CAD Development : 9367


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primer/tutorial on BFC? —Franklin W. Cain

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)

Re: primer/tutorial on BFC? —Chris Dee

(...) 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 (...) (21 years ago, 27-Dec-03, to lugnet.cad.dev)

Re: primer/tutorial on BFC? —Steve Bliss

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? —Chris Dee

(...) OK - it's not a technique I use, but in an email conversation recently somebody convinced me that inverting the matrix would switch the winding. Now that I test it again I found I was mistaken. Chris (21 years ago, 28-Dec-03, to lugnet.cad.dev)

Re: primer/tutorial on BFC? —Andrew Westrate

(...) 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)

Re: primer/tutorial on BFC? —Steve Bliss

(...) 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? —Travis Cobbs

(...) 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? —Tore Eriksson

(...) L3Lab supports BFC INVERTNEXT. /Tore (21 years ago, 3-Jan-04, to lugnet.cad.dev)

Re: primer/tutorial on BFC? —Lars C. Hassing

(...) 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? —Travis Cobbs

(...) You're right; I'm wrong. I'm still having a hard time visualizing it, but your stud example below convinced me that negating the one value in the matrix will indeed flip a 2D primitive like a disk, and this is the expected behavior. In fact, (...) (21 years ago, 3-Jan-04, to lugnet.cad.dev)

Re: primer/tutorial on BFC? —Steve Bliss

(...) Hmmm, very good point. I don't like treating specific object specially, but I don't see any way around it. I played around with the stud and with a 'solid' cylinder object, I couldn't find a way to get L3Lab's BFC handling to fail. Steve (21 years ago, 4-Jan-04, to lugnet.cad.dev)

Re: primer/tutorial on BFC? —Steve Bliss

(...) 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 (...) (21 years ago, 4-Jan-04, to lugnet.cad.dev)

Re: primer/tutorial on BFC? —Orion Pobursky

(...) 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)

Re: primer/tutorial on BFC? —Niels Karsdorp

(...) 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)

Re: primer/tutorial on BFC? —Travis Cobbs

(...) [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 (...) (21 years ago, 4-Jan-04, to lugnet.cad.dev)

Re: primer/tutorial on BFC? —Franklin W. Cain

(...) 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? —Niels Karsdorp

(...) I started parts authoring without knowing about BFC. When I read something about BFC-ing here on lugnet, I started to dig myself into it, reading documentation (from www.ldraw.org), trying things out and now I know enough about it. I only (...) (21 years ago, 30-Dec-03, to lugnet.cad.dev)

Re: primer/tutorial on BFC? —Willy Tschager

(...) 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? —Steve Bliss

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)