[LSC] Ambiguities - PLEASE DISREGARD PREVIOUS

[Chris Dee]

Hi

 

I think the Parts Tracker submit process also complains about '0 BFC CERTIFY
INVERTNEXT' .

 

Chris

 

  _____  

From: lsc-bounces at ldraw.org [mailto:lsc-bounces at ldraw.org] On Behalf Of
Travis Cobbs
Sent: 12 October 2006 17:53
To: LDraw Standards Committee
Subject: Re: [LSC] Ambiguities - PLEASE DISREGARD PREVIOUS

 

Thanks for bringing that up.  I had forgotten about that.  I believe that
LDView is the only tool that spits out warnings when 0 BFC CERTIFY is used
as the start text for every single BFC command.  You are correct that there
is some ambiguity in this, and I'll admit that when I added that warning to
LDView, I wasn't intending it as a way to influence the allowed behavior in
the parts tracker.  I certainly wasn't aware that MLCad changed all BFC
statements to that format, or I probably would have forgone producing that
warning. 

As a note, in order to prevent 0 BFC (all by itself) from being a valid
match to the last of the three options you give, we'll need to also note
that at least one option is required.  I may have missed something, but it
appears that the current spec allows a 0 BFC line (with no options),
although it also appears that such a line would be a no-op. 

--Travis

On 10/12/06, William Howard <william at howard-family.fsworld.co.uk> wrote: 

PLEASE DISREGARD THIS - IT GOT SENT BEFORE I WAS FINISHED!!!!

-----Original Message----- 
From: lsc-bounces at ldraw.org [mailto:lsc-bounces at ldraw.org] On Behalf Of
William Howard
Sent: 12 October 2006 14:44
To: 'LDraw Standards Committee' 
Subject: [LSC] Ambiguities in the draft BFC spec


I'm using the term ambiguity to mean a difference in interpretation of the
spec amoung 2 or more people.

The following two ambiguities *HAVE* occured in the Parts Library, either by

authors using them or tools used by authors adding them.  The difference in
interpretation has been flagged by Reviewers holding the files.

1) The draft specification gives the syntax of the BFC meta-command as 
    0 BFC [CERTIFY|NOCERTIFY] [CLIP|NOCLIP] [CW|CCW] [INVERTNEXT]
and there is an ambiguity here in that the syntax *permits* the construct
    0 BFC CERTIFY INVERTNEXT
but this is generally considered wrong (albeit not by one tool author) 

2) While the draft specification permits the winding to change direction
through the file
    "There may be any number of changes to the winding direction in a file,
although it is
     recommended that changes to winding be kept to a minimum." 
there have been parts on the tracker held for this reason.


To address point 1, I would like to see the syntax definition changed to
    0 BFC NOCERTIFY
    0 BFC CERTIFY [CW|{CCW}]
    0 BFC [CLIP|NOCLIP] [CW|CCW] [INVERTNEXT] 
where [] indicates an optional item and {} the default value


This makes set of valid BFC meta-commands as follows
  0 BFC NOCERTIFY
  0 BFC CERTIFY       (defaults to CCW)
  0 BFC CERTIFY CW
  0 BFC CERTIFY CCW 
  0 BFC CLIP CW INVERTNEXT
  0 BFC CLIP CW INVERTNEXT
  0 BFC CLIP CW INVERTNEXT
  0 BFC CLIP CW INVERTNEXT
  0 BFC CLIP CW INVERTNEXT
  0 BFC CLIP CW INVERTNEXT
  0 BFC CLIP CW INVERTNEXT
  0 BFC CLIP CW INVERTNEXT 
  0 BFC CLIP CW INVERTNEXT
  0 BFC CLIP CW INVERTNEXT
  0 BFC CLIP CW INVERTNEXT
  0 BFC CLIP CW INVERTNEXT
  0 BFC CLIP CW INVERTNEXT
  0 BFC CLIP CW INVERTNEXT


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