Michael T. Jones (mtj++at++babar.asd.sgi.com)
Sun, 23 Jun 1996 07:10:34 -0700
|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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