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 02:25:49 GMT
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Viewed:
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1874 times
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In lugnet.cad.dev, Steve Bliss wrote:
> In lugnet.cad.dev, Andrew Westrate wrote:
> > 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)
>
> 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 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
>
> Steve
If this is the case then we need to go back through all the BFC'd parts and find
instances of this type of matrix. Since L3Lab allows inverting the sign of the
Y component and it's currently the only program to easily check for correct
winding, I assumed (without reading the specification) that doing so was legal.
This is also the way I've been teaching others.
-Orion
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Message has 1 Reply:
 | | Re: primer/tutorial on BFC?
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| (...) I do this all the time, too. Just a minus sign in stead of 'BFC INVERTNEXT' each time can save some diskspace, which I've been told is something to go for, too. Niels (21 years ago, 3-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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