/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
"use strict";
/**
* Import `createTask` to communicate with `devtools/shared/worker`.
*/
importScripts(
"resource://gre/modules/workers/require.js");
const { createTask } = require(
"resource://devtools/shared/worker/helper.js");
/**
* @see LineGraphWidget.prototype.setDataFromTimestamps in Graphs.js
* @param number id
* @param array timestamps
* @param number interval
* @param number duration
*/
createTask(self,
"getBgRGBA", ({ dataTextBuf, dataBackgroundBuf }) =>
getBgRGBA(dataTextBuf, dataBackgroundBuf)
);
/**
* Calculates the luminance of a rgba tuple based on the formula given in
* https://www.w3.org/TR/2008/REC-WCAG20-20081211/#relativeluminancedef
*
* @param {Array} rgba An array with [r,g,b,a] values.
* @return {Number} The calculated luminance.
*/
function calculateLuminance(rgba) {
for (let i =
0; i <
3; i++) {
rgba[i] /=
255;
rgba[i] =
rgba[i] <
0.
03928
? rgba[i] /
12.
92
: Math.pow((rgba[i] +
0.
055) /
1.
055,
2.
4);
}
return 0.
2126 * rgba[
0] +
0.
7152 * rgba[
1] +
0.
0722 * rgba[
2];
}
/**
* Get RGBA or a range of RGBAs for the background pixels under the text. If luminance is
* uniform, only return one value of RGBA, otherwise return values that correspond to the
* min and max luminances.
* @param {ImageData} dataTextBuf
* pixel data for the accessible object with text visible.
* @param {ImageData} dataBackgroundBuf
* pixel data for the accessible object with transparent text.
* @return {Object}
* RGBA or a range of RGBAs with min and max values.
*/
function getBgRGBA(dataTextBuf, dataBackgroundBuf) {
let min = [
0,
0,
0,
1];
let max = [
255,
255,
255,
1];
let minLuminance =
1;
let maxLuminance =
0;
const luminances = {};
const dataText =
new Uint8ClampedArray(dataTextBuf);
const dataBackground =
new Uint8ClampedArray(dataBackgroundBuf);
let foundDistinctColor =
false;
for (let i =
0; i < dataText.length; i = i +
4) {
const tR = dataText[i];
const bgR = dataBackground[i];
const tG = dataText[i +
1];
const bgG = dataBackground[i +
1];
const tB = dataText[i +
2];
const bgB = dataBackground[i +
2];
// Ignore pixels that are the same where pixels that are different between the two
// images are assumed to belong to the text within the node.
if (tR === bgR && tG === bgG && tB === bgB) {
continue;
}
foundDistinctColor =
true;
const bgColor = `rgb(${bgR}, ${bgG}, ${bgB})`;
let luminance = luminances[bgColor];
if (!luminance) {
// Calculate luminance for the RGB value and store it to only measure once.
luminance = calculateLuminance([bgR, bgG, bgB]);
luminances[bgColor] = luminance;
}
if (minLuminance >= luminance) {
minLuminance = luminance;
min = [bgR, bgG, bgB,
1];
}
if (maxLuminance <= luminance) {
maxLuminance = luminance;
max = [bgR, bgG, bgB,
1];
}
}
if (!foundDistinctColor) {
return null;
}
return minLuminance === maxLuminance ? { value: max } : { min, max };
}
