Well, nothing constructive in this post, I just would like to express my disappointment in fact that there is so low HW support for GL_MIRRORED_CLAMP modes. Actually, only ATI HW supports them (except mirrored clamp to border).
This is mistery to me, since very similar (but less useful, IMO) mode, the GL_MIRRORED_REPEAT, had been promoted to ARB, and later to core GL (1.4).
I sometimes use MIRRORED_REPEAT in situations where MIRRORED_CLAMP is needed (mostly in dependant reads techniques). This forces me to do tricks to hide the repetition of images. They are not always succesful.
Obviously, I could emulate mirrored_clamp by using standard CLAMP mode + mirroring teximage manually + applying x*0.5+0.5 texcoord transformation. However:
- this prevents me from using maximum texture resolution available for 1D lookup (when you have 8-bits precision only, every single bit is precious)
- it may happen to be impossible to apply the scale & bias to the texcoords, because of limitations of the NV_texture_shaders.
Just a bit frustrated