Subject:
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Re: Detemining Polygon Winding (Was: New Plugin for LDDesignPad)
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Newsgroups:
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lugnet.cad.dev
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Date:
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Thu, 8 Aug 2002 22:03:03 GMT
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Viewed:
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697 times
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In lugnet.cad.dev, Anders Isaksson writes:
> "Don Heyse" <dheyse@hotmail.spam.go.away.com> skrev i meddelandet
> news:H0I44E.2vE@lugnet.com...
> >
> > However, like I said, if you find something that works, post the code
> > or the algorithm and you'll be my hero. I don't think I'll ever add
> > code to parse the BFC meta-commands in ldglite. (I just don't like
> > them). But I will add code that BFCs parts automatically if someone
> > comes up with it.
>
> An idea:
>
> Drawing with a software Z-buffer it's trivial to note _which_ polygons are
> the finally visible ones (at every pixel). Those are on the outside.
>
> So, take a part, look at it from a lot of angles (at least 8, probably 144
> or more...), and make notes of the outside polygons, then correct their
> winding if necessary.
>
> Caveat: An incorrect part, where you can see into the 'material' will get
> too many polygons marked as 'outside'.
>
> Will not work for real-time use, but maybe for batch-processing the parts...
Also, once you know the direction for one (or more) polygons, any polygons
that share an edge can have their direction determined. If polygon #1 has
wrapping ABCD, and polygon #2 has vertices ABEF, then polygon #2's wrapping
will involve a B->A transition.
Steve
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