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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Tue, 30 Dec 2003 01:40:47 GMT
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Viewed:
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1660 times
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In lugnet.cad.dev, Steve Bliss wrote:
> In lugnet.cad.dev, Chris Dee wrote:
> [snip]
>
> Thanks for writing this up, Chris!
>
> Your explanation was very good in all respects except for one small point:
>
> > ... although for cylinders it
> > is possible to turn them inside out by negating the transformation matrix, and
> > adjusting the position).
>
> Actually, negating the transformation matrix should not invert any object; and even
> if it does, it's not a valid technique for BFC'ing.
>
> Steve
For the two-dimensional primitives (disc, ndis, ring, chrd) you can do the
following:
Say you have a disc in the x-z plane, like:
1 16 0 0 0 10 0 0 0 1 0 0 0 10 4-4disc.dat
If this has the wrong BFC winding, you can just flip (mirror) the primitive by
changing the matrix to:
1 16 0 0 0 10 0 0 0 -1 0 0 0 10 4-4disc.dat
Any reason why that isn't valid? (I do it all the time)
Using a mirror matrix doesn't work for the 3d primitives, like the cylinder
Chris mentions.
Andy
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Message has 2 Replies:
 | | 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)
| | | Re: primer/tutorial on BFC?
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| (...) [snip] (...) I just wanted to add one more post in an attempt to clear up any confusion that may have been caused in this thread. What Andy says above is correct, and my earlier post indicating otherwise was incorrect. The two dimensional (...) (20 years ago, 4-Jan-04, to lugnet.cad.dev)
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Message is in Reply To:
| | Re: primer/tutorial on BFC?
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| In lugnet.cad.dev, Chris Dee wrote: [snip] Thanks for writing this up, Chris! Your explanation was very good in all respects except for one small point: (...) Actually, negating the transformation matrix should not invert any object; and even if it (...) (21 years ago, 28-Dec-03, to lugnet.cad.dev)
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