title: glReadPixels() "data" argument usage?
body: <p>I'm trying to use glReadPixels to get color data from an image. I'm supposed to be using glReadPixels but I can't seem to figure it out. It's part of a much larger project, but right now all I want is to know how to properly use this. </p>
  
  <p>I looked it up and got something like this: </p>
  
  <pre><code>    void glReadPixels(GLint x, 
         GLint y, 
         GLsizei width, 
         GLsizei height, 
         GLenum format, 
         GLenum type, 
         GLvoid* data);
  </code></pre>
  
  <p>But I'm not sure what I should be putting in as that last argument, and when I do, how I would even use it. Help would really be appreciated! (ie: a simple example of how to use it, or how to get the color) </p>