Generate QR code by dart native.

gen_qr_code.dart

import 'dart:io';

import 'package:image/image.dart';
import 'package:qr/qr.dart';

void main() async {
  var bytes1 = _genQRCode('大宝好厉害！！！', rectSize: 20);
  File('test1.png').writeAsBytesSync(bytes1);
  var bytes2 = _genQRCode('大宝好厉害！！！', size: 500);
  File('test2.png').writeAsBytesSync(bytes2);
}

List<int> _genQRCode(
  String data, {
  int size,
  int rectSize,
  int qrTypeNumber = 2,
  int qrErrorCorrectLevel = QrErrorCorrectLevel.L,
  int gap = 20,
  String frontColor = '#000000',
  String backgroundColor = '#ffffff',
  bool withBorder = true,
  String borderColor = '#666666',
}) {
  assert(!(size == null && rectSize == null));
  var qrCode = QrCode(qrTypeNumber, qrErrorCorrectLevel)
    ..addData(data)
    ..make();
  var rect;
  var rawGap;
  if (rectSize != null) {
    rect = rectSize;
    rawGap = gap;
    size = qrCode.moduleCount * rect + rawGap * 2;
  } else {
    var cw = size - 2 * gap;
    var r = cw / qrCode.moduleCount;
    rawGap = gap + (cw - qrCode.moduleCount * r) ~/ 2;
    rect = ((size - 2 * rawGap) / qrCode.moduleCount).floor();
  }
  print('gap size: $gap => $rawGap, rect size: $rect');
  var image = Image(size, size);
  fill(image, _parseColor(backgroundColor));
  for (var x = 0; x < qrCode.moduleCount; x++) {
    for (var y = 0; y < qrCode.moduleCount; y++) {
      var y1 = y * rect + rawGap;
      var x1 = x * rect + rawGap;
      var x2 = x1 + rect;
      var y2 = y1 + rect;
      if (qrCode.isDark(y, x)) {
        fillRect(image, x1, y1, x2, y2, _parseColor(frontColor));
        if (withBorder) {
          drawRect(image, x1, y1, x2, y2, _parseColor(borderColor));
        }
      }
    }
  }
  return encodePng(image);
}

int _parseColor(String color) {
  var length = color.length;
  if (length == 6) {
    return int.parse('ff' + color, radix: 16);
  } else if (length == 7) {
    return int.parse('ff' + color.substring(1), radix: 16);
  } else if (length == 8) {
    return int.parse(color, radix: 16);
  } else if (length == 9) {
    return int.parse(color.substring(1), radix: 16);
  }
  throw 'Unsupported color string<$color>.';
}