[ODE] newbie joint question

[Piotr Obrzut]

Hi,

DL> I'm not sure what you are asking, but if you are using Cal3D to draw your
DL> model and you are setting the bone rotations manually (taken from ODE rigid
DL> body positions) then make sure you call calculateState() for each bone that
DL> you modify, it would look something like this:
pBone->>setRotation ( pBone->getRotation() * DeltaQuat );

pBone->>calculateState();

actualy this is the way by which i'm updating Cal3d model pos (it is
writien with use of CrystalSpace interface on ODE, but i think that
the idea is clear enough, it looks quite nice only for geting bodies
positions and aplaing them to the Cal3d model)

  CalSkeleton* skeleton = cal_model->getSkeleton ();
  std::vector<CalBone*> bone_vect = skeleton->getVectorBone ();

  bone_vect[0]->setRotation (get_cal_quaternion (bodies[0]->GetOrientation ()));
  csVector3 vec = bodies[0]->GetPosition ();
  bone_vect[0]->setTranslation (CalVector (vec [0], vec[1], vec[2]));

  for (unsigned int i = 1; i < bodies.size (); i++)
  {
    int p_id = bone_vect[i]->getCoreBone ()->getParentId ();
    csReversibleTransform trans = bodies[i]->GetTransform () / bodies[p_id]->GetTransform ();
    bones[i]->setRotation (get_cal_quaternion (trans.GetO2T ()));
    csVector3 vect = trans.GetO2TTranslation (); 
    bones[i]->setTranslation (CalVector (vect[0], vect[1], vect [2]));
  }

  skeleton->calculateState ();

The problem is in joints between mentioned ODE bodies and this is
the way i'm making joints:

  for (unsigned int i = 0; i < bodies.size (); i++)
  {
    std::string name = bones[i]->getCoreBone ()->getName ();

    CalCoreBone* cbone = bones[i]->getCoreBone ();
    std::list<int> ch_list = cbone->getListChildId ();
    
    for (std::list<int>::iterator ch_it = ch_list.begin (); ch_it != ch_list.end (); ch_it++)
    {
      csRef<iJoint> joint = dyn_sys->CreateJoint ();
      joint->SetTransConstraints (1, 1, 1);
      joint->SetRotConstraints (0,0,0);
      joint->SetTransform (csReversibleTransform ()); //0 transform
      joint->Attach (bodies[i], bodies[*ch_it]);
      
      /*here CrystalSpace is making ODE joint like this:
      
        jointID = dJointCreateBall (dynsys->GetWorldID(), 0);
          dJointAttach (jointID, bodyID[0], bodyID[1]);
        pos = transform.GetOrigin();
        dJointSetBallAnchor (jointID, pos.x, pos.y, pos.z);

        it is a ball joint b/c its translation is all constrainted and
        its rotation is not
      */
    }
  }

and after   bodies[2]->AddForce (csVector3 (0,20,0)) Caly model
looks like that: http://mathrick.org/files/joint_error.JPG

-- 
greetings,
 Piotr Obrzut