Detecting Window Boundary in JavaFX? - object

Question

I've been trying to create a program that displays a ball in the center of a window, with 4 buttons titled Up, Down, Left and Right at the bottom. When you press the buttons the ball moves in the corresponding direction. I've got that part figured out, but I also need to figure out how to make it so if making the ball go in a certain direction obscures it from view, it stops it from going in that direction. I need to find a way to detect the boundaries of the window, and stopping the ball from being able to go outside of the boundary. Here's what I have so far:
import javafx.application.Application;
import javafx.event.ActionEvent;
import javafx.event.EventHandler;
import javafx.geometry.Pos;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.layout.BorderPane;
import javafx.scene.layout.HBox;
import javafx.scene.layout.Pane;
import javafx.scene.paint.Color;
import javafx.scene.shape.Circle;
import javafx.stage.Stage;
public class Ball extends Application {
private BallControl circle = new BallControl();
#Override
public void start(Stage primaryStage) {
HBox pane = new HBox();
pane.setSpacing(10);
pane.setAlignment(Pos.CENTER);
Button btUp = new Button("UP");
Button btDown = new Button("DOWN");
Button btLeft = new Button("LEFT");
Button btRight = new Button("RIGHT");
pane.getChildren().add(btLeft);
pane.getChildren().add(btRight);
pane.getChildren().add(btUp);
pane.getChildren().add(btDown);
BorderPane borderPane = new BorderPane();
borderPane.setCenter(circle);
borderPane.setBottom(pane);
BorderPane.setAlignment(pane, Pos.CENTER);
btUp.setOnAction(new UpHandler());
btDown.setOnAction(new DownHandler());
btLeft.setOnAction(new LeftHandler());
btRight.setOnAction(new RightHandler());
Scene scene = new Scene(borderPane, 250, 250);
primaryStage.setTitle("Ball"); // Set the stage title
primaryStage.setScene(scene); // Place the scene in the stage
primaryStage.show();
}
class UpHandler implements EventHandler<ActionEvent> {
public void handle(ActionEvent e) {
circle.up();
System.out.println("Up Button Pressed");
}
}
class DownHandler implements EventHandler<ActionEvent> {
public void handle(ActionEvent e) {
circle.down();
System.out.println("Down Button Pressed");
}
}
class LeftHandler implements EventHandler<ActionEvent> {
public void handle(ActionEvent e) {
circle.left();
System.out.println("Left Button Pressed");
}
}
class RightHandler implements EventHandler<ActionEvent> {
public void handle(ActionEvent e) {
circle.right();
System.out.println("Right Button Pressed");
}
}
public static void main(String[] args) {
launch(args);
}
}
class BallControl extends Pane {
public final double radius = 20;
private double x = radius, y = radius;
private double dx = 1, dy = 1;
private Circle circle = new Circle();
public BallControl() {
getChildren().add(circle);
circle.setCenterX(125.0f);
circle.setCenterY(115.0f);
circle.setRadius(25.0f);
circle.setStroke(Color.BLACK);
circle.setFill(Color.WHITE);
}
protected void moveBall() {
// Check boundaries
if (x < radius || x > getWidth() - radius) {
dx = 0; // Change ball move direction
}
if (y < radius || y > getHeight() - radius) {
dy = 0; // Change ball move direction
}
// Adjust ball position
x += dx;
y += dy;
circle.setCenterX(x);
circle.setCenterY(y);
}
public void up() {
circle.setCenterY(circle.getCenterY() - 10);
}
public void down() {
circle.setCenterY(circle.getCenterY() + 10);
}
public void left() {
circle.setCenterX(circle.getCenterX() - 10);
}
public void right() {
circle.setCenterX(circle.getCenterX() + 10);
}
}
Here is the part that I was hoping would make the program check for boundaries, but it doesn't seem to work:
protected void moveBall() {
// Check boundaries
if (x < radius || x > getWidth() - radius) {
dx = 0; // Change ball move direction
}
if (y < radius || y > getHeight() - radius) {
dy = 0; // Change ball move direction
}
// Adjust ball position
x += dx;
y += dy;
circle.setCenterX(x);
circle.setCenterY(y);

Answer 1

Someone else already asked a very similar question How to make the ball bounce off the walls in JavaFX?
Nevertheless, all you were missing was a check method before making the next move. I added moveAcceptable() and deleted BallControl for simplicity.
public class Ball extends Application
{
Circle circle = new Circle();
Pane bc = new Pane();
public BorderPane borderPane;
#Override
public void start(Stage primaryStage)
{
bc.getChildren().add(circle);
circle.setCenterX(125.0f);
circle.setCenterY(115.0f);
circle.setRadius(25.0f);
circle.setStroke(Color.BLACK);
circle.setFill(Color.WHITE);
HBox pane = new HBox();
pane.setSpacing(10);
pane.setAlignment(Pos.CENTER);
Button btUp = new Button("UP");
Button btDown = new Button("DOWN");
Button btLeft = new Button("LEFT");
Button btRight = new Button("RIGHT");
pane.getChildren().add(btLeft);
pane.getChildren().add(btRight);
pane.getChildren().add(btUp);
pane.getChildren().add(btDown);
borderPane = new BorderPane();
borderPane.setCenter(bc);
borderPane.setBottom(pane);
BorderPane.setAlignment(pane, Pos.CENTER);
btUp.setOnAction(new UpHandler());
btDown.setOnAction(new DownHandler());
btLeft.setOnAction(new LeftHandler());
btRight.setOnAction(new RightHandler());
Scene scene = new Scene(borderPane, 250, 250);
primaryStage.setTitle("Ball"); // Set the stage title
primaryStage.setScene(scene); // Place the scene in the stage
primaryStage.show();
}
class UpHandler implements EventHandler<ActionEvent>
{
public void handle(ActionEvent e)
{
if (moveAcceptable("up"))
circle.setCenterY(circle.getCenterY() - 10);
System.out.println("Up Button Pressed");
}
}
class DownHandler implements EventHandler<ActionEvent>
{
public void handle(ActionEvent e)
{
if (moveAcceptable("Down"))
circle.setCenterY(circle.getCenterY() + 10);
System.out.println("Down Button Pressed");
}
}
class LeftHandler implements EventHandler<ActionEvent>
{
public void handle(ActionEvent e)
{
if (moveAcceptable("Left"))
circle.setCenterX(circle.getCenterX() - 10);
System.out.println("Left Button Pressed");
}
}
class RightHandler implements EventHandler<ActionEvent>
{
public void handle(ActionEvent e)
{
if (moveAcceptable("Right"))
circle.setCenterX(circle.getCenterX() + 10);
System.out.println("Right Button Pressed");
}
}
public boolean moveAcceptable(String direction)
{
final Bounds bounds = borderPane.getLayoutBounds();
if (direction.equalsIgnoreCase("up"))
{
return (circle.getCenterY() > (bounds.getMinY() + circle.getRadius()));
} else if (direction.equalsIgnoreCase("down"))
{
return circle.getCenterY() < (bounds.getMaxY() - circle.getRadius());
} else if (direction.equalsIgnoreCase("right"))
{
return circle.getCenterX() < (bounds.getMaxX() - circle.getRadius());
} else //left
{
return circle.getCenterX() > (bounds.getMinX() + circle.getRadius());
}
}
public static void main(String[] args)
{
launch(args);
}
}