import javafx.application.Application;
import javafx.stage.Stage;
import javafx.scene.Scene;
import javafx.scene.Node;
import javafx.scene.layout.Pane;
import javafx.scene.shape.Ellipse;
import javafx.scene.paint.Color;
import javafx.collections.ObservableList;

/** Example of a reactive drawing.
 * @author Jaanus
 */
public class DrawResizeableEllipse extends Application {

   /** Typical main method for applications. */
   public static void main (String[] args) {
      launch (args);
   }

   /** Compulsory method for Application.
    * @param myStage JavaFX main stage for this application
    */
   @Override
   public void start (Stage myStage) {
      Pane myPane = new Pane();
      Scene myScene = new Scene (myPane, 100., 100.);
      myStage.setScene (myScene);
      myStage.setTitle ("My own ellipse");
      ObservableList<Node> nodes = myPane.getChildren();
      drawEllipse (myScene.getWidth(), myScene.getHeight(), nodes);
      myScene.widthProperty().addListener (
            (obsv, oldv, newv) -> { 
               drawEllipse (myScene.getWidth(), myScene.getHeight(), nodes);
         });
      myScene.heightProperty().addListener (
            (obsv, oldv, newv) -> {
               drawEllipse (myScene.getWidth(), myScene.getHeight(), nodes);
         });
      myStage.show();
   }

   /** Local helper method to draw an ellipse. */
   protected static void drawEllipse (double w, double h, ObservableList<Node> nl) {
      Ellipse myShape = new Ellipse (w/2., h/2., w/2., h/2.);
      myShape.setStroke (Color.BLACK);
      myShape.setFill (Color.WHITE);
      nl.clear();
      nl.add (myShape); 
   }  
}