Libgdx arcball camera and billboard

Question

I just implemented an arcball cam in libgdx

    private void rotate(float pitch, float yaw, float roll) {
        tempQuat.setEulerAngles(pitch, yaw, roll);
        rotationQuat.mulLeft(tempQuat);
    }

...

    float aspect = camera.viewportWidth / camera.viewportHeight;
    camera.projection.setToProjection(Math.abs(camera.near), Math.abs(camera.far), camera.fieldOfView, aspect);
    camera.view.setToLookAt(camera.position, tempVector.set(camera.position).add(camera.direction), camera.up);

        rotate(MyGestureListener.mXAngle, MyGestureListener.mYAngle, 0);
        camera.view.rotate(rotationQuat);

    camera.combined.set(camera.projection);
    Matrix4.mul(camera.combined.val, camera.view.val);

    camera.invProjectionView.set(camera.combined);
    Matrix4.inv(camera.invProjectionView.val);
    camera.frustum.update(camera.invProjectionView);

Everything works fine, but one thing is not good:

I have some decal that always rotated to the camera as a billboard:

        p.decalPoint.setPosition(p.pos.x, p.pos.y, p.pos.z);
        p.decalPoint.setRotation(camera.direction, camera.up);

Now this is broken. Why? How can I fix this?

I need an arcball camera like here:

https://youtu.be/YxNjjyv8W0I

The above code works well, but billboarding not working with the cam.

Answer 1

I ended up using two rotation matrix and a camfocusvector as an arcball

Quaternions are not suitable for this