PHP GD库水印自动换行无法显示函数文字

<?php  if(isset($_get['str']) and $_get['str']!=""){  $im = imagecreatefromjpeg('gd.jpg');  $font_size = 12;  $fontname = '33.ttf';  $black = imagecolorallocate($im,0,0,0);  $str = $_get['str'] ;    function chararray($str,$charset="gbk"){        $re['utf-8']   = "/[\x01-\x7f]|[\xc2-\xdf][\x80-\xbf]|[\xe0-\xef][\x80-\xbf]{2}|[\xf0-\xff][\x80-\xbf]{3}/";        $re['gb2312'] = "/[\x01-\x7f]|[\xb0-\xf7][\xa0-\xfe]/";        $re['gbk']    = "/[\x01-\x7f]|[\x81-\xfe][\x40-\xfe]/";        $re['big5']   = "/[\x01-\x7f]|[\x81-\xfe]([\x40-\x7e]|\xa1-\xfe])/";        preg_match_all($re[$charset], $str, $match);        return $match;    }    /* 返回一个字符串在图片中所占的宽度 */    function charwidth($fontsize,$fontangle,$ttfpath,$char){        $box = @imagettfbbox($fontsize,$fontangle,$ttfpath,$char);        $width = max($box[2], $box[4]) - min($box[0], $box[6]);        return $width;    }        /* 这几个变量分别是 字体大小, 角度, 字体名称, 字符串, 预设宽度, 编码 */    function autowrap($fontsize,$fontangle,$ttfpath,$str,$width,$charset='gbk'){        $_string = "";        $_width = 0;        $temp = chararray($str);        //var_dump($temp);        foreach ($temp[0] as $k=>$v){            $w = charwidth($fontsize,$fontangle,$ttfpath,$v);            $_width += intval($w);            if (($_width > $width) && ($v !== "")){                $_string .= "\n";                $_width = 0;            }            $_string .= $v;            $w = 0;            //echo $v;        }        $_string = mb_convert_encoding($_string, "html-entities","gbk" );        return $_string;    }    $str = autowrap(12,0,'33.ttf','返回一个字符的数组',250);  imagettftext($im,$font_size,0,35,160,$black,$fontname,$str);  header('content-type: image/jpeg');  imagejpeg($im);  imagedestroy($im) ;  } ?>