Hi,
>I remember seeing 2 or 3 cloth simulations around. Is anyone else still
>writing cloth code? Maybe we could share notes, my current algorithm is far
>from being stable.
I'm also working on cloth simulation, with external utilities written
in C++ (not pov-script, I found it way too slow).  I started off using
Hugo Elias' spring model, but, like you, found it very unstable in
terms of being *really* stretchy in unwanted places.  I have since
switched to using (basically) Xavier Provot's method (it's just the
standard physical model of springs, really) which lets me reduce
damping, and hence make the cloth look *much* more real/alive than it
did before (I posted to p.b.a a while back, and yours looks pretty
similar to that, though I haven't tried anything like that cool
rolling sphere...) - it's really surprising the difference a slightly
different spring model makes.  The gist of it is:
  force = (|dp| - normal_length)*normalise(dp)
(where dp is the vector between the two points connected by the
spring).
I currently have no friction in my model, nor detailed collision (just
planes and spheres, so far).  I do have mass, velocity, acceleration,
smooth triangles etc. (the smooth triangles have problems, but work
better than bezier patches, IME).
Currently I am working on a generalised cloth/gel/string system, which
will hopefully let me build entire models that move/bounce/interact
within their environment.  I have also been spending time trying to
make decent articulated structures (people) to wear all this cloth...

- Michael

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