Re: [Mesa3d-dev] [mesa patch 1/3] dri2: Event driven buffer validation.

[Michel D. <mi...@da...>]

On Fri, 2010-01-22 at 00:10 +0100, Francisco Jerez wrote: 
> Michel Dänzer <mi...@da...> writes:
> 
> > On Sat, 2010-01-16 at 23:01 +0100, Francisco Jerez wrote: 
> >> When a buffer invalidation event is received from the X server, the
> >> "invalidate" hook of the DRI2 flush extension is executed: A generic
> >> implementation (dri2InvalidateDrawable) is provided that just bumps
> >> the "pStamp" sequence number in __DRIdrawableRec.
> >> 
> >> For old servers not supporting buffer invalidation events, the
> >> invalidate hook will be called after flushing the fake front/back
> >> buffer (that's typically once per frame -- not a lot worse than the
> >> situation we were in before).
> >
> > When the invalidate event is available, IMO the buffers should also only
> > be invalidated after a buffer swap / front buffer flush, not 'in the
> > middle of a frame'.
> >
> Event-driven applications want the new buffers immediately after getting
> the resize event, otherwise they could try to draw outside the bounds of
> the old buffers, and that rendering would be lost.

I still don't see any benefit to changing the buffers while the app is
rendering a frame, but I guess the problem is that the DRI2 code in
libGL doesn't know if that's the case or not...

> Patches 2 and 3 make the affected drivers fabricate a flush before
> switching buffers, so the previous rendering shouldn't be lost either.

That may help for the fake front but not for the back buffer. Then again
I guess the worst case is intermittent incomplete frames during a window
resize, which may be acceptable.


-- 
Earthling Michel Dänzer           |                http://www.vmware.com
Libre software enthusiast         |          Debian, X and DRI developer