When resizing an X11 window with OpenGL content, the image becomes garbled and certain parts of the window, usually at the parts that wasn’t originally part of the initial framebuffer.
I couldn’t find any documentation on if I supposed to call some extra functions when the window is being resized or not. I otherwise process that even as a system event, so it can be further processed by the program using my API.
This is a wild guess but you probably need to rerender the framebuffer when you get the resize event. I’d expect most libraries/frameworks/engines would take care of that for you, but if you’ve rolled your own using the base X11 and OpenGL libraries you might need to set that up. X11 has a lot of strange quirks due to its network centric design.