newton does not seem to affect object

[roy844]

hi,

i have been trying to implement the physics engine and it compiles well. but i am expecting it to fall right now because i added 1 rigidbody no floor or anything, just 1 box that is suposed to be affected by gravity. but it does not.
what i dont understand is how the model is affected by newton, is the model affected because newton affects the matrix of the model ?

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   dVector minBox;
   dVector maxBox;
   //NewtonCollisionCalculateAABB (shape, &matrix[0][0], &minBox[0], &maxBox[0]);

   // add some extra padding
   minBox.m_x -=  5000.0f;
   minBox.m_y -= 50000.0f;
   minBox.m_z -=  5000.0f;

   maxBox.m_x +=  5000.0f;
   maxBox.m_y += 50000.0f;
   maxBox.m_z +=  5000.0f;

   // set the new world size
   NewtonSetWorldSize (g_world, &minBox[0], &maxBox[0]);

   
   NewtonCollision* shape;
   NewtonBody* box;

   
   
   shape = CreateNewtonBox (g_world, &kubus , 0);
   box = CreateRigidBody (g_world, &kubus, shape, 10.0f);
   NewtonReleaseCollision (g_world, shape);

   dMatrix matrix (kubus.m_curRotation, kubus.m_curPosition);
   NewtonBodySetMatrix (box, &matrix[0][0]);

[JernejL]

You need to call newtonupdate and apply the gravity in forcetorque callback.

[roy844]

thanks for your reply, i use the AdvanceSimulation function from the tutorial and in that function is this line:

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// run the newton update function
NewtonUpdate (g_world, (1.0f / DEMO_PHYSICS_FPS));

and the CreateRigidBody function this function is called also from the tutorial files:

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// callback to apply external forces to body
void ApplyForceAndTorqueCallback (const NewtonBody* body, dFloat timestep, int threadIndex)
{
   dFloat Ixx;
   dFloat Iyy;
   dFloat Izz;
   dFloat mass;

   // for this tutorial the only external force in the Gravity
   NewtonBodyGetMassMatrix (body, &mass, &Ixx, &Iyy, &Izz);

   dVector gravityForce  (0.0f, mass * GRAVITY, 0.0f, 1.0f);
   NewtonBodySetForce(body, &gravityForce[0]);
}

[Julio Jerez]

in this code

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shape = CreateNewtonBox (g_world, &kubus , 0);
   box = CreateRigidBody (g_world, &kubus, shape, 10.0f);
   NewtonReleaseCollision (g_world, shape);

   dMatrix matrix (kubus.m_curRotation, kubus.m_curPosition);
   NewtonBodySetMatrix (box, &matrix[0][0]);

you did not set the box mass, NewtonBodySetMassMatrix

[roy844]

i use the following function on the bottom from the tutorial project.

this also includes the function below

NewtonBodySetMassMatrix (body, mass, mass * inertia.m_x, mass * inertia.m_y, mass * inertia.m_z);

so the mass of the box is 10
box = CreateRigidBody (g_world, &kubus, shape, 10.0f);

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NewtonBody* CreateRigidBody (NewtonWorld* world, Entity* ent, NewtonCollision* collision, dFloat mass)
{
   dVector minBox;
   dVector maxBox;
   dVector origin;
   dVector inertia;
   NewtonBody* body;
 
   // Now with the collision Shape we can crate a rigid body
   body = NewtonCreateBody (world, collision);
 
   // bodies can have a destructor.
   // this is a function callback that can be used to destroy any local data stored
   // and that need to be destroyed before the body is destroyed.
   NewtonBodySetDestructorCallback (body, DestroyBodyCallback);
 
   // save the entity as the user data for this body
   NewtonBodySetUserData (body, ent);
 
   // we need to set physics properties to this body
   dMatrix matrix (ent->m_curRotation, ent->m_curPosition);
   NewtonBodySetMatrix (body, &matrix[0][0]);
 
   // we need to set the proper center of mass and inertia matrix for this body
   // the inertia matrix calculated by this function does not include the mass.
   // therefore it needs to be multiplied by the mass of the body before it is used.
   NewtonConvexCollisionCalculateInertialMatrix (collision, &inertia[0], &origin[0]);   
 
   // set the body mass matrix
   NewtonBodySetMassMatrix (body, mass, mass * inertia.m_x, mass * inertia.m_y, mass * inertia.m_z);
 
   // set the body origin
   NewtonBodySetCentreOfMass (body, &origin[0]);
 
   // set the function callback to apply the external forces and torque to the body
   // the most common force is Gravity
   NewtonBodySetForceAndTorqueCallback (body, ApplyForceAndTorqueCallback);
 
   // set the function callback to set the transformation state of the graphic entity associated with this body
   // each time the body change position and orientation in the physics world
   NewtonBodySetTransformCallback (body, SetTransformCallback);
 
   return body;
}

[Julio Jerez]

it should work then.
put a break point on the transform call back and see if the position is changing

[roy844]

reading this line i asume that if transformation of the object has changed it will call the code below

NewtonBodySetTransformCallback (body, SetTransformCallback);

but after putting a breakpoint in the code below i found that it is never called

a function that is called every loop is

ApplyForceAndTorqueCallback. i hope someone can help me understand what i am doing wrong.

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// Transform callback to set the matrix of a the visual entity
void SetTransformCallback (const NewtonBody* body, const dFloat* matrix, int threadIndex)
{
   c_Object* ent;

   // Get the position from the matrix
   dVector posit (matrix[12], matrix[13], matrix[14], 1.0f);
   dQuaternion rotation;

   // we will ignore the Rotation part of matrix and use the quaternion rotation stored in the body
   NewtonBodyGetRotation(body, &rotation.m_q0);

   // get the entity associated with this rigid body
   ent = (c_Object*) NewtonBodyGetUserData(body);

   // since this tutorial run the physics and a different fps than the Graphics
   // we need to save the entity current transformation state before updating the new state.
   ent->m_prevPosition = ent->m_curPosition;
   ent->m_prevRotation = ent->m_curRotation;
   if (ent->m_curRotation.DotProduct (rotation) < 0.0f) {
      ent->m_prevRotation.Scale(-1.0f);
   }

   // set the new position and orientation for this entity
   ent->m_curPosition = posit;
   ent->m_curRotation = rotation;
}

[Julio Jerez]

SetTransformCallback call back most be called each frame by the engine. there must be and error some where that is no setting teh call back correctly.
check the demo.