function hflip() {
		$tmp=imagecreatetruecolor(
			$width=$this->width(),$height=$this->height());
		imagesavealpha($tmp,TRUE);
		imagefill($tmp,0,0,IMG_COLOR_TRANSPARENT);
		imagecopyresampled($tmp,$this->data,
			0,0,$width-1,0,$width,$height,-$width,$height);
		imagedestroy($this->data);
		$this->data=$tmp;
		return $this->save();
	}