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In lugnet.cad.dat.parts, Tony Hafner wrote:
> Okay... if this is the case, then what's the status on bringing the
> less-primitive primitives into BFC certification?
Sorry, I got distracted. I'll get back to BFC'ing and submitting those
primitives.
[snip]
> But bottom studs are quite commonly used upside-down (ie a negative y size).
> This means that either:
> - The primitive has to be certified in a really odd way
> (top disc as you look at the raw primitive is flipped)
> - All parts that use the stud need to be redone to handle
> the stud in the "correct" orientation (and INVERTNEXT
> won't work right because then the cylinders get
> hosed... right?)
You're working on an incorrect assumption here. Reflecting a subfile
(ie, negating the multipliers for one dimension) will not invert the
subfile. Reflection is frequently used in LDraw files, and has never
been intended to imply inversion. Take a look at <part: 3935 Wing 4 x 4
Right>. It only has a single line of code: a reflection of <part: 3936
Wing 4 x 4 Left>.
Since reflection is an allowed operation on subfiles, BFC-capable
rendering programs have to detect reflection and make accomodations for
it (since reflection reverses the vectors used in BFC processing).
The part author (or person BFC'ing existing part files) doesn't have to
take any special steps to deal with cases of reflected subfiles.
We went around and around on this awhile ago; I had figured that
reflection would handle all inversions, and no separate statement or
coding would be necessary. I don't remember the technical reasons now,
but relying on reflections for inverting subfiles is not a good way to
go. Besides being a lot of work to straighten out all the existing
code. :)
Steve
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