This is also one of my favorite and most helpful posts I’ve found working with X so far: <a href="http://jichu4n.com/posts/how-x-window-managers-work-and-how-to-write-one-part-i/" rel="nofollow">http://jichu4n.com/posts/how-x-window-managers-work-and-how-...</a>
The XCB tutorial is quite good as well <a href="https://xcb.freedesktop.org/tutorial/" rel="nofollow">https://xcb.freedesktop.org/tutorial/</a><p>Also, if you want to do simple graphics stuff with X11, then I highly recommend looking at <a href="https://www.cairographics.org/" rel="nofollow">https://www.cairographics.org/</a> instead of trying to use the builtin drawing functions that come with X11.
For those that miss it, there's multiple pages. If you go back one page (by hitting the left arrow link), you get an introduction and table of contents.
I don't have anything this cool and interactive, but for those interested I've been working on a comprehensive Wayland book:<p><a href="https://wayland-book.com" rel="nofollow">https://wayland-book.com</a><p>It's a little over halfway done.