Fix High Contrast extension

ui/accessibility/extensions/highcontrast/highcontrast.js

 // Copyright (c) 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 var mode;
 var enabled = false;
 var scheme = '';
 var timeoutId = null;
 
 var filterMap = {
   '0': 'url("#hc_extension_off")',
   '1': 'url("#hc_extension_highcontrast")',
   '2': 'url("#hc_extension_grayscale")',
   '3': 'url("#hc_extension_invert")',
   '4': 'url("#hc_extension_invert_grayscale")',
   '5': 'url("#hc_extension_yellow_on_black")'
 };
 
-var svgContent = '<svg xmlns="http://www.w3.org/2000/svg" version="1.1"><defs><filter id="hc_extension_off"><feComponentTransfer><feFuncR type="table" tableValues="0 1"/><feFuncG type="table" tableValues="0 1"/><feFuncB type="table" tableValues="0 1"/></feComponentTransfer></filter><filter id="hc_extension_highcontrast"><feComponentTransfer><feFuncR type="gamma" exponent="3.0"/><feFuncG type="gamma" exponent="3.0"/><feFuncB type="gamma" exponent="3.0"/></feComponentTransfer></filter><filter id="hc_extension_highcontrast_back"><feComponentTransfer><feFuncR type="gamma" exponent="0.33"/><feFuncG type="gamma" exponent="0.33"/><feFuncB type="gamma" exponent="0.33"/></feComponentTransfer></filter><filter id="hc_extension_grayscale"><feColorMatrix type="matrix" values="0.2126 0.7152 0.0722 0 0 0.2126 0.7152 0.0722 0 0 0.2126 0.7152 0.0722 0 0 0 0 0 1 0"/><feComponentTransfer><feFuncR type="gamma" exponent="3"/><feFuncG type="gamma" exponent="3"/><feFuncB type="gamma" exponent="3"/></feComponentTransfer></filter><filter id="hc_extension_grayscale_back"><feComponentTransfer><feFuncR type="gamma" exponent="0.33"/><feFuncG type="gamma" exponent="0.33"/><feFuncB type="gamma" exponent="0.33"/></feComponentTransfer></filter><filter id="hc_extension_invert"><feComponentTransfer><feFuncR type="gamma" amplitude="-1" exponent="3" offset="1"/><feFuncG type="gamma" amplitude="-1" exponent="3" offset="1"/><feFuncB type="gamma" amplitude="-1" exponent="3" offset="1"/></feComponentTransfer></filter><filter id="hc_extension_invert_back"><feComponentTransfer><feFuncR type="table" tableValues="1 0"/><feFuncG type="table" tableValues="1 0"/><feFuncB type="table" tableValues="1 0"/></feComponentTransfer><feComponentTransfer><feFuncR type="gamma" exponent="1.7"/><feFuncG type="gamma" exponent="1.7"/><feFuncB type="gamma" exponent="1.7"/></feComponentTransfer></filter><filter id="hc_extension_invert_grayscale"><feColorMatrix type="matrix" values="0.2126 0.7152 0.0722 0 0 0.2126 0.7152 0.0722 0 0 0.2126 0.7152 0.0722 0 0 0 0 0 1 0"/><feComponentTransfer><feFuncR type="gamma" amplitude="-1" exponent="3" offset="1"/><feFuncG type="gamma" amplitude="-1" exponent="3" offset="1"/><feFuncB type="gamma" amplitude="-1" exponent="3" offset="1"/></feComponentTransfer></filter><filter id="hc_extension_yellow_on_black"><feComponentTransfer><feFuncR type="gamma" amplitude="-1" exponent="3" offset="1"/><feFuncG type="gamma" amplitude="-1" exponent="3" offset="1"/><feFuncB type="gamma" amplitude="-1" exponent="3" offset="1"/></feComponentTransfer><feColorMatrix type="matrix" values="0.3 0.5 0.2 0 0 0.3 0.5 0.2 0 0 0 0 0 0 0 0 0 0 1 0"/></filter><filter id="hc_extension_yellow_on_black_back"><feComponentTransfer><feFuncR type="table" tableValues="1 0"/><feFuncG type="table" tableValues="1 0"/><feFuncB type="table" tableValues="1 0"/></feComponentTransfer><feComponentTransfer><feFuncR type="gamma" exponent="0.33"/><feFuncG type="gamma" exponent="0.33"/><feFuncB type="gamma" exponent="0.33"/></feComponentTransfer></filter></defs></svg>';
+var svgContent = '<svg xmlns="http://www.w3.org/2000/svg" version="1.1"><defs><filter x="0" y="0" width="99999" height="99999" id="hc_extension_off"><feComponentTransfer><feFuncR type="table" tableValues="0 1"/><feFuncG type="table" tableValues="0 1"/><feFuncB type="table" tableValues="0 1"/></feComponentTransfer></filter><filter x="0" y="0" width="99999" height="99999" id="hc_extension_highcontrast"><feComponentTransfer><feFuncR type="gamma" exponent="3.0"/><feFuncG type="gamma" exponent="3.0"/><feFuncB type="gamma" exponent="3.0"/></feComponentTransfer></filter><filter x="0" y="0" width="99999" height="99999" id="hc_extension_highcontrast_back"><feComponentTransfer><feFuncR type="gamma" exponent="0.33"/><feFuncG type="gamma" exponent="0.33"/><feFuncB type="gamma" exponent="0.33"/></feComponentTransfer></filter><filter x="0" y="0" width="99999" height="99999" id="hc_extension_grayscale"><feColorMatrix type="matrix" values="0.2126 0.7152 0.0722 0 0 0.2126 0.7152 0.0722 0 0 0.2126 0.7152 0.0722 0 0 0 0 0 1 0"/><feComponentTransfer><feFuncR type="gamma" exponent="3"/><feFuncG type="gamma" exponent="3"/><feFuncB type="gamma" exponent="3"/></feComponentTransfer></filter><filter x="0" y="0" width="99999" height="99999" id="hc_extension_grayscale_back"><feComponentTransfer><feFuncR type="gamma" exponent="0.33"/><feFuncG type="gamma" exponent="0.33"/><feFuncB type="gamma" exponent="0.33"/></feComponentTransfer></filter><filter x="0" y="0" width="99999" height="99999" id="hc_extension_invert"><feComponentTransfer><feFuncR type="gamma" amplitude="-1" exponent="3" offset="1"/><feFuncG type="gamma" amplitude="-1" exponent="3" offset="1"/><feFuncB type="gamma" amplitude="-1" exponent="3" offset="1"/></feComponentTransfer></filter><filter x="0" y="0" width="99999" height="99999" id="hc_extension_invert_back"><feComponentTransfer><feFuncR type="table" tableValues="1 0"/><feFuncG type="table" tableValues="1 0"/><feFuncB type="table" tableValues="1 0"/></feComponentTransfer><feComponentTransfer><feFuncR type="gamma" exponent="1.7"/><feFuncG type="gamma" exponent="1.7"/><feFuncB type="gamma" exponent="1.7"/></feComponentTransfer></filter><filter x="0" y="0" width="99999" height="99999" id="hc_extension_invert_grayscale"><feColorMatrix type="matrix" values="0.2126 0.7152 0.0722 0 0 0.2126 0.7152 0.0722 0 0 0.2126 0.7152 0.0722 0 0 0 0 0 1 0"/><feComponentTransfer><feFuncR type="gamma" amplitude="-1" exponent="3" offset="1"/><feFuncG type="gamma" amplitude="-1" exponent="3" offset="1"/><feFuncB type="gamma" amplitude="-1" exponent="3" offset="1"/></feComponentTransfer></filter><filter x="0" y="0" width="99999" height="99999" id="hc_extension_yellow_on_black"><feComponentTransfer><feFuncR type="gamma" amplitude="-1" exponent="3" offset="1"/><feFuncG type="gamma" amplitude="-1" exponent="3" offset="1"/><feFuncB type="gamma" amplitude="-1" exponent="3" offset="1"/></feComponentTransfer><feColorMatrix type="matrix" values="0.3 0.5 0.2 0 0 0.3 0.5 0.2 0 0 0 0 0 0 0 0 0 0 1 0"/></filter><filter x="0" y="0" width="99999" height="99999" id="hc_extension_yellow_on_black_back"><feComponentTransfer><feFuncR type="table" tableValues="1 0"/><feFuncG type="table" tableValues="1 0"/><feFuncB type="table" tableValues="1 0"/></feComponentTransfer><feComponentTransfer><feFuncR type="gamma" exponent="0.33"/><feFuncG type="gamma" exponent="0.33"/><feFuncB type="gamma" exponent="0.33"/></feComponentTransfer></filter></defs></svg>';
 
-function addSvgIfMissing() {
+var cssTemplate = 'html[hc="a0"] {   -webkit-filter: url("#hc_extension_off"); } html[hcx="0"] img[src*="jpg"], html[hcx="0"] img[src*="jpeg"], html[hcx="0"] svg image, html[hcx="0"] img.rg_i, html[hcx="0"] embed, html[hcx="0"] object, html[hcx="0"] video {   -webkit-filter: url("#hc_extension_off"); }  html[hc="a1"] {   -webkit-filter: url("#hc_extension_highcontrast"); } html[hcx="1"] img[src*="jpg"], html[hcx="1"] img[src*="jpeg"], html[hcx="1"] img.rg_i, html[hcx="1"] svg image, html[hcx="1"] embed, html[hcx="1"] object, html[hcx="1"] video {   -webkit-filter: url("#hc_extension_highcontrast_back"); }  html[hc="a2"] {   -webkit-filter: url("#hc_extension_grayscale"); } html[hcx="2"] img[src*="jpg"], html[hcx="2"] img[src*="jpeg"], html[hcx="2"] img.rg_i, html[hcx="2"] svg image, html[hcx="2"] embed, html[hcx="2"] object, html[hcx="2"] video {   -webkit-filter: url("#hc_extension_grayscale_back"); }  html[hc="a3"] {   -webkit-filter: url("#hc_extension_invert"); } html[hcx="3"] img[src*="jpg"], html[hcx="3"] img[src*="jpeg"], html[hcx="3"] img.rg_i, html[hcx="3"] svg image, html[hcx="3"] embed, html[hcx="3"] object, html[hcx="3"] video {   -webkit-filter: url("#hc_extension_invert_back"); }  html[hc="a4"] {   -webkit-filter: url("#hc_extension_invert_grayscale"); } html[hcx="4"] img[src*="jpg"], html[hcx="4"] img[src*="jpeg"], html[hcx="4"] img.rg_i, html[hcx="4"] svg image, html[hcx="4"] embed, html[hcx="4"] object, html[hcx="4"] video {   -webkit-filter: url("#hc_extension_invert_back"); }  html[hc="a5"] {   -webkit-filter: url("#hc_extension_yellow_on_black"); } html[hcx="5"] img[src*="jpg"], html[hcx="5"] img[src*="jpeg"], html[hcx="5"] img.rg_i, html[hcx="5"] svg image, html[hcx="5"] embed, html[hcx="5"] object, html[hcx="5"] video {   -webkit-filter: url("#hc_extension_yellow_on_black_back"); }';
+
+/**
+ * Add the elements to the pgae that make high-contrast adjustments possible.
+ */
+function addOrUpdateExtraElements() {
+  if (!enabled)
+    return;
+
+  // We used to include the CSS, but that doesn't work when the document
+  // uses the <base> element to set a relative url. So instead we
+  // add a <style> element directly to the document with the right
+  // urls hard-coded into it.
+  var style = document.getElementById('hc_style');
+  if (!style) {
+    var baseUrl = window.location.href.replace(window.location.hash, '');
+    var css = cssTemplate.replace(/#/g, baseUrl + '#');
+    style = document.createElement('style');
+    style.id = 'hc_style';
+    style.setAttribute('type', 'text/css');
+    style.innerHTML = css;
+    document.head.appendChild(style);
+  }
+
+  // Starting in Chrome 45 we can't apply a filter to the html element,
+  // so instead we create an element with low z-index that copies the
+  // body's background.
+  var bg = document.getElementById('hc_extension_bkgnd');
+  if (!bg) {
+    bg = document.createElement('div');
+    bg.id = 'hc_extension_bkgnd';
+    bg.style.position = 'fixed';
+    bg.style.left = '0px';
+    bg.style.top = '0px';
+    bg.style.right = '0px';
+    bg.style.bottom = '0px';
+    bg.style.zIndex = -1999999999;
+    document.body.appendChild(bg);
+  }
+  bg.style.display = 'block';
+  bg.style.background = window.getComputedStyle(document.body).background;
+
+  // As a special case, replace a zero-alpha background with white,
+  // otherwise we can't invert it.
+  var c = bg.style.backgroundColor;
+  c = c.replace(/\s\s*/g,'');
+  if (m = /^rgba\(([\d]+),([\d]+),([\d]+),([\d]+|[\d]*.[\d]+)\)/.exec(c)) {
+    if (m[4] == '0') {
+      bg.style.backgroundColor = '#fff';
+    }
+  }
+
+  // Add a hidden element with the SVG filters.
   var wrap = document.getElementById('hc_extension_svg_filters');
   if (wrap)
     return;
+
   wrap = document.createElement('span');
   wrap.id = 'hc_extension_svg_filters';
   wrap.setAttribute('hidden', '');
   wrap.innerHTML = svgContent;
   document.body.appendChild(wrap);
 }
 
+/**
+ * This is called on load and every time the mode might have changed
+ * (i.e. enabling/disabling, or changing the type of contrast adjustment
+ * for this page).
+ */
 function update() {
   var html = document.documentElement;
   if (enabled) {
     if (!document.body) {
       window.setTimeout(update, 100);
       return;
     }
-    addSvgIfMissing();
+    addOrUpdateExtraElements();
     if (html.getAttribute('hc') != mode + scheme)
       html.setAttribute('hc', mode + scheme);
     if (html.getAttribute('hcx') != scheme)
       html.setAttribute('hcx', scheme);
 
     if (window == window.top) {
       window.scrollBy(0, 1);
       window.scrollBy(0, -1);
     }
-
-    /**
-    if (mode == 'a') {
-      html.style.webkitFilter = filterMap[scheme];
-    }
-    else {
-      html.style.webkitFilter = 'none';
-    }**/
-
   } else {
     html.setAttribute('hc', mode + '0');
     html.setAttribute('hcx', '0');
     window.setTimeout(function() {
       html.removeAttribute('hc');
       html.removeAttribute('hcx');
+      var bg = document.getElementById('hc_extension_bkgnd');
+      if (bg)
+        bg.style.display = 'none';
     }, 0);
   }
 }
 
+/**
+ * Called when we get a message from the background page.
+ */
 function onExtensionMessage(request) {
   if (enabled != request.enabled || scheme != request.scheme) {
     enabled = request.enabled;
     scheme = request.scheme;
     update();
   }
 }
 
-function onEvent(evt) {
+/**
+ * KeyDown event handler
+ */
+function onKeyDown(evt) {
   if (evt.keyCode == 122 /* F11 */ &&
       evt.shiftKey) {
     chrome.extension.sendRequest({'toggle_global': true});
     evt.stopPropagation();
     evt.preventDefault();
     return false;
   }
   if (evt.keyCode == 123 /* F12 */ &&
       evt.shiftKey) {
     chrome.extension.sendRequest({'toggle_site': true});
     evt.stopPropagation();
     evt.preventDefault();
     return false;
   }
   return true;
 }
 
 function init() {
   if (window == window.top) {
     mode = 'a';
   } else {
     mode = 'b';
   }
   chrome.extension.onRequest.addListener(onExtensionMessage);
   chrome.extension.sendRequest({'init': true}, onExtensionMessage);
-  document.addEventListener('keydown', onEvent, false);
+  document.addEventListener('keydown', onKeyDown, false);
 
-  // Work around bug that causes filter to be lost when the HTML element's attributes change.
-  var html = document.documentElement;
-  var config = { attributes: true, childList: false, characterData: false };
-  var observer = new MutationObserver(function(mutations) {
-    observer.disconnect();
-    html.removeAttribute('hc');
-    html.removeAttribute('hcx');
-    window.setTimeout(function() {
-      update();
-      window.setTimeout(function() {
-        observer.observe(html, config);
-      }, 0);
-    }, 0);
+  // Update again after a few seconds and again after load so that
+  // the background isn't wrong for long.
+  window.setTimeout(addOrUpdateExtraElements, 2000);
+  window.addEventListener('load', function() {
+    addOrUpdateExtraElements();
+
+    // Also update when the document body attributes change.
+    var config = { attributes: true, childList: false, characterData: false };
+    var observer = new MutationObserver(function(mutations) {
+      addOrUpdateExtraElements();
+    });
+    observer.observe(document.body, config);
   });
-  observer.observe(html, config);
 }
 
 init();