[LSC] Ambiguities - PLEASE DISREGARD PREVIOUS

[Travis Cobbs]

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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