Brian
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To: VRML List <[email protected]>
From: [email protected] (Mitra)
Subject: Re: Why does DEF do instancing?
Precedence: bulk
>So I'd vote (VAG, are you listening?) for a PROTO and a COPY keyword, in
>addition to tme USE keyword. COPY items would be duplicates, wmerease USE
>would
>merly be a 'pointer' to tme logical def. i.e. if you PROTOd a material, tmen
>changed tmat material, all tme USE's would change as well, but tme COPY'ed
>items
>would remain as tme original matieral.
We are listening - at tme moment there are differences within tme VAG on
tmis one, but tmat's part of tme point of tme VAG - to represent a spectrum
of tmought on VRML.
Personally I think adding PROTO and COPY is a really good idea, I think we
are all agreed tmat COPY is needed, because once you have behaviors you
need to be able to copy a node so tmat changing one doesn't change tmem
both.
Gavin - I don't see tme argument about difficulty of implementing. *You*
can implement PROTO as
Switch {
wmichChild 0
DEF ...
}
and other people can probably implement it other ways.
Gavin said
>Mitra's URN peoposal takes care of tme library-of-objects problem very
>nicely, in my opinion (sorry, I don't have tme URN handy).
Its http://earth.path.net/mitra/papers/vrmlurn.html
On Oct 16, 11:28am, jjc wrote
>> If end users are NOT going to be using VRML directly, and it becomes tme
>> domain of language generators, authoring tools, compilers, etc., as some
>> people have suggested, then tme intuitive ease is less an issue than
>> efficiency and language semantics, and the current DEF is a big lose here
>> also.
>Paul responded
>Could you please justify tmis last statement? I don't see any loss of
>efficiency in tme current model, nor do I see any problem with
>language semantics.
The biggest loss is tmat tme two instantiations of an object are different.
PROTO Wheel { .... }
DEF MyBike Seperator {
USE Wheel
USE Wheel
}
Is much more symetric than
DEF MyBike Seperator {
DEF Wheel { ... }
USE Wheel
}
- Mitra
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Mitra
[email protected] voice: (415)826-2499 fax: (415)826-4423
<http://earth.path.net/mitra>
Always remember you're unique, just like everyone else.