Quick question about NewtonContactProcess()

[Pyritie]

When you get the NewtonContact and you get the body0 and body1 from it, how is it decided which body is body0 and which is body1?

Does it depend on the MaterialID, which was created first, or what?

[JernejL]

Which version of newton are you using? this sounds like it used to be in 1.53?

[Pyritie]

Okay fine, I'm using MogreNewt (which uses 2.x) and the method I use there is called OnProcess() and I get a ContactJoint instead of NewtonContact, but it's the same idea.

[JernejL]

It doesn't work the same in newton 2.0 anymore.

To answer your question, the order is totally random in 1.53, while it's predictable (same simulation input will repeat calls in same order) in 2.0 if you use a specific newton initialization setup.

[Pyritie]

What sort of setup?

[Julio Jerez]

yo uyget teh bodyes by makin call to the contact joint in teh call back, from the SDK here is a contact callback sample

Code: Select all

void GenericContactProcess (const NewtonJoint* contactJoint, dFloat timestep, int threadIndex)
{
   NewtonBody* body0 = NewtonJointGetBody0 (contactJoint);
   NewtonBody* body1 = NewtonJointGetBody1 (contactJoint);

   for (void* contact = NewtonContactJointGetFirstContact (contactJoint); contact; contact = NewtonContactJointGetNextContact (contactJoint, contact)) {
      dFloat speed;
      dVector point;
      dVector normal;   
      dVector dir0;   
      dVector dir1;   
      NewtonMaterial* material;

      material = NewtonContactGetMaterial (contact);
      NewtonMaterialGetContactPositionAndNormal (material, &point.m_x, &normal.m_x);
      NewtonMaterialGetContactTangentDirections (material, &dir0.m_x, &dir1.m_x);
      speed = NewtonMaterialGetContactNormalSpeed(material);
      //speed = NewtonMaterialGetContactNormalSpeed(material);
      // play sound base of the contact speed.
      //
   }

   // the application can implement some kind of contact debug here
   ShowJointContacts (contactJoint);
}

[Pyritie]

Yes I got that. I just want to know how newton decides which is body0 and which is body1.

[Julio Jerez]

The collision system pick then depend on whitch one is found first in the multigrid.
you need to use functions GetBody0, GetBody1 as the order is not guaranteed.

[Pyritie]

So I'll just have to check every time then. Okay thanks for answering.