ThinkPHP做文字水印时提示call an undefined function exif_imag

<?php
/*
PHP添加文字水印类 V1.0
作者：Yu Tiedun
邮箱：
修改日期：2010-03-07
支持图片格式：gif,jpg,png
水印的位置自己根据需要调整
如能修改得更好,请发一份给我
*/
class WaterPrint
{
//类开始
??? public $text,$color,$size,$font,$angle,$px,$py,$im;
//要添加的文字
public function GetWpText($text)
{
?? $this->text = $text;
}
//添加文字的颜色
public function GetFtColor($color)
{
?? $this->color = $color;
}
//添加文字的字体
public function GetFtType($font)
{
?? $this->font = $font;
}
?
//添加文字的大小
public function GetFtSize($size)
{
?? $this->size = $size;
}
//文字旋转的角度
public function GetTtAngle($angle)
{
?? $this->angle = $angle;
}
//添加文字的位置
public function GetTtPosit()
{
?? $this->px = 10;
?? $this->py = imagesy($this->im) - 20;
}
//添加文字水印
public function AddWpText($pict)
{
?? $ext = exif_imagetype($pict);
??? switch ($ext) {
?? case 1:
?? $picext = "gif";
??? $this->im = imagecreatefromgif($pict);
??? break;
?? case 2:
?? $picext = "jpg";
??? $this->im = imagecreatefromjpeg($pict);
??? break;
?? case 3:
?? $picext = "png";
??? $this->im = imagecreatefrompng($pict);
??? break;
?? default:
?? $this->Errmsg("不支持的文件格式!");
??? break;
?? }
?? //$this->picext = $picext;
?? $this->GetTtPosit();
?? $im?? = $this->im;
?? $size = $this->size;
?? $angle= $this->angle;
?? $px?? = $this->px;
?? $py?? = $this->py;
?? $color= $this->color;
?? $font = $this->font;
?? $text = $this->text;
?? $color= imagecolorallocate($im,255,0);
?? imagettftext($im,$text);
?? switch ($picext) {
?? case "gif":
?? imagegif($im,$pict);
??? break;
?? case "jpg":
?? imagejpeg($im,$pict,100);
??? break;
?? case "png":
????? imagealphablending($im,false);
??????? imagesavealpha($im,true);
?????? imagepng($im,$pict);
??? break;
?? }
?? imagedestroy($im);
}
//错误信息提示
public function Errmsg($msg)
{
??? echo "<script language='javascript'>alert('".$msg."');</script>";
}
//类结束
}
?>

<?php
header("Content-type: text/html; charset=gbk");
require("wptext_class.php");
$pict = "images/button2.png"; //目标图片
//$text = "XP/Vista/Win7"; //要添加的文字
$text = "文字水印测试";
$text = iconv("gb2312","utf-8",$text); //防止中文乱码
$size = 20; //文字大小
$font = "c:/windows/fonts/arial.ttf"; //字体
$angle = 0; //旋转角度,逆时针
$wptext = new WaterPrint();
$wptext->GetWpText($text);
$wptext->GetFtSize($size);
$wptext->GetFtType($font);
$wptext->GetTtAngle($angle);
$wptext->AddWpText($pict);
$wptext = null;
?>
<a href="images/button2.png" target="_blank">查看结果</a>