title: openGL rotation with respect to x axis in view coordinator
body: <p>Suppose I have a starting view like this</p>
  
  <p><a href="https://i.stack.imgur.com/iGHJD.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/iGHJD.png" alt="enter image description here"></a>
  With code </p>
  
  <blockquote>
    <p>gluLookAt(eye.x, eye.y, eye.z, ref.x, ref.y, ref.z,
    viewup.x,viewup.y,viewup.z);</p>
  </blockquote>
  
  <p>here </p>
  
  <blockquote>
    <p>(eye.x, eye.y, eye.z) = (5.0, 5.0, 10.0);
    (ref.x, ref.y, ref.z) = (0,0, 0) ;
    (viewup.x, viewup.y, viewup.z) = (0, 1, 0);</p>
  </blockquote>
  
  <p>May I know how do I change eye.x, eye.y and eye.z's value so the view coordinate will have a rotation respect to x axis like the following two screenshots.</p>
  
  <p><a href="https://i.stack.imgur.com/l2Afk.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/l2Afk.png" alt="enter image description here"></a>
  <a href="https://i.stack.imgur.com/7kduT.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/7kduT.png" alt="enter image description here"></a></p>
  
  <p>Is there a rotation matrix operation in view coordinate just like model coordinate's rotation?</p>
  
  <p>Thanks</p>