title: How are GUI's really made?
body: <p>My question is<br>
  Gui libraries like Qt and lets say for Windows operating systems
  how do they create all those graphical user interfaces(windows etc).  </p>
  
  <p>Does each operating system gives API's or something else to do so?If yes, then how operating systems draw all those windows and things.Do they (operating systems) "control" the screen and then draw each pixel one by one to achieve their goal the GUI?  </p>
  
  <p>I would like an answer that explains things at the lowest level possible but well i don't demand someone to write me everything that happens( even if i would like to) because i know many things are behind all these.So for this reason comments with links or suggested books which explain with <strong>details</strong><br>
  on what is happening under the hood would be appreciated.</p>