Texture Units and filtering

[Jan]

Well, of course i want my app to look as nice as possible. Therefore i use anistropic filtering for most textures.

However some time ago i read, that not every texture unit is able to do some filtering modes and that nVidia and ATI disable some modes on other texture units (usually all but the first) as a speedup.

Therefore i put my basetexture into texture unit 0, but what about the other units? Which one should i use if i need another good filtering mode?

I also read, that most cards achieve their 4 or 8 texture units, by simply doing 2 or more texture-fetches on the same unit. Shouldn´t that mean, that if my texture unit 0 supports 8x anistropic filtering, that texture unit 1 (or 2) does support that, too?

I am a bit confused about how the hardware works here, so if anyone knows some details, i´d like to here them.

At the moment i work on a Gf 4, but i´d like to know the details of all cards.

Thanks,
Jan.

[JanHH]

at least on your gf 4 you could simply try (and tell us http://www.opengl.org/discussion_boards/ubb/wink.gif ).

Jan

[Korval]

However some time ago i read, that not every texture unit is able to do some filtering modes and that nVidia and ATI disable some modes on other texture units (usually all but the first) as a speedup.

If you set your texture driver panel to "Application Settings", or something of the like, then you should get what you ask for on any texture unit. In the past, ATi's been pretty good about this, though nVidia has not. I don't know what nVidia's current situation is with reguard to drivers giving you what you asked for on any texture unit.

[V-man]

I think he's talking about the case where on some ATI cards with some driver version, trilinear filtering was only done on the first tex unit.

I think it was during R200.

You can write a test program and visually check differences.

[jeremyz]

Aniso filtering looks good, but it has a cost.
You should definitely try to limit your use
of it to important textures (like base
decal textures). Also, you don't get a lot of
benefit using aniso with low frequency textures
(like light maps).

[Zengar]

As current applications are fill-limited, aniso won't really count. On my card I don't notice any performance dirrefence with anso on/off.