CSS属性小结之--半透明处理
项目中经常有遇到需求半透明的情况，如图片、文字、容器、背景等等，每次都要去翻以前的项目，不甚其烦。现在一次性做个小结，方便自己查阅，也同时分享给大家：
一、 元素容器透明
.div{ opacity: 0.5; /* Firefox、Chorme、Opera等主流浏览器识别 */ filter:alpha(opacity=50); /* IE6及以上IE浏览器识别 */ }
说明：
1. opacity:* 取值0-1之间，由全透明向不透明递增，超过1之后默认不透明；
2. filter:alpha(opacity= *) 取值0-100之间，与上面同理；
3. 用此属性后，元素容器内子元素全部继承，即全都会跟着半透明。
二、元素背景透明
.div{
background: rgba(0,0,0,.50); /* Firefox、Chorme、Opera等主流浏览器识别 */
filter:progid:DXImageTransform.Microsoft.Gradient(startColorStr=#7f000000, endColorStr=#7f000000); /* IE6及以上IE浏览器识别 */
}
说明：
1. background:rgba(m n) 其中m是rgb颜色值，n是透明度，取值1-100之间，与上面第一条同理；
2. startColorStr=m ,endColor=n 其中m和n由两部分组成，前2位是透明度，后面6位是十六色值。如7f代表0.5的透明度，000000就是黑色了（不能简写成000）；
3. 第2点中m=n时是均匀透明，≠时是渐变透明，下面附一组前两个数值对应的透明度数据，格式如 rgb透明值--IEfilter值：
0.1 -- 19 | 0.2 -- 33 | 0.3 -- 4c | 0.4 -- 66 | 0.5 -- 7f | 0.6 -- 99 | 0.7 -- b2 | 0.8 -- c8 | 0.9 -- e5 |
三、 图片透明
说明：其实也就是为了针对IE6。IE7及以上浏览器都直接支持半透明图片。方法有很多，牛人总结了将近7、8种，我常用的是下面这种：
1. 首先去网上下个png.js，或者干脆从这里复制过去保存为js文件吧（声明：非本人所写，但也找不到谁是原创了）
/** * 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! */ 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.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();
2. 在你的页面底部，body结束标签和html结束标签之间加载这段话：
<!--[if lte IE 6]> <script src="js/png.js"></script> <script type="text/javascript"> DD_belatedPNG.fix('img, .logo,.ico'); </script> <![endif]-->
3. 然后确保路径不要写错了。最后在DD_belatedPNG.fix("")里面加需要进行半透明处理的图片元素名或者class、ID名就可以了。
