Bug 1302035 - implement an algorithm to better detect whether a page is dark or bright and use that to toggle the dimming mode of the find toolbar. r=jaws

MozReview-Commit-ID: 2yJsHfivEBO

--HG--
extra : rebase_source : 3ab85f9ccd5aa9a600aa3fbb73d7963ef533237d

toolkit/modules/FinderHighlighter.jsm

@@ -20,6 +20,7 @@ XPCOMUtils.defineLazyGetter(this, "kDebug", () => {
 });
 
 const kContentChangeThresholdPx = 5;
+const kBrightTextSampleSize = 5;
 const kModalHighlightRepaintFreqMs = 100;
 const kHighlightAllPref = "findbar.highlightAll";
 const kModalHighlightPref = "findbar.modalHighlight";
@@ -357,7 +358,6 @@ FinderHighlighter.prototype = {
 
     this._removeHighlightAllMask(window);
     this._removeModalHighlightListeners(window);
-    delete dict.brightText;
 
     dict.visible = false;
   },
@@ -413,11 +413,6 @@ FinderHighlighter.prototype = {
         return;
       }
 
-      let fontStyle = this._getRangeFontStyle(foundRange);
-      if (typeof dict.brightText == "undefined") {
-        dict.brightText = this._isColorBright(fontStyle.color);
-      }
-
       if (data.findAgain)
         dict.updateAllRanges = true;
 
@@ -426,7 +421,7 @@ FinderHighlighter.prototype = {
       else
         this._maybeCreateModalHighlightNodes(window);
 
-      this._updateRangeOutline(dict, textContent, fontStyle);
+      this._updateRangeOutline(dict, textContent);
     }
 
     let outlineNode = dict.modalHighlightOutline;
@@ -462,6 +457,7 @@ FinderHighlighter.prototype = {
     dict.dynamicRangesSet.clear();
     dict.frames.clear();
     dict.modalHighlightRectsMap.clear();
+    dict.brightText = null;
   },
 
   /**
@@ -711,6 +707,48 @@ FinderHighlighter.prototype = {
     return new Color(...cssColor).isBright;
   },
 
+  /**
+   * Detects if the overall text color in the page can be described as bright.
+   * This is done according to the following algorithm:
+   *  1. With the entire set of ranges that we have found thusfar;
+   *  2. Get an odd-numbered `sampleSize`, with a maximum of `kBrightTextSampleSize`
+   *     ranges,
+   *  3. Slice the set of ranges into `sampleSize` number of equal parts,
+   *  4. Grab the first range for each slice and inspect the brightness of the
+   *     color of its text content.
+   *  5. When the majority of ranges are counted as contain bright colored text,
+   *     the page is considered to contain bright text overall.
+   *
+   * @param {Object} dict Dictionary of properties belonging to the
+   *                      currently active window. The page text color property
+   *                      will be recorded in `dict.brightText` as `true` or `false`.
+   */
+  _detectBrightText(dict) {
+    let sampleSize = Math.min(dict.modalHighlightRectsMap.size, kBrightTextSampleSize);
+    let ranges = [...dict.modalHighlightRectsMap.keys()];
+    let rangesCount = ranges.length;
+    // Make sure the sample size is an odd number.
+    if (sampleSize % 2 == 0) {
+      // Make the currently found range weigh heavier.
+      if (dict.currentFoundRange) {
+        ranges.push(dict.currentFoundRange);
+        ++sampleSize;
+        ++rangesCount;
+      } else {
+        --sampleSize;
+      }
+    }
+    let brightCount = 0;
+    for (let i = 0; i < sampleSize; ++i) {
+      let range = ranges[Math.floor((rangesCount / sampleSize) * i)];
+      let fontStyle = this._getRangeFontStyle(range);
+      if (this._isColorBright(fontStyle.color))
+        ++brightCount;
+    }
+
+    dict.brightText = (brightCount >= Math.ceil(sampleSize / 2));
+  },
+
   /**
    * Checks if a range is inside a DOM node that's positioned in a way that it
    * doesn't scroll along when the document is scrolled and/ or zoomed. This
@@ -1012,6 +1050,8 @@ FinderHighlighter.prototype = {
 
     // Make sure the dimmed mask node takes the full width and height that's available.
     let {width, height} = dict.lastWindowDimensions = this._getWindowDimensions(window);
+    if (typeof dict.brightText != "boolean" || dict.updateAllRanges)
+      this._detectBrightText(dict);
     let maskStyle = this._getStyleString(kModalStyles.maskNode,
       [ ["width", width + "px"], ["height", height + "px"] ],
       dict.brightText ? kModalStyles.maskNodeBrightText : [],