public void setAlignment(Alignment alignment) {
        this.alignment = alignment;
    }
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