Pimcore\Image\Adapter\GD::mirror PHP Method

    public function mirror($mode)
    {
        $this->preModify();
        if ($mode == "vertical") {
            imageflip($this->resource, IMG_FLIP_VERTICAL);
        } elseif ($mode == "horizontal") {
            imageflip($this->resource, IMG_FLIP_HORIZONTAL);
        }
        $this->postModify();
        return $this;
    }