title: Request a DepthBuffer in OpenGL ES for iPhone
body: <p>I'm creating a 3D OpenGL ES view on the iPhone and want to set up a depth buffer, so I can use it.  I'm calling <code>glEnable(GL_DEPTH_TEST)</code> and such, but because I haven't set up the z-buffer, it does nothing.</p>
  
  <p>I'm looking for an equivalent call to
  <code>glutInitDisplayMode(GLUT_DEPTH)</code></p>
  
  <p>Any help would be most welcome.  Thanks!</p>