@Override
    public void write(JmeExporter e) throws IOException {
        super.write(e);
        OutputCapsule capsule = e.getCapsule(this);
        capsule.write(orient, "orient", null);
        capsule.write(look, "look", null);
        capsule.write(left, "left", null);
        capsule.write(alignment, "alignment", Alignment.Screen);
    }
Sets the type of rotation this Billboard will have. The alignment can
be Camera, Screen, AxialY, or AxialZ. Invalid alignments will
assume no billboard rotation.

@param alignment the desired alignment (Camera/Screen/AxialY/AxialZ)
jme3-core/src/main/java/com/jme3/scene/control/BillboardControl.java