How do I create a Resize animation for JavaFX stage?

Question

I've been trying to make a scaling transition for a JavaFX stage to replaces the current Scene (in this case a login frame) for an application's main window.
When this happens, since the new scene is bigger, the windows gets re-sized abruptly in a non-elegant manner.

Is there any way to set up a scaling or re-size transition to do this to the stage resizing?

Relevant code:

InputStream is = null;
try {
    is = getClass().getResourceAsStream("/fxml/principal.fxml");
    Region pagina = (Region) cargadorFXML.load(is);
    cargadorFXML.<ContenedorPrincipal>getController().setEscenario(escenario);

    final Scene escena = new Scene(pagina, 900, 650);

    escena.setFill(Color.TRANSPARENT);
    escenario.setScene(escena);
    escenario.sizeToScene();
    escenario.centerOnScreen();
    escenario.show();
} catch (IOException ex) {
    // log "Unable to load the main application driver"
    log.error("No fue posible cargar el controlador principal de la aplicación."); 
    log.catching(ex);
} finally {
    if (is != null) {
        try {
            is.close();
        } catch (IOException e) {}
    }
}

Answer 1

I really liked your idea so I managed to do a little something. I hope this will help you.

I used a Timer to change the stage width and height every 25ms in order to give the impression of an animation.

import java.util.Timer;
import java.util.TimerTask;

import javafx.application.Application;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.stage.Stage;

public class SmoothResize extends Application {

    @Override
    public void start(final Stage stage) throws Exception {
        stage.setTitle("Area Chart Sample");
        Group root = new Group();
        Scene scene  = new Scene(root, 250, 250);
        stage.setResizable(false);

        Timer animTimer = new Timer();
        animTimer.scheduleAtFixedRate(new TimerTask() {
            int i=0;

            @Override
            public void run() {
                if (i<100) {
                    stage.setWidth(stage.getWidth()+3);
                    stage.setHeight(stage.getHeight()+3);
                } else {
                    this.cancel();
                }
                i++;
            }

        }, 2000, 25);

        stage.setScene(scene);
        stage.show();
    }

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

Answer 2

You can also use animation mechanism with Timeline.
Some example is available here.

The only problem is that Stage do not have writable height or width property and You have to create it by Your own. Example below.

WritableValue<Double> writableHeight = new WritableValue<Double>() {
    @Override
    public Double getValue() {
        return stage.getHeight();
    }

    @Override
    public void setValue(Double value) {
        stage.setHeight(value);
    }
};