/*

     *说明：函数功能是生成验证码

     * 参数说明：输入 长度，宽度，高度

     */

    function vcode($_code_length = , $_width = , $_height = ){

        $_font=dirname(__FILE__).'/font/Elephant.ttf';//注意字体路径要写对，否则显示不了图片

        $_fontsize=$_height/1.8;

        $_nmsg="";

        for($i=;$i<$_code_length;$i++){

            $_nmsg .= dechex(mt_rand(,));

        }

        if(!isset($_SESSION)){

            session_start();

        }

        $_SESSION["vcode"] = $_nmsg;

        $_img = imagecreatetruecolor($_width, $_height);

        $_white = imagecolorallocate($_img, , , );

        imagefill($_img, , , $_white);

        $_gray = imagecolorallocate($_img, , , );

        imagerectangle($_img, , , $_width-, $_height-, $_gray);

        for ($i=; $i < ; $i++) {

            $_md_color = imagecolorallocate($_img, mt_rand(,), mt_rand(,), mt_rand(,));

            imageline($_img, mt_rand(,$_width), mt_rand(, $_height),mt_rand(,$_width), mt_rand(, $_height), $_md_color);

        }

        for ($i=; $i < ; $i++) {

            $_md_color = imagecolorallocate($_img, mt_rand(,), mt_rand(,), mt_rand(,));

            imagestring($_img, , mt_rand(,$_width-), mt_rand(, $_height-), "*", $_md_color);

        }

        for ($i=; $i < $_code_length ; $i++) {

            $_md_color = imagecolorallocate($_img, mt_rand(,), mt_rand(,), mt_rand(,));

            //imagestring($_img, 5, $i * $_width/$_code_length+ mt_rand(1, 10), mt_rand(1, $_height/2), $_SESSION["vcode"][$i], $_md_color);

            imagettftext($_img,$_fontsize,mt_rand(-,),$_fontsize*$i+mt_rand(,),$_height / 1.4,$_md_color,$_font,$_SESSION["vcode"][$i]);

        }

        header("Content-Type:image/png");

        imagepng($_img);

        imagedestroy($_img);

    }