I'm trying to figure out how to create a slider constraint, but so far none of my attempts have worked properly.
In the fork lift demo from the SDK, the slider constraint for the fork is set up like this:
btTransform localA;
btTransform localB;
[...]
localA.setIdentity();
localB.setIdentity();
localA.getBasis().setEulerZYX(0, 0, M_PI_2);
localA.setOrigin(btVector3(0.0f, -1.9f, 0.05f));
localB.getBasis().setEulerZYX(0, 0, M_PI_2);
localB.setOrigin(btVector3(0.0, 0.0, -0.1));
m_forkSlider = new btSliderConstraint(*m_liftBody, *m_forkBody, localA, localB, true);
m_forkSlider->setLowerLinLimit(0.1f);
m_forkSlider->setUpperLinLimit(0.1f);
m_forkSlider->setLowerAngLimit(0.0f);
m_forkSlider->setUpperAngLimit(0.0f);
m_dynamicsWorld->addConstraint(m_forkSlider, true);The parameters to create a new slider constraint are:
btSliderConstraint (btRigidBody &rbA, btRigidBody &rbB, const btTransform &frameInA, const btTransform &frameInB, bool useLinearReferenceFrameA)
In the demo, the slide direction is set up with these two lines:
localA.getBasis().setEulerZYX(0, 0, M_PI_2);
[...]
localB.getBasis().setEulerZYX(0, 0, M_PI_2);
I'm assuming these are euler angles with z = pitch, y = yaw and x = roll.
In this case the fork is moving upwards and downwards.
Changing it to (M_PI_2, 0, 0) allows it to move left / right, and with (0, M_PI_2, 0) it's forward / backward.
M_PI_2 is a rotation of 90 degrees so that makes sense to me. Problem is, this only seems to work if the angles are aligned on an axis, meaning something like (M_PI_4, M_PI_2, 0) ends up doing the same as (0, M_PI_2, 0), which I don't really understand.
Could someone please enlighten me how to actually use setEulerZYX, or how to set up the slider constraint for a specific (non-world-axis-aligned) axis?
