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In lugnet.cad.dev, Jacob Sparre Andersen wrote:
> [ Still discussing http://www.geocities.com/partsref/bfcspec.txt ]
> > 0 WINDING CW
> > 0 CERTIFY BFC
> >
> > ... the winding should be CW, right?
>
> Maybe. It depends on the definition of "operational
> command-line".
>
> I understand why you sometimes use specialised "programming"
> languages for writing specifications.
Did you mean you=Steve or you=anyone?
> > If the CERTIFY statement 'implied' the winding, then this
> > example would not be clear (at least to the human reader)
> > if the winding for this file is CW or CCW.
> > Does CERTIFY override the earlier WINDING or not?
>
> If "0 WINDING CW" is an operational command-line, it doesn't
> matter. Otherwise the result is somewhat unclear. I would
> prefer that that sequence wasn't allowed.
I agree, the sequence should be illegal.
My point was, does CERTIFY BFC change the value of the internal local_clipping
variable, or not? My intention was that it does not. From a practical
viewpoint, it might as well, but it is not necessary for it to do so.
> The default value is not for the WINDING _statement_, but
> for the "winding" variable.
Good point. I will incorporate this into the document.
> I don't think so. If you could translate my explanation
> above to proper English, then the problem should be solved,
> with the effect I understand you intended.
How about some pseudo-code? Skipping a few beside-the-point details:
Recursive Procedure RenderFile
Parameters:
ModelFile string // File to render
AccumClip boolean // global clipping value yes/no
AccumInvert boolean // current inversion odd/even or normal/inverted
Declare
LocalClip boolean = TRUE
Winding trivalue(CCW, CW, UNKNOWN) = CCW
Certified boolean = FALSE
InvertNext boolean = FALSE
OpenFile(ModelFile)
Do Until EOF(ModelFile)
Get Next Command
Case Command.LineType
CERTIFY
Certified = (Command.Option = "BFC")
CLIPPING
LocalClip = (Command.Option = "ON")
WINDING_CCW
If AccumInvert Then
Winding = CW
Else
Winding = CCW
WINDING_CW
If AccumInvert Then
Winding = CCW
Else
Winding = CW
WINDING_UNKNOWN
Winding = UNKNOWN
INVERTNEXT
InvertNext = True
SUBFILE
RenderFile Command.Subfile,
(AccumClip and LocalClip),
(AccumInvert xor InvertNext)
LINE, CONDITIONAL_LINE
Deal with primitive command
TRIANGLE, QUAD
If AccumClip and LocalClip Then
If BFC(Command, TransformMatrix, Winding) Then
Render Command
Else
Don't render Command
Else
Render Command
End If
End Case
If Command.LineType != INVERTNEXT Then
InvertNext = FALSE
End If
Loop
End Procedure
Ick. Longer than I thought. Maybe I'll go back to plain English.
Steve
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[ Still discussing http://www.geocities.com/partsref/bfcspec.txt ]
Steve:
> In lugnet.cad.dev, Jacob Sparre Andersen wrote:
> > I understand why you sometimes use specialised "programming"
> > languages for writing specifications.
>
> Did you mean you=Steve or you=anyone?
You=anyone (kind of - English is a very imprecise language - "on"
in French, "man" in Danish, ...)
> My point was, does CERTIFY BFC change the value of the
> internal local_clipping variable, or not? My intention
> was that it does not. From a practical viewpoint, it
> might as well, but it is not necessary for it to do so.
That depends on how the program is written. You could
imagine that the variable "local_clipping" isn't defined
until it is verified that it is relevant.
> > I don't think so. If you could translate my explanation
> > above to proper English, then the problem should be solved,
> > with the effect I understand you intended.
>
> How about some pseudo-code? Skipping a few beside-the-point details:
[...]
Good. I think this clarifies a lot.
> Ick. Longer than I thought. Maybe I'll go back to plain English.
I don't think you can make it shorter as plain English, but
I will not complain if you attempt.
Play well,
Jacob
------------------------------------------------
-- E-mail: sparre@cats.nbi.dk --
-- Web...: <URL:http://www.ldraw.org/FAQ/> --
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Steve Bliss wrote ...
> How about some pseudo-code
I think your pseudo-code delivers a fine evidence why the CERTIFY
is unnecessary ;-)
/Lars
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Oops! Forget a few important details in the psuedo-code!
In lugnet.cad.dev, Steve Bliss writes:
> ModelFile string // File to render
> AccumClip boolean // global clipping value yes/no
> AccumInvert boolean // current inversion odd/even or normal/inverted
>
> Declare
> LocalClip boolean = TRUE
> Winding trivalue(CCW, CW, UNKNOWN) = CCW
> Certified boolean = FALSE
> InvertNext boolean = FALSE
>
> SUBFILE
> RenderFile Command.Subfile,
> (AccumClip and LocalClip),
The last line above should be:
(AccumClip and LocalClip and
(Winding != UNKNOWN) and Certified),
> (AccumInvert xor InvertNext)
> LINE, CONDITIONAL_LINE
> Deal with primitive command
> TRIANGLE, QUAD
> If AccumClip and LocalClip Then
And the line above should be:
If AccumClip and LocalClip
And Certified Then
> If BFC(Command, TransformMatrix, Winding) Then
> Render Command
> Else
> Don't render Command
> Else
> Render Command
> End If
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Steve Bliss wrote in message ...
> Oops! Forget a few important details in the psuedo-code!
>
> In lugnet.cad.dev, Steve Bliss writes:
>
> > ModelFile string // File to render
> > AccumClip boolean // global clipping value yes/no
> > AccumInvert boolean // current inversion odd/even or normal/inverted
> >
> > Declare
> > LocalClip boolean = TRUE
> > Winding trivalue(CCW, CW, UNKNOWN) = CCW
> > Certified boolean = FALSE
> > InvertNext boolean = FALSE
> >
> > SUBFILE
> > RenderFile Command.Subfile,
> > (AccumClip and LocalClip),
>
> The last line above should be:
> (AccumClip and LocalClip and
> (Winding != UNKNOWN) and Certified),
No, WINDING is local! It does not affect subfiles, this is the very reason
why we have invented the CLIPPING command.
/Lars
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In lugnet.cad.dev, Lars C. Hassing wrote:
> No, WINDING is local! It does not affect subfiles, this is the very reason
> why we have invented the CLIPPING command.
Argh. You are correct, sir. Serves me right, trying to post quickly.
Here's a correction:
> > > SUBFILE
> > > RenderFile Command.Subfile,
> > > (AccumClip and LocalClip),
> >
> > The last line above should be:
> > (AccumClip and LocalClip and Certified),
Steve
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