有关ie6下PNG图片背景不透明的一个js的解决办法

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：

点击查看代码

  1 /**
  2 * DD_belatedPNG: Adds IE6 support: PNG images for CSS background-image and HTML <IMG/>.
  3 * Author: Drew Diller
  4 * Email: [e-mail]
  5 * URL: http://www.dillerdesign.com/experiment/DD_belatedPNG/
  6 * Version: 0.0.8a
  7 * Licensed under the MIT License: http://dillerdesign.com/experiment/DD_belatedPNG/#license
  8 *
  9 * Example usage:
 10 * DD_belatedPNG.fix('.png_bg'); // argument is a CSS selector
 11 * DD_belatedPNG.fixPng( someNode ); // argument is an HTMLDomElement
 12 **/
 13 
 14 /*
 15 PLEASE READ:
 16 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!
 17 */
 18 
 19 /** rewrite by waitingbar 2012.1.12 
 20    为了解决IE6下透明的png图片缩小时不能完全显示问题
 21    el.vml.image.fill.type = 'tile'; 改为：
 22    el.vml.image.fill.type = 'frame';
 23 */
 24 
 25 
 26 var DD_belatedPNG = {
 27     ns: 'DD_belatedPNG',
 28     imgSize: {},
 29     delay: 10,
 30     nodesFixed: 0,
 31     createVmlNameSpace: function () { /* enable VML */
 32         if (document.namespaces && !document.namespaces[this.ns]) {
 33             document.namespaces.add(this.ns, 'urn:schemas-microsoft-com:vml');
 34         }
 35     },
 36     createVmlStyleSheet: function () { /* style VML, enable behaviors */
 37         /*
 38             Just in case lots of other developers have added
 39             lots of other stylesheets using document.createStyleSheet
 40             and hit the 31-limit mark, let's not use that method!
 41             further reading: http://msdn.microsoft.com/en-us/library/ms531194(VS.85).aspx
 42         */
 43         var screenStyleSheet, printStyleSheet;
 44         screenStyleSheet = document.createElement('style');
 45         screenStyleSheet.setAttribute('media', 'screen');
 46         document.documentElement.firstChild.insertBefore(screenStyleSheet, document.documentElement.firstChild.firstChild);
 47         if (screenStyleSheet.styleSheet) {
 48             screenStyleSheet = screenStyleSheet.styleSheet;
 49             screenStyleSheet.addRule(this.ns + '\\:*', '{behavior:url(#default#VML)}');
 50             screenStyleSheet.addRule(this.ns + '\\:shape', 'position:absolute;');
 51             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/ */
 52             this.screenStyleSheet = screenStyleSheet;
 53             
 54             /* Add a print-media stylesheet, for preventing VML artifacts from showing up in print (including preview). */
 55             /* Thanks to R閙i Pr関ost for automating this! */
 56             printStyleSheet = document.createElement('style');
 57             printStyleSheet.setAttribute('media', 'print');
 58             document.documentElement.firstChild.insertBefore(printStyleSheet, document.documentElement.firstChild.firstChild);
 59             printStyleSheet = printStyleSheet.styleSheet;
 60             printStyleSheet.addRule(this.ns + '\\:*', '{display: none !important;}');
 61             printStyleSheet.addRule('img.' + this.ns + '_sizeFinder', '{display: none !important;}');
 62         }
 63     },
 64     readPropertyChange: function () {
 65         var el, display, v;
 66         el = event.srcElement;
 67         if (!el.vmlInitiated) {
 68             return;
 69         }
 70         if (event.propertyName.search('background') != -1 || event.propertyName.search('border') != -1) {
 71             DD_belatedPNG.applyVML(el);
 72         }
 73         if (event.propertyName == 'style.display') {
 74             display = (el.currentStyle.display == 'none') ? 'none' : 'block';
 75             for (v in el.vml) {
 76                 if (el.vml.hasOwnProperty(v)) {
 77                     el.vml[v].shape.style.display = display;
 78                 }
 79             }
 80         }
 81         if (event.propertyName.search('filter') != -1) {
 82             DD_belatedPNG.vmlOpacity(el);
 83         }
 84     },
 85     vmlOpacity: function (el) {
 86         if (el.currentStyle.filter.search('lpha') != -1) {
 87             var trans = el.currentStyle.filter;
 88             trans = parseInt(trans.substring(trans.lastIndexOf('=')+1, trans.lastIndexOf(')')), 10)/100;
 89             el.vml.color.shape.style.filter = el.currentStyle.filter; /* complete guesswork */
 90             el.vml.image.fill.opacity = trans; /* complete guesswork */
 91         }
 92     },
 93     handlePseudoHover: function (el) {
 94         setTimeout(function () { /* wouldn't work as intended without setTimeout */
 95             DD_belatedPNG.applyVML(el);
 96         }, 1);
 97     },
 98     /**
 99     * This is the method to use in a document.
100     * @param {String} selector - REQUIRED - a CSS selector, such as '#doc .container'
101     **/
102     fix: function (selector) {
103         if (this.screenStyleSheet) {
104             var selectors, i;
105             selectors = selector.split(','); /* multiple selectors supported, no need for multiple calls to this anymore */
106             for (i=0; i<selectors.length; i++) {
107                 this.screenStyleSheet.addRule(selectors[i], 'behavior:expression(DD_belatedPNG.fixPng(this))'); /* seems to execute the function without adding it to the stylesheet - interesting... */
108             }
109         }
110     },
111     applyVML: function (el) {
112         el.runtimeStyle.cssText = '';
113         this.vmlFill(el);
114         this.vmlOffsets(el);
115         this.vmlOpacity(el);
116         if (el.isImg) {
117             this.copyImageBorders(el);
118         }
119     },
120     attachHandlers: function (el) {
121         var self, handlers, handler, moreForAs, a, h;
122         self = this;
123         handlers = {resize: 'vmlOffsets', move: 'vmlOffsets'};
124         if (el.nodeName == 'A') {
125             moreForAs = {mouseleave: 'handlePseudoHover', mouseenter: 'handlePseudoHover', focus: 'handlePseudoHover', blur: 'handlePseudoHover'};
126             for (a in moreForAs) {            
127                 if (moreForAs.hasOwnProperty(a)) {
128                     handlers[a] = moreForAs[a];
129                 }
130             }
131         }
132         for (h in handlers) {
133             if (handlers.hasOwnProperty(h)) {
134                 handler = function () {
135                     self[handlers[h]](el);
136                 };
137                 el.attachEvent('on' + h, handler);
138             }
139         }
140         el.attachEvent('onpropertychange', this.readPropertyChange);
141     },
142     giveLayout: function (el) {
143         el.style.zoom = 1;
144         if (el.currentStyle.position == 'static') {
145             el.style.position = 'relative';
146         }
147     },
148     copyImageBorders: function (el) {
149         var styles, s;
150         styles = {'borderStyle':true, 'borderWidth':true, 'borderColor':true};
151         for (s in styles) {
152             if (styles.hasOwnProperty(s)) {
153                 el.vml.color.shape.style[s] = el.currentStyle[s];
154             }
155         }
156     },
157     vmlFill: function (el) {
158         if (!el.currentStyle) {
159             return;
160         } else {
161             var elStyle, noImg, lib, v, img, imgLoaded;
162             elStyle = el.currentStyle;
163         }
164         for (v in el.vml) {
165             if (el.vml.hasOwnProperty(v)) {
166                 el.vml[v].shape.style.zIndex = elStyle.zIndex;
167             }
168         }
169         el.runtimeStyle.backgroundColor = '';
170         el.runtimeStyle.backgroundImage = '';
171         noImg = true;
172         if (elStyle.backgroundImage != 'none' || el.isImg) {
173             if (!el.isImg) {
174                 el.vmlBg = elStyle.backgroundImage;
175                 el.vmlBg = el.vmlBg.substr(5, el.vmlBg.lastIndexOf('")')-5);
176             }
177             else {
178                 el.vmlBg = el.src;
179             }
180             lib = this;
181             if (!lib.imgSize[el.vmlBg]) { /* determine size of loaded image */
182                 img = document.createElement('img');
183                 lib.imgSize[el.vmlBg] = img;
184                 img.className = lib.ns + '_sizeFinder';
185                 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! */
186                 imgLoaded = function () {
187                     this.width = this.offsetWidth; /* weird cache-busting requirement! */
188                     this.height = this.offsetHeight;
189                     lib.vmlOffsets(el);
190                 };
191                 img.attachEvent('onload', imgLoaded);
192                 img.src = el.vmlBg;
193                 img.removeAttribute('width');
194                 img.removeAttribute('height');
195                 document.body.insertBefore(img, document.body.firstChild);
196             }
197             el.vml.image.fill.src = el.vmlBg;
198             noImg = false;
199         }
200         el.vml.image.fill.on = !noImg;
201         el.vml.image.fill.color = 'none';
202         el.vml.color.shape.style.backgroundColor = elStyle.backgroundColor;
203         el.runtimeStyle.backgroundImage = 'none';
204         el.runtimeStyle.backgroundColor = 'transparent';
205     },
206     /* 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 */
207     vmlOffsets: function (el) {
208         var thisStyle, size, fudge, makeVisible, bg, bgR, dC, altC, b, c, v;
209         thisStyle = el.currentStyle;
210         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};
211         fudge = (size.L + size.bLW == 1) ? 1 : 0;
212         /* vml shape, left, top, width, height, origin */
213         makeVisible = function (vml, l, t, w, h, o) {
214             vml.coordsize = w+','+h;
215             vml.coordorigin = o+','+o;
216             vml.path = 'm0,0l'+w+',0l'+w+','+h+'l0,'+h+' xe';
217             vml.style.width = w + 'px';
218             vml.style.height = h + 'px';
219             vml.style.left = l + 'px';
220             vml.style.top = t + 'px';
221         };
222         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);
223         makeVisible(el.vml.image.shape, (size.L + size.bLW), (size.T + size.bTW), (size.W), (size.H), 1 );
224         bg = {'X':0, 'Y':0};
225         if (el.isImg) {
226             bg.X = parseInt(thisStyle.paddingLeft, 10) + 1;
227             bg.Y = parseInt(thisStyle.paddingTop, 10) + 1;
228         }
229         else {
230             for (b in bg) {
231                 if (bg.hasOwnProperty(b)) {
232                     this.figurePercentage(bg, size, b, thisStyle['backgroundPosition'+b]);
233                 }
234             }
235         }
236         el.vml.image.fill.position = (bg.X/size.W) + ',' + (bg.Y/size.H);
237         bgR = thisStyle.backgroundRepeat;
238         dC = {'T':1, 'R':size.W+fudge, 'B':size.H, 'L':1+fudge}; /* these are defaults for repeat of any kind */
239         altC = { 'X': {'b1': 'L', 'b2': 'R', 'd': 'W'}, 'Y': {'b1': 'T', 'b2': 'B', 'd': 'H'} };
240         if (bgR != 'repeat' || el.isImg) {
241             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 */
242             if (bgR.search('repeat-') != -1) { /* now let's revert to dC for repeat-x or repeat-y */
243                 v = bgR.split('repeat-')[1].toUpperCase();
244                 c[altC[v].b1] = 1;
245                 c[altC[v].b2] = size[altC[v].d];
246             }
247             if (c.B > size.H) {
248                 c.B = size.H;
249             }
250             el.vml.image.shape.style.clip = 'rect('+c.T+'px '+(c.R+fudge)+'px '+c.B+'px '+(c.L+fudge)+'px)';
251         }
252         else {
253             el.vml.image.shape.style.clip = 'rect('+dC.T+'px '+dC.R+'px '+dC.B+'px '+dC.L+'px)';
254         }
255     },
256     figurePercentage: function (bg, size, axis, position) {
257         var horizontal, fraction;
258         fraction = true;
259         horizontal = (axis == 'X');
260         switch(position) {
261             case 'left':
262             case 'top':
263                 bg[axis] = 0;
264                 break;
265             case 'center':
266                 bg[axis] = 0.5;
267                 break;
268             case 'right':
269             case 'bottom':
270                 bg[axis] = 1;
271                 break;
272             default:
273                 if (position.search('%') != -1) {
274                     bg[axis] = parseInt(position, 10) / 100;
275                 }
276                 else {
277                     fraction = false;
278                 }
279         }
280         bg[axis] = Math.ceil(  fraction ? ( (size[horizontal?'W': 'H'] * bg[axis]) - (size[horizontal?'w': 'h'] * bg[axis]) ) : parseInt(position, 10)  );
281         if (bg[axis] % 2 === 0) {
282             bg[axis]++;
283         }
284         return bg[axis];
285     },
286     fixPng: function (el) {
287         el.style.behavior = 'none';
288         var lib, els, nodeStr, v, e;
289         if (el.nodeName == 'BODY' || el.nodeName == 'TD' || el.nodeName == 'TR') { /* elements not supported yet */
290             return;
291         }
292         el.isImg = false;
293         if (el.nodeName == 'IMG') {
294             if(el.src.toLowerCase().search(/\.png$/) != -1) {
295                 el.isImg = true;
296                 el.style.visibility = 'hidden';
297             }
298             else {
299                 return;
300             }
301         }
302         else if (el.currentStyle.backgroundImage.toLowerCase().search('.png') == -1) {
303             return;
304         }
305         lib = DD_belatedPNG;
306         el.vml = {color: {}, image: {}};
307         els = {shape: {}, fill: {}};
308         for (v in el.vml) {
309             if (el.vml.hasOwnProperty(v)) {
310                 for (e in els) {
311                     if (els.hasOwnProperty(e)) {
312                         nodeStr = lib.ns + ':' + e;
313                         el.vml[v][e] = document.createElement(nodeStr);
314                     }
315                 }
316                 el.vml[v].shape.stroked = false;
317                 el.vml[v].shape.appendChild(el.vml[v].fill);
318                 el.parentNode.insertBefore(el.vml[v].shape, el);
319             }
320         }
321         el.vml.image.shape.fillcolor = 'none'; /* Don't show blank white shapeangle when waiting for image to load. */
322         //el.vml.image.fill.type = 'tile'; /* Makes image show up. */
323         el.vml.image.fill.type = 'frame'; /* 2012.1.12 */
324         el.vml.color.fill.on = false; /* Actually going to apply vml element's style.backgroundColor, so hide the whiteness. */
325         lib.attachHandlers(el);
326         lib.giveLayout(el);
327         lib.giveLayout(el.offsetParent);
328         el.vmlInitiated = true;
329         lib.applyVML(el); /* Render! */
330     }
331 };
332 try {
333     document.execCommand("BackgroundImageCache", false, true); /* TredoSoft Multiple IE doesn't like this, so try{} it */
334 } catch(r) {}
335 DD_belatedPNG.createVmlNameSpace();
336 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。