Chipmunk Physics

Posted: **Sun Aug 22, 2010 9:59 am**

Hello,

I noticed that the angular velocity limit of cpBody (w_limit) is only applied in cpBodyUpdateVelocity but not in cpBodyApplyImpulse. I did a small patch:

Code: Select all

static inline void
cpBodyApplyImpulse(cpBody *body, cpVect j, cpVect r)
{
   cpFloat w_limit = body->w_limit;
   body->v = cpvadd(body->v, cpvmult(j, body->m_inv));
   body->w = cpfclamp(body->w + body->i_inv*cpvcross(r, j), -w_limit, w_limit);
}

Seems to fix the issue for me, but there might be something that I've missed (i.e. perhaps it should not be applied here for other reasons?).

Thanks a lot for creating a very useful library!

Posted: **Mon Aug 23, 2010 8:57 am**

It's not really a bug. That's the way it should work for the collision solver.

If you want to make a clamped one you could write a second function I guess. You really should be clamping the velocity as well if that's what you wanted.

Posted: **Mon Aug 23, 2010 2:07 pm**

Thanks for the reply!

Ah, yes, that is true, the velocity should be clamped aswell. I figured I must had misunderstood something regarding the function. Are there any dangers with doing this, perhaps with regards to numerical stability or something?

Posted: **Mon Aug 23, 2010 3:57 pm**

It would probably cause problems for the solver and slow it waaaaaaaay down if you modified that header before compiling Chipmunk.

The intended purpose of the velocity clamping is to impose soft limits for things like falling speed for a platformer game. If you need hard limits you probably need to make a constraint to handle that.

Chipmunk Physics

Angular velocity limit not applied in cpBodyApplyImpulse

Angular velocity limit not applied in cpBodyApplyImpulse

Re: Angular velocity limit not applied in cpBodyApplyImpulse

Re: Angular velocity limit not applied in cpBodyApplyImpulse

Re: Angular velocity limit not applied in cpBodyApplyImpulse