Re: pfASD and culling

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From: Yair Kurzion (yair++at++polygon.engr.sgi.com)
Date: 07/17/2001 19:37:21

Hi Tom !

pfASD evaluates its visible geometry in an asynchronous process (COMPUTE).
A COMPUTE frame may take longer than a regular APP/CULL/DRAW frame, and so
the visible geometry may be correct for an eye position in the past.

To solve that, pfASD has to be culled for a larger frustum than the channel
viewing frustum. How large depends on the application:

o The larger (more complex) the pfASD model, the longer it takes to evaluate,
  and the older the geometry you render is.

o The faster the eye position moves (especially - angular rate), the wider the
  cull frustum has to be.

Take a look at the man page for pfASD::setCullEnlarge. It lets you modify the
cull frustum of a pfASD.

-yair

> I am seeing what looks like unusual culling effects with geometry
> in a pfASD node. I have the pfASD node as a child of a pfDCS node.
> When I change the eyepoint position and the DCS position by the
> same amount parts of the geometry in the pfASD node, that should
> be visible, are culled. When the positions stop changing the
> culling catches up and the geometry looks the way I expect it to.
>
> I see the same thing using asdfly (using run_simple) when I rapidly
> change the eyepoint position backwards. It looks like it takes a
> couple of frames for the culling to catch up.
>
> Anyone have any explanations or solutions? Can ASD be used in an
> application with channels covering 360 degrees or with side channels
> and a high roll rate?
>
> --
> Tom Jolley
> jolley++at++fltsim.stl.mo.boeing.com
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