How to use Javafx and scenebuilder to draw on canvas (Group element)

Question

i am new to scenebuilder and fx and need some help. I have the class Puffer , TestMain and MainViewController. I tried to paint on the canvas and it worked.I tried Puffer and it worked too. Now I wanted to use scenebuilder and have my problems.I would like to draw the Group from Puffer on the canvas with a button and don't know what's the best solution.I already tried to modify Puffer without any result.

public class Puffer {
    
    Group root = new Group();
    
public void draw() {
    for (int x = 0; x < 800; x++) {
        for (int y = 0; y < 600; y++) {
            Complex z0 = new Complex(0.11, 0.123); //!!!!!!!!!!!!! under 1
            Complex c = new Complex(x / 400.0 - 2, 1 - y / 400.0);

            if (isBounded(iterate(z0, c))) {
                drawPoint(x, y, root);
            }
        }
    }

//    primaryStage.setScene(new Scene(root, 800, 600));
//    primaryStage.show();
}


public void drawPoint(int x, int y, Group root) {
    int max = 255;
    int min = 0;
    int range = max - min + 1;


    Line line = new Line(x, y, x, y);
   // line.setStroke(Color.rgb((int)(Math.random() * range) + min,(int)(Math.random() * range) + min,(int)(Math.random() * range) + min));
    root.getChildren().add(line);
}

public Complex iterate(Complex z0, Complex c) {
    Complex zn = z0;

    for (int i = 0; i < 20; i++) {
        zn.square().add(c);
    }

    return zn;
}

public boolean isBounded(Complex zn) {
    return zn.module() < 2;
}

---

public class MainViewController {
    @FXML
    Canvas canvas;

    // Event Listener on Button.onAction
    @FXML
    public void btnOkClicked(ActionEvent event) {
        System.out.println("Test");
    
    }
    
     @FXML
        public void drawCanvas(){

         
//          GraphicsContext gc = canvas.getGraphicsContext2D();
//          gc.setLineWidth(3);
//          gc.setStroke(Color.BLACK);
//          System.out.println("drawCanvas");
//
//          try {
//              canvas.setOnMousePressed(event -> {
//                  System.out.println("Mouse click");
//                  gc.beginPath();
//                  gc.lineTo(event.getSceneX(), event.getSceneY());
//                  gc.stroke();
//              });
//
//              canvas.setOnMouseDragged(event -> {
//                  System.out.println("Mouse dragged");
//                  gc.lineTo(event.getSceneX(), event.getSceneY());
//                  gc.stroke();
//              });
//          }catch (Exception e){
//              System.out.println(e);
//              System.exit(0);
//          }

        }

---

 public class TestMain extends Application {

    @Override
    public void start(Stage s1) throws Exception {
    try {
        Parent root = FXMLLoader.load(getClass().getResource("MainView.fxml"));
        Scene scene = new Scene(root);
        
        s1.setTitle("Test");
        s1.setScene(scene);
        s1.show();
        
    }catch(Exception ex) {
        ex.printStackTrace();
    }
        
        
        
    }
    
    public static void main(String[] args) {
        launch(args);
    }