@nuintun/qrcode/esm/common/image/utils/lzw/index.js

A pure JavaScript QRCode encode and decode library.

/**
 * @module QRCode
 * @package @nuintun/qrcode
 * @license MIT
 * @version 5.0.2
 * @author nuintun <nuintun@qq.com>
 * @description A pure JavaScript QRCode encode and decode library.
 * @see https://github.com/nuintun/qrcode#readme
 */

import { Dict } from './Dict.js';
import { DictStream } from './DictStream.js';

/**
 * @module index
 * @see https://github.com/google/dart-gif-encoder
 */
function compress(pixels, depth, stream) {
  const dict = new Dict(depth);
  const buffer = new DictStream(dict);
  buffer.write(dict.bof);
  if (pixels.length > 0) {
    let code = pixels[0];
    const { length } = pixels;
    for (let i = 1; i < length; i++) {
      const pixelIndex = pixels[i];
      const nextCode = dict.get(code, pixelIndex);
      if (nextCode != null) {
        code = nextCode;
      } else {
        buffer.write(code);
        // Reset dict when full.
        if (!dict.add(code, pixelIndex)) {
          buffer.write(dict.bof);
          dict.reset();
        }
        code = pixelIndex;
      }
    }
    buffer.write(code);
  }
  buffer.write(dict.eof);
  buffer.pipe(stream);
}

export { compress };