Animations

Buttons

• Add button(s) to top of frame

  JButton button = new JButton("Move");
  JPanel buttonPanel = new JPanel();
  buttonPanel.add(button);
  add(buttonPanel, BorderLayout.NORTH); 

• Add behavior to button—lots of boilerplate in Java

  class MoveListener implements ActionListener
  {
     public void actionPerformed(ActionEvent event)
     {
        // behavior goes here
     }
  }
  
  button.addActionListener(new MoveListener());

Animation Behavior

• Component class has objects (ex. cars)
• Let's use button to move objects
• Button tells component class to update positions

  public void actionPerformed(ActionEvent event)
  {
     carComponent.updatePositions();
  }

• Component moves its objects by a small amount
• Component repaints itself

  public void updatePositions()
  {
     for (Car car : cars) car.move(5, 0);
     repaint();
  }

• repaint calls paintComponent, which draws objects in new position

Using a Timer

• Don't really want to click a button for every move
• Timer sends a stream of timer events
• As if you clicked a button lots of times

• Timer t = new Timer(100, new MoveListener()); // 100 milliseconds between actions
  t.start();

• Use only one timer

Using Icon Images

• Can be tedious to get realistic effects with Graphics2D
• Use canned images

• public class Dog
  {
     private int x;
     private int y;
     private Image image;
  
     public Dog(int x, int y)
     {
        this.x = x;
        this.y = y;
        try 
        {
           image = ImageIO.read(new File("dog.png"));
        }
        catch (IOException ex)
        {
           System.out.println("Can't read image.");
        }
     }
  
     public void draw(Graphics2D g2)
     {
        g2.drawImage(image, x, y, null);
     }
  
     public void move(int dx, int dy) 
     {
        x = x + dx;
        y = y + dy;
     }
  }
      

• Can also pass the image file name in the constructor—each dog would have its own image

Manipulating Objects

• Can use buttons if there is a default object
• Ex. Tetris: Buttons to turn, drop
• Can click on component
• Install mouse listener

  class MousePressListener implements MouseListener
  {
     public void mousePressed(MouseEvent event)
     {
        int x = event.getX();
        int y = event.getY();
        // behavior goes here
     }
     // Do-nothing methods
     public void mouseReleased(MouseEvent event) {}
     public void mouseClicked(MouseEvent event) {}
     public void mouseEntered(MouseEvent event) {}
     public void mouseExited(MouseEvent event) {}
  }
  component.addMouseListener(new MousePressListener());

• Usually, need to look for matching object

  for (Car car : cars) if (car.contains(x, y)) /* Do something with car */

• Implement Car.contains to test that (x, y) falls inside the car

Animations in Alice

• Code samples: Robot in lab 6, VisualArrayList in lab 10
• No timers necessary
• move, turn etc. take time (default 1 sec.)
• To move multiple objects in parallel, use DoTogether. Syntax is icky:

  DoTogether.invokeAndWait(
     new Runnable() { public void run() { /* movement #1 */ } },
     new Runnable() { public void run() { /* movement #2 */ } },
     new Runnable() { public void run() { /* movement #3 */ } });

• Placing objects is tricky because of the 3D.

  public Robot(int x, int y)
  {
     this.x = x;
     this.y = y;
     setLocalPointOfView(new PointOfView(
        new Quaternion(0, 0, 0, 1), // orientation
        new Position(x, -0.05, y))); // Alice x is left-right, y is bottom-top, z is front-back
  }

• Every object can listen to mouse clicks

  final Car car = ...;
  
  class ClickListener implements MouseButtonListener
  {
     public void mouseButtonClicked(MouseButtonEvent mbe) 
     {
        car.say("Hello");
     }
  }
  
  car.addMouseButtonListener(new ClickListener());