php生成缩略图代码

/**
* 生成缩略图
* $srcName----为原图片路径
* $newWidth，$newHeight----分别缩略图的最大宽，高
* $newName----为缩略图文件名（含路径），默认为加入thumbnail
* @param string $srcName
* @param int $newWidth
* @param int $newHeight
* @param string $newName
* return viod
*/
function resizeImg($srcName,$newWidth,$newHeight,$newName="")
{
        if($newName=="")
        {
                $nameArr=explode('.',$srcName);
                $expName=array_pop($nameArr);
                $expName='thumbnail.'.$expName;
                array_push($nameArr,$expName);
                $newName = implode('.',$nameArr);
        }
        $info = "";
        $data = getimagesize($srcName,$info);
        switch ($data[2])
        {
                case 1:
                        if(!function_exists("imagecreatefromgif")){
                                echo "你的GD库不能使用GIF格式的图片，请使用Jpeg或PNG格式！返回";
                                exit();
                        }
                        $im = ImageCreateFromGIF($srcName);
                        break;
                case 2:
                        if(!function_exists("imagecreatefromjpeg")){
                                echo "你的GD库不能使用jpeg格式的图片，请使用其它格式的图片！返回";
                                exit();
                        }
                        $im = ImageCreateFromJpeg($srcName);
                        break;
                case 3:
                        $im = ImageCreateFromPNG($srcName);
                        break;
        }
        $srcW=ImageSX($im);
        $srcH=ImageSY($im);
        $newWidthH=$newWidth/$newHeight;
        $srcWH=$srcW/$srcH;
        if($newWidthH<=$srcWH){
                $ftoW=$newWidth;
                $ftoH=$ftoW*($srcH/$srcW);
        }
        else{
                $ftoH=$newHeight;
                $ftoW=$ftoH*($srcW/$srcH);
        }
        if($srcW>$newWidth||$srcH>$newHeight)
        {
                if(function_exists("imagecreatetruecolor"))
                {
                        @$ni = ImageCreateTrueColor($ftoW,$ftoH);
                        if($ni) ImageCopyResampled($ni,$im,0,0,0,0,$ftoW,$ftoH,$srcW,$srcH);
                        else
                        {
                                $ni=ImageCreate($ftoW,$ftoH);
                                ImageCopyResized($ni,$im,0,0,0,0,$ftoW,$ftoH,$srcW,$srcH);
                        }
                }
                else
                {
                        $ni=ImageCreate($ftoW,$ftoH);
                        ImageCopyResized($ni,$im,0,0,0,0,$ftoW,$ftoH,$srcW,$srcH);
                }
                if(function_exists('imagejpeg')) ImageJpeg($ni,$newName);
                else ImagePNG($ni,$newName);
                ImageDestroy($ni);
        }
        ImageDestroy($im);
}

resizeImg('123.JPG',150,150);
?>