@Override
                    public void invoke(final long window, final boolean focus) {
                        if (wasActive != focus) {
                            if (!wasActive) {
                                listener.gainFocus();
                                timer.reset();
                            } else {
                                listener.loseFocus();
                            }
                            wasActive = !wasActive;
                        }
                    }
Let's grab the display selected, if not found it will return
primaryMonitor. if not full screen just use primary display data.
jme3-lwjgl3/src/main/java/com/jme3/system/lwjgl/LwjglWindow.java