XRender With Vsync

[Ryan McClue]

I'm rendering with XRender:
XRenderComposite(display, PictOpSrc, src_pict, 0, dst_pict, 0, 0, 0, 0, 0, 0, 
window_width, window_height);
I want this to sync with the monitor's VBLANK, i.e. vsync.
How can this be achieved?
Thanks
--
Ryan McClue, Sydney