PHP 生成缩略图片的有关问题

PHP 生成缩略图片的问题
我是这样想....
我设置要生成的缩略图片大小为100*50

我的原图片是1000*600

我想把原图片等比缩放，水平或垂直居中.其它的地方用白色填充，不知道我的意思表达清了没

------解决方案--------------------
原图 w1 h1
新图 w2 h2

if w1/h1 > w2/h2 //缩放后高度不足
新图高 h = h2/w2*w1
垂直居中时的偏移y = (h2-h)/2
x = 0
if w1/h1 新图宽 w = w2/h2*h1
水平居中时的偏移x = (x2-x)/2
y = 0


------解决方案--------------------
某cms的图片处理类

PHP code

 __construct($targetfile, $cfg_thumb, $cfg_watermarktext, $photo_waterpos, $photo_diaphaneity, $photo_wheight, $photo_wwidth, $cfg_watermarktype, $photo_marktrans,$trueMarkimg, $attach);    }    // 析构函数    function __construct($targetfile, $cfg_thumb, $cfg_watermarktext, $photo_waterpos, $photo_diaphaneity, $photo_wheight, $photo_wwidth, $cfg_watermarktype, $photo_marktrans,$trueMarkimg, $attach = array())    {        $this->thumbstatus = $cfg_thumb;        $this->watermarktext = $cfg_watermarktext;        $this->watermarkstatus = $photo_waterpos;        $this->watermarkquality = $photo_marktrans;        $this->watermarkminwidth = $photo_wwidth;        $this->watermarkminheight = $photo_wheight;        $this->watermarktype = $cfg_watermarktype;        $this->watermarktrans = $photo_diaphaneity;        $this->animatedgif = 0;        $this->targetfile = $targetfile;        $this->attachinfo = @getimagesize($targetfile);        $this->attach = $attach;        switch($this->attachinfo['mime'])        {            case 'image/jpeg':                $this->imagecreatefromfunc = function_exists('imagecreatefromjpeg') ? 'imagecreatefromjpeg' : '';                $this->imagefunc = function_exists('imagejpeg') ? 'imagejpeg' : '';                break;            case 'image/gif':                $this->imagecreatefromfunc = function_exists('imagecreatefromgif') ? 'imagecreatefromgif' : '';                $this->imagefunc = function_exists('imagegif') ? 'imagegif' : '';                break;            case 'image/png':                $this->imagecreatefromfunc = function_exists('imagecreatefrompng') ? 'imagecreatefrompng' : '';                $this->imagefunc = function_exists('imagepng') ? 'imagepng' : '';                break;        }//为空则匹配类型的函数不存在        $this->attach['size'] = empty($this->attach['size']) ? @filesize($targetfile) : $this->attach['size'];        if($this->attachinfo['mime'] == 'image/gif')        {            $fp = fopen($targetfile, 'rb');            $targetfilecontent = fread($fp, $this->attach['size']);            fclose($fp);            $this->animatedgif = strpos($targetfilecontent, 'NETSCAPE2.0') === false ? 0 : 1;        }    }    /**     *  生成缩略图     *     * @access    public     * @param     int  $thumbwidth  图片宽度     * @param     int  $thumbheight  图片高度     * @param     int  $preview  是否预览     * @return    void     */    function thumb($thumbwidth, $thumbheight, $preview = 0)    {        $this->thumb_gd($thumbwidth, $thumbheight, $preview);        if($this->thumbstatus == 2 && $this->watermarkstatus)        {            $this->image($this->targetfile, $this->attach);            $this->attach['size'] = filesize($this->targetfile);        }    }        /**     *  使用gd生成缩略图     *     * @access    public     * @param     int  $thumbwidth  图片宽度     * @param     int  $thumbheight  图片高度     * @param     int  $preview  是否预览     * @return    void     */    function thumb_gd($thumbwidth, $thumbheight, $preview = 0)    {        if($this->thumbstatus && function_exists('imagecreatetruecolor') && function_exists('imagecopyresampled') && function_exists('imagejpeg'))        {            $imagecreatefromfunc = $this->imagecreatefromfunc;            $imagefunc = $this->thumbstatus == 1 ? 'imagejpeg' : $this->imagefunc;            list($imagewidth, $imageheight) = $this->attachinfo;            if(!$this->animatedgif && ($imagewidth >= $thumbwidth || $imageheight >= $thumbheight))            {                $attach_photo = $imagecreatefromfunc($this->targetfile);                $x_ratio = $thumbwidth / $imagewidth;                $y_ratio = $thumbheight / $imageheight;                if(($x_ratio * $imageheight) thumbstatus == 1 ? $this->targetfile.'.thumb.jpg' : $this->targetfile) : './watermark_tmp.jpg';                $thumb_photo = imagecreatetruecolor($thumb['width'], $thumb['height']);                imagecopyresampled($thumb_photo, $attach_photo, 0, 0, 0, 0, $thumb['width'], $thumb['height'], $imagewidth, $imageheight);                if($this->attachinfo['mime'] == 'image/jpeg')                {                    $imagefunc($thumb_photo, $targetfile, 100);                }                else                {                    $imagefunc($thumb_photo, $targetfile);                }                $this->attach['thumb'] = $this->thumbstatus == 1 ? 1 : 0;            }        }    }    }//End Class

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