Subject:
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Re: Comprehensive meta-command list
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Newsgroups:
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lugnet.cad.dev
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Date:
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Mon, 4 Oct 1999 15:13:30 GMT
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Viewed:
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1436 times
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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 ;-)
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Message has 2 Replies:
 | | Re: Comprehensive meta-command list
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| (...) 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] (...) (27 years ago, 4-Oct-99, to lugnet.cad.dev)
| | | Re: Comprehensive meta-command list
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| 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 (...) (27 years ago, 4-Oct-99, to lugnet.cad.dev)
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Message is in Reply To:
| | Comprehensive meta-command list
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| 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 (...) (27 years ago, 3-Oct-99, to lugnet.cad.dev)
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