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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Fri, 12 Nov 1999 21:10:45 GMT
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Viewed:
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3783 times
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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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Message has 3 Replies:
 | | Re: Line in the Sand
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| [ Still discussing (URL) ] Steve: (...) You=anyone (kind of - English is a very imprecise language - "on" in French, "man" in Danish, ...) (...) That depends on how the program is written. You could imagine that the variable "local_clipping" isn't (...) (25 years ago, 13-Nov-99, to lugnet.cad.dev)
| | | Re: Line in the Sand
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| Steve Bliss wrote ... (...) I think your pseudo-code delivers a fine evidence why the CERTIFY is unnecessary ;-) /Lars (25 years ago, 13-Nov-99, to lugnet.cad.dev)
| | | Re: Line in the Sand
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| Oops! Forget a few important details in the psuedo-code! (...) The last line above should be: (AccumClip and LocalClip and (Winding != UNKNOWN) and Certified), (...) And the line above should be: If AccumClip and LocalClip And Certified Then (...) (25 years ago, 15-Nov-99, to lugnet.cad.dev)
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Message is in Reply To:
| | Re: Line in the Sand
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| [ Still discussing (URL) ] Steve: (...) [...] (...) "INVERTNEXT" is good. It makes the effect much more clear. (...) It gets much too messy when you mix the states of a parameter and the setting of that parameter. CERTIFY BFC does imply CLIPPING ON, (...) (25 years ago, 11-Nov-99, to lugnet.cad.dev)
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