After reading this tutorial, one would be able to write very simple graphical programs, but not programs with a descent user interface. For such programs, one of the previously mentioned libraries would be used.
The Client And Server Model Of The X Window System
The X window system was developed with one major goal - flexibility. The idea was that the way things look is one thing, but the way things work is another matter. Thus, the lower levels provide the tools required to draw windows, handle user input, allow drawing graphics using colors (or black and white screens), etc. To this point, a decision was made to separate the system into two parts. A client that decides what to do, and a server that actually draws on the screen and reads user input in order to send it to the client for processing.
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