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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Fri, 7 Apr 2000 21:26:30 GMT
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Viewed:
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2477 times
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In lugnet.cad.dev, Rui Martins wrote:
> > This point hasn't been discussed since, I believe. This is very valid,
> > these "singular transformation matrices" should be fixed.
>
> I believe that the only problem is that these matrixes can't be inverted !
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 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.
> > 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.
:)
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.
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.
> Nope, the hardcoded transparent sections should have cliiping disabled,
> for a BFC certifyed part/piece.
That's looking like the simplest option.
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.
> > Lars pointed out that we should not require parts-authors to code
> > anything that the rendering engine can figure out for itself.
> >
> > And that was the end of intelligent discussion on that point.
>
> Not always, but let's assume yes.
>
> > ------------------------------------------------------------------------
> > A side issue of that discussion: can transparent surfaces be clipped?
>
> To be correct NO, but that can be left has an option to the user.
> There is not TOO much difference, and while editing would be a nice feature
> (clipping), because of speed increase, for final drawing don't disable
> trasnparent clipping.
See my other posts from today, I'm thinking that yes trans-surfaces can
be clipped.
Steve
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Message has 1 Reply:
 | | Re: BFC: LITS 2
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| Steve Bliss wrote... (...) 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 (...) (25 years ago, 18-Apr-00, to lugnet.cad.dev)
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Message is in Reply To:
| | Re: BFC: LITS 2
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| (...) I believe that the only problem is that these matrixes can't be inverted ! I'not sure if placing a one on the specific place has exactly the same graphic behaviour ? can someone confirm ? (...) Use my proposal: 0 CERTIFY BFC MTX where MTX is (...) (25 years ago, 2-Apr-00, to lugnet.cad.dev)
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