GL Redirection to offscreen

[Owen Taylor]

On Sat, 2004-10-30 at 12:19 +0100, Keith Whitwell wrote:
> Amir Bukhari wrote:
> >>Have you made any progress with the redirect issues?  It seems like in 
> >>September you were coming to terms with some fairly deep questions about GL 
> >>and composite - how is that panning out?
> >>
> > 
> > I have done some experiment with software Rendering in Xorg and I end up
> > that Composite work OK with, but for DRI it needs alot of change in DRI
> > structure.
> > what I am thinking about how GL redirection work is like following:
> > 1- Composite Extension should define interfaces for others X parts (GL,
> > Xv ...), which it call those interfaces if they exists.
> > 2- each Part of X need a redirection should implement those interface
> > and register them by Composite extension.
> 
> What would this interface look like?
> 
> It seems like it would almost have to replace the current GLX/DRI interfaces, 
> but maybe I'm reading too much into it.  All the open drivers currently use 
> shared Z and depth buffers, for instance - I don't see how that could continue 
> under composite.

There are actually two sides here:

 * Allowing OpenGL windows to be redirected. This indeed tends to
   require a Z/depth/back buffer per window. You could do tricks where
   you gave windows non-overlapping virtual positions in the screen,
   but that's going to be considerably less efficient in memory usage
   then linear allocation.

 * Allowing DRI clients access to window images as textures. As I
   understand, this is what the Looking Glass people are talking about
   at the moment. This isn't particularly simple either, as far as I can
   see, but shouldn't require changes to the GL buffer allocation.

   I could speculate about how you could accomplish this, but I'm sure
   the Looking Glass people have done concrete work here, so I'll 
   hold off on that.

Regards,
						Owen

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