How do I wait for vertical retrace?

Barry Scott barry.scott at
Wed May 7 03:30:07 PDT 2008

Carsten Haitzler (The Rasterman) wrote:
> yup. a "vsync" event would b a godsend. personally - if you are not local...
> don't use this method. give up. the real reason for this is to make a vsync fps
> limited composite manager. so the composite manager will limit screen upates to
> X frames per seconds - irrespective of what client apps actually redraw at, AND
> also force updats to be synced to vblank. a composite manager that isn't local
> is going to be pretty nasty anyway.

We use the DRM VSYNC to do smooth tear-free animation. When we added 
we had to change xcompmgr to VSYNC and then have it send the signal to 
the rest of the
system to that allows the apps to update windows in time for xcompmgr to 
compose the
next frame.

If X supports an event to tell apps to draw-now-to-avoid-problems then 
that event will need
to come from the compositing manager if you have one and not the X server.


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