Subject:
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Re: Line in the Sand
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Newsgroups:
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lugnet.cad.dev
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Date:
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Wed, 10 Nov 1999 00:44:17 GMT
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Viewed:
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3149 times
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Steve Bliss wrote...
> Yes. WINDING UNKNOWN allows a DAT author to specify what is happening in • the
> file more precisely than CLIPPING OFF. Adding WINDING DOUBLE-SIDED would • allow
> even more author-precision, but there is no practical difference between
> DOUBLE-SIDED and UNKNOWN, AFAIK.
>
> There is a slight practical difference between WINDING UNKNOWN and CLIPPNG • OFF
> -- WINDING is a file-specific setting; the file's author can assume that • they
> always know the current WINDING setting. CLIPPING is passed down the • reference
> branch, and the current file should make *as few* assumptions about the • CLIPPING
> setting as possible.
Good point!
Jacob Sparre Andersen wrote:
> [ Still discussing http://www.geocities.com/partsref/bfcspec.txt ]
> certification = "0" "CERTIFY" ( "BFC" | "NOBFC" ) { certification_flag }
> winding = "0" "WINDING" ( "CW" | "CCW" | "UNKNOWN" )
> clipping = "0" "CLIPPING" ( "ON" | "OFF" )
> invert = "0" "INVERT"
Or you could write:
0 CERTIFY BFC | 0 CERTIFY NOBFC
0 WINDING CW | 0 WINDING CCW | 0 WINDING UNKNOWN
(I don't think "0 WINDING" alone makes much sense)
0 CLIPPING ON | 0 CLIPPING OFF
0 INVERT
(or maybe "0 INVERTNEXT" to stress that it is only the following
line, which must be of type 1, that is turned inside-out)
Still discussing http://www.geocities.com/partsref/bfcspec.txt :
The CERTIFY section:
> operational command-line in the file. No other statements are required • for
> backface culling to be applied to a file.
Then please add:
0 CERTIFY BFC implies 0 CLIPPING ON and 0 WINDING CCW.
The WINDING section:
> 0 WINDING [ CW | CCW | UNKNOWN ]
> default: CCW
As "0 WINDING" alone doesn't make much sense, the "default: CCW" should
be deleted. The default value should not refer to what 0 CERTIFY BFC
implies - you don't have a default for CLIPPING.
> UNKNOWN = winding direction is unknown or variable. This setting will • disable
> clipping, until the winding is reset.
>
> The WINDING setting is a local setting, it applies only to the polygons in
> the file in which the WINDING meta-statement appears.
"...This setting will disable clipping..." - I hope readers do not confuse
this with CLIPPING OFF. Although the next sentence says WINDING is local,
it should be made clear that clipping is not turned off for subfiles.
Can you think of a better wording of the two sentences?
Also there should be some words about using 0 CLIPPING OFF for a
double-sided
section of a file.
Well, we could start working right now by updating the primitives reference
http://www.ldraw.org/memorial/archive/FAQ/Primitives_Reference
by adding newer primitives and stating the orientation.
If we "invent" another meta command, like
0 ORIENTATIONARROW x1 y1 z1 x2 y2 z2
rendering programs could optionally draw an arrow and you could save
a nice bitmap for the primitives reference.
/Lars
PS. Jean-Pierre PARIS, how are you doing?
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Message has 1 Reply:
 | | Re: Line in the Sand [DAT]
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| On Wed, 10 Nov 1999 00:44:17 GMT, "Lars C. Hassing" <lch@ccieurope.com> wrote: Still discussing (URL) (...) Yes, but the 0 CERTIFY ( BFC | NOBFC ) format is more common. And it emphasizes that is one statement with various parameters. And it's less (...) (25 years ago, 10-Nov-99, to lugnet.cad.dev)
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Message is in Reply To:
| | Re: Line in the Sand
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| (...) Yes. WINDING UNKNOWN allows a DAT author to specify what is happening in the file more precisely than CLIPPING OFF. Adding WINDING DOUBLE-SIDED would allow even more author-precision, but there is no practical difference between DOUBLE-SIDED (...) (25 years ago, 9-Nov-99, to lugnet.cad.dev)
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