[ODE] XML and ODE

[John Donovan]

> Hopefully it shouldn't be hard to port it to C/C++.

It's not too hard, the trickiest part is getting to grips with XML when
you've never done any coding for it!


> If you do and make it open source,

It's part of a nodekit for the OpenSceneGraph (www.openscenegraph.org),
and I'm putting it under the OSGPL, which is a more relaxed version of
the LGPL. I don't think this will clash with the LGPL of ODE because I'm
creating a work "using" ODE, rather than one "based on". As it's not
been publically released yet, if there is a licensing issue, if someone
could let me know and I'll see what the implications are for using a
different license.

> please tell me about it and I shall link to you from the site. 

Thanks. I've got a bunch more stuff to write first, so it'll be probably
a couple of months before I'm happy with it. Also, there are no plans to
make it a general C++ XODE reader, because my project involves OSG quite
heavily. But as my OSG ODE wrapper is very lightweight, it won't be hard
for someone to make it more general.

> If you have any other questions, please ask away.

I do have one or two. They may be because I'm not an XML expert, rather
than any issues with the XODE istelf.

1) Why does adjust element have _both_ density and total attributes? Is
there a way of making them mutually excusive? Maybe by making them
elements of type xs:simpletype, and wrapping them in a xs:choice.
2) Why are the density and total attributes of the adjust element also
attributes of the mass_shape and mass_struct? This looks like you can
have:
<mass>
   <mass_struct density="12" > <!-- Do we use this density... -->
      <centerGravity>
         <!-- Stuff goes here -->
      </centerGravity>
      <imatrix>
         <!-- More stuff goes here -->
      </imatrix>
   </mass_struct>
   <adjust density="30" /> <!-- ...or this density? -->
</mass>

3) Does the reference implementation parse masses? The latest source
(30/10/2004) only seems to handle adjust elements.
4) Are the versions of the XODE spec backwards compatible? My code
explicity checks for r23 at the moment.
5) Is there any need to store all 9 elements of the inertia tensor? The
ODE functions only take the lower triangle.
6) There are a few typos in the spec, would you mind if I go through and
correct ones I find?

-J

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