[ODE] Boxes floating in a plane

[Tim Sorrells]

I should preface this email with the statement that I'm not a physics
guru.  I can only handle basic non-solver physics without help, which of
course is why I'm using ODE :-)

I like the idea of a "hard" position-based correcting algorithm instead
of a force-based approach.  I have seen a lot of ODE demos that used
gravity much lower than Earth standard.  I think they all did this to
minimize the effect of objects sinking into the floor.  I've also
noticed this effect on chains of objects.  I don't know what ODE uses to
determine what the penetration correction force should be, but I don't
think it takes into account that an object may have another object on
top of it, or another dozen on top of it, or some other force being
applied.

I wonder how easy it is to determine how far back along an object's
velocity vector you would have to place it before it stopped colliding
with the current object?  Even if an object smacked into the corner of a
room, penetrating with the floor and 2 walls simultaneously, you would
simply move it back along its velocity vector until it was only just
touching a wall.  Then of course you would apply the regular collision
response dynamics.