On Thu, Oct 17, 2002 at 04:08:25PM +0100, Keith Whitwell wrote:
> Ian Romanick wrote:
> > Over the past year an issue of OpenGL versioning has come up a few times.
> > Basically, we have conflicting goals of wanting to advertise OpenGL 1.3 or
> > 1.4 but not wanting to advertise extensions that aren't hardware accelerated
> > (cube textures and shadow maps come to mind).
> >
> > I believe that a solution exists, but it will require some trivial changes
> > to Mesa. Basically, we advertise whatever OpenGL version we want (assuming
> > that the driver knows how to fall-back for unsported functionality), but
> > only advertise extension strings for functionality that is hardware
> > accelerated. For example, advertise version 1.2, but only advertise
> > GL_EXT_texture3D in the extension string if it's hardware supported.
> >
> > This may sound silly, but I think it's a good compromise. It turns out that
> > this is what Nvidia does. That's not to say that Nvidia is always right,
> > but I think this is better than being stuck back at 1.2. :)
>
> Does GL_EXT_texture3D still work, even though it's not listed?
>
> If not, that takes all the hard work out of advancing mesa -- no need to code
> stuff up, just bump the version number...
>From what I have been told, this is how it works on the Nvidia drivers. I
have not verified this first hand.
if ( extension string contains "GL_EXT_texture3D" )
3D textures are hardware accelerated
else if ( advertised OpenGL version >= 1.2 )
3D textures are a software fallback
else
3D textures are not supported at all
So, a TNT will advertise OpenGL version 1.2 but not GL_EXT_texture3D. 3D
textures will work, but they will be sw rendered. On whichever Geforce
supports 3D textures in hw, OpenGL version 1.2 AND GL_EXT_texture3D would be
advertised. It's not a perfect system, but it fixes most of the cases where
an app checks the extension string to see of some feature is supported in
hardware and gets an upleasant surprise from a sw fallback.
--
Smile! http://antwrp.gsfc.nasa.gov/apod/ap990315.html
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