How to drag undecorated window

Question

I have this undecorated window:

public static void initStartPage(final Stage primaryStage) {

        final Stage startPage = new Stage();
        startPage.initStyle(StageStyle.UNDECORATED);
        //startPage.initOwner(primaryStage);
        //startPage.toFront();
        Scene scene = new Scene(agentsPanel(), 900, 500);
        startPage.setScene(scene);
        startPage.show();

    }

I'm interested how I can make it drag dragable? I want the I pres the mouse cursor over it to drag it to change it's position.

P.S

I tested this solution but it's not working:

private static FlowPane flow;
    private static BorderPane bpi;

    public static void initStartPage(final Stage primaryStage) {

        final Stage startPage = new Stage();
        startPage.initStyle(StageStyle.UNDECORATED);
        startPage.initOwner(primaryStage);
        //startPage.toFront();
        Scene scene = new Scene(agentsPanel(primaryStage), 900, 500);
        startPage.setScene(scene);
        startPage.show();

    }

    private static double xOffset = 0;
    private static double yOffset = 0;

    public static BorderPane agentsPanel(final Stage primaryStage) {

        BorderPane bp = new BorderPane();
        bp.setPrefSize(900, 500);
        bp.setMaxSize(900, 500);

        HBox thb = new HBox(10); // Set spacing between each child into the HBox
        thb.setPadding(new Insets(15, 15, 15, 15));


        HBox bhb = new HBox(10); // Set spacing between each child into the HBox
        bhb.setPadding(new Insets(15, 15, 15, 15));

        bp.setTop(thb);
        bp.setBottom(bhb);
        bp.setCenter(navigationPanel());


        bp.setOnMousePressed(new EventHandler<MouseEvent>() {
            @Override
            public void handle(MouseEvent event) {
                xOffset = event.getSceneX();
                yOffset = event.getSceneY();
            }
        });
        bp.setOnMouseDragged(new EventHandler<MouseEvent>() {
            @Override
            public void handle(MouseEvent event) {
                primaryStage.setX(event.getScreenX() - xOffset);
                primaryStage.setY(event.getScreenY() - yOffset);
            }
        });

        return bp;

    }

Answer 1

Just change your setOnMousePressed method to this:

bp.setOnMousePressed(new EventHandler<MouseEvent>() {
            @Override
            public void handle(MouseEvent event) {
                xOffset = primaryStage.getX() - event.getScreenX();
                yOffset = primaryStage.getY() - event.getScreenY();
            }
        });

and your setOnMouseDragged to this:

bp.setOnMouseDragged(new EventHandler<MouseEvent>() {
            @Override
            public void handle(MouseEvent event) {
                primaryStage.setX(event.getScreenX() + xOffset);
                primaryStage.setY(event.getScreenY() + yOffset);
            }
        });