> Date: Tue, 24 Aug 1999 14:20:56 -0400
> From: Bob Gray <[EMAIL PROTECTED]>
>
> I have tried transparency modes of NICEST, BLENDED and FASTEST. None of
> these work for me. They do not allow the 2nd polyhedron to show through and
> leave big blck areas where the 2nd polyhedron surface should be.
>
> Can anyone tell me why?
I haven't taken a close look at your code, but I believe you're running
into a limitation of Java 3D here.
In the general case, traditional Z-buffering techniques don't work for
transparent objects. In order for the colors to be blended properly their
facets must be rendered in a view-dependent order, from back to front. This
isn't a trivial task for most applications, and Java 3D doesn't provide any
help here. You'll only get reasonable results if most of your objects are
opaque and you have only a few, non-overlapping transparent surfaces.
There are techniques that work for many cases. All opaque objects can first
be rendered using the normal Z-buffer technique. Transparent facets can
then be sorted from back to front in the view projection space using some
metric; for most objects using the centroid (averaged vertices) works OK. A
reasonable effect can then be achieved if the Z buffer values from the
opaque objects are frozen and the transparent facets rendered in their
sorted order on top of them.
This is not directly supported by Java 3D; perhaps some other users have
tackled this problem and could help you out. Your only other alternative is
to use SCREEN_DOOR, which doesn't have any view dependencies, but has other
lousy rendering characteristics, as you point out.
-- Mark Hood
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