Fedora's OpenGL Composite Desktop -- nVidia's whitepaper is enlightening

[Bryan J. Smith]

Rahul Sundaram <sundaram at fedoraproject.org> wrote:
> Hi
> Fedora Rendering Project 
> (http://fedoraproject.org/wiki/RenderingProject) hit slashdot today
> and osnews before that.
> http://linux.slashdot.org/linux/06/02/22/1638228.shtml
> http://osnews.com/comment.php?news_id=13734

nVidia's Whitepaper arguing for Render/Composite atop of DDX instead
of the Xgl server was enlightening.  I always (and incorrectly)
assumed nVidia would be for the latter.  But then I quickly realized
why that while they did give kudos to Xgl, they clearly prefer the
former -- for a variety of reasons, and not just selfish ones either.
 Some are very sound, technically.

First there is the difficulty of Xgl not address hardware-specific
details like multi-card/multi-display with the same driver/buffer. 
An entire new set of APIs would need to address that, which have not,
and sometimes that's just not feasible with various hardware out
there.  Especially when new support is needed that was not previously
thought of.  In other words, the Xgl is "too generic" of a server
between the hardware and the end-user, where the end-user knows what
monitors and (possibly) cards are in use, but Xgl doesn't (at least
not directly).  I never, ever thought of that before, but now I
totally understand why it's a major issue.  It makes far more sense
for X and server driver to be integrated whereas Xgl makes too much
far too arbitrary.

Secondly, it does force OpenGL on everyone.  Not only does not
everyone have a capable accelerated OpenGL driver for X, but not all
OpenGL is created equal (especially chipset-integrated) for that
matter.  I personally like their comment -- Xgl essentially makes the
desktop the "lowest common denominator," and that's pretty low in the
case of many vendors who are well behind even OpenGL 1.3 (let alone
2.0).

Lastly, and most interestingly coming from nVidia, sometimes you just
don't want to use OpenGL at all.  Most people forget that nVidia does
provide a good amount of work into the MIT licensed 2D drivers that
come with XF86/Xorg, and the new Xorg X11R7+ model will make updates
much easier.  nVidia is _not_ just thinking about their proprietary
drivers here.  They are considering that Render/Composite doesn't
have to be OpenGL, and there might be many cases when you don't want
it.

Given what was said in the whitepaper, I'm looking forward to both
MIT licensed "nv" driver developments in Xorg X11R7+ was well as
nVidia "nvidia" driver developments in ForceWare 85.  The cool thing
is that in _any_case_, nVidia is supporting _all_ developments --
AIGLX, Xgl, Looking Glass, etc...  But it's clear that not only their
preference is on the Render/Composite approach and working with AIGLX
from their perspective, but that its more beneficial for even other
drivers, including 2D-only hardware support.


-- 
Bryan J. Smith     Professional, Technical Annoyance
b.j.smith at ieee.org      http://thebs413.blogspot.com
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*** Speed doesn't kill, difference in speed does ***