[Xquartz-dev] Custom use interface

Hi! Can you give me a clue where to start developing my own window system? I have read code from original extention: https://github.com/freedesktop/xorg-xserver/tree/master/hw/xquartz Basically, i understand what happening in the code. But, cant understand how to translate it to my situation. For example, how create simple window with hallo world app in it? I know, may be quetion can have long explanation. May be just show me parts of code?   Thanks for your attention. Have a nice day!