"Greg M. Johnson" wrote:

> Amazing.  I have been unable to "do the physics of" a ball that is BOTH able to
> bounce AND does not fall through the floor when it comes to rest.  I probably
> end up with a particle whose surface is say 1E-7 from the floor but is
> plummeting toward the ground at 1E-5, or something like that.

The secret is to detect resting contact and switch modes to Dynamic Constraints.
Dynamic constraints calculate the forces required to nullify the normal
acceleration of a particle in order to avoid breaking constraints like falling
through the floor.  Once resting contact has been determined, the system calculates
the acceleration of the particle then calculates the force necessary to prevent the
particle from falling through the floor.  It applies the force, then calculates the
physics.

For all the gory details, check out:

http://www-2.cs.cmu.edu/afs/cs/user/baraff/www/pbm/pbm.html

David Buck
Simberon Inc
www.simberon.com

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