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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Wed, 31 Dec 2003 01:35:04 GMT
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Viewed:
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1849 times
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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
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Message has 2 Replies:
 | | Re: primer/tutorial on BFC? [DAT]
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| (...) 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. (...) I'm sorry that LDView is crashing your system, but it (...) (21 years ago, 3-Jan-04, to lugnet.cad.dev)
| | | Re: primer/tutorial on BFC?
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| (...) 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 (...) (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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| (...) 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 (...) (21 years ago, 30-Dec-03, to lugnet.cad.dev)
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