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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Tue, 21 Dec 1999 17:45:25 GMT
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Reply-To:
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RUI.MARTINS@LINK.PTavoidspam
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Viewed:
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2924 times
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> > Mirroring is not a problem. It causes a "negative determinant matrix"
> > which can be detected and adjusted for (by toggling winding).
> > So matrix-inversions are not evil.
>
> Matrix-inversions are not evil. But for some reason, using them to actually
> invert subfiles is evil (as opposed to using INVERTNEXT to invert subfiles).
>
> If I reallly needed an answer to this, I'd go read past messages. But I *do*
> remember:
>
> a) I originally thought INVERTNEXT was redundant, because inversions could be
> handled by inverting matrices.
> b) I was later convinced that INVERTNEXT was needed.
>
> I don't remember *why* INVERTNEXT is needed. But I am sure it is needed.
I do, it's because of those cases like an hollow cylindir DAT file is
referenced by another DAT file. Since the cylinder is supposed to be
define outwards, but you can use it to make the inside/outside of a stud
(for example) and the if the renderer corrected the inverted matrix, it
will clip the inside cylinder since it would seam to be facing outwards.
Actually this is needed for backwards compatibility, and expecially
because of our laziness in doing the correct editing, and NOT mirroring
things.
Another fact is that INVERTNEXT is NOT to correct for the Matrix with
negative determinant, but for the lego cad builder to inform the renderer,
I want to use this particular DAT file inverted (NOT MIRRORED) i.e. Every
face which was facing outwards will now considered to be facing inwards,
and viceversa, and upwards has downwards and viceversa.
Actually what we are saying is:
"now all the unclipable polygons will be clippable, and viceversa"
But all this has been debated too many times, and a long time ago already,
so make up your minds.
Either we support the INVERTNEXT to support our laziness, or we don't, and
we will have to have 2 versions of the DAT files we eventually would like
to use inverted (inside-out).
See ya.
Rui Martins
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Message is in Reply To:
 | | Re: Line in the Sand
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| (...) Matrix-inversions are not evil. But for some reason, using them to actually invert subfiles is evil (as opposed to using INVERTNEXT to invert subfiles). If I reallly needed an answer to this, I'd go read past messages. But I *do* remember: a) (...) (24 years ago, 21-Dec-99, to lugnet.cad.dev)
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