title: What is the meaning of screenSurface->format in SDL?
body: <p>I have recently started studying SDL and I would like to get a good understanding of it. I have followed Lazy Foo' Productions' tutorials and there is one statement that I don't get. What is the meaning behind the <code>gScreenSurface-&gt;format</code> or <code>screenSurface-&gt;format</code> in the examples below?</p>
  
  <pre class="lang-cpp prettyprint-override"><code>SDL_ConvertSurface( screenSurface, gScreenSurface-&gt;format, 0 );
  </code></pre>
  
  <pre class="lang-cpp prettyprint-override"><code>SDL_FillRect( screenSurface, NULL, SDL_MapRGB( screenSurface-&gt;format, 0xFF, 0xFF, 0xFF ));
  </code></pre>
  
  <p>Hope someone can explain it, brief explanation needed only. Thanks!</p>