Re: Texture mapping co-ordinates

[Katie Lucas <katie@fysh.org>]

> Katie Lucas wrote:
> > 
> > I've got a problem with texture coords for a plane - I've got the
> > vertex coords and the colours for the verticies and the texture coords
> > all stashed away in structures and selected into arrays. The textures
> > slide about on the surface of the plane as the camera rotates about
> > it.
> > 
> > Now normally I'd say "clown, you've screwed up the coord generation",
> > but the thing works FINE in software Mesa rendering - on a VoodooII in
> > hardware: texture problem. This is the same exe, just picking between
> > the software/hardware by setting the environment variable.
> 
> Without seeing the effect (or the source code), it's hard to diagnose this.
> 
> Here are some possibilities:
> 
>   1) You might be moving the eyepoint around using the projection
>      matrix instead of the modelview matrix.  Some OpenGL's don't
>      like that.
> 
>      Here is a FAQ:  http://web2.airmail.net/sjbaker1/projection_abuse.html
> 
>   2) You might have very large texture coordinates - that can cause the
>      texture to drift around.  The Voodoo is especially sensitive to this
>      due to poor (~14 bit) internal numerical precision.  Software OpenGL
>      is highly insensitive to it (because it's all done in 'float's).

This isn't the problem (which was a Mesa needing upgrading thing) but
it is something that I would have needed to know later on in the
project.. I'll have to bear that in mind.
 
> 
>   4) Are you using the GL_TEXTURE matrix?  Different implementations
>      of OpenGL have different matrix stack lengths from others - with
>      the Projection and Texture stacks sometimes being just one or two
>      elements deep.  Hence you might be overflowing the stack in one case
>      and not in the other.

Only to set it to identity to make sure it is..

Messing with projecting those coords as well is too much like hard work...