Subject:
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Re: CW/CCW, vertex sequence, co-planar, convex, (115kB)
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Newsgroups:
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lugnet.cad.dev
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Date:
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Fri, 1 Oct 1999 18:23:41 GMT
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Viewed:
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702 times
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On Fri, 1 Oct 1999 14:24:00 GMT, sparre@sys-323.risoe.dk (Jacob Sparre
Andersen) wrote:
> Lars:
>
> > Leonardo Zide wrote
>
> [...]
>
> > > About that discussion, IMO it would be better to have *everything* CCW
> > > instead of adding a keyword.
That would be nice, but it's unrealistic.
> It looks like (C)CW settings should propagate to included
> files.
No, they shouldn't. Just because the part XYZ is CW, a program can't
assume that the primitive ABC is also CW.
> What about:
> 0 FACE DOUBLE-SIDED
> 1 16 0 -4 0 6 0 0 0 4 0 0 0 6 4-4cyli.dat
I like this. I don't like it for use on primitives, but DOUBLE-SIDED could
solve the problem Leo pointed out, with being able to view the back side of
patterns on transparent parts. Just make all the quads/triangles for
patterns double-sided.
> > A part with no keywords is interpreted like it had begun
> > with "0 FACE UNKNOWN".
>
> Shouldn't it rather inherit the setting from the file that
> calls it? Or do we need a specific "0 FACE INHERITED" for
> this purpose?
I agree with Lars on this one. 0 FACE UNKNOWN should be the default for
unmarked part files.
It seems like it would be as easy to write "0 FACE CW" as "0 FACE
INHERITED". And generally, sub-files can't know anything about the state
of the file calling them.
> Open primitives should definitly work with inherited (C)CW
> settings, unless they are intended to be closed up when
> used (like primitives for patterned parts).
I don't get this. If a part is CCW and another is CW, how can a primitive
be written to work with both by inheritance?
> > The only use for the UNKNOWN keyword I can see, is for a
> > section of a part you want to make compliant at a later
> > time.
>
> Yes.
(It's also useful as a default value.)
There is a lot of "low hanging fruit", sections of the parts library which
can be easily verified/corrected. Using the UNKNOWN keyword will let us
put off fixing more difficult sections, in favor of fixing those parts
which are easier (or more important) to fix.
0 FACE CW
0 FACE CCW
0 FACE DOUBLE-SIDED
0 FACE UNKNOWN
Is there a practical difference between UNKNOWN and DOUBLE-SIDED? They'd
have the same basic effect: the surfaces would always be drawn. But
UNKNOWN could include artifacts like concave and bowtie quads.
Steve
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Message has 1 Reply:
 | | Re: CW/CCW, vertex sequence, co-planar, convex, (115kB)
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| [ I got a bit too much good French red wine, so maybe I shouldn't try to answer now, but ... ] Steve: (...) Right. (...) Shouldn't all elements of transparent parts be drawn? (...) Yes. (I start to suspect that wine has a good influence on my (...) (25 years ago, 1-Oct-99, to lugnet.cad.dev)
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