Future<BitmapDescriptor?> method() async {
  for (var index = 0; index < 3; index++) {
    await _generateMarker(index);
  }
}

Future<BitmapDescriptor?> _generateMarker(int index) async {
  final markerSize = 28;
  final iconSize = markerSize + (_strokeWidth * 2).round();
  final centerMarker = iconSize / 2;
  final radius = markerSize / 2;

  final backgroundPaint = Paint()..isAntiAlias = true;
  final pictureRecorder = ui.PictureRecorder();
  final canvas = Canvas(pictureRecorder);

  final textSpan = TextSpan(
    text: index.toString(),
    style: TextStyle(
      fontSize: 14,
      fontFamily: 'Inter',
      fontWeight: FontWeight.normal,
      height: 20 / 14,
      letterSpacing: 0,
      textBaseline: TextBaseline.alphabetic,
      decoration: TextDecoration.none,
      leadingDistribution: TextLeadingDistribution.even,
    ),
  );

  final textPainter =
      TextPainter(
        text: textSpan,
        textDirection: TextDirection.ltr,
      )..layout(
        minWidth: 0,
        maxWidth: iconSize.toDouble(),
      );
  backgroundPaint.color = Colors.green;

  canvas.drawCircle(Offset(centerMarker, centerMarker), radius, backgroundPaint);

  textPainter.paint(
    canvas,
    Offset(
      (iconSize - textPainter.width) / 2,
      (iconSize - textPainter.height) / 2,
    ),
  );

  final pic = pictureRecorder.endRecording();
  final img = await pic.toImage(iconSize.toInt(), iconSize.toInt());
  final byteData = await img.toByteData(format: ui.ImageByteFormat.png); //<-- Exception throws here
  final buffer = byteData?.buffer.asUint8List();

  if (buffer == null) return null;

  return BitmapDescriptor.fromBytes(buffer);
}