PHP生成图片缩略图类示例都有什么？

class App_image_helper {
 protected $imgFileName;
 protected $imgWidth;
 protected $imgHeight;
 protected $imgMime;
 protected $imgResource;
 static $imgMineList
  = array(
   'jpeg' => 'image/jpeg',
   'gif' => 'image/gif',
   'png' => 'image/png',
   'wbmp' => 'image/wbmp',
  );
 /**
  * 根据文件名，初始化图片，
  * 计算出给定图片的宽、高、图片类型，并获取图片的资源保存到内存，便于下次使用
  * App_image_helper constructor.
  *
  * @param $fileName
  */
 public function __construct($fileName) {
  $this->imgFileName = $fileName;
  list($this->imgWidth, $this->imgHeight, $this->imgMime) = $this->getImageInfo($this->imgFileName);
  $this->imgResource = $this->getImageResource($this->imgFileName);
 }
 /**
  * 根据图片路径获取相关宽、高、MIME类型信息
  *
  * @param $fileName
  *
  * @return array|null
  */
 protected function getImageInfo($fileName) {
  $result = null;
  if ( is_file($fileName) ) {
   $tmpImageInfo = getimagesize($fileName);
   if ( $tmpImageInfo ) {
    $result = array($tmpImageInfo[0], $tmpImageInfo[1], $tmpImageInfo['mime']);
   }
  }
  return $result;
 }
 /**
  * 将图片文件转为资源类类型
  *
  * @param $fileName
  *
  * @return null|resource
  */
 protected function getImageResource($fileName) {
  $image = null;
  if ( is_file($fileName) ) {
   switch ($this->imgMime) {
    case self::$imgMineList['jpeg']:
     $image = imagecreatefromjpeg($fileName);
     break;
    case self::$imgMineList['gif']:
     $image = imagecreatefromgif($fileName);
     break;
    case self::$imgMineList['png']:
     $image = imagecreatefrompng($fileName);
     break;
    case self::$imgMineList['wbmp']:
     $image = imagecreatefromwbmp($fileName);
     break;
    default:
     break;
   }
  }
  return $image;
 }
 /**
  * 可根据固定宽，等比缩放图片；或根据百分比，等比缩放图片
  *
  * @param int $width
  * @param int $percent
  *
  * @return array|null
  */
 protected function getSizeByScale($width = 360, $percent = 1) {
  $result = null;
  if ( $this->imgWidth && $this->imgHeight ) {
   if ( $width ) {
    $result = array($width, intval($width * $this->imgHeight / $this->imgWidth));
   } elseif ( $percent ) {
    $result = array(intval($this->imgWidth * $percent), intval($this->imgHeight * $percent));
   }
  }
  return $result;
 }
 /**
  * 外调
  *
  * @param int $percentOrWidth int整数表示图片缩放为固定宽度，0.0~0.99999表示缩放百分比
  * @param null $fileName
  * @param int $quality
  * @param bool $reSample  重新采样图片，默认是
  *
  * @return bool
  */
 public function createImage($percentOrWidth = 1, $fileName = null, $quality = 75, $reSample = true) {
  $result = false;
  $fileName ? header('Content-Type: ' . $this->imgMime) : false;
  $size = $this->getSizeByScale(($percentOrWidth <= 1) ? null : $percentOrWidth, $percentOrWidth);
  if ( $size ) {
   $thumb = imagecreatetruecolor($size[0], $size[1]);
   if ( $reSample ) {
    imagecopyresampled($thumb, $this->imgResource, 0, 0, 0, 0, $size[0], $size[1], $this->imgWidth, $this->imgHeight);
   } else {
    imagecopyresized($thumb, $this->imgResource, 0, 0, 0, 0, $size[0], $size[1], $this->imgWidth, $this->imgHeight);
   }
   $result = imagejpeg($thumb, $fileName, $quality);
  }
  return $result;
 }
}