[[ Forwarded from dx-users ]]
I'm writing a general "3D model" to DX converter based on one of the more
capable open-source scene graphs (it has loaders for 3DS, Lightwave, Performer,
OpenFlight, etc.), with texturing support and all the OpenGL primitives
(including polygons). I'm tired of hand-converting models...
So I thought I'd pose the question: would anyone else find polygon support
in DX useful? Also, if someone has insights into what areas would need
modified to add this functionality, I'd like to hear from you.
A little background: AFAICT DX doesn't support general polygons in the
data flow. Faces-loops-edges fields presume a valid 2D topology (no edges in
any face loops cross, no loops/faces are contained within others unless they're
listed as contained loops, etc.). So these fields can't be used for
run-of-the-mill polygons. If you try to Refine("triangles") or render faces
with such fields, the result is a "topology error" and an dxexec core dump on
the next execution.
I realize we could require everyone writing a DX native format writer to
tessellate all polygons before conversion and write "triangles" fields.
However, ignoring this duplication of effort, ShowConnections with such a field
yields a bunch of artificial tesselation lines, and for polygons with lots of
vertices the results are useless.
In keeping with the data model, I propose this new polygon field would
have an "edges" component and a "polygons" component. "edges" would be
analogous to "edges" in FLE fields (a indexed list of positions for each
polygon), and "polygons" would be like "loops" in FLE fields (an list of
starting indices for each polygon in "edges"). I'm excluding polygons with
holes because I don't need that (opinions?).
As for processing and surface rendering, perhaps DX would always just
tesselate with Refine("triangles") internally, limiting the scope of the source
changes.
Thoughts?
Randy
--
Randall Hopper (mailto:[EMAIL PROTECTED])
Lockheed Martin Operation Support
EPA Scientific Visualization Center
US EPA MD/24 ERC-1A; RTP, NC 27711
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