On Thu, Oct 17, 2002 at 04:39:19PM +0100, Keith Whitwell wrote:
> Ian Romanick wrote:
>
> >>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.
>
> It does seem semantically richer than the standard way of doing things. I
> wonder if the spec gives some wiggle room on this.
That's actually how all this got started. I noticed that Mesa / DRI doesn't
advertise extension strings for a LOT of OpenGL 1.2 functionality that IS
supported:
- EXT_draw_range_elements
- EXT_separate_specular_color
- EXT_texture_edge_clamp / SGIS_texture_edge_clamp
- SGIS_texture_border_clamp
- SGIS_texture_lod
So, I asked a couple people around IBM what the accepted practice was. I
was told that an implementation is not required to export extension strings
for extensions that are required for its adverteised OpenGL version. I was
then told about Nvidia's technique.
--
Smile! http://antwrp.gsfc.nasa.gov/apod/ap990315.html
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