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 CAD / Development / 3010
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Subject: 
Interpreting the proposed FACE meta-command
Newsgroups: 
lugnet.cad.dev
Date: 
Mon, 4 Oct 1999 06:26:46 GMT
Viewed: 
733 times
  
Michael Lachmann wrote in message ...
Does that mean if a program would find the CW directive it can assume that
every-thing in this file is compliant? E.g. the program would not have to
test if possible included parts are compliant, but assume that they are
since the parent is complient. I understand that this would be valid when
drawing the specific compliant part only, not if the included part is used
in a different part which is not compliant!



Here's my take on the matter.

The meta-command:

0 FACE <CW|CCW|DS|UNKNOWN>

...should only be used to indicate the order of the vertices of the polygons
_in the file that contains it_.

If A.dat has a '0 FACE CW' and it references B.dat, it is invalid to assume
that B.dat has the same polygon vertex order.  B.dat should be treated as if
its polygon vertex order was unknown until the FACE meta-command is
encountered within it.

B.dat may be an official part and it may be completely re-written at some
point, and its polygon vertex order could conceivably change.  To avoid
having an official parts update invalidate any models previously built using
one of its parts, each file has to operate independently.

Also note that the FACE meta-command could conceivably appear multiple times
within a single file, each instance having forward (as opposed to global)
scope until the next instance.

While we're discussing this I'd like to propose abbreviating the
'DOUBLE-SIDED' parameter to simply 'DS'.

-Gary



Message has 1 Reply:
  Re: Interpreting the proposed FACE meta-command
 
Gary Williams: (...) Very sensible (now that Steve has convinced me). (...) Hmm. I don't like it, but we have already abbreviated (counter)clockwise, so it does make sense to abbreviate double-sided too. :-( Play well, Jacob ---...--- -- E-mail: (...) (25 years ago, 4-Oct-99, to lugnet.cad.dev)

Message is in Reply To:
  Re: Hidden surface removal, and vertex order in part/primitive DAT files
 
Steve Bliss wrote in message <37f6c258.270062819@...et.com>... (...) 30 (...) Does that mean if a program would find the CW directive it can assume that every-thing in this file is compliant? E.g. the program would not have to test if possible (...) (25 years ago, 4-Oct-99, to lugnet.cad.dev)

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