[ODE] contact joints / attaching them

[Steve Baker]

Flavien Brebion wrote:
> If a ball is on one side of a wall at the start of a timestep,
> and on the other side at the next timestep, no collisions will
> be reported, and the ball will pass through it. That's what
> i call the "tunneling" effect, as opposed to "sweep collisions".
> And that's why i need different timesteps.

OK - I'm really new to ODE and I didn't know how that happened.

The 'tunnelling' problem is a serious issue.

The way I've dealt with that in the past is to 'extrude'
objects along their flight path - so I do intersection testing
on (say) a sphere using two spheres and a cylinder.  One sphere
at the start of the motion, one at the end and the cylinder
filling in the gap between them.   This guarantees that you'll
find a collision whenever one occurs - although it can be
challenging to get the precise moment of collision exactly
right.

That seems a much better approach than brute force shrinkage of
the time-step which is likely to do bad things to the CPU consumption.

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