public void adjustGuiDistance(float adjustAmount) {
        guiDistance += adjustAmount;
    }
Adjust the GUI distance from the observer.
This method increment / decrement the {@link #getGuiDistance() GUI distance} by the given value.
@param adjustAmount the increment (if positive) / decrement (if negative) value of the GUI distance.
jme3-vr/src/main/java/com/jme3/util/VRGuiManager.java