IE6中 PNG 背景透明的最佳解决方案
2014-01-23 20:40
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为什么要使用 PNG 图片？
简单来说，使用 PNG 格式比起 GIF 来表现色彩更丰富，特别是表现渐变以及背景透明的渐变要比GIF格式出色很多。目前，最新的浏览器基本上都支持PNG格式。唯独有万恶的 IE6 不支持 PNG 背景透明，在 IE6 中的 PNG 背景图会显示一个灰色的背景。IE6 中 PNG 背景图片透明的方法
其实方法有很多，但网络上提供的方法也有诸多缺陷。比如不支持 css 中 backgrond-position 与 background-repeat 等，所以园子推荐你使用 DD_belatedPNG，方法如下：1.首先下载 DD_belatedPNG.js 文件，本文下方有提供下载，将此文件放置到你的网站中的 js 目录下。
2.在你使用了 PNG 背景的页面头部嵌入以下代码，一般是加在 head 区域。
1 2 3 4 5 6 7 8 | <!--[if IE 6]>
<script src="js/DD_belatedPNG.js" mce_src="DD_belatedPNG.js"></script>
<script type="text/javascript">
/* EXAMPLE */
DD_belatedPNG.fix('.png_bg');
/* 将 .png_bg 改成你应用了透明PNG的CSS选择器,例如我例子中的'.trans'*/
</script>
<![endif]--> |
需要注意的一些问题：
1.如果你放置的 DD_belatedPNG.js 路径不同的话，也需要更改上述代码中的路径。2.以上代码中的
1 | DD_belatedPNG.fix('.png_bg'); |
1 | DD_belatedPNG.fix('.png_bg1, .png_bg2'); |
12 | <!--[if IE 6]>
<script type="text/javascript" src="js/DD_belatedPNG.js" ></script>
<script type="text/javascript">
DD_belatedPNG.fix('.trans,.box a:hover');
</script>
<![endif]--> |
1 /** 2 * DD_belatedPNG: Adds IE6 support: PNG images for CSS background-image and HTML <IMG/>. 3 * Author: Drew Diller 4 * Email: drew.diller@gmail.com 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 var DD_belatedPNG = { 20 ns: 'DD_belatedPNG', 21 imgSize: {}, 22 delay: 10, 23 nodesFixed: 0, 24 createVmlNameSpace: function () { /* enable VML */ 25 if (document.namespaces && !document.namespaces[this.ns]) { 26 document.namespaces.add(this.ns, 'urn:schemas-microsoft-com:vml'); 27 } 28 }, 29 createVmlStyleSheet: function () { /* style VML, enable behaviors */ 30 /* 31 Just in case lots of other developers have added 32 lots of other stylesheets using document.createStyleSheet 33 and hit the 31-limit mark, let's not use that method! 34 further reading: http://msdn.microsoft.com/en-us/library/ms531194(VS.85).aspx 35 */ 36 var screenStyleSheet, printStyleSheet; 37 screenStyleSheet = document.createElement('style'); 38 screenStyleSheet.setAttribute('media', 'screen'); 39 document.documentElement.firstChild.insertBefore(screenStyleSheet, document.documentElement.firstChild.firstChild); 40 if (screenStyleSheet.styleSheet) { 41 screenStyleSheet = screenStyleSheet.styleSheet; 42 screenStyleSheet.addRule(this.ns + '\\:*', '{behavior:url(#default#VML)}'); 43 screenStyleSheet.addRule(this.ns + '\\:shape', 'position:absolute;'); 44 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/ */ 45 this.screenStyleSheet = screenStyleSheet; 46 47 /* Add a print-media stylesheet, for preventing VML artifacts from showing up in print (including preview). */ 48 /* Thanks to R閙i Pr関ost for automating this! */ 49 printStyleSheet = document.createElement('style'); 50 printStyleSheet.setAttribute('media', 'print'); 51 document.documentElement.firstChild.insertBefore(printStyleSheet, document.documentElement.firstChild.firstChild); 52 printStyleSheet = printStyleSheet.styleSheet; 53 printStyleSheet.addRule(this.ns + '\\:*', '{display: none !important;}'); 54 printStyleSheet.addRule('img.' + this.ns + '_sizeFinder', '{display: none !important;}'); 55 } 56 }, 57 readPropertyChange: function () { 58 var el, display, v; 59 el = event.srcElement; 60 if (!el.vmlInitiated) { 61 return; 62 } 63 if (event.propertyName.search('background') != -1 || event.propertyName.search('border') != -1) { 64 DD_belatedPNG.applyVML(el); 65 } 66 if (event.propertyName == 'style.display') { 67 display = (el.currentStyle.display == 'none') ? 'none' : 'block'; 68 for (v in el.vml) { 69 if (el.vml.hasOwnProperty(v)) { 70 el.vml[v].shape.style.display = display; 71 } 72 } 73 } 74 if (event.propertyName.search('filter') != -1) { 75 DD_belatedPNG.vmlOpacity(el); 76 } 77 }, 78 vmlOpacity: function (el) { 79 if (el.currentStyle.filter.search('lpha') != -1) { 80 var trans = el.currentStyle.filter; 81 trans = parseInt(trans.substring(trans.lastIndexOf('=')+1, trans.lastIndexOf(')')), 10)/100; 82 el.vml.color.shape.style.filter = el.currentStyle.filter; /* complete guesswork */ 83 el.vml.image.fill.opacity = trans; /* complete guesswork */ 84 } 85 }, 86 handlePseudoHover: function (el) { 87 setTimeout(function () { /* wouldn't work as intended without setTimeout */ 88 DD_belatedPNG.applyVML(el); 89 }, 1); 90 }, 91 /** 92 * This is the method to use in a document. 93 * @param {String} selector - REQUIRED - a CSS selector, such as '#doc .container' 94 **/ 95 fix: function (selector) { 96 if (this.screenStyleSheet) { 97 var selectors, i; 98 selectors = selector.split(','); /* multiple selectors supported, no need for multiple calls to this anymore */ 99 for (i=0; i<selectors.length; i++) { 100 this.screenStyleSheet.addRule(selectors[i], 'behavior:expression(DD_belatedPNG.fixPng(this))'); /* seems to execute the function without adding it to the stylesheet - interesting... */ 101 } 102 } 103 }, 104 applyVML: function (el) { 105 el.runtimeStyle.cssText = ''; 106 this.vmlFill(el); 107 this.vmlOffsets(el); 108 this.vmlOpacity(el); 109 if (el.isImg) { 110 this.copyImageBorders(el); 111 } 112 }, 113 attachHandlers: function (el) { 114 var self, handlers, handler, moreForAs, a, h; 115 self = this; 116 handlers = {resize: 'vmlOffsets', move: 'vmlOffsets'}; 117 if (el.nodeName == 'A') { 118 moreForAs = {mouseleave: 'handlePseudoHover', mouseenter: 'handlePseudoHover', focus: 'handlePseudoHover', blur: 'handlePseudoHover'}; 119 for (a in moreForAs) { 120 if (moreForAs.hasOwnProperty(a)) { 121 handlers[a] = moreForAs[a]; 122 } 123 } 124 } 125 for (h in handlers) { 126 if (handlers.hasOwnProperty(h)) { 127 handler = function () { 128 self[handlers[h]](el); 129 }; 130 el.attachEvent('on' + h, handler); 131 } 132 } 133 el.attachEvent('onpropertychange', this.readPropertyChange); 134 }, 135 giveLayout: function (el) { 136 el.style.zoom = 1; 137 if (el.currentStyle.position == 'static') { 138 var tags=el.nodeName.toLowerCase(); 139 if(tags!='html' && tags!='a'&& tags!='img'){ 140 el.style.position = 'relative' 141 }; 142 } 143 }, 144 copyImageBorders: function (el) { 145 var styles, s; 146 styles = {'borderStyle':true, 'borderWidth':true, 'borderColor':true}; 147 for (s in styles) { 148 if (styles.hasOwnProperty(s)) { 149 el.vml.color.shape.style[s] = el.currentStyle[s]; 150 } 151 } 152 }, 153 vmlFill: function (el) { 154 if (!el.currentStyle) { 155 return; 156 } else { 157 var elStyle, noImg, lib, v, img, imgLoaded; 158 elStyle = el.currentStyle; 159 } 160 for (v in el.vml) { 161 if (el.vml.hasOwnProperty(v)) { 162 el.vml[v].shape.style.zIndex = elStyle.zIndex; 163 } 164 } 165 el.runtimeStyle.backgroundColor = ''; 166 el.runtimeStyle.backgroundImage = ''; 167 noImg = true; 168 if (elStyle.backgroundImage != 'none' || el.isImg) { 169 if (!el.isImg) { 170 el.vmlBg = elStyle.backgroundImage; 171 el.vmlBg = el.vmlBg.substr(5, el.vmlBg.lastIndexOf('")')-5); 172 } 173 else { 174 el.vmlBg = el.src; 175 } 176 lib = this; 177 if (!lib.imgSize[el.vmlBg]) { /* determine size of loaded image */ 178 img = document.createElement('img'); 179 lib.imgSize[el.vmlBg] = img; 180 img.className = lib.ns + '_sizeFinder'; 181 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! */ 182 imgLoaded = function () { 183 this.width = this.offsetWidth; /* weird cache-busting requirement! */ 184 this.height = this.offsetHeight; 185 lib.vmlOffsets(el); 186 }; 187 img.attachEvent('onload', imgLoaded); 188 img.src = el.vmlBg; 189 img.removeAttribute('width'); 190 img.removeAttribute('height'); 191 document.body.insertBefore(img, document.body.firstChild); 192 } 193 el.vml.image.fill.src = el.vmlBg; 194 noImg = false; 195 } 196 el.vml.image.fill.on = !noImg; 197 el.vml.image.fill.color = 'none'; 198 el.vml.color.shape.style.backgroundColor = elStyle.backgroundColor; 199 el.runtimeStyle.backgroundImage = 'none'; 200 el.runtimeStyle.backgroundColor = 'transparent'; 201 }, 202 /* 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 */ 203 vmlOffsets: function (el) { 204 var thisStyle, size, fudge, makeVisible, bg, bgR, dC, altC, b, c, v; 205 thisStyle = el.currentStyle; 206 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}; 207 fudge = (size.L + size.bLW == 1) ? 1 : 0; 208 /* vml shape, left, top, width, height, origin */ 209 makeVisible = function (vml, l, t, w, h, o) { 210 vml.coordsize = w+','+h; 211 vml.coordorigin = o+','+o; 212 vml.path = 'm0,0l'+w+',0l'+w+','+h+'l0,'+h+' xe'; 213 vml.style.width = w + 'px'; 214 vml.style.height = h + 'px'; 215 vml.style.left = l + 'px'; 216 vml.style.top = t + 'px'; 217 }; 218 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); 219 makeVisible(el.vml.image.shape, (size.L + size.bLW), (size.T + size.bTW), (size.W), (size.H), 1 ); 220 bg = {'X':0, 'Y':0}; 221 if (el.isImg) { 222 bg.X = parseInt(thisStyle.paddingLeft, 10) + 1; 223 bg.Y = parseInt(thisStyle.paddingTop, 10) + 1; 224 } 225 else { 226 for (b in bg) { 227 if (bg.hasOwnProperty(b)) { 228 this.figurePercentage(bg, size, b, thisStyle['backgroundPosition'+b]); 229 } 230 } 231 } 232 el.vml.image.fill.position = (bg.X/size.W) + ',' + (bg.Y/size.H); 233 bgR = thisStyle.backgroundRepeat; 234 dC = {'T':1, 'R':size.W+fudge, 'B':size.H, 'L':1+fudge}; /* these are defaults for repeat of any kind */ 235 altC = { 'X': {'b1': 'L', 'b2': 'R', 'd': 'W'}, 'Y': {'b1': 'T', 'b2': 'B', 'd': 'H'} }; 236 if (bgR != 'repeat' || el.isImg) { 237 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 */ 238 if (bgR.search('repeat-') != -1) { /* now let's revert to dC for repeat-x or repeat-y */ 239 v = bgR.split('repeat-')[1].toUpperCase(); 240 c[altC[v].b1] = 1; 241 c[altC[v].b2] = size[altC[v].d]; 242 } 243 if (c.B > size.H) { 244 c.B = size.H; 245 } 246 el.vml.image.shape.style.clip = 'rect('+c.T+'px '+(c.R+fudge)+'px '+c.B+'px '+(c.L+fudge)+'px)'; 247 } 248 else { 249 el.vml.image.shape.style.clip = 'rect('+dC.T+'px '+dC.R+'px '+dC.B+'px '+dC.L+'px)'; 250 } 251 }, 252 figurePercentage: function (bg, size, axis, position) { 253 var horizontal, fraction; 254 fraction = true; 255 horizontal = (axis == 'X'); 256 switch(position) { 257 case 'left': 258 case 'top': 259 bg[axis] = 0; 260 break; 261 case 'center': 262 bg[axis] = 0.5; 263 break; 264 case 'right': 265 case 'bottom': 266 bg[axis] = 1; 267 break; 268 default: 269 if (position.search('%') != -1) { 270 bg[axis] = parseInt(position, 10) / 100; 271 } 272 else { 273 fraction = false; 274 } 275 } 276 bg[axis] = Math.ceil( fraction ? ( (size[horizontal?'W': 'H'] * bg[axis]) - (size[horizontal?'w': 'h'] * bg[axis]) ) : parseInt(position, 10) ); 277 if (bg[axis] % 2 === 0) { 278 bg[axis]++; 279 } 280 return bg[axis]; 281 }, 282 fixPng: function (el) { 283 el.style.behavior = 'none'; 284 var lib, els, nodeStr, v, e; 285 if (el.nodeName == 'BODY' || el.nodeName == 'TD' || el.nodeName == 'TR') { /* elements not supported yet */ 286 return; 287 } 288 el.isImg = false; 289 if (el.nodeName == 'IMG') { 290 if(/\.png(?:\W|$)/.test(el.src.toLowerCase())) { 291 el.isImg = true; 292 el.style.visibility = 'hidden'; 293 } 294 else { 295 return; 296 } 297 } 298 else if (el.currentStyle.backgroundImage.toLowerCase().search('.png') == -1) { 299 return; 300 } 301 lib = DD_belatedPNG; 302 el.vml = {color: {}, image: {}}; 303 els = {shape: {}, fill: {}}; 304 for (v in el.vml) { 305 if (el.vml.hasOwnProperty(v)) { 306 for (e in els) { 307 if (els.hasOwnProperty(e)) { 308 nodeStr = lib.ns + ':' + e; 309 el.vml[v][e] = document.createElement(nodeStr); 310 } 311 } 312 el.vml[v].shape.stroked = false; 313 el.vml[v].shape.appendChild(el.vml[v].fill); 314 el.parentNode.insertBefore(el.vml[v].shape, el); 315 } 316 } 317 el.vml.image.shape.fillcolor = 'none'; /* Don't show blank white shapeangle when waiting for image to load. */ 318 el.vml.image.fill.type = 'tile'; /* Makes image show up. */ 319 el.vml.color.fill.on = false; /* Actually going to apply vml element's style.backgroundColor, so hide the whiteness. */ 320 lib.attachHandlers(el); 321 lib.giveLayout(el); 322 lib.giveLayout(el.offsetParent); 323 el.vmlInitiated = true; 324 lib.applyVML(el); /* Render! */ 325 } 326 }; 327 try { 328 document.execCommand("BackgroundImageCache", false, true); /* TredoSoft Multiple IE doesn't like this, so try{} it */ 329 } catch(r) {} 330 DD_belatedPNG.createVmlNameSpace(); 331 DD_belatedPNG.createVmlStyleSheet();
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