public function cutImg($target_width,$target_height,$source_x,$source_y,$source_path)
    {
        $source_info = getimagesize($source_path); //获取图像信息

        $source_mime = $source_info['mime']; // 文件类型

        $cropped_width = $target_width;  //截取的宽

        $cropped_height = $target_height;  //截取的高

        switch ($source_mime)

        {
            case 'image/gif':

                $source_image = imagecreatefromgif($source_path);

                break;

            case 'image/jpeg':

                $source_image = imagecreatefromjpeg($source_path);

                break;

            case 'image/png':

                $source_image = imagecreatefrompng($source_path);

                break;

            default:

                return false;

                break;

        }


        imagesavealpha($source_image, true); // 保留源图片透明度
        $cropped_image = imagecreatetruecolor($cropped_width, $cropped_height);
        $color=imagecolorallocatealpha($cropped_image,0,0,0,127); //创建颜色
        imagefill($cropped_image, 0, 0, $color); //设置白底
        // 裁剪
        imagecopy($cropped_image, $source_image, 0, 0, $source_x, $source_y, $cropped_width,$cropped_height);
        $alpha = imagecolorallocatealpha($cropped_image, 0, 0, 0, 127);//透明
        imagecolortransparent($cropped_image,$alpha); //3.设置透明色
        imagefill($cropped_image, 0, 0, $alpha);
        //保存图片到本地
        $res = imagepng($cropped_image,'a.png');
    }