title: Swap buffer synchronization
body: <p>I have four windows on a single display system where each is with its own context and its own drawable (saving that two of them are children to one others). I wish to synchronize the process of swapping the buffer of these windows that it be executed at the same time. A quick search yields me with these possible alternatives.</p>
  
  <ul>
  <li><code>GLX_SGIX_swap_group</code> : Is only available on X11 system.</li>
  <li><code>NV_swap_group</code> (<code>WGL_NV_swap_group</code>/<code>GLX_NV_swap_group</code>) : Is available only on Quadro GPUs with framelock support.</li>
  <li><code>GLX_OML_sync_control</code> : Offer sync control with counter offered on vsync and swap, but may require more tuning in order to implement one for group swapping. Also is not available NV and fglrx system(?) But does have support for both window and X11 system.</li>
  </ul>
  
  <p>Each seemed to be with their own limitation, especially in terms of hardware support. I have read that Software Swap Synchronization is also feasible, like the swap barrier offered in Equalizer? Is it possible to have a pointer on how one might be implement? Or if there are alternatives I may be redirected to?    </p>