Tire rotation axis

[Leadwerks]

My tires are being aligned to rotate around the Z axis. I want them to rotate around the X axis, since my vehicle models are always modeled along the Z axis. Right now my tires are 90 degrees sideways.

I remember this was an issue in old versions of Newton. Can you remind me how to fix this? Changing the matrix in the vehicle creation function does not appear to do anything.

It looks to me like the vehicle frame parameter is being ignored:

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void dCustomVehicleController::Init(NewtonBody* const body, const dMatrix& vehicleFrame___, NewtonApplyForceAndTorque forceAndTorque, void* const userData, dFloat gravityMag)
{

[Julio Jerez]

the vehicle manager has callback named PostUpdate
when you make you own manager
class MyVehicleControllerManager: public dCustomVehicleControllerManager
you must overload that function more of less like this

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   virtual void PostUpdate (dFloat timestep)
   {
      // do the base class post update
      dCustomVehicleControllerManager::PostUpdate(timestep);
      
      // update the visual transformation matrices for all vehicle tires
      for (dListNode* node = GetFirst(); node; node = node->GetNext()) {
         dCustomVehicleController* const controller = &node->GetInfo();
         SuperCarEntity* const vehicleEntity = (SuperCarEntity*)NewtonBodyGetUserData (controller->GetBody());
         vehicleEntity->UpdateTireTransforms();
      }

there you can iterate over the tires and get the transform, in the demos you can see that the function UpdateTireTransform apply a local 90 rotation aligmentMatrix->m_matrix the body matrix to the tire matrix

Code: Select all

   void UpdateTireTransforms()
   {
      NewtonBody* const body = m_controller->GetBody();
      DemoEntityManager* const scene = (DemoEntityManager*) NewtonWorldGetUserData(NewtonBodyGetWorld(body));

      for (dList<dCustomVehicleController::dBodyPartTire>::dListNode* node = m_controller->GetFirstTire(); node; node = m_controller->GetNextTire(node)) {
         const dCustomVehicleController::dBodyPartTire* const part = &node->GetInfo();
         dCustomVehicleController::dBodyPart* const parent = part->GetParent();

         NewtonBody* const body = part->GetBody();
         NewtonBody* const parentBody = parent->GetBody();

         dMatrix matrix;
         dMatrix parentMatrix;
         NewtonBodyGetMatrix(body, &matrix[0][0]);
         NewtonBodyGetMatrix(parentBody, &parentMatrix[0][0]);

         DemoEntity* const tirePart = (DemoEntity*) part->GetUserData();
         TireAligmentTransform* const aligmentMatrix = (TireAligmentTransform*)tirePart->GetUserData();
         matrix = aligmentMatrix->m_matrix * matrix * parentMatrix.Inverse();

         dQuaternion rot (matrix);
         tirePart->SetMatrix(*scene, rot, matrix.m_posit);
      }
   }


[Leadwerks]

Will the old vehicle code work with the current build of Newton?

[Julio Jerez]

if you mean the 3.13, the answer is not because the new vehicle is all rigid body, so I had to make some changes.

[pHySiQuE]

This is what I tried, and all it does is make the car fly around:

Code: Select all

   void NewtonDynamicsVehicle::UpdateTireTransforms()
   {
      for (int i = 0; i < tire.size(); ++i)
      {
         NewtonDynamicsBody* body = (NewtonDynamicsBody*)tire[i]->GetUserData();
         dFloat mat0[16];
         dFloat mat1[16];
         NewtonBodyGetMatrix(body->body, mat0);
         mat1[0] = mat0[8];
         mat1[1] = mat0[9];
         mat1[2] = mat0[10];
         mat1[3] = mat0[11];

         mat1[4] = mat0[4];
         mat1[5] = mat0[5];
         mat1[6] = mat0[6];
         mat1[7] = mat0[7];
         
         mat1[8] = -mat0[0];
         mat1[9] = -mat0[1];
         mat1[10] = -mat0[2];
         mat1[11] = -mat0[3];
         
         mat1[12] = mat0[12];
         mat1[13] = mat0[13];
         mat1[14] = mat0[14];
         mat1[15] = mat0[15];
         NewtonBodySetMatrix(body->body, mat1);
      }
   }

This is a complete mess. I might have to disable vehicles in order to release version 4.4 on time.

Either that or I am going to have to code my own vehicles from scratch.

[Julio Jerez]

You can code your own vehicle if you want, that's not under my control.

if you want to get the right callback, here is how the it should be written.
You get that matrix from the tire body and apply a local rotation by 90 degree before you apply to the visual mesh, you and applying back to the rigid body, and them you say is a mess.

assuming the rotation is around the z axis, tham roation aroun y will align z to x here is a pseudo code

Code: Select all

void NewtonDynamicsVehicle::UpdateTireTransforms()
{
      static dMatrix localRotation (dYawMatrix (3.1416f * 0.5));
      for (int i = 0; i < tire.size(); ++i)
      {
            dMatrix matrix;
            NewtonBodyGetMatrix(body->body, matrix);
            matrix = localRotation * matrix;
             // here apply that rotation to matrix the visual tire mesh)

        }
}

[pHySiQuE]

Our vehicle is set up to work with tire rotation around the X axis. I can't change that behavior without breaking people's games. Simply changing the visual mesh does nothing.

[Julio Jerez]

the code a posted do not changes the visual is simple set the matrix of the visual.
is like a an animation changing a bone transform of an entity.
is the same method you use to update the matrix of any other entity that is controlled by a rigid body.

[Julio Jerez]

even that demos that comes with sdk has the tire rotation along an axis that does not matches the axis of the vehicle tire so I have to do the same thing.
I added comments to the function that does the same tire rotation.

Code: Select all

void UpdateTireTransforms()
   {
      NewtonBody* const body = m_controller->GetBody();
      DemoEntityManager* const scene = (DemoEntityManager*) NewtonWorldGetUserData(NewtonBodyGetWorld(body));

      for (dList<dCustomVehicleController::dBodyPartTire>::dListNode* node = m_controller->GetFirstTire(); node; node = m_controller->GetNextTire(node)) {
         const dCustomVehicleController::dBodyPartTire* const part = &node->GetInfo();
         dCustomVehicleController::dBodyPart* const parent = part->GetParent();

         NewtonBody* const body = part->GetBody();
         NewtonBody* const parentBody = parent->GetBody();

         dMatrix matrix;
         dMatrix parentMatrix;
         NewtonBodyGetMatrix(body, &matrix[0][0]);

// Here it get that tire body matrix whi is in world space.
         NewtonBodyGetMatrix(parentBody, &parentMatrix[0][0]);

         DemoEntity* const tirePart = (DemoEntity*) part->GetUserData();

// Here is Take the 90 dregree rotaion to aligne the visual matrix to the tire body matrix
         TireAligmentTransform* const aligmentMatrix = (TireAligmentTransform*)tirePart->GetUserData();

// here the aligment matrix is applyied to the tire, al also the global matrix is conveted to local bone space
         matrix = aligmentMatrix->m_matrix * matrix * parentMatrix.Inverse();

// here that matrix is set to the visual tire bone.
         dQuaternion rot (matrix);
         tirePart->SetMatrix(*scene, rot, matrix.m_posit);
      }
   }


[pHySiQuE]

I understand that I can make a hack to rotate the matrix for a mesh with a different orientation. This is not useful. In our engine, the entity 4x4 matrix always matches the physics body matrix. Every entity is (potentially) a physics body, and they share the same orientation at all times. We have tools for building physics shapes from meshes, for example, and we can't start arbitrarily rotating our vehicle body around without breaking a lot of things.

All of our existing code is based on the assumption that the front of a vehicle faces in the +Z direction, and the tires rotate around the X axis, as the vehicleFrame parameter allowed in the previous implementation.

[Julio Jerez]

is it not a hack, is totally correct, you are just setting a bone matrix on a mesh.
you think of the body matrix coming pout with a 90 rotation matrix that needs to be undone.

all is a offset rotation just try that function and it will work.

[pHySiQuE]

Except I'm not making a simple little demo that I can just hard-code. I'm making an engine with 700 documented commands that work in a certain manner, with hundreds of examples. Introducing a low-level change like this will break peoples' code all across the engine.

[Julio Jerez]

I do not know what that mean, that tire of the vehicle spin around one axis, for you to set the transform to the mesh that representing the shape if you mesh spin around a different axis you need to apply a rotation matrix. that does not required you to change anything in you code, it only requires to write that transform callback for the tires whish is called form the PostUpdate method of the vehicle manager. If you display the debug you will see the shape rotate the proper way, all it nee is that offset rotation to align the visual mesh, I do not get why this is so difficult

[pHySiQuE]

I introduced an additional offsetmatrix into my body class, and I am attempting to insert it into any places where the engine converts matrices from Newton to my engine. I am not very happy about it, but it will probably work.

[pHySiQuE]

Okay, here is the behavior I have at this point.
https://www.leadwerks.com/files/NewtonCar.zip

The application can be debugged from Visual Studio.