前言
政府网站会遇到公祭日的时候，网站整体颜色变灰的情况。今天正好调了一下。在此把解决方案分享给大家。方案简单实用，笔者已在生产环境使用过。通过整体的html使用filter来进行过滤。如下，只要引入即可。
解决方案
html {
filter: url("data:image/svg+xml;utf8,#grayscale");
-webkit-filter: grayscale(100%);
filter: grayscale(100%);
filter: gray;
filter:progid:DXImageTransform.Microsoft.BasicImage(grayscale=1);
}
IE11 和 IE10的解决方案
经过测试发现，以上代码的方式对于谷歌，火狐，IE8，9都很好使。对于IE11和IE10效果不奏效。于是我们采取另一种方式，通过引用grayscale.js来使用。由于不能上传文件，在此将grayscale.js的代码写下来。
/*
* -- grayscale.js --
* Copyright (C) James Padolsey (http://james.padolsey.com)
* Download by http://www.jb51.net
*/
var grayscale = (function(){
var config = {
colorProps: ['color','backgroundColor','borderBottomColor','borderTopColor','borderLeftColor','borderRightColor','backgroundImage'],
externalImageHandler : {
/* Grayscaling externally hosted images does not work
- Use these functions to handle those images as you so desire */
/* Out of convenience these functions are also used for browsers
like Chrome that do not support CanvasContext.getImageData */
init : function(el, src) {
if (el.nodeName.toLowerCase() === 'img') {
// Is IMG element...
} else {
// Is background-image element:
// Default - remove background images
data(el).backgroundImageSRC = src;
el.style.backgroundImage = '';
}
},
reset : function(el) {
if (el.nodeName.toLowerCase() === 'img') {
// Is IMG element...
} else {
// Is background-image element:
el.style.backgroundImage = 'url(' + (data(el).backgroundImageSRC || '') + ')';
}
}
}
},
log = function(){
try { window.console.log.apply(console, arguments); }
catch(e) {};
},
isExternal = function(url) {
// Checks whether URL is external: 'CanvasContext.getImageData'
// only works if the image is on the current domain.
return (new RegExp('https?://(?!' + window.location.hostname + ')')).test(url);
},
data = (function(){
var cache = [0],
expando = 'data' + (+new Date());
return function(elem) {
var cacheIndex = elem[expando],
nextCacheIndex = cache.length;
if(!cacheIndex) {
cacheIndex = elem[expando] = nextCacheIndex;
cache[cacheIndex] = {};
}
return cache[cacheIndex];
};
})(),
desatIMG = function(img, prepare, realEl) {
// realEl is only set when img is temp (for BG images)
var canvas = document.createElement('canvas'),
context = canvas.getContext('2d'),
height = img.naturalHeight || img.offsetHeight || img.height,
width = img.naturalWidth || img.offsetWidth || img.width,
imgData;
canvas.height = height;
canvas.width = width;
context.drawImage(img, 0, 0);
try {
imgData = context.getImageData(0, 0, width, height);
} catch(e) {}
if (prepare) {
desatIMG.preparing = true;
// Slowly recurse through pixels for prep,
// :: only occurs on grayscale.prepare()
var y = 0;
(function(){
if (!desatIMG.preparing) { return; }
if (y === height) {
// Finished!
context.putImageData(imgData, 0, 0, 0, 0, width, height);
realEl ? (data(realEl).BGdataURL = canvas.toDataURL())
: (data(img).dataURL = canvas.toDataURL())
}
for (var x = 0; x < width; x++) {
var i = (y * width + x) * 4;
// Apply Monoschrome level across all channels:
imgData.data[i] = imgData.data[i+1] = imgData.data[i+2] =
RGBtoGRAYSCALE(imgData.data[i], imgData.data[i+1], imgData.data[i+2]);
}
y++;
setTimeout(arguments.callee, 0);
})();
return;
} else {
// If desatIMG was called without 'prepare' flag
// then cancel recursion and proceed with force! (below)
desatIMG.preparing = false;
}
for (var y = 0; y < height; y++) {
for (var x = 0; x < width; x++) {
var i = (y * width + x) * 4;
// Apply Monoschrome level across all channels:
imgData.data[i] = imgData.data[i+1] = imgData.data[i+2] =
RGBtoGRAYSCALE(imgData.data[i], imgData.data[i+1], imgData.data[i+2]);
}
}
context.putImageData(imgData, 0, 0, 0, 0, width, height);
return canvas;
},
getStyle = function(el, prop) {
var style = document.defaultView && document.defaultView.getComputedStyle ?
document.defaultView.getComputedStyle(el, null)[prop]
: el.currentStyle[prop];
// If format is #FFFFFF: (convert to RGB)
if (style && /^#[A-F0-9]/i.test(style)) {
var hex = style.match(/[A-F0-9]{2}/ig);
style = 'rgb(' + parseInt(hex[0], 16) + ','
+ parseInt(hex[1], 16) + ','
+ parseInt(hex[2], 16) + ')';
}
return style;
},
RGBtoGRAYSCALE = function(r,g,b) {
// Returns single monochrome figure:
return parseInt( (0.2125 * r) + (0.7154 * g) + (0.0721 * b), 10 );
},
getAllNodes = function(context) {
var all = Array.prototype.slice.call(context.getElementsByTagName('*'));
all.unshift(context);
return all;
};
var init = function(context) {
// Handle if a DOM collection is passed instead of a single el:
if (context && context[0] && context.length && context[0].nodeName) {
// Is a DOM collection:
var allContexts = Array.prototype.slice.call(context),
cIndex = -1, cLen = allContexts.length;
while (++cIndex -1) {
var urlPatt = /\(['"]?(.+?)['"]?\)/,
url = style.match(urlPatt)[1];
if (isExternal(url)) {
config.externalImageHandler.init(cur, url);
data(cur).externalBG = true;
continue;
}
// data(cur).BGdataURL refers to caches URL (from preparation)
try {
var imgSRC = data(cur).BGdataURL || (function(){
var temp = document.createElement('img');
temp.src = url;
return desatIMG(temp).toDataURL();
})();
cur.style[prop] = style.replace(urlPatt, function(_, url){
return '(' + imgSRC + ')';
});
} catch(e) { config.externalImageHandler.init(cur, url); }
}
}
}
}
};
init.reset = function(context) {
// Handle if a DOM collection is passed instead of a single el:
if (context && context[0] && context.length && context[0].nodeName) {
// Is a DOM collection:
var allContexts = Array.prototype.slice.call(context),
cIndex = -1, cLen = allContexts.length;
while (++cIndex -1) {
var urlPatt = /\(['"]?(.+?)['"]?\)/,
url = style.match(urlPatt)[1];
if (!isExternal(url)) {
var temp = document.createElement('img');
temp.src = url;
desatIMG(temp, true, cur);
}
}
}
}
};
return init;
})();
使用方式如下，中心思想就是当我们是ie10和ie11浏览器的时候，调用graystyle的js函数。
这里建议直接捕捉body，如果想针对某一个，换其中的捕捉元素就可以。
总结
至此，网站变灰的方案就完美了。完美兼容各种浏览器，笔者已经在生产环境使用过了，大家放心使用。