On Fri, Jun 4, 2010 at 10:55 AM, Philip Winston <pwinston@gmail.com> wrote:
That's not very encouraging...  so are "texture arrays" even worse?
Portability is not really such a huge problem.  It's just not given functionality.  Newer cards probably support it; it's much older cards that will difficulty, as is evident here: http://www.opengl.org/resources/code/samples/sig99/advanced99/notes/node390.html.  Although, if you're writing for cards with programmable shaders, then chances are 3D texturing will be supported in all its glory.
That's what we do now and it is a little complex.  The shader needs to know the shape/size of the texture and do a bit of math to convert from RGB index to UV.  With a 3D texture it seems we can directly use the RGB index as the STR coordinates for a 256x256xN texture.  The texture can be only as deep as is needed, based on the size of the colormap.

So older cards don't like 3D Textures or does it continue to be a problem even for newer hardware?  We have only two dozen users, mostly newish Quadro 3800 cards.
Then you're probably fine.  A 3D texture is great, especially for new cards and future cards.  
-Philip
Ian