Question

i am using spacemanager and i want to calculate the force with which the objects collide so that i can adjust the sounds and appropirate spirtes depending on the damage. can some one tell me how to calculate the forces. here is the code i got on this site.

if(!cpArbiterIsFirstContact(arb)) return;

cpFloat impulse = cpvlength(cpArbiterTotalImpulse(arb));

float volume = MIN(impulse/500.0f, 1.0f);
NSLog(@”impulse is :%f”,volume);

NSLog(@” impluse x:%f y:%f”, cpArbiterTotalImpulse(arb).x , cpArbiterTotalImpulse(arb).y);
if(volume > 0.05f){
[SimpleSound playSoundWithVolume:volume];
}

i have this in my POSTSOLVE method.i tried it in BEGIN aswell and all it prints is 0. i went through this site and found that i needs to do this.
smgr.space->elasticIterations = smgr.space->iterations;

even after doing the above , sometimes i get 1 and some times it says “nan”. is there something basic i need to know?

Thanks

Answer 1

From the documentation for cpArbiterTotalImpulse():

Returns the impulse that was applied
this step to resolve the collision.
These functions should only be called
from a postSolve() callback, otherwise
the result is undefined.

Note: If you
are using the deprecated elastic
iterations setting on your space, it
will cause you to get incorrect
results. Elastic iterations should no
longer be needed, and you should be
able to safely turn them off.