Subject:
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Re: Some Words To BFC
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Newsgroups:
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lugnet.cad.dev
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Date:
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Thu, 6 Apr 2000 19:12:19 GMT
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Viewed:
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2929 times
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In lugnet.cad.dev, Leonardo Zide wrote:
> When it finds that any face of a primitive needs to be inverted. We
> would have to fix the current primitives so that all faces are pointing
> to the same direction. Take a look at the sphere primitive for example,
> it has faces pointing inside and outside the sphere.
The primitives should be the first thing fixed, in any case. :) I
think it would be safe for the cleanup program to assume that primitives
are BFC-ready. Which could be a help for automatic cleanup of part
files.
> > Question #2: why is adding "pi\" preferable to substituting a different
> > file name (so the inverted primitives are in the p\ directory) or
> > inserting a 0 INVERTNEXT statement?
>
> I think the "pi\" dir was just an example, it could have any other
> name. Adding a 0 INVERTNEXT would require more time to parse a file.
Some technical points:
Parsing and processing a 0 INVERTNEXT statement requires very little
time. And each file should only be parsed once in a single rendering.
Interactive viewers/editors should only reparse a file if it changes.
Having extra primitive files would also slow down processing, because it
would take slightly longer to locate the correct file on the disk. If
all the extra primitives are in the ldraw\p directory, then each time
*any* primitive is loaded, the file-find step takes longer, because the
directory list if larger. If the inverted primitives are kept in a
subdirectory, then locating the inverted primitives takes more time,
because the OS would first have an extra step in the directory-tree
search. But again, each file should only be loaded once in a single
rendering.
Using INVERTNEXT would take a few more bytes of storage than using
mirrored primitive files.
I don't think this issue (to INVERTNEXT or to clone primitive files)
will be decided on technical issues.
I think the key issue is which approach makes it easier to code DAT
files, and maintain the parts library. Unfortunately, I don't have much
of an opinion here, except that having extra files means parts authors
have more to learn about p-files, and there would more files which would
need to be maintained. From a language point of view, the difference
between the two approaches is strictly syntactic. And if the cleanup
program can detect inversion automatically, then neither approach puts
any burden on the author.
> > > It seems to me that Leonardo's program is up to this task, perhaps with a
> > > little improvement.
> >
> > Have you used Leonardo's program? I've heard of some different programs
> > that can help with sorting polygons, but I haven't heard of anyone
> > publishing one yet...
>
> If anyone wants to take a look, just ask. I don't have the time to
> create a web page and make something official so I'll need some help to
> finish the program.
I'm asking. :)
Steve
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Message has 3 Replies:
 | | Re: Some Words To BFC
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| Steve Bliss <blisses@worldnet.att.net> wrote in message news:a5mpess6nipq4bp...4ax.com... snip (...) Me too. -John Van (25 years ago, 6-Apr-00, to lugnet.cad.dev)
| | | BFC checking program (was Re: Some Words To BFC)
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| (...) I'm assuming that you're calling "BFC-ready" primitives that have all faces in the same direction. Primitives are not closed volumes so you'll always be able to see the backfaces. (...) I agree technically it doesn't make much difference, I (...) (25 years ago, 7-Apr-00, to lugnet.cad.dev)
| | | Re: Some Words To BFC
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| Steve Bliss wrote on April 6th... (...) The program should refuse to certify a part if not all subfiles are certified. (...) Agreed! We should not put any constraints on the authors. They may scale/rotate/mirror primitives as they wish (not (...) (25 years ago, 19-Apr-00, to lugnet.cad.dev)
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Message is in Reply To:
| | Re: Some Words To BFC
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| (...) When it finds that any face of a primitive needs to be inverted. We would have to fix the current primitives so that all faces are pointing to the same direction. Take a look at the sphere primitive for example, it has faces pointing inside (...) (25 years ago, 6-Apr-00, to lugnet.cad.dev)
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