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.
Yeah, MIRRORED_CLAMP … and what about MIRRORED_REPEAT_TO_BORDER_CLAMP_TO_EDGE ?
Basically the idea of CLAMP is computing texture coordinates always in the range [0,1] and the idea of MIRRORED_REPEAT is to define a new way of repeating outside the range [0,1].
I can hardly imagine what MIRRORED_CLAMP corresponds to. Clamp to [0,2] or [-1,+1] with mirror ?
Do you mean, by Mirrored clamp, that the bilinear filtering at edges of a texture gets texels from the mirror edges? Since when does ATi hardware support this (and how do I use it)?
If it is an ATI-specific extension, why do you expect other vendors to support it ? If it is really useful, needless to say it will be promoted to ARB sooner or later.
The extension can be quite useful, unlike the mirrored_repeat, which I have yet to find a good use of.
In my experience however, while mirror_once is sometimes useful it’s never really neccesary either. And since noone except ATi seams to support it I have yet to use it in any of my demos since I can always just use a larger texture and do 0.5 * (texCoord + 1) and use normal clamp_to_edge. The mirror_once functionality if available in DX too, but I think only ATi supports it there too. To me this is a mystery, since if you already support clamp_to_edge and mirror_repeat I can’t see how hard it can possibly be to support mirror_once too.
Originally posted by Humus: The extension can be quite useful, unlike the mirrored_repeat, which I have yet to find a good use of.
afair the “good use” is written in the spec
Has anyone else been stuck on repeating textures because seams looked awful ?
If you don’t find a good use of MIRRORED_REPEAT I guess you have even less good use for REPEAT
