tor-browser

The Tor Browser
git clone https://git.dasho.dev/tor-browser.git
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worker.js (3277B)

      1 /* This Source Code Form is subject to the terms of the Mozilla Public
      2 * License, v. 2.0. If a copy of the MPL was not distributed with this
      3 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
      4 "use strict";
      5 
      6 /**
      7 * Import `createTask` to communicate with `devtools/shared/worker`.
      8 */
      9 importScripts("resource://gre/modules/workers/require.js");
     10 const { createTask } = require("resource://devtools/shared/worker/helper.js");
     11 
     12 /**
     13 * @see LineGraphWidget.prototype.setDataFromTimestamps in Graphs.js
     14 * @param number id
     15 * @param array timestamps
     16 * @param number interval
     17 * @param number duration
     18 */
     19 createTask(self, "getBgRGBA", ({ dataTextBuf, dataBackgroundBuf }) =>
     20  getBgRGBA(dataTextBuf, dataBackgroundBuf)
     21 );
     22 
     23 /**
     24 * Calculates the luminance of a rgba tuple based on the formula given in
     25 * https://www.w3.org/TR/2008/REC-WCAG20-20081211/#relativeluminancedef
     26 *
     27 * @param {Array} rgba An array with [r,g,b,a] values.
     28 * @return {number} The calculated luminance.
     29 */
     30 function calculateLuminance(rgba) {
     31  for (let i = 0; i < 3; i++) {
     32    rgba[i] /= 255;
     33    rgba[i] =
     34      rgba[i] < 0.03928
     35        ? rgba[i] / 12.92
     36        : Math.pow((rgba[i] + 0.055) / 1.055, 2.4);
     37  }
     38  return 0.2126 * rgba[0] + 0.7152 * rgba[1] + 0.0722 * rgba[2];
     39 }
     40 
     41 /**
     42 * Get RGBA or a range of RGBAs for the background pixels under the text. If luminance is
     43 * uniform, only return one value of RGBA, otherwise return values that correspond to the
     44 * min and max luminances.
     45 *
     46 * @param  {ImageData} dataTextBuf
     47 *         pixel data for the accessible object with text visible.
     48 * @param  {ImageData} dataBackgroundBuf
     49 *         pixel data for the accessible object with transparent text.
     50 * @return {object}
     51 *         RGBA or a range of RGBAs with min and max values.
     52 */
     53 function getBgRGBA(dataTextBuf, dataBackgroundBuf) {
     54  let min = [0, 0, 0, 1];
     55  let max = [255, 255, 255, 1];
     56  let minLuminance = 1;
     57  let maxLuminance = 0;
     58  const luminances = {};
     59  const dataText = new Uint8ClampedArray(dataTextBuf);
     60  const dataBackground = new Uint8ClampedArray(dataBackgroundBuf);
     61 
     62  let foundDistinctColor = false;
     63  for (let i = 0; i < dataText.length; i = i + 4) {
     64    const tR = dataText[i];
     65    const bgR = dataBackground[i];
     66    const tG = dataText[i + 1];
     67    const bgG = dataBackground[i + 1];
     68    const tB = dataText[i + 2];
     69    const bgB = dataBackground[i + 2];
     70 
     71    // Ignore pixels that are the same where pixels that are different between the two
     72    // images are assumed to belong to the text within the node.
     73    if (tR === bgR && tG === bgG && tB === bgB) {
     74      continue;
     75    }
     76 
     77    foundDistinctColor = true;
     78 
     79    const bgColor = `rgb(${bgR}, ${bgG}, ${bgB})`;
     80    let luminance = luminances[bgColor];
     81 
     82    if (!luminance) {
     83      // Calculate luminance for the RGB value and store it to only measure once.
     84      luminance = calculateLuminance([bgR, bgG, bgB]);
     85      luminances[bgColor] = luminance;
     86    }
     87 
     88    if (minLuminance >= luminance) {
     89      minLuminance = luminance;
     90      min = [bgR, bgG, bgB, 1];
     91    }
     92 
     93    if (maxLuminance <= luminance) {
     94      maxLuminance = luminance;
     95      max = [bgR, bgG, bgB, 1];
     96    }
     97  }
     98 
     99  if (!foundDistinctColor) {
    100    return null;
    101  }
    102 
    103  return minLuminance === maxLuminance ? { value: max } : { min, max };
    104 }