how to have a scene over another in javafx

Question

I'm writing a small game. And i want a pause menu over the blured game menu to be shown when esc is pressed in the middle of the game. What I do is that i make a new scene which has a stackPane wrapping the past root and the pause menu root and then i set the opacity of the past root 0.4 .

Then when the resume button in the pause menu is clicked i change the opacity back to 1 and set the past scene on stage but then its freezed. does anyone know why? can anyone help me achieve this?

Here is the part i make the new scene and then i put this on stage:

        StackPane wrapper = new StackPane();
        previousScene = main.getPrimaryStage().getScene();
        previousScene.getRoot().setOpacity(.4);
        vBox.setId("pausedWrapper");
        wrapper.getChildren().add(previousScene.getRoot());
        wrapper.getChildren().add(vBox);
        scene = new Scene(wrapper, 1200, 700);
        return scene;

Here is the part i change it back to where it was:

        resumeGame.setOnAction(event -> {
            System.out.println("game resumed!");
            previousScene.getRoot().setOpacity(1);
            main.getPrimaryStage().setScene(previousScene);
        });

But then it does not work and the opacity does not change back to normal and the strange thing is when i check the sound on box the music is played but the box does not get checked like everything works but the view is freezed.

Answer 1

A node cannot be part of two different scene graphs. This happens in your code to the root of previousScene, because it is part of both previousScene and the new scene you create in your first block of code. Most likely what is happening is that it is removed from the first scene when you add it to the second (though it is hard to tell from the code you posted).

Consider instead using a Popup to display the pauseMenu on top of the existing window, or just use a modal Stage with undecorated StageStyle, as in the following SSCCE:

import javafx.animation.Animation;
import javafx.animation.TranslateTransition;
import javafx.application.Application;
import javafx.geometry.Insets;
import javafx.geometry.Pos;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.Label;
import javafx.scene.effect.GaussianBlur;
import javafx.scene.layout.BorderPane;
import javafx.scene.layout.Pane;
import javafx.scene.layout.VBox;
import javafx.scene.paint.Color;
import javafx.scene.shape.Rectangle;
import javafx.stage.Modality;
import javafx.stage.Popup;
import javafx.stage.Stage;
import javafx.stage.StageStyle;
import javafx.util.Duration;

public class PauseExample extends Application {

    @Override
    public void start(Stage primaryStage) {

        Rectangle rect = new Rectangle(50, 50, 50, 50);
        rect.setFill(Color.CORAL);

        TranslateTransition animation = createAnimation(rect);

        Button pauseButton = new Button("Pause");

        Pane pane = new Pane(rect);
        pane.setMinSize(600, 150);

        BorderPane root = new BorderPane(pane, null, null, pauseButton, new Label("This is\nthe main\nscene"));

        pauseButton.setOnAction(e -> {
            animation.pause();
            root.setEffect(new GaussianBlur());

            VBox pauseRoot = new VBox(5);
            pauseRoot.getChildren().add(new Label("Paused"));
            pauseRoot.setStyle("-fx-background-color: rgba(255, 255, 255, 0.8);");
            pauseRoot.setAlignment(Pos.CENTER);
            pauseRoot.setPadding(new Insets(20));

            Button resume = new Button("Resume");
            pauseRoot.getChildren().add(resume);

            Stage popupStage = new Stage(StageStyle.TRANSPARENT);
            popupStage.initOwner(primaryStage);
            popupStage.initModality(Modality.APPLICATION_MODAL);
            popupStage.setScene(new Scene(pauseRoot, Color.TRANSPARENT));


            resume.setOnAction(event -> {
                root.setEffect(null);
                animation.play();
                popupStage.hide();
            });

            popupStage.show();
        });

        BorderPane.setAlignment(pauseButton, Pos.CENTER);
        BorderPane.setMargin(pauseButton, new Insets(5));
        Scene scene = new Scene(root);
        primaryStage.setScene(scene);
        primaryStage.show();
    }

    private TranslateTransition createAnimation(Rectangle rect) {
        TranslateTransition animation = new TranslateTransition(Duration.seconds(1), rect);
        animation.setByX(400);
        animation.setCycleCount(Animation.INDEFINITE);
        animation.setAutoReverse(true);
        animation.play();
        return animation;
    }

    public static void main(String[] args) {
        launch(args);
    }
}