@Override
    public void onMouseButtonEvent(MouseButtonEvent evt) {
        if (evt.getButtonIndex() >= 0 && evt.getButtonIndex() <= 2) {
            if (evt.isReleased() || inputManager.isCursorVisible()) {
                // Always pass mouse button release events to nifty,
                // even if the mouse cursor is invisible.
                inputQueue.add(evt);
            }
        }
    }
@param height The height of the viewport. Used to convert
bottom-left origin to upper-left origin.
jme3-niftygui/src/main/java/com/jme3/niftygui/InputSystemJme.java