EndroidQrCodeProvider: allow transparent for color

[Buffele]

This enables support for the EndroidQrCodeProvider to allow transparent to be passed for color or bgcolor.

It is useful for bgcolor, but probably not too much for color.
That could be restricted. However, I do not really think that is needed.

[NicolasCARPi]

Hello,

Thank you for your contribution. Please also document this functionality in the documentation.

[willpower232]

Great idea, thanks for the fix. I always forget transparency in PHP is sort of backwards!

Also passing non-hex characters to hexdec (i.e. tr, an, sp) currently raises a deprecation warning so probably something else to catch in the future when they make it a more dramatic failure.

Would it be worth adding some check to confirm that $split is exactly 3 elements long too? Or perhaps checking that $color is exactly 6 characters if it isn't transparent...

[RobThree]

Maybe I'm mistaken but Endroid QR appears to support Alpha?

Then shouldn't this work?

$split = str_split($color, 2);
if (sizeof($split) >= 3) {
  $r = hexdec($split[0]);
  $g = hexdec($split[1]);
  $b = hexdec($split[2]);
  $a = sizeof($split) >= 4 ? hexdec($split[3]) : 0;
}

Handling could be a lot better, maybe even a regex. But the general idea should work, shouldn't it?

Edit:

function parseColor(string $color) : Color {
  if (preg_match('/^#?([0-9a-f]{3,8})$/i', trim($color), $matches) !== false) {
    $len = strlen($matches[1]);
    if ($len !== 5 && $len !== 7) {
        list($r, $g, $b, $a) = str_split($matches[1], $len <= 4 ? 1 : 2);
        return new Color(hexdec($r), hexdec($g), hexdec($b), hexdec($a));
    }
  }
  throw new Exception('Invalid color format');
}

Should handle optional starting # and then RGB, RGBA, RRGGBB and RRGGBBAA.