Linux GUI C++

I'd like to know if any of you know of any good tutorials for learning GUIs for the X windowing system.

Like GTK or QT? Or like full screen gaming graphics?

Like GTK or QT, but I'd prefer to know the actual API instead of just the toolkits…

EDIT: Was looking into it and noticed a few places saying that programming for X windowing system is incredibly difficult and not worthwhile, so maybe I';ll have to go with GTK or QT, anyone have any opinions on which one is better and why?

try glade. it's a toolkit for GTK+ (with an ide i think), runs on both Win32 and *nix

I'd prefer to learn the actual code rather than use a designer, though GTK or QT I suppose are as good as actual API so (I might learn them…

And I don't care about it working on Windows, I no longer use Windows and don't really care if my programs don't work on Windows, or even compile