https://blog.faceutil.com/2017/04/01/%eb%b9%88%eb%b8%94%eb%9e%ad%ed%81%ac-doom-1-%eb%91%a01-%eb%8b%a4%ec%9a%b4-%eb%8b%a4%ec%9a%b4%eb%b0%9b%ea%b8%b0-%eb%8b%a4%ec%9a%b4%eb%a1%9c%eb%93%9c-%e3%88%9b/