Re: Altering Geometry

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Kowsik Guruswamy (giraffe.asd.sgi.com!sgi.sgi.com!cory.portal.com!buggy.coryphaeus.com!kowsik)
Wed, 8 Nov 1995 14:05:02 -0800


On Nov 8, 6:57pm, Lionel Maiaux wrote:
> Subject: Re: Altering Geometry
> On Nov 8, 9:24am, David Russell wrote:
> > Subject: Altering Geometry
> > Given that Performer operates best of staic geometry data, has anyone else
> > tried to alter the geometry of a scene on the fly? I've seen systems that
> > alter vertices of geosets in order to produce dynamic terrain, fluid, etc.
> > that work produce relatively fast response. Unfortunately, for my
> > application, this approach doesn't work. I am required to generate all of
> > the geosets, etc. for the new geometry each time a change is necessary.

The way to go about in Performer 1.2 is to have a pfSwitch node with different
geometry on it and if you are rendering say child 0, then you modify child 1
and so on.

> > Now that I've rambled on, does anyone have any experience with generating
> > and swapping new geometry into the Performer tree? I'm mostly interested
> > in any tricks to help increase the speed of response. We have a GL based
> > test program which only takes about a second to update where the Performer
> > based program requires nearly five seconds to change the geometry on the
> > same machine.
> >

Performer 2.0 allows you to add geometry/scene graphs from a separate process
through a pfBuffer mechanism. The idea is to create your scene graphs and
'merge' the scene graph with that maintained in the APP process.

So if your geometry changes based on some kinda user input and if you are ready
to tolerate some delayed response, then you can use the [any] separate process
to modify geometry and then attach it back to the scene graph.

The other way of doing this in Performer 2.0 is to mkae all the geometry
multibuffered through a new mechanism called pfCycleBuffer, which essentially
provides an MP safe and frame accurate way of updating any chunk of memory,
especially pfGeoSet attribute lists.

Hope that helps,

K.

-- 
kowsik++at++coryphaeus.com

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