Mike42\Escpos\Printer::wrapperSendGraphicsData PHP Method

    private function wrapperSendGraphicsData($m, $fn, $data = '')
    {
        if (strlen($m) != 1 || strlen($fn) != 1) {
            throw new InvalidArgumentException("wrapperSendGraphicsData: m and fn must be one character each.");
        }
        $header = $this->intLowHigh(strlen($data) + 2, 2);
        $this->connector->write(self::GS . "(L" . $header . $m . $fn . $data);
    }