Re: pfGeoSet attr binding (was 2.1 PACKED ATTRS)

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Sharon Clay (src++at++rose.asd.sgi.com)
Sun, 7 Jul 1996 18:04:50 -0700

+>---- On Jul 3, 5:13pm, Marcus Barnes wrote:
> Subject: Re: 2.1 PACKED ATTRS
->
->On Jul 4, 1:25pm, Nacho Sanz-Pastor. Computer Arts + Developments wrote:
->> Subject: 2.1 PACKED ATTRS
->> Hi all,
->>
->> Does anybody know if it's possible ( I guess it's not ) to use vertex arrays
->> in 2.1 that only pack normals, texvertices and vertices, without the per
->> vertex color field ?
->
->Yes this is okay for pfGeoSet's. Just set the PFGS_COLOR4 attribute binding to
->PFGS_OFF when creating geosets.
->
->> Most of the objects we use have normals, texverts and coords but colors are
->> used in only around 10% of the objects, so that seems a waste of host to gfx
->> bandwith ...
->
->Yes it is a waste of bandwidth. I believe Performer will be getting "smarter"
->about immediate mode drawing wrt the current graphics state in a future release
->(I haven't noticed it in 2.0 or 2.1). For instance, there is no reason to
->download texCoords when texturing is disabled or to issue color commands for
->lit geometry when pfMtlColorMode is PFMTL_CMODE_COLOR.

This is a separate issue but a really good point. It is also hard to
deal with perfectly in a peak performance manner.
When a pfGeoSet has been told to use PER_VERTEX colors, it does so and checks nothing
in its environment. Minimization lack of last minute checking is critical to
optimization - small pfGeoSets need to have less overhead on their drawing and
not more. This also provides consistent behavior for when those pfGeoSets
are compiled into GL display lists.
FYI, the above behavior is also really useful for tuning when looking for
bottlenekcs :-)

I wonder (hope) if it is really just a special case where folks have specified
PER_VERTEX attributes on their pfGeoSets but then effectively disabled them
with their pfGeoState binding and that this is not the common mode of drawing.
I'd also suggest that probably the only efficient place to put a statement
like "pfGeoSets ignore your colors" would be at the pfGeoState or global level
so pfGeoState sharing would not be a reason to add this mode.

Thanx,
src.

-- 
-----{-----{---++at++   -----{----{---++at++   -----{----{---++at++   -----{----{---++at++
Sharon Rose Clay (Fischler) - Silicon Graphics, Advanced Systems Dev.
src++at++sgi.com  (415) 933 - 1002  FAX: (415) 965 - 2658  MS 8U-590
http://www.sgi.com/Technology/Performer/
-----{-----{---++at++   -----{----{---++at++   -----{----{---++at++   -----{----{---++at++


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