private void updateSizes() {
        // framebuffer size (resolution) may differ from window size (e.g. HiDPI)

        glfwGetWindowSize(window, width, height);
        int windowWidth = width[0] < 1 ? 1 : width[0];
        int windowHeight = height[0] < 1 ? 1 : height[0];
        if (settings.getWindowWidth() != windowWidth || settings.getWindowHeight() != windowHeight) {
            settings.setWindowSize(windowWidth, windowHeight);
            for (WindowSizeListener wsListener : windowSizeListeners.getArray()) {
                wsListener.onWindowSizeChanged(windowWidth, windowHeight);
            }
        }

        glfwGetFramebufferSize(window, width, height);
        int framebufferWidth = width[0];
        int framebufferHeight = height[0];
        if (framebufferWidth != oldFramebufferWidth || framebufferHeight != oldFramebufferHeight) {
            settings.setResolution(framebufferWidth, framebufferHeight);
            listener.reshape(framebufferWidth, framebufferHeight);

            oldFramebufferWidth = framebufferWidth;
            oldFramebufferHeight = framebufferHeight;
        }

        float xScale = framebufferWidth / windowWidth;
        float yScale = framebufferHeight / windowHeight;
        if (oldScale.x != xScale || oldScale.y != yScale) {
            listener.rescale(xScale, yScale);

            oldScale.set(xScale, yScale);
        }
    }
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