Contact Solver Not considering m_localMatrix

[Esharc]

Good morning Julio,

In our system we set up a height field for our dynamic ground, but we offset the height field so that the origin of the height field is at the centre.

We then use a "ghost object" to determine if something is in contact with the dynamic ground. In the ghost object I use the ContactSolver's CalculateContacts to determine if the ghost object shape is intersecting with the height field. But I noticed that it misses a lot of the "collisions".

I them noticed that if I changed

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void ndContactSolver::CalculateContacts(
   const ndShapeInstance* const instanceA, const ndMatrix& matrixA, const ndVector& velocA,
   const ndShapeInstance* const instanceB, const ndMatrix& matrixB, const ndVector& velocB,
   ndFixSizeArray<ndContactPoint, 16>& contactOut, ndContactNotify* const contactNotify)
{
   ndContact contact;
   ndBodyKinematic bodyA;
   ndBodyKinematic bodyB;
   ndContactPoint contactBuffer[D_MAX_CONTATCS];

   ndShape* const shapeA = (ndShape*)(instanceA->GetShape());
   ndShape* const shapeB = (ndShape*)(instanceB->GetShape());

   m_instance0.SetShape(shapeA);
   m_instance0.SetMaterial(instanceA->GetMaterial());
   m_instance0.SetGlobalMatrix(matrixA);
   m_instance1.SetShape(shapeB);
   m_instance1.SetMaterial(instanceB->GetMaterial());
   m_instance1.SetGlobalMatrix(matrixB);
   bodyA.SetCollisionShape(m_instance0);
   bodyB.SetCollisionShape(m_instance1);

   bodyA.SetMatrix(matrixA);
   bodyB.SetMatrix(matrixB);
   bodyA.SetVelocity(velocA);
   bodyB.SetVelocity(velocB);

   if (!shapeA->GetAsShapeStaticMesh())
   {
      bodyA.SetMassMatrix(ndFloat32(1.0f), ndFloat32(1.0f), ndFloat32(1.0f), ndFloat32(1.0f));
   }
   if (!shapeB->GetAsShapeStaticMesh())
   {
      bodyB.SetMassMatrix(ndFloat32(1.0f), ndFloat32(1.0f), ndFloat32(1.0f), ndFloat32(1.0f));
   }
   contact.SetBodies(&bodyA, &bodyB);

   m_closestPoint0 = ndVector::m_zero;
   m_closestPoint1 = ndVector::m_zero;
   m_separatingVector = ndVector(ndFloat32(0.0f), ndFloat32(1.0f), ndFloat32(0.0f), ndFloat32(0.0f));
   m_contact = &contact;
   m_freeFace = nullptr;
   m_notification = contactNotify;
   m_contactBuffer = contactBuffer;
   m_timestep = ndFloat32 (1.0f);
   m_skinMargin = ndFloat32(0.0f);
   m_separationDistance = ndFloat32(1.0e10f);
   m_maxCount = D_MAX_CONTATCS;
   m_vertexIndex = 0;
   m_pruneContacts = 1;
   m_intersectionTestOnly = 0;

   const ndInt32 count = dMin (CalculateContactsDiscrete(), contactOut.GetCapacity());
   for (ndInt32 i = 0; i < count; ++i)
   {
      ndContactPoint& contactPoint = contactBuffer[i];
      contactPoint.m_body0 = nullptr;
      contactPoint.m_body1 = nullptr;
      contactPoint.m_shapeInstance0 = instanceA;
      contactPoint.m_shapeInstance1 = instanceB;
      contactOut.PushBack(contactPoint);
   }
}


to this

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void ndContactSolver::CalculateContacts(
   const ndShapeInstance* const instanceA, const ndMatrix& matrixA, const ndVector& velocA,
   const ndShapeInstance* const instanceB, const ndMatrix& matrixB, const ndVector& velocB,
   ndFixSizeArray<ndContactPoint, 16>& contactOut, ndContactNotify* const contactNotify)
{
   ndContact contact;
   ndBodyKinematic bodyA;
   ndBodyKinematic bodyB;
   ndContactPoint contactBuffer[D_MAX_CONTATCS];

   ndShape* const shapeA = (ndShape*)(instanceA->GetShape());
   ndShape* const shapeB = (ndShape*)(instanceB->GetShape());

   m_instance0.SetShape(shapeA);
   m_instance0.SetMaterial(instanceA->GetMaterial());
   m_instance0.SetGlobalMatrix(instanceA->GetLocalMatrix() * matrixA);
   m_instance1.SetShape(shapeB);
   m_instance1.SetMaterial(instanceB->GetMaterial());
   m_instance1.SetGlobalMatrix(instanceB->GetLocalMatrix() * matrixB);
   bodyA.SetCollisionShape(m_instance0);
   bodyB.SetCollisionShape(m_instance1);

   bodyA.SetMatrix(matrixA);
   bodyB.SetMatrix(matrixB);
   bodyA.SetVelocity(velocA);
   bodyB.SetVelocity(velocB);

   if (!shapeA->GetAsShapeStaticMesh())
   {
      bodyA.SetMassMatrix(ndFloat32(1.0f), ndFloat32(1.0f), ndFloat32(1.0f), ndFloat32(1.0f));
   }
   if (!shapeB->GetAsShapeStaticMesh())
   {
      bodyB.SetMassMatrix(ndFloat32(1.0f), ndFloat32(1.0f), ndFloat32(1.0f), ndFloat32(1.0f));
   }
   contact.SetBodies(&bodyA, &bodyB);

   m_closestPoint0 = ndVector::m_zero;
   m_closestPoint1 = ndVector::m_zero;
   m_separatingVector = ndVector(ndFloat32(0.0f), ndFloat32(1.0f), ndFloat32(0.0f), ndFloat32(0.0f));
   m_contact = &contact;
   m_freeFace = nullptr;
   m_notification = contactNotify;
   m_contactBuffer = contactBuffer;
   m_timestep = ndFloat32 (1.0f);
   m_skinMargin = ndFloat32(0.0f);
   m_separationDistance = ndFloat32(1.0e10f);
   m_maxCount = D_MAX_CONTATCS;
   m_vertexIndex = 0;
   m_pruneContacts = 1;
   m_intersectionTestOnly = 0;

   const ndInt32 count = dMin (CalculateContactsDiscrete(), contactOut.GetCapacity());
   for (ndInt32 i = 0; i < count; ++i)
   {
      ndContactPoint& contactPoint = contactBuffer[i];
      contactPoint.m_body0 = nullptr;
      contactPoint.m_body1 = nullptr;
      contactPoint.m_shapeInstance0 = instanceA;
      contactPoint.m_shapeInstance1 = instanceB;
      contactOut.PushBack(contactPoint);
   }
}


the collisions are detected correctly.
Notice the

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m_instance0.SetGlobalMatrix(instanceA->GetLocalMatrix() * matrixA);

and

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m_instance1.SetGlobalMatrix(instanceB->GetLocalMatrix() * matrixB);

change.

[Julio Jerez]

oh yes, it will only work for identity. Good finding, thanks

fixed.

[Esharc]

Thanks

[Esharc]

Good morning Julio,

In the process of updating Newton, I noticed that you have the local matrices as

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m_instance0.SetGlobalMatrix(m_instance0->GetLocalMatrix() * matrixA);

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m_instance1.SetGlobalMatrix(m_instance1->GetLocalMatrix() * matrixA);

but it shouldn't it rather be the local matrices of the passed in shape instances instead?

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m_instance0.SetGlobalMatrix(instanceA->GetLocalMatrix() * matrixA);

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m_instance1.SetGlobalMatrix(instanceB->GetLocalMatrix() * matrixA);

[Julio Jerez]

ah, I think the problem was because I never set the local matrices.

I set up like this, please see if that works.

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   m_instance0.SetShape(shapeA);
   m_instance0.SetLocalMatrix(instanceA->GetLocalMatrix());
   //Setting the global matrix before setting the collision shape of the body
   m_instance0.SetGlobalMatrix(m_instance0.GetLocalMatrix() * matrixA);

[Esharc]

Yes thanks, that solved the problem