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c++openglrotationquaternionsbullet

how to rotate a btCollisionShape

I have created a bullet vehicle with a compound as the chassis and the compound is formed of 2 bodies, a chassis and a turret.

I can obtain the turret transform and opengl matrix like this:

// get chassis and turret transforms
btTransform chassisTransform = m_vehicle->getChassisWorldTransform();
btTransform turretTransform = compound->getChildTransform(1);
// multiply transforms to get updated turret transform
turretTransform *= chassisTransform;

// get turret matrix
btScalar turretMatrix[16];
turretTransform.getOpenGLMatrix(turretMatrix);

The turretTransform is the transform of a btCollisionShape object (turretShape).

I am now trying to rotate this turret around it's Y axis.

I have tried this:

turretTransform.setRotation(btQuaternion(btVector3(0, 1, 0), angle));

Where angle is a float, but nothing happens.

I'm definitely missing something, but do not fully understand how these rotations work.

Solution

  • I had to change the car-turret setup and created a separate rigid body for the turret. So now I have 2 different rigid bodies, the car and the turret.

    After going through the ConstraintDemo I came out with this:

    // create constraint
btVector3 axisA(0.f, 1.f, 0.f);
btVector3 axisB(0.f, 0.f, 0.f);
btVector3 pivotA(0.f, 1.f, 0.f);
btVector3 pivotB(0.f, 0.f, 0.f);
hinge = new btHingeConstraint(*m_carChassis, *turretBody, pivotA, pivotB, axisA, axisB);

// add constraint to world
bt_dynamicsWorld->addConstraint(hinge, true);

    I can now use hinge->enableAngularMotor(true, 0, 1); to stop the turret rotation abdhinge->enableAngularMotor(true, angle, 1); (float angle) to rotate it when I want to.