Special:
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[DAT] (requires LDraw-compatible viewer)
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Subject:
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Re: primer/tutorial on BFC?
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Newsgroups:
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lugnet.cad.dev
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Date:
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Sat, 3 Jan 2004 00:35:27 GMT
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Viewed:
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1743 times
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In lugnet.cad.dev, Steve Bliss wrote:
> That shouldn't work -- the rendering program should detect that you've mirrored the
> object, and adjust accordingly. Unfortunately, I see that it does 'work' in L3Lab.
I do agree that it isn't supposed to work, because the BFC spec very carefully
states that any polygons drawn with an aggregate matrix that causes mirroring
must be flipped back.
> LDView is crashing my system right now, so I couldn't check it.
I'm sorry that LDView is crashing your system, but it won't help here anyway,
since it doesn't have BFC support.
> What you should do is flip the 2D object. Inverting both X and Y is the same as
> rotating 180 degrees around the Z axis:
> 1 16 0 0 0 -10 0 0 0 -1 0 0 0 10 4-4disc.dat
Or you could just use INVERTNEXT, which will work for both 2D and 3D objects,
and doesn't require any additional matrix math (Isn't that what it's there
for?):
0 BFC INVERTNEXT
1 16 0 0 0 10 0 0 0 1 0 0 0 10 4-4disc.dat
(Note that I haven't looked an L3Lab's handling of BFC, but I have examined the
BFC spec fairly closely. If INVERTNEXT was introduced into the spec after L3Lab
was written, then it won't be supported by L3Lab.)
--Travis Cobbs
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Message has 3 Replies:
 | | Re: primer/tutorial on BFC? [DAT]
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| (...) I think it works just fine. L3Lab correctly detects that the matrix is mirroring, see View/Tree View... and click the BFC radio button, it should say INVERT in front of the line. When we discussed the BFC business the general assumption was (...) (21 years ago, 3-Jan-04, to lugnet.cad.dev)
| | | Re: primer/tutorial on BFC?
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| (...) Actually, I *think* it's the new ATA controller card I installed, and LDView was just an innocent bystander. However, since LDView doesn't do BFC, I guess I didn't miss anything. (...) Yes, you could use INVERTNEXT, but that introduces (...) (20 years ago, 4-Jan-04, to lugnet.cad.dev)
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Message is in Reply To:
| | Re: primer/tutorial on BFC? [DAT]
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| (...) That shouldn't work -- the rendering program should detect that you've mirrored the object, and adjust accordingly. Unfortunately, I see that it does 'work' in L3Lab. LDView is crashing my system right now, so I couldn't check it. What you (...) (21 years ago, 31-Dec-03, to lugnet.cad.dev)
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