[compiz] Using glitz directly vs using XRender

[David Reveman]

On Tue, 2006-04-11 at 11:22 +0100, Mike Hearn wrote:
> Hi,
> 
> In the past I've found that using the glitz backend to Cairo with Xorg 
> made some simple animation tests I wrote go much faster. I haven't yet 
> tried them with Xgl but I was wondering which backend is theoretically 
> 'best' in this configuration?
> 
> My understanding is that Xgl feeds everything drawn to the screen via 
> OpenGL - a bit like Quartz 2D Extreme will when Apple get it stable 
> enough to enable by default. So the paths would look like:
> 
> app -> cairo -> xrender backend -> [xgl  xrender -> glitz -> gl]
> 
>    and
> 
> app -> cairo -> glitz backend -> glx -> [xgl -> gl]
> 
> Does that look right? Which makes more sense to use within a Compiz 
> plugin? Can the second pipeline offer more acceleration for things like 
> some of the SVG filter effects that are being moved into Cairo?

Looks correct. I highly recommend using xrender. Any filter support
being added to cairo should be able to use the existing filter interface
that is part of xrender and already accelerated by Xgl. Using glitz
backend shouldn't give you anything extra. Using it will just add some
overhead from creating an additional GL context instead of having Xgl
use its core GL context.

-David