Allan Schaffer (allan++at++southpark.engr.sgi.com)
Mon, 2 Nov 1998 18:22:02 -0800 (PST)
I'd first say "it depends".
A high number of children per node (6+) means a larger aggregate
bounding sphere, and so the CULL and Intersect traversals are more
likely to have to visit each of the children to evaluate whether
they're within view / being hit, instead of just knocking off the
whole subtree with one bounding sphere test. By comparison, a low (1
or 2) number of children per group node means more groups to check,
guaranteed -- ideally you'd want more "work" to be done per check.
So no answer is ideal for every situation but I've always used ~4
adjacent children per group node as a rule of thumb.
Once the database has been modelled check your CULL stats for lots of
tested, but trivially rejected nodes. This means you're too heavy
with case #1 above. Lots of non-trivially culled nodes implies case #2.
I talked in some depth about this during my Performer Tuning lab at
the Developer's Conference last year, you're welcome to look through
the slides, which are online:
http://www.sgi.com/Technology/Performer/presentations/euroforum98-pflab.sc
(showcase format)
This is a link from the Performer Tech Info page,
http://www.sgi.com/Technology/Performer/technical.html
Allan
-- Allan Schaffer allan++at++sgi.com Silicon Graphics http://reality.sgi.com/allan
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