PHP按最大宽高等比例缩放图片类

<?php
class slpic {
    //原图片文件，包含路径和文件名
    var $orpic; 
    //原图的临时图像
    var $tempic;
    //缩略图
    var $thpic;
    //原宽度
    var $width; 
    //原高度
    var $height;
    //图片类型
    var $type;
    //缩略后的宽度
    var $thwidth;
    //缩略后的高度
    var $thheight;
     
    function __construct($file){
        $this->orpic = $file;
        $infos = getimagesize($file);
        $this->width = $infos[0];
        $this->height = $infos[1];
        $this->type = $infos[2];
    }
     
    //根据用户所指定最大宽高来计算缩略图尺寸
    function cal_size($maxwidth, $maxheight){
        //缩略图最大宽度与最大高度比
        $thcrown = $maxwidth/$maxheight;    
        //原图宽高比
        $crown = $this->width/$this->height;    
        if($crown/$thcrown >= 1){
            $this->thwidth = $maxwidth;
            $this->thheight = $maxwidth/$crown;
        } else {
            $this->thheight = $maxheight;
            $this->thwidth = $maxheight*$crown;
        }
    }
     
    function init(){
        switch($this->type){
            case 1:     //GIF
                $this->tempic = imagecreatefromgif($this->orpic);
                break;
            case 2:     //JPG
                $this->tempic = imagecreatefromjpeg($this->orpic);
                break;
            case 3:     //PNG
                $this->tempic = imagecreatefrompng($this->orpic);
                break;
            default:
                echo '暂不支持该图片格式';
        }
    }
 
    function resize($maxwidth, $maxheight){
        //初始化图像
        $this->init();
        //计算出缩略图尺寸
        $this->cal_size($maxwidth, $maxheight);
         
        $this->thpic = imagecreatetruecolor($this->thwidth, $this->thheight);
        imagecopyresampled($this->thpic, $this->tempic, 0, 0, 0 ,0, $this->thwidth, $this->thheight, $this->width, $this->height);
    }
     
    function save($filename, $type){
        switch($type){
            case 'jpg':
            case 'jpeg':
                imagejpeg($this->thpic, $filename);
                break;
            case 'png':
                imagepng($$this->thpic, $filename);
                break;
            case 'gif':
                imagegif($$this->thpic, $filename);
                break;
            default:
                echo '暂不支持您所选择的格式';
        }
    }
}
?>