This seems like a very different idea of semantics. These aren't intended to
be hardware resources, and there is no concept of querying the driver to figure
out how many the hardware supports. Further, the indices for different
semantic names are considered to be disjoint, permitting FOG[0], COLOR[0] and
GENERIC[0], each of which would potentially consume an interpolator on some
hardware, subverting the idea of a maximum semantic index.
There's currently no concept of driver-specified maximum semantic indexes, and
I don't think it's the right direction to be taking things. If we are going to
have a limit, it would be on the total number of inputs/outputs from a given
stage, not the way that individual ones are labelled.
I think if you want to improve linkage semantics, some of your other
suggestions are more promising. I'd like to dig into those a little more if
that's ok.
Keith
________________________________________
From: luca.barbi...@gmail.com [luca.barbi...@gmail.com] On Behalf Of Luca
Barbieri [l...@luca-barbieri.com]
Sent: Monday, February 01, 2010 6:11 AM
To: Keith Whitwell
Cc: Brian Paul; mesa3d-dev@lists.sourceforge.net
Subject: Re: [PATCH] glsl: put varyings in texcoord slots
> In GL, there doesn't seem to be a requirement for sequential usage - an app
> using ARB_vp/fp could explicitly pass TEXCOORD[10] and ignore 0..9 if it
> wanted to. In ARB_vp, that effectively means the shader would be using
> discontiguous register numbers, ie OUTPUT[0], OUTPUT[10], etc.
Yes, but TEXCOORD[10] will only work if the hardware supports 11 textures.
>
> In DX9, there is also no requirement for sequential usage - an app can use
> TEXCOORD[1] without [0], or COLOR[0] and [2] without [1] or [3]. I would
> expect any DX9 gallium state tracker would also end up using non-sequential
> indices if it directly translated DX9 semantics to gallium.
I think there is some terminology confusion.
I'm not proposing to require indices to be "sequential" in the way you
are describing.
By "sequential" I mean that if the hardware supports 8 interpolators,
then the available semantic indices should run from 0 to 7.
Thus, the *available* semantic indices are sequential, but the user is
free to use any subset of them.
So you can start with OUTPUT[10], but only if at least 11
interpolators are supported (so that the used set {10} is a subset of
the available set [0-10]).
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