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/** \file
* \brief Library of functions for the Canvas API wrappers
*
* \see https://www.w3.org/TR/generic-sensor/
*
* \author Copyright (C) 2022 Libor Polčák
* \author Copyright (C) 2021 Matus Svancar
*
* \license SPDX-License-Identifier: GPL-3.0-or-later
*/
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program. If not, see <https://www.gnu.org/licenses/>.
//
/** \file
* \ingroup wrappers
*
* Supporting fuctions for Canvas API Wrappers
*/
/**
* Farble image data, original Brave implementation-like
*
* \param data RGBA shallow array, (0,0) coordinates are at the top left,
* see CanvasRenderingContext2D.prototype.getImageData for more details on the
* expected format. Note that the data are modified during the call.
* \param height Height of the original canvas.
* \param width Width of the original canvas.
*/
function farbleCanvasDataBrave(rowIterator, width) {
// PRNG function needs to depend on the original canvas, so that the same
// image is farbled the same way but different images are farbled differently
// See https://pagure.io/JShelter/webextension/issue/23
let crc = new CRC16();
for (row of rowIterator()) {
crc.next(row);
}
var thiscanvas_prng = alea(domainHash, "CanvasFarbling", crc.crc);
var data_count = width * 4;
for (row of rowIterator()) {
for (let i = 0; i < data_count; i++) {
if ((i % 4) === 3) {
// Do not modify alpha
continue;
}
if (thiscanvas_prng.get_bits(1)) { // Modify data with probability of 0.5
// Possible improvements:
// Copy a neighbor pixel (possibly with modifications
// Make bigger canges than xoring with 1
row[i] ^= 1;
}
}
}
}
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