I see issues with implementing Stencil and accumulation buffers in a
scenegraph architecture. Ideally a scenegraph would lend itself well to take
advantage of hardware accelerated shadows reflections and other effects, so
that the programmers and artists have to worry about these things less, but
then there are various techniques to achieve them and diffrent situations
that each technique would be ideal for, a program would have to inform the
scenegraph, or the scenegraph would have to be able to analize a scene to
figure out the best technique to use.
I recall John Carmack talking about how the new Doom (or is it Doom 3) demo
they showed on Mac with a GeForce3, does not use any specialized tricks for
diffrent geometries, that each object could cast a shadow and be hit by a
shadow, no special cases were made, and no treating static objects and lights
diffrently then dynamic objects and lights. That sounds like the best case
for a scenegraph.
But that is far ahead, not only is the hardware expensive and new (most users
will probably not upgrade to it for a while), but also to program something
like this will take a fair amount of time. Stencil buffers and other raster
controls could probably be incorperated into this, and who knows it may even
work well in the Java3D scenegraph, maybe have a stencil group, where all the
child objects of the stencil group will only be visible with in some geometry
in the stencil group, but that is also assuming that the stencil buffer has
other uses besides shadows and reflections.
One thing I do recall being mentioned earlier in this mailing list, was that
they were considering a way for others to create their own renderers. That
may also work, for example in creating a renderer that will do shadows as
well using a technique. That way if you want to do shadows you just pop in
the renderer you want, or maybe create your own renderer and inherit from
another one that is optimized.
Leyland Needham
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