php 图片生成缩略图方法

<?php
/*构造函数-生成缩略图,参数说明:
$srcFile-图片文件名,
$name-另存文件名,
$maxwidth-图片保存宽度,
$maxheight-图片保存高度
*/
resizeImage('a.jpg', '100', '100', '100', '100', '100');
function ResizeImage($srcFile, $name, $maxwidth=120, $maxheight=120){
    

     $data = GetImageSize($srcFile); 
     print_r($data);
     switch($data[2]) 
     { 
         case 1: 
             $im=@ImageCreateFromGIF($srcFile); 
         break; 
         case 2: 
             $im=@ImageCreateFromJPEG($srcFile); 
         break; 
         case 3: 
             $im=@ImageCreateFromPNG($srcFile); 
         break; 
     } 
     if(!$im) return False; 
    
     $width = imagesx($im);
     $height = imagesy($im);
     if(($maxwidth && $width > $maxwidth) || ($maxheight && $height > $maxheight)){
         if($maxwidth && $width > $maxwidth){
             $widthratio = $maxwidth/$width;
             $RESIZEWIDTH=true;
         }
         if($maxheight && $height > $maxheight){
             $heightratio = $maxheight/$height;
             $RESIZEHEIGHT=true;
         }
         if($RESIZEWIDTH && $RESIZEHEIGHT){
             if($widthratio < $heightratio){
                 $ratio = $widthratio;
             }else{
                 $ratio = $heightratio;
             }
         }elseif($RESIZEWIDTH){
             $ratio = $widthratio;
         }elseif($RESIZEHEIGHT){
             $ratio = $heightratio;
         }
         $newwidth = $width * $ratio;
         $newheight = $height * $ratio;
         if(function_exists("imagecopyresampled")){
             $newim = imagecreatetruecolor($newwidth, $newheight);
             imagecopyresampled($newim, $im, 0, 0, 0, 0, $newwidth, $newheight, $width, $height);
         }else{
             $newim = imagecreate($newwidth, $newheight);
             imagecopyresized($newim, $im, 0, 0, 0, 0, $newwidth, $newheight, $width, $height);
         }
         ImageJpeg ($newim, $name);
         ImageDestroy ($newim);
     }
     else{
         ImageJpeg ($im, $name);
     }
    
     ImageDestroy ($im);
}