protected function exitVerticalFrames(array $lines, $line_method)
    {
        $keyframes  = [];
        $line_count = count($lines);

        for ($i = $line_count - 1; $i >= 0; $i--) {
            $keyframes[] = $this->$line_method($lines, $line_count, $i);
        }

        return $keyframes;
    }