Lance R. Marrou (marrou++at++vsl.ist.ucf.edu)
Fri, 19 May 1995 15:04:31 -0400 (EDT)
> On Thu, 11 May 1995, `Bwana' Bob Buckley wrote:
>
> > > are free to write new values for your vertex information to memory.
> >
> > However, when multiprocessing you MUST multi-buffer your pfGeoSet data. When
> > updating vertex,normal, and texture coordinates in the app process you don't
> > want the draw process to render in the midst of an update. We just spawned a
> > separate rebuilding process and let the visuals continue to run typically at
> > 60Hz.
>
> Slightly off the topic question I'm afraid...
>
> 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.
The spawned process modifies the geoset data: "vertex, normal, and texture
coordinates". The terrain geosets, geodes, and other structures are allocated
before the rebuilding process is forked. You should immediately notice a
possible conflict in modifying visual data at this low level. However, some
synchronization locks are built in and only the original app process issues
the changes to pfSwitch nodes. The draw process is never held up, though a
possible 2 frame delay may occur in the data update. Things change a little
bit with the pfCycleBuffer structure in 2.0, but that's a topic that can wait
until 2.0's release. :)
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