[ODE] Stupid newbie questions

[Billy Zelsnack]

<-- snip -->

> From what I understand collision detection is only run once during a
>simulation step and makes no attempt at trying to prevent bodies from 

>interpenetrating.  How is the impact on the simulation quality and  
>numerical stability ?

Quality is subjective, but.. Objects in a penetrating physics engine
tend to look a bit more spongy because when objects do penetrate, the
error needs to be resolved in the next, or next couple of frames.
As for numerically stabilitiy, it is actually more stable because you
don't have to worry about garanteeing that objects don't intersect with
lots of epsilons and such.

>In case of a fixed framerate simulation (let's say 60 or 50 Hz on a  
>console), would running twice the collision detection and dynamics
>with  
>a halfed timestep improve significantly the quality of the simulation 

>(at the expense of a heavier computational load) ? Or would it be 

Yes. Running at half the timestep is higher quality.

>more  
>efficient to implement a system where collision detection finds exact 

>contact points and simulation is stepped back then restarted from the 

>first collision time ?

Depends on the scene. In general. No. Once you start stacking things
you end up backtracking so much you never get to move forward in time.
Worse, that backtracking takes a random amount of time from frame to
frame.

-billy


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