Re: Demo program in buttonfly.

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Richard Mercille (rim++at++loukoum.neu.sgi.com)
Tue, 7 Mar 1995 08:53:21 +0100

On Mar 1, 12:15pm, Pat Parker wrote:
> Subject: Demo program in buttonfly.
>
> I know this is isn't a Performer question but I do not know who else to
ask. I tried the comp.sys.sgi.graphics newsgroup but got no response.
>
> Can anyone explain how the demo "distort" in buttonfly is implemented?
It's under the Performance Features, Reality Engine buttons. It is a
texture of a dog that you can pick with the mouse and cause a ripple
effect or a rubber effect.
>

It's just a mesh that is being distort according to some physical behavior
(rubber, ripple, etc...) see also the Tele demo. The texture (static or
sirius video) is just apply to the entire mesh (0..1, 0..1). It's under
the Performance Features because it's very cpu intensive (the dynamics).

> I am interested in creating that same effect in a Performer application.
I am assuming I will use a pfGeoSet and change the texture coordinate
array. Maybe thistype effect can only be done through a GL object? Any
suggestions are welcome.

Not the texture coordinates, the vertex information. At each frame in the
APP process you would modify the geometry. If you want to use
multi-processing don't forget that Performer only use multi-buffering for
libpf nodes. So in order to modify your data in the APP process without
disturbing the CULL/DRAW process you will need to manage your own
multi-buffering startegy.

ex.: Switch with 3 Geode has children (one for the APP, CULL and DRAW)
     since Switch are multi-buffer changing the index in the APP is safe.

      CAREFUL if you overshoot a frame (maybe more than 3 Geodes)

Ciao

>
>
> Thanks in advance,
>
> Pat
> ===============================================================
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>
>
>-- End of excerpt from Pat Parker

-- 
Richard Mercille				Core Technology Group
European Graphics Lab			        Silicon Graphics
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