleSheet.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 = this;
        var handlers = {resize: 'vmlOffsets', move: 'vmlOffsets'};
        if (el.nodeName == 'A') {
            var moreForAs = {mouseleave: 'handlePseudoHover', mouseenter: 'handlePseudoHover', focus: 'handlePseudoHover', blur: 'handlePseudoHover'};
            for (var a in moreForAs) {
                handlers[a] = moreForAs[a];
            }
        }
        for (var h in handlers) {
            el.attachEvent('on' + h, function() {
                self[handlers[h]](el);
            });
        }
        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 = {'borderStyle':true, 'borderWidth':true, 'borderColor':true};
        for (var s in styles) {
            el.vml.color.shape.style[s] = el.currentStyle[s];
        }
    },
    
    vmlFill: function(el) {
        if (!el.currentStyle) {
            return;
        } else {
            var elStyle = el.currentStyle;
        }
        for (var v in el.vml) {
            el.vml[v].shape.style.zIndex = elStyle.zIndex;
        }
        el.runtimeStyle.backgroundColor = '';
        el.runtimeStyle.backgroundImage = '';
        var noColor = (elStyle.backgroundColor == 'transparent');
        var 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;
            }
            var lib = this;
            if (!lib.imgSize[el.vmlBg]) { /* determine size of loaded image */
                var 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;'; /* make sure to set behavior to none to prevent accidental matching of the helper elements! */
                img.attachEvent('onload', function() {
                    this.width = this.offsetWidth; /* weird cache-busting requirement! */
                    this.height = this.offsetHeight;
                    lib.vmlOffsets(el);
                });
                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 = el.currentStyle;
        var 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};
        var fudge = (size.L + size.bLW == 1) ? 1 : 0;
        
        /* vml shape, left, top, width, height, origin */
        var 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);
        
        var bg = {'X':0, 'Y':0};
        var figurePercentage = function(axis, position) {
            var fraction = true;
            switch(position) {
                case 'left':
                case 'top':
                    bg[axis] = 0;
                    break;
                case 'center':
                    bg[axis] = .5;
                    break;
                case 'right':
                case 'bottom':
                    bg[axis] = 1;
                    break;
                default:
                    if (position.search('%') != -1) {
                        bg[axis] = parseInt(position)*.01;
                    }
                    else {
                        fraction = false;
                    }
            }
            var horz = (axis == 'X');
            bg[axis] = Math.ceil(fraction ? ( (size[horz?'W': 'H'] * bg[axis]) - (size[horz?'w': 'h'] * bg[axis]) ) : parseInt(position));
            if (bg[axis] == 0) {
                bg[axis]++;
            }
        };
        for (var b in bg) {
            figurePercentage(b, thisStyle['backgroundPosition'+b]);
        }
        
        el.vml.image.fill.position = (bg.X/size.W) + ',' + (bg.Y/size.H);
        
        var bgR = thisStyle.backgroundRepeat;
        var dC = {'T':1, 'R':size.W+fudge, 'B':size.H, 'L':1+fudge}; /* these are defaults for repeat of any kind */
        var altC = { 'X': {'b1': 'L', 'b2': 'R', 'd': 'W'}, 'Y': {'b1': 'T', 'b2': 'B', 'd': 'H'} };
        if (bgR != 'repeat') {
            var 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 */
                var 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)';
        }
    },
    
    fixPng: function(el) {
        el.style.behavior = 'none';
        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;
        }
        var lib = DD_belatedPNG;
        el.vml = {color: {}, image: {}};
        var els = {shape: {}, fill: {}};
        for (var r in el.vml) {
            for (var e in els) {
                var nodeStr = lib.ns + ':' + e;
                el.vml[r][e] = document.createElement(nodeStr);
            }
            el.vml[r].shape.stroked = false;
            el.vml[r].shape.appendChild(el.vml[r].fill);
            el.parentNode.insertBefore(el.vml[r].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'; /* Ze magic!! Makes image show up. */
        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);
        
        /* set up element */
        lib.applyVML(el);
    }
    
};
try {
    document.execCommand("BackgroundImageCache", false, true); /* TredoSoft Multiple IE doesn't like this, so try{} it */
} catch(r) {}
DD_belatedPNG.createVmlNameSpace();
DD_belatedPNG.createVmlStyleSheet();

html代码：

<!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" dir="ltr" lang="zh-CN">
<head>    
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
    <title>png透明插件</title>    
<style type="text/css">
*{ padding:0; margin:0;}

.main_w{ width:1000px; height:200px; margin:0 auto; background:url(tm.png) no-repeat;}

.main_black{ width:1000px; margin:40px auto; height:200px; background:#900 url(tm.png) no-repeat;}
</style>
</head>

<body>

<div class="main_w"></div> <div class="main_black"></div> <!--[if IE 6]> <script type="text/javascript" src="js/DD_belatedPNG.js"></script> <script type="text/javascript"> DD_belatedPNG.fix('.main_black,.main_w'); </script> <![endif]--> </body> </html>

使用方法：

引用函数是 DD_belatedPNG.fix() , 括号里分别填写应用PNG的CSS选择器（可使用ID选择器和类选择器）和应用类型（分为img和background两种）。

如DD_belatedPNG.fix(‘#box-one, img’) 或者 DD_belatedPNG.fix(‘.header, background’) 等。

这些可以简写成 DD_belatedPNG.fix(‘#box-one, .header, img,background’);  。

更多选择器的如 DD_belatedPNG.fix(‘#box-one, .header,#footer,.box-two a:hover, img,background’);  等等。

另外，为解决IE6下背景图闪烁，可以在页面中添加如下脚本

<!--[if IE 6]>
<script type=”text/javascript”>
// <![CDATA[
if((window.navigator.appName.toUpperCase().indexOf("MICROSOFT")>=0)&&(document.execCommand))
try{
document.execCommand("BackgroundImageCache", false, true);
}
catch(e){}
// ]]>
</script>
<![endif]-->

参考原文：http://zmingcx.com/dd_belatedpng-solve-png-images-under-ie6-transparent-application-tutorial.html