Re: info-performer Oct 11 1999
Angus Dorbie (dorbie++at++sgi.com)
Tue, 12 Oct 1999 12:48:10 -0700
Yair Kurzion wrote:
>
> > upstream and downstream:
> >
> >
> > Yair,
> >
> > Doesn't the dBase process communicate "upstream"? Exactly what does that
> > mean? What is upstream of dBase?????
>
> Larry,
>
> We make a distinction between processes that have a copy of the scene graph and
> processes that do not. App, Cull and Isect each have their own copy of the
> scene graph. Any scene graph changes made by the App process will travel
> downstream to Cull and to Isect.
>
> DBase may have its own pfBuffer, but it does not contain a copy of the main
> scene graph. So, Dbase is not even on the main scene graph propagation stream.
> The DBase process creates new nodes in its own pfBuffer. These nodes are
> essentially a secondary scene graph. At the end of a Dbase frame, we merge the
> new nodes from the Dbase pfBuffer into the main scene graph stream (the App
> pfBuffer).
>
> After merging, the Dbase process may no longer access these nodes because they
> get moved from the DBase pfBuffer to the App pfBuffer. The only exception to
> this rule is the pfBuffer* calls (pfBufferAddChild, pfBufferRemoveChild or
> pfGroup::bufferAddChild, pfGroup::bufferRemoveChild). These calls allow access
> to nodes of the main scene graph.
Just to make the distinction even clearer, pfBufferAddChild isn't
applied in the dbase process. It happens in the application after the
buffers have been merged. The add child call is attached to the current
dbase pfbuffer as an operation which will be completed in the app when
merged.
Cheers,Angus.
--
"One of the best-known folk theorems of software engineering is that
60% to 75% of conventional software projects are either never
completed or rejected by their intended users. If that range is
anywhere near true (and I've never met a manager of any experience
who disputes it) then more projects than not are being aimed at goals
which are either (a) not realistically attainable, or (b) just plain
wrong."
Eric S. Raymond - The Cathedral and The Bazaar
For advanced 3D graphics Performer + OpenGL based examples and tutors:
http://www.dorbie.com/
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on Tue Oct 12 1999 - 12:48:16 PDT