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, 27 Dec 2003 13:19:58 GMT
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Viewed:
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1785 times
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In lugnet.cad.dev, Franklin W. Cain wrote:
> Anyone out there willing to teach me how to certify a DAT file for backface
> culling (BFC)? Posting to LUGNet would be preferable, especially if you are
> providing images (visual aids are usually helpful when teaching a complicated
> subject).
>
> I recall one or two people had volunteered to do this via email, but I haven't
> received any of those messages. Since I'm asking again, I thought I'd ask for a
> public tutorial, so that more people than just myself could benefit...
>
> Thanks!
> Franklin
I think ease or difficulty depends on which tools you use to author parts.
I use LDAO as the editor with L3Lab for preview and find it reasonably easy.
Others may wish to comment with reference to their favourite tools.
To BFC an existing DAT file:
Ensure that you have a "BFC CERTIFY [C]CW" statement in the part file and that
BFC mode sensitivity is on in L3Lab (View | BFC is checked).
Set the two windows so that you can see the LDAO editor and L3Lab display
concurrently.
In the LDAO editor, select the "stop at cursor" option ( Option |
Stop-at_Cursor).
In L3P, select File | Poll for changes | Poll, silent update, and Test |
mytest6.
In the editor, single step through the DAT file checking that the outside faces
show green (and inside faces show red) in L3Lab. To switch the vertex winding of
a type 3 or 4 line, there is a menu-bar button (Yin-Yan symbol). To switch the
vertex winding of a subfile or primitive insert a "0 BFC INVERTNEXT" line
immediately before the type 1 line you want to invert (although for cylinders it
is possible to turn them inside out by negating the transformation matrix, and
adjusting the position).
You might need to turn off the "stop at cursor" option or the "mytest6" option
intermittently to understand the location of the newly revealed quad or
triangle.
To BFC a new DAT file as you write it:
Be consistent about the sequence in which you specify vertices for quads and
triangles. Use the techniques above to ensure correct winding of primitives.
I hope this brief overview is enough to get you started.
Chris
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Message has 4 Replies:
 | | 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)
| | | Re: primer/tutorial on BFC?
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| (...) I use Notepad (NOTEPAD.EXE), until the DAT file gets too huge, whereupon I use WordPad (WORDPAD.EXE) to continue editing the file. I use a calculator and scratch paper (to do a rough sketch and to keep notes of important locations). Whenever I (...) (21 years ago, 30-Dec-03, to lugnet.cad.dev)
| | | Re: primer/tutorial on BFC?
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| (...) I use LDDP and L3Lab with "Poll to L3Lab & LDview" + "Poll to selected line only" turned on. going through the code with CRTL+W (orion please don't forget my special request) rewinding what's needed. w. (21 years ago, 30-Dec-03, to lugnet.cad.dev)
| | | Re: primer/tutorial on BFC?
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| In lugnet.cad.dev, Chris Dee wrote: [snip] One other thing: before you update a file for BFC, be sure there are no serious L3P errors -- vertex order is the big problem, but you should also take care of non-coplanar quads and singular matrices as (...) (21 years ago, 31-Dec-03, to lugnet.cad.dev)
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Message is in Reply To:
| | primer/tutorial on BFC?
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| Anyone out there willing to teach me how to certify a DAT file for backface culling (BFC)? Posting to LUGNet would be preferable, especially if you are providing images (visual aids are usually helpful when teaching a complicated subject). I recall (...) (21 years ago, 24-Dec-03, to lugnet.cad.dev)
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