`Bwana' Bob Buckley (bbuckley++at++ctaeng.com)
Fri, 19 May 1995 13:09:30 -0600
On May 19, 2:36pm, Simon Bennett wrote:
> Subject: Re: dynamic terrain
>
> But, I've always been led to believe that Performer 1.2 did not let processes
> forked off the application process modify the scenegraph... So either this
> is not true or "a separate rebuilding process [that] let the visuals continue
> to run typically at 60Hz. " did not directly modify the scenegraph and
> achieved this some other way. Maybe I've missed something here.
>
libpr objects can be created and modified safely in processes forked off of the
application process. libpf objects, which use a global structure, cannot be
safely created from such a process. The only safe way to modify libpf objects
created prior to the fork would be to enforce mutual exclusion via locks or
semaphores. However, there are certain routines that should only be run from
the application process (pfDelete). Check out the programmers guide under
Successful Multiprocessing with Iris Performer.
To implement our Dynamic Terrain the whole scene graph is created (multi-
buffered) prior to the fork and throughout the simulation run the complete
structure never changes. Only the pfGeoSet (libpf) data changes including
texture, normal, and vertex coordinates. Also, the parent pfGeode's bounding
sphere is forced to recompute. Which makes me realize two things: 1) I don't
have any mutual exclusion access to the parent pfGeode (Bad, Bad, Bad
Programmer!!) and 2) a forced recomputation of a bounding sphere of one of my
pfGeodes, although set as dynamic, might not force an upward propogation of the
bounding sphere recomputation. According to the man page for pfNodeBSphere only
additions, deletions, and matrix changes force the upward propogation through
pfGroups. But, it works! So, the man page may not address the complete set of
circumstances for an upward propogation of recomputing bounding spheres.
===========================================================================
'Bwana' Bob Buckley CTA, Inc.
Sr. Software Engineer 5670 Greenwood Plaza Blvd
Visual Systems Englewood, CO 80111
(303) 889-1207 (303) 889-1200
bbuckley++at++ctaeng.com (303) 889-1398 Fax
===========================================================================
This archive was generated by hypermail 2.0b2 on Mon Aug 10 1998 - 17:51:30 PDT