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Old 12-03-02, 02:36 AM   #22
Gargr
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Join Date: Aug 2002
Posts: 195
Default Re: hmm... missing something...

Quote:
Originally posted by ragejg
No pixel/vs shaders?
Dang! Maybe there's other unpublished trick that work around this fact...
its called a TEV

Here is a quote from Beyond3D:

Quote:
The TEV and "pixel shaders" are basically cute acronyms for what used to be called color combiners. The TEV also incorporates the Texture reading part of the pipeline.

A color combiner is in general implemented as a single logic op, in NVidia's case thats public (register combiner docs) and is of the form
A op1 B op2 C op1 D
where op1 is either Dot Product or multiply, op2 is either add or select.
As you can see by repeating this multiple times with some register manipulation between stages you can do most basic math. Pixel shaders just provide a simple consistent interface to this (and other vendors implementations).

The TEV uses a different basic combine operation which is a little more limited. However since the Texture reads can be interleaved with the combiner operations it allows you to do things that would require multipass render on NV2X.

So as an example
on NV2X I have to write


Texture Read
Texture Read
.
.

Combiner Op
Combiner Op
Combiner Op
Combiner Op
.
.
.

On Flipper I can write

Texture Read
Combiner Op
Combiner Op
Texture Read
Combiner Op
Combiner Op
Texture Read
Combiner Op
Combiner Op
.
.
.

I guess the easiest explanation is that Flipper has simpler units for combining and reading textures, but allows more complex arrangements of the units.
So if one of the texture reads is dependant on a previous combiner Op and you can't squeeze the ops into the texture addressing instructions the NV2X would require multipass to do the same thing.
http://www.beyond3d.com/forum/viewtopic.php?t=1603

Last edited by Gargr; 12-03-02 at 02:45 AM.
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