PHP生成条形码有关问题

PHP生成条形码问题
官网地址http://www.barcodephp.com/en/userguide

我现在想将这个方法打包成函数，然后传数值进去，返回的是html代码，例如这种字符串

PHP code

function barcode($listing)    {    // Including all required classes        require_once('class/BCGFontFile.php');        require_once('class/BCGColor.php');        require_once('class/BCGDrawing.php');                // Including the barcode technology        require_once('class/BCGcode39.barcode.php');                // Loading Font        $font = new BCGFontFile('./class/font/Arial.ttf', 18);                // The arguments are R, G, B for color.        $color_black = new BCGColor(0, 0, 0);        $color_white = new BCGColor(255, 255, 255);                $drawException = null;        try {            $code = new BCGcode39();            $code->setScale(2); // Resolution            $code->setThickness(30); // Thickness            $code->setForegroundColor($color_black); // Color of bars            $code->setBackgroundColor($color_white); // Color of spaces            $code->setFont($font); // Font (or 0)            $code->parse($listing); // Text        } catch(Exception $exception) {            $drawException = $exception;        }                /* Here is the list of the arguments        1 - Filename (empty : display on screen)        2 - Background color */        $drawing = new BCGDrawing('', $color_white);        if($drawException) {            $drawing->drawException($drawException);        } else {            $drawing->setBarcode($code);            $drawing->draw();        }                // Header that says it is an image (remove it if you save the barcode to a file)        header('Content-Type: image/png');                // Draw (or save) the image into PNG format.        $drawing->finish(BCGDrawing::IMG_FORMAT_PNG);     }