Re: Occulsion Culling

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Angus Dorbie (dorbie++at++bitch.reading.sgi.com)
Sun, 23 Jun 1996 15:54:57 +0100

I'd like to add that polygon level culling on meshed primitives would
be problematic. Primitive level culling might make sense although if the
geoset is display listed (drawMode PFGS_COMPILE_GL = PF_ON) then again
you have problems.

You always have the option of splitting the geosets to obtain whatever
resolution of culling you like but the benifits could outweigh the
advantages, not just because your cull processing & memory use would
increase but because your overhead for DMAs on impact & iR could offset
savings, it depends on the size of your geosets.

Rgds,
Angus.

On Jun 23, 7:10am, Michael T. Jones wrote:
> Subject: re: Occulsion Culling
> Eric Brittain asks:
>
> |Is there anyway to use occulusion culling in Performer? I have a
> |polygon based occulusion algorithm which culls individual polygons
> |of an object based on occulders blocking the culled polygon view
> |from the eye point.
> |
> |I ask this question because from what I've seen, Performer's culling
> |capabilities are useful in culling subtrees during traversal but not
> |individual polygons of a geoset. Am I missing a point here?
>
> IRIS Performer traversals treat pfGeoSets as atomic units. The cull
> traversal tests node bounding spheres and geoset bounding boxes with
> the channel's viewing frustum; the intersection traversal tests rays
> with these spheres and boxes as well. In each case once a pfGeoSet is
> "in" the entire thing is processed: all primitives rendered and all
> primitives are intersection tested.
>
> Also, the only culling Performer does is for "inclusion" in the view
> frustum -- no object-to-object occlusion relationships are evaluated
> by Performer. This is not to suggest that such important computations
> can not be implemented in the performer context. Several interesting
> approaches have been seen to date and at least one has been made
> available here on the mailing list. (These have been object-object
> though, and not object-polygon or polygon-polygon as you mention).
>
> Michael Jones
>
> Be seeing you, Phone:415.933.1455 Fax:415.965.2658 M/S:8U-590
> Michael T. Jones Silicon Graphics, Advanced Systems Division
> mtj++at++sgi.com 2011 N. Shoreline Blvd., Mtn. View, CA 94039-7311
> "Du musst Amboss oder Hammer sein" -- Goethe
>
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>-- End of excerpt from Michael T. Jones

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