如何基于filter实现网站整体变灰功能

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 //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<cLen) { init.call(this, allContexts[cIndex]); }
      return;
    }

    context = context || document.documentElement;

    if (!document.createElement('canvas').getContext) {
      context.style.filter = 'progid:DXImageTransform.Microsoft.BasicImage(grayscale=1)';
      context.style.zoom = 1;
      return;
    }

    var all = getAllNodes(context),
      i = -1, len = all.length;

    while (++i<len) {
      var cur = all[i];

      if (cur.nodeName.toLowerCase() === 'img') {
        var src = cur.getAttribute('src');
        if(!src) { continue; }
        if (isExternal(src)) {
          config.externalImageHandler.init(cur, src);
        } else {
          data(cur).realSRC = src;
          try {
            // Within try statement just encase there's no support....
            cur.src = data(cur).dataURL || desatIMG(cur).toDataURL();
          } catch(e) { config.externalImageHandler.init(cur, src); }
        }

      } else {
        for (var pIndex = 0, pLen = config.colorProps.length; pIndex < pLen; pIndex++) {
          var prop = config.colorProps[pIndex],
          style = getStyle(cur, prop);
          if (!style) {continue;}
          if (cur.style[prop]) {
            data(cur)[prop] = style;
          }
          // RGB color:
          if (style.substring(0,4) === 'rgb(') {
            var monoRGB = RGBtoGRAYSCALE.apply(null, style.match(/\d+/g));
            cur.style[prop] = style = 'rgb(' + monoRGB + ',' + monoRGB + ',' + monoRGB + ')';
            continue;
          }
          // Background Image:
          if (style.indexOf('url(') > -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<cLen) { init.reset.call(this, allContexts[cIndex]); }
      return;
    }
    context = context || document.documentElement;
    if (!document.createElement('canvas').getContext) {
      context.style.filter = 'progid:DXImageTransform.Microsoft.BasicImage(grayscale=0)';
      return;
    }
    var all = getAllNodes(context),
      i = -1, len = all.length;
    while (++i<len) {
      var cur = all[i];
      if (cur.nodeName.toLowerCase() === 'img') {
        var src = cur.getAttribute('src');
        if (isExternal(src)) {
          config.externalImageHandler.reset(cur, src);
        }
        cur.src = data(cur).realSRC || src;
      } else {
        for (var pIndex = 0, pLen = config.colorProps.length; pIndex < pLen; pIndex++) {
          if (data(cur).externalBG) {
            config.externalImageHandler.reset(cur);
          }
          var prop = config.colorProps[pIndex];
          cur.style[prop] = data(cur)[prop] || '';
        }
      }
    }
  };

  init.prepare = 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<cLen) { init.prepare.call(null, allContexts[cIndex]); }
      return;
    }

    // Slowly recurses through all elements
    // so as not to lock up on the user.

    context = context || document.documentElement;

    if (!document.createElement('canvas').getContext) { return; }

    var all = getAllNodes(context),
      i = -1, len = all.length;

    while (++i<len) {
      var cur = all[i];
      if (data(cur).skip) { return; }
      if (cur.nodeName.toLowerCase() === 'img') {
        if (cur.getAttribute('src') && !isExternal(cur.src)) {
          desatIMG(cur, true);
        }

      } else {
        var style = getStyle(cur, 'backgroundImage');
        if (style.indexOf('url(') > -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。

<script type="text/javascript">
 var navStr = navigator.userAgent.toLowerCase();
 if(navStr.indexOf("msie 10.0")!==-1||navStr.indexOf("rv:11.0")!==-1){ // 判断是IE10或者IE11
  $(function () {
    grayscale($('body'));
  })
 }
</script>

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。

以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持我们。