DX9 semantic indexes are apparently unlimited, and you can definitely specify 
COLOR 0..3, I haven't tried to go further.

Keith
________________________________________
From: luca.barbi...@gmail.com [luca.barbi...@gmail.com] On Behalf Of Luca 
Barbieri [l...@luca-barbieri.com]
Sent: Monday, February 01, 2010 8:44 AM
To: Keith Whitwell
Cc: Christoph Bumiller; mesa3d-dev@lists.sourceforge.net
Subject: Re: light_twoside RE: [Mesa3d-dev] [PATCH] glsl: put varyings in       
texcoord slots

On Mon, Feb 1, 2010 at 5:31 PM, Keith Whitwell <kei...@vmware.com> wrote:
> Christoph,  Luca,
>
> Twoside lighting has is a bit of a special case GL-ism.  On a lot of hardware 
> we end up implementing it by passing both front and back colors to the 
> fragment shader and selecting between them using the FACE variable.  If we 
> removed the implicit fixed-function support for two-side lighting in the 
> rasterizer, it would solve the issue of how this is represented in any 
> routing table.
>
> How does that sit with your drivers?

nv40 (and perhaps r300 too?) appears to have 2 hardware "back color"
registers in the vertex shader that are automatically routed, so it
would probably be best to leave it that way.

Of course, a generic face-dependent routing table could be yet another
optional feature.
Does any API expose such a thing, perhaps in the form of unlimited
rather than 2 front/back colors? (other than by using FACE)

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