@nuintun/qrcode/esm/detector/utils/pattern.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 { accumulate } from '../../common/utils.js';
import { DIFF_PATTERN_RATIO, DIFF_PATTERN_ALLOWANCE } from './constants.js';
import { getCrossScanline, centerFromScanlineEnd, calculateScanlineNoise, sumScanlineNonzero } from './scanline.js';

/**
 * @module pattern
 */
function isDiagonalScanlineCheckPassed(slash, backslash, ratios, strict) {
  return strict
    ? isMatchPattern(slash, ratios) && isMatchPattern(backslash, ratios)
    : isMatchPattern(slash, ratios) || isMatchPattern(backslash, ratios);
}
function alignCrossPattern(matrix, x, y, overscan, ratios, isVertical) {
  const [scanline, end] = getCrossScanline(matrix, x, y, overscan, isVertical);
  return [isMatchPattern(scanline, ratios) ? centerFromScanlineEnd(scanline, end) : NaN, scanline];
}
function isEqualsSize(size1, size2, ratio) {
  if (size1 > size2) {
    [size1, size2] = [size2, size1];
  }
  return size2 - size1 <= size2 * ratio;
}
function isMatchPattern(scanline, { ratios, modules }) {
  const { length } = scanline;
  const scanlineTotal = sumScanlineNonzero(scanline);
  if (scanlineTotal >= modules) {
    const moduleSize = scanlineTotal / modules;
    const threshold = moduleSize * DIFF_PATTERN_RATIO + DIFF_PATTERN_ALLOWANCE;
    // Allow less than DIFF_PATTERN_RATIO variance from 1-1-3-1-1 or 1-1-1-1-1 proportions.
    for (let i = 0; i < length; i++) {
      const ratio = ratios[i];
      const count = scanline[i];
      const countDiff = Math.abs(count - moduleSize * ratio);
      if (countDiff > threshold) {
        return false;
      }
    }
    return true;
  }
  return false;
}
function calculatePatternNoise(ratios, ...scanlines) {
  let noises = 0;
  let averageNoises = 0;
  const { length } = scanlines;
  const averages = [];
  // scanline length must be equals ratios length.
  for (const scanline of scanlines) {
    const [noise, average] = calculateScanlineNoise(scanline, ratios);
    noises += noise;
    averages.push(average);
  }
  const total = accumulate(averages);
  const averagesAvg = total / length;
  for (const average of averages) {
    averageNoises += Math.abs(average - averagesAvg);
  }
  return noises + averageNoises / total;
}

export { alignCrossPattern, calculatePatternNoise, isDiagonalScanlineCheckPassed, isEqualsSize, isMatchPattern };