Re: Per axis filtering would be cool.

Stephen,

If you want mipmapping, I think that the best option right now is to use
cubemap faces, although that only allows you to have 6 textures at the same
time and you will have to adjust the texture coordinates manually.

--
Ignacio Castaño
[email protected]


--- Stephen J Baker <[email protected]> escribió:
> Something that's coming up more and more in our work with shaders is
> that we're using textures as general lookup tables - and especially,
> we find 3D textures vastly more useful than they were in the past.
> 
> However, nearly every non-traditional application trips up with the
> problem of filtering.
> 
> For example:  There are many cases where we'd like to pack multiple
> small 2D maps into a single 3D map so that the shader can choose which
> 2D map to use on a pixel-by-pixel basis depending on some other criteria
> without having to bind several dozen 2D maps at once.  It's also a great
> way to make a texture atlas without losing the ability to have maps that
> wrap around.
> 
> What screws us for this (and many other) application of texture is
> that MIPmapping (and other forms of filtering) have to be applied
> uniformly in all axes of the texture.  So as my 3D texture 'atlas'
> drops down the MIP pyramid, I not only get (desirable) blurring between
> the S,T axis texels - but also a blurring of two completely unrelated
> maps caused by MIPmapping in the third dimension.  Argh!
> 
> It would be spectacularly useful if you could choose to filter with
> GL_LINEAR in (say) S,T - and use GL_NEAREST on the third axis.
> 
> Something like:
> 
>     glTexParameteri ( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR_S_EXT
> ) ;
>     glTexParameteri ( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER,
> GL_NEAREST_T_EXT ) ;
> 
> ...analogous to the way clamping is allowed independently in either axis.
> 
> It's really painful to fake this behavior - especially if you want
> MIPmapping.
> 
> For simple LINEAR and NEAREST filtering, it seems to me that existing
> hardware
> might even be capable of doing this - if only the API had the hooks to turn
> it
> on.  Things are perhaps trickier for MIPmapping because the map sizes get
> kinda strange.
> 
> So - if any IHV's or ARB members are listening...pretty please?
> 
> -----------------------------------------------------------------------
> The second law of Frisbee throwing states: "Never precede any maneuver
> by a comment more predictive than "Watch this!"...it turns out that
> this also applies to writing Fragment Shaders.
> -----------------------------------------------------------------------
> Steve Baker                      (817)619-2657 (Vox/Vox-Mail)
> L3Com/Link Simulation & Training (817)619-2466 (Fax)
> Work: [email protected]           http://www.link.com
> Home: [email protected]       http://www.sjbaker.org
> 
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> -- 
> Author: Stephen J Baker
>   INET: [email protected]
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