Subject:
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Re: BFC: LITS 2
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Newsgroups:
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lugnet.cad.dev
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Date:
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Tue, 18 Apr 2000 22:13:44 GMT
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Viewed:
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838 times
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Steve Bliss wrote...
> Another problem (that L3P handles in most cases) is that POV-Ray refuses
> to process objects with singular matrices.
>
> > I'not sure if placing a one on the specific place has exactly the
> > same graphic behaviour ?
> > can someone confirm ?
>
> A reference with a singular matrix only works correctly on 2D objects.
> Well, it can be used to flatten 3D objects, but this is considered a Bad
> Thing. I should know, because I once proposed that we didn't need ring
> primitives, we could just use conic primitives with singular matrices.
> I got severly clobbered for that one.
>
> As far as I know, there are no singular matrix references in the LDraw
> parts library, except against 2D primitives like 4-4disc and 2-4edge.
Running "l3p -check" (checks all DAT's in P and PARTS) revals:
SKIPPING "4285.DAT" Line 981: Singular matrix: 1 16 10 4 10 6 0 0 0 0 0 0 0 6 1-4cyli.dat
SKIPPING "6043.DAT" Line 17: Singular matrix: 1 16 0 20 -16 8 0 0 0 0 8 0 0 0 4-4cyli.dat
SKIPPING "3741.DAT" Line 7: Singular matrix: 1 16 0 16 0 1 0 0 0 0 0 0 0 1 stud4.dat
SKIPPING "6267.DAT" Line 85: Singular matrix: 1 16 110 96 -10 2 0 0 0 0 0 0 0 -2 1-4con3.dat
SKIPPING "6267.DAT" Line 86: Singular matrix: 1 16 110 96 -10 2 0 0 0 0 0 0 0 -2 1-4con4.dat
SKIPPING "6267.DAT" Line 88: Singular matrix: 1 16 -110 96 -10 -2 0 0 0 0 0 0 0-2 1-4con3.dat
SKIPPING "6267.DAT" Line 89: Singular matrix: 1 16 -110 96 -10 -2 0 0 0 0 0 0 0-2 1-4con4.dat
SKIPPING "4095.DAT" Line 15: Singular matrix: 1 16 0 12 0 4 0 0 0 0 0 0 0 4 4-4cyli.dat
SKIPPING "4095.DAT" Line 18: Singular matrix: 1 16 0 0 0 6 0 0 0 0 0 0 0 6 4-4cyli.dat
Running "l3p -check -w3" (highest warning level, lots of output) revals
15985 (!) singular matrix references to 2D primitives, that L3P is able to fix.
But L3Lab will have to turn clipping off for these!
> > > BTW, this gives the CERTIFY tag something to define besides clipping and
> > > winding. In order to cleanly certify a file, it should *not* have any
> > > subfile commands with singular matrices.
> > >
> > > Even so, CERTIFY is still functionally redundant...
> >
> > Use my proposal:
> > 0 CERTIFY BFC MTX
> >
> > where MTX is Matrix, correct non singular matrices
>
> But that would be an extra flag that would complicate processing, and
> slow the rendering engine down.
I see the MTX more like an administrative info. The renderer should always
check the file...
> Actually, I did once consider having a BFC-flag to indicate that the
> subfile references were all clean. I'm not sure if I ever publicized
> that one or not.
The BFC-checker program must refuse to certify a part if any subfile
is not certified. So that flag would be implied in CERTIFY.
> No matter what we specify, the rendering engine should still check for
> singular matrices (that's pretty low impact, as it's the same
> calculation as checking for matrix reversal) and disable BFC processing
> if necessary.
Right.
> I'm not yet convinced that there isn't another way that renderers could
> handle the problem. Which is part of the reason I've been in favor of a
> NOWIND or DOUBLESIDED option -- most renders would treat it just like a
> NOCLIP command, but if a better solution was found in the future, the
> part files would already contain the little bit of extra information
> needed to take advantage of the new solution.
Good point.
/Lars
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Message has 1 Reply:
 | | Re: BFC: LITS 2
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| (...) Whew! Only one of those files is mine! :\ (...) True. (...) I don't think that's necessary. If a subfile is not certified, then the renderer will not apply BFC processing to the subfile. Besides, if having all subfiles certified was a (...) (24 years ago, 19-Apr-00, to lugnet.cad.dev)
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Message is in Reply To:
| | Re: BFC: LITS 2
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| (...) Actually, the problem is that their determinant is 0, neither positive nor negative. So the renderer would have to disable BFC processing for any file with this kind of reference. Another problem (that L3P handles in most cases) is that (...) (24 years ago, 7-Apr-00, to lugnet.cad.dev)
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