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 CAD / Development / 3014
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Subject: 
Re: Comprehensive meta-command list
Newsgroups: 
lugnet.cad.dev
Date: 
Mon, 4 Oct 1999 15:13:30 GMT
Viewed: 
472 times
  
Gary Williams wrote in message ...

Proposed:

0 FACE { CW | CCW | DOUBLE-SIDED | UNKNOWN }

Used to indicate the vertex order for all polygon definitions that follow.
Assumed UNKNOWN until this line is encountered.

0 INVERT

0 INVERT END (only needed if 0 INVERT has a persistent meaning)

No, never needed, since "0 INVERT" is a toggle!

Used to invert sub-parts / primitives that are referenced between the two
commands so that inside and outside faces are to be reversed from the way
they're actually represented in their original definition.  Used to allow
rendering routines to employ backface culling.

These may be needed if there's no way to invert an asymmetrical part simply
by manipulating its orientation matrix alone.

If an INVERT is nested directly or indirectly within another INVERT, then
the second one cancels the first until the next INVERT END is encountered.

Since INVERT is directly related to the CW and CCW parameters of the FACE
meta-command, why not let it be yet another parameter to FACE ?

I think the INVERT is only meant as a convenience, since
0 FACE CCW
...
0 FACE INVERT
1 16 ...
0 FACE INVERT

is the same as

0 FACE CCW
...
0 FACE CW
1 16 ...
0 FACE CCW

To make this whole CCW-business a success I believe it is important to
have the part authors in mind: it should be as easy and understandable
as possible. This might be THE argument for having the otherwise
redundant FACE INVERT keyword. Actually I already suggested something
like it Friday Oct 1st:
or maybe to make it easier to use for part authors:
1 16 0 -4 0 4 0 0 0 4 0 0 0 4 4-4cyli.dat
0 INSIDE-OUT 1
1 16 0 -4 0 6 0 0 0 4 0 0 0 6 4-4cyli.dat
0 INSIDE-OUT 0
- but nevertheless I still think it is redundant.

However, the "CCW-checker-tool" will help the part authors. It could
insert FACE INVERT the appropriate places.
/Lars
(and yes, the 0/1 after INSIDE-OUT should be deleted ;-)



Message has 2 Replies:
  Re: Comprehensive meta-command list
 
(...) True. '0 INVERT END' may be allowed as a syntactic convenience to authors. Or 0 INVERT could be rewritten as 0 INVERT [ON|OFF|TOGGLE] where TOGGLE would be the default action. (...) [example snipped] 0 INVERT is different from 0 FACE [CW|CCW] (...) (25 years ago, 4-Oct-99, to lugnet.cad.dev)
  Re: Comprehensive meta-command list
 
Lars C. Hassing wrote in message <939050465.592693@ns.cci.dk>... (...) True. But when manually examining a file, if you come across a 0 INVERT you wouldn't know whether this was the beginning or the end of the inverted references, without a bit of (...) (25 years ago, 4-Oct-99, to lugnet.cad.dev)

Message is in Reply To:
  Comprehensive meta-command list
 
I'm attempting to compile a list of all meta-commands...did I miss anything? Current (From the LDraw FAQ): 0 <description> If the first line of the file is a comment, it's assumed to be the description of the file. 0 STEP Used to indicate the end of (...) (25 years ago, 3-Oct-99, to lugnet.cad.dev)

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