title: opengl glReadPixels
body: <p>I want to get color of a pixel. The pixel is mouse position. I use <code>glReadPixels</code> but i can't </p>
  
  <pre><code>    POINT pt;
      GetCursorPos(&amp;pt);
      unsigned char pixel[3];
      glReadPixels(pt.x, pt.y, 1, 1, GL_RGB, GL_UNSIGNED_BYTE, pixel);
  </code></pre>
  
  <p>After this codes value of pixel is: <code>'Ì'</code>
  any idea?</p>