[ODE] Collision response etc

[David Walker]

could you check the velocity of the body associated with a geom as you
create the contact joint?
the other possibility is to keep track of contacts and only play the sound
on when the first contact is created, so,
get contacts,
check if contacts were there during last collision check,
if not play sound.
problem is you'd have to reset the last state after every collision call
back which might be a pain but this sounds like the best option to me. I
don't know, like I said, I'm still working up to this. I'm sure someone else
has the best way sorted out already.

David.

----- Original Message -----
From: "Byron Wright" <bslayerw@mindspring.com>
To: "'David Walker'" <david.walker530@ntlworld.com>; <ode@q12.org>
Sent: Wednesday, January 29, 2003 2:56 AM
Subject: RE: [ODE] Collision response etc


> I initially attempted that. The problem is that the existence of contact
> points does not constitute a "bump" (or high impact). The problem is
> that if the object is resting on a ground plane for example,  then the
> collision callback is called every time step  (and contact joints are
> created) create a horrible array of sound effects. That is why I was
> attempting to figure out the forces applied to the objects since that
> will most likely help me figure out if the objects are bouncing or have
> collided and are not simply resting on/against one another. The problem
> still remains that when retrieving the force on a body (in the callback
> or not) I still get a result of 0.
>
> -Byron
>
> -----Original Message-----
> From: David Walker [mailto:david.walker530@ntlworld.com]
> Sent: Tuesday, January 28, 2003 6:38 PM
> To: Byron Wright
> Subject: Re: [ODE] Collision response etc
>
>
> Hello,
>
> I think the best place to do this is in the collision callback. when you
> actually create the contact joints. that would probably be a good place
> to play the sound. I don't know for sure because I haven't done this yet
> (It's on my list of things to do) but that's how I'm going to tackle it.
> I'm also going to put scoring in there somewhere.
>
> Does this make sense?
>
> David
>
>
> ----- Original Message -----
> From: "Byron Wright" <bslayerw@mindspring.com>
> To: <ode@q12.org>
> Sent: Tuesday, January 28, 2003 6:21 PM
> Subject: RE: [ODE] Collision response etc
>
>
> > *bump*.
> >
> > Anyone have any idea on how I might solve this?
> >
> > -Byron
> >
> > -----Original Message-----
> > From: ode-admin@q12.org [mailto:ode-admin@q12.org] On Behalf Of Byron
> > Wright
> > Sent: Friday, January 24, 2003 5:30 PM
> > To: ode@q12.org
> > Subject: [ODE] Collision response etc
> >
> >
> > New to ODE, trying to figure out how to play a sound effect when
> > objects collide.
> >
> > Here are the steps I take to produce a "bump" sound effects.
> >
> > - do collision detection and response
> > - world step
> > - check all bodies for contact joints, if they have contact joints and
>
> > their forces are greater than 0 then play a the bump sound effect
> >
> >
> >
> > The problem is that after a collision and the contact joints have been
>
> > created the magnitude of the force is alway 0. When should I get be
> > requisting the force from my bodies? Or should I be checking something
>
> > else to find out if the body has been "bumped"?
> >
> > Here is my update function :
> >
> > void update(float dt) {
> >     dSpaceCollide(space, 0, &NearCallback);
> >     dWorldStep (world, dt);
> >     //iterate though all boxes, if they have contact joints
> (collision)
> >     //then play a sound effect if the box's force is greater than 0
> >
> >     //BodyCollection is = typedef vector<dBodyID> BodyCollection;
> >     BodyCollection::iterator it = boxBodies.begin();
> >
> >     while(it != boxBodies.end()) {
> >         int numJoints = dBodyGetNumJoints(*it);
> >         if(numJoints > 0) {
> >         for(int joints = 0; joints < numJoints; ++ joints) {
> >             dJointID joint = dBodyGetJoint (*it, joints);
> >                 if(dJointGetType(joint) == dJointTypeContact) {
> >                 //it's a contact joint. check force of
> > bodies
> >                   const dReal * forceA = dBodyGetForce(*it);
> >
> >       cout << magnitude(forceA) << endl;
> >                   if(magnitude(forceA) > 0.05 ) {
> >       Mix_PlayChannel(-1,bump,0);
> >                   }
> >             }
> >         }
> >
> >         }
> >        ++it;
> >     }
> >
> >     //remove all contact joints from the system
> >     dJointGroupEmpty(contactGroup);
> > }
> >
> > Byron Wright
> >
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