php利用GD库生成缩略图

        header("content-type:text/html;charset=gbk");
    ini_set("date.timezone","Asia/chong");
    //判断文件是否为空
    if(empty($_FILES)){
        echo"上传文件过大";
        exit;
    }
    //判断文件上传是否有错误
    if($_FILES['pic']['error']){
        echo "上传文件";
        exit;
    }
    //判断文件类型是否非法获取文件后缀
    $allowtype=array("jpg","png","jpeg","gif");
    $a=explode('.',$_FILES['pic']['name']);
    $index=count($a)-1;
    $ex=strtolower($a[$index]);
    if(!in_array($ex,$allowtype)){
        echo "上传文件非法";
        exit;
    }
    $file=date('YmdHis').rand().".".$ex;
    $src=$_FILES['pic']['tmp_name'];
    $des="upload/".$file;
    $rs=move_uploaded_file($src,$des);


    //缩略图
    //读取已经上传图片
    $image=imagecreatefromjpeg($des);
    $a=getimagesize($des);
    $w=$a[0];
    $h=$a[1];
    if($w>$h){
        $width=300;
        $height=$width/$w*$h;
    }else if($w        $height=300;
        $width=$height/$h*$w;
    }else{
        $width=300;
        $height=300;
    }
    //创建空白新图片
    $newimage=imagecreatetruecolor($width, $height);
    //copy源图片内容 copy新图片
    imagecopyresized($newimage, $image, 0,0, 0,0, $width, $height, $w, $h);
    $filename="upload/s_".$file;
    imagejpeg($newimage,$filename);

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