Logic to move an item in the circular boundary only

Question

I'm newbie to Game programming. I'm trying to develp a simple shooting game. The game ground which I'm trying is a circular one. The game has one shooter and 5 driods. The shooter and the driods have to move with-in the circular area only. Following is the code snippet i tried.

I tried implementing the game using the State design pattern. Got struct in the logic where the Shooter is not allowed to cross the circular boundary. Please help in completing the StateImpl class which has the logic of changing the shooter positon

public class Board extends JPanel implements ActionListener {
        private static final long serialVersionUID = -397810249729996307L;
        private final Timer timer;
        private final Shooter shooter;

    public Board(Point boardDimensions) {
        addKeyListener(new TAdapter());
        setFocusable(true);
        setBackground(Color.WHITE);
        setDoubleBuffered(true);
        setSize(boardDimensions.x, boardDimensions.y);
        shooter = new Shooter(new Point(200, 225), boardDimensions);
        timer = new Timer(5, this);
        timer.start();
    }

    @Override
    public void paint(Graphics g) {
        super.paint(g);
        Graphics2D g2d = (Graphics2D) g;
        // g2d.draw(new Ellipse2D.Double(20, 10,350,350));
        Ellipse2D.Double circle1 = new Ellipse2D.Double(20, 10, 350, 350);
        g2d.draw(circle1);
        g2d.drawImage(shooter.getImage(), shooter.getShooterPosition().x,
                shooter.getShooterPosition().y, this);

        g2d.setColor(Color.BLUE);

        Toolkit.getDefaultToolkit().sync();
        g.dispose();
    }

    /**
     * Called by the AWT just after the user informs the listened-to component
     * that an action should occur.
     */
    public void actionPerformed(ActionEvent e) {
        repaint();
    }

    private class TAdapter extends KeyAdapter {

        @Override
        public void keyPressed(KeyEvent e) {

            // Method to enable use of keys for control of the craft;
            int key = e.getKeyCode();

            if (key == KeyEvent.VK_LEFT) {
                shooter.moveLeft();
            }
            if (key == KeyEvent.VK_UP) {
                shooter.moveForward();
            }
            if (key == KeyEvent.VK_RIGHT) {
                shooter.moveRight();
            }
            if (key == KeyEvent.VK_DOWN) {
                shooter.moveBackward();
            }
        }
    }

    public void twait() {
        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            System.out.println("main thread interrupted");
        }
    }
}


public class Shooter {

    private Point shooterPosition;

    private final State state;

    protected Image image;

    public Shooter(Point shooterPosition, Point boardSize) {
        super();
        this.shooterPosition = shooterPosition;
        this.state = new StateImpl(this);
        ImageIcon ii = new ImageIcon(this.getClass().getResource("bld2.png"));
        image = ii.getImage();
    }

    public Point getShooterPosition() {
        return shooterPosition;
    }

    public void setShooterPosition(Point shooterPosition) {
        this.shooterPosition = shooterPosition;
    }

    public void moveLeft() {
        this.shooterPosition = state.moveLeft();
    }

    public void moveRight() {
        this.shooterPosition = state.moveright();
    }

    public void moveForward() {
        this.shooterPosition = state.moveForward();
    }

    public void moveBackward() {
        this.shooterPosition = state.moveBackward();
    }

    public Image getImage() {
        return image;
    }

    public void setImage(Image image) {
        this.image = image;
    }

    @Override
    public String toString() {
        return "Shooter [shooterPosition=" + shooterPosition + ", state="
                + state + ", image=" + image + "]";
    }

}


public interface State {

    public Point moveForward();

    public Point moveBackward();

    public Point moveLeft();

    public Point moveright();

    public void shoot();

}

public class StateImpl implements State {

    private final Shooter shooter;
    private final int boardSize = 200;

    public StateImpl(Shooter shooter) {
        this.shooter = shooter;
    }

    public Point moveForward() {
        Point currentShooterPosition = this.shooter.getShooterPosition();
        int newY = (currentShooterPosition.y + 1) > boardSize ? boardSize
                : currentShooterPosition.y + 1;
        return new Point(currentShooterPosition.x, newY);
    }

    public Point moveBackward() {
        Point currentShooterPosition = this.shooter.getShooterPosition();
        return new Point(currentShooterPosition.x, currentShooterPosition.y - 1);
    }

    public Point moveLeft() {
        Point currentShooterPosition = this.shooter.getShooterPosition();
        return new Point(currentShooterPosition.x - 1, currentShooterPosition.y);
    }

    public Point moveright() {

        Point currentShooterPosition = this.shooter.getShooterPosition();
        int newX = (currentShooterPosition.x + 1) > boardSize ? boardSize
                : currentShooterPosition.x + 1;
        return new Point(newX, currentShooterPosition.y);
    }

    public void shoot() {

    }
}

Answer 1

Instead of initializing the circle in the paint() method, keep it (and more importantly its centre) in a class variable. Then, whenever the shooter moves, measure the distance between the centre of the circle and the shooter's new location. If that distance is larger than the radius of the circle, block the shooter's movement.