QR code background is transparent when it should be white

[rohintoncollins]

I am using your example code and was able to produce a barcode, but the background looks transparent when I think it should be white. Your example code cannot read this barcode but has no problems reading barcodes produced by other libraries.

The QR code looks alright in Finder preview on macOS, I think because the Finder preview has a white background:

But if I open it in the Preview app, which has a grey background then it looks like this:

This is an example of another barcode, opened by preview, which I can open with zxing2:

My guess is that the background of the image is transparent when it should be white which is causing the decoder to fail. A shame because I really liked your library. Surely I can fix this easily enough by changing the background to white?

[rohintoncollins]

I was right and managed to fix this by drawing white squares. Here is the working encode function. I would suggest you update your documentation:

Uint8List encode(String mnemonic) {
  final qrcode = Encoder.encode(mnemonic, ErrorCorrectionLevel.h);
  final matrix = qrcode.matrix!;
  const scale = 4;

  var image = img.Image(
      width: matrix.width * scale,
      height: matrix.height * scale,
      numChannels: 4);

  for (var x = 0; x < matrix.width; x++) {
    for (var y = 0; y < matrix.height; y++) {
      if (matrix.get(x, y) == 1) {
        img.fillRect(image,
            x1: x * scale,
            y1: y * scale,
            x2: x * scale + scale,
            y2: y * scale + scale,
            color: img.ColorRgba8(0, 0, 0, 0xFF),
            maskChannel: img.Channel.luminance);
      } else {
        img.fillRect(image,
            x1: x * scale,
            y1: y * scale,
            x2: x * scale + scale,
            y2: y * scale + scale,
            color: img.ColorRgba8(0xFF, 0xFF, 0xFF, 0xFF),
            maskChannel: img.Channel.luminance);
      }
    }
  }

  return img.encodePng(image);
}