[osg-users] OpenGL 3.1 at GDC

Tueller, Shayne R Civ USAF AFMC 519 SMXS/MXDEC Shayne.Tueller at HILL.af.mil
Wed Mar 25 09:15:54 PDT 2009


Robert,

Thanks for the clarification. I think this discussion is good for all
involved when it comes to understanding the differences between D3D and
OpenGL.

For the record, I'm not an advocate of D3D or Microsoft. Far from it in
fact...

-Shayne

-----Original Message-----
From: osg-users-bounces at lists.openscenegraph.org
[mailto:osg-users-bounces at lists.openscenegraph.org] On Behalf Of Robert
Osfield
Sent: Wednesday, March 25, 2009 9:23 AM
To: OpenSceneGraph Users
Subject: Re: [osg-users] OpenGL 3.1 at GDC

Hi Shayne,


2009/3/25 Tueller, Shayne R Civ USAF AFMC 519 SMXS/MXDEC
<Shayne.Tueller at hill.af.mil>


	Are you implying that the current D3D is not backwards compatible
with
	previous versions? I believe that a current D3D application can
query
	earlier versions of the D3D interface through COM. A D3D 3.0
application can
	still run under D3D 10.0 as I understand it...
	


The problem is not the the old D3D versions API aren't available, but the
fact that the jump between versions is discrete.  If you want D3D 10.0
functionality you have to use D3D 10, you can't just use one part of D3D 10
and keep the rest of your app building against D3D 9.  You can't get access
to D3D features unless you are on Vista. 

This a very different situation to that of OpenGL based apps that like the
OSG have been able to evolve bit by bit as few hardware + API features were
exposed in OpenGL.

If you are trying to maintain an application for a long period then handling
widely different hardware and OS combinations is key.  The D3D model really
doesn't help you at all.  The D3D model only suits making an app for
specific era, once that era is gone the app just stays in that era unless
you retool in a significant way.  For a game that is developed and sells for
a couple of years it might be able to come and go in just one era, but for
most applications this isn't the case.

Interestingly for open source games that take many years to write and evolve
over time their lifetime is potentially far longer than commericial games,
so open source games have more similar needs to API evolution and
portability that conventional long lived graphis applications have.

Robert.



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