[Fwd: Re: CVS Update: xc (branch: trunk)]

[Roland Mainz]

Adam Jackson wrote:
> 
> On Tuesday 04 January 2005 17:27, Roland Mainz wrote:
> > Keith Whitwell wrote:
> > > Please don't do this - this is not "better" or reccomended GL usage.
> >
> > Uhm... why ? Multiple GL experts claimed that X11R6.8.0 glxgears is
> > "broken" (based in the internal feedback from
> > https://bugs.freedesktop.org/show_bug.cgi?id=1793)
> 
> I'm sorry, but #1793 is about glxgears showing time-domain aliasing on
> Solaris.  This is completely expected behaviour for GL apps not using vsync
> or a synchronization extension.

No, bug #1793 wasn't about time domain aliasing (I just didn't comment
on your comment yet).

> > and suggested either
> > an event-driven application model or to call at least |glFinish()|. The
> > first option wasn't possible (which would be preferable here as both
> > client and Xserver can run "decoupled" but still avoiding that the
> > client can send rendering instructions faster then the server can handle
> > them) as it seems to require GLX 1.3 so I used |glFinish()|.
> 
> The bug, then, is that we don't support GLX 1.3.

;-/

> > > The problem as such is with the driver not the application, and GL
> > > applications in general do not do this.   By hiding the behaviour in
> > > glxgears you are removing the incentive to fix the real problem.
> >
> > The original behaviour (in Xorg X11R6.7.x) was to call |XSync()| which
> > was considered a ugly hack. Then I removed that for X11R6.8.x, resulting
> > in the current problem. But if you look at my patch you'll see that you
> > can get all the old behaviour:
> > % glxgears -no_glfinish_after_frame # will restore the original
> > X11R6.8.0 spam-to-death behaviour,
> > % glxgears -no_glfinish_after_frame -xsync_after_frame # will restore
> > the original X11R6.7.0 behaviour. Additionally you can ask for two other
> > methods of sync'ing (see -sched_yield_after_frame and
> > -xflush_after_frame) so everyone should be happy (well, I would prefer
> > the event-driven model but it seems someone will have to update the GLX
> > wire protocol level first... ;-().
> 
> You do four methods of syncing in a row.  All by default.  Including XSync.
> How is that better than the 6.7 behaviour, if that was considered a hack?

No, only one option is active by default: glFinish(). All other methods
are off by default unless enabled by the matching command-line switch.

----

Bye,
Roland

-- 
  __ .  . __
 (o.\ \/ /.o) roland.mainz at nrubsig.org
  \__\/\/__/  MPEG specialist, C&&JAVA&&Sun&&Unix programmer
  /O /==\ O\  TEL +49 641 7950090
 (;O/ \/ \O;)