All of the ancillary buffers pose a problem for scene graph API's. Java 3D
makes it even more difficult because it has no application controlled
traversal semantic. Many of the issues with stencil buffers and shadows
that have been brought up are the kinds of things that we hope to address
in Java 3D 1.4. The changes needed in the scene graph to support high level
implicit features (like shadows or reflections) or explicit multipass control
with ancillary buffer access are both very large. So that is why we have
been pushing them off to 1.4.
Doug Twilleager
Java 3D Team
Sun Microsystems
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>Subject: Re: [JAVA3D] Stencil buffers
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>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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