• Java library for casual games
  • Introduced as 'ForPlay' at Google I/O 2011
• Targets: HTML5, Flash, Android
• Desktop JVM used for development and debugging
• developers.google.com/playn
  • Open source
  • Already seeing significant contributions
  • Early days: contributions welcome!

• Simple
• Reductionist
• Cross-platform
• Focused on the 'middle of the bell-curve'

• Simply implement playn.core.Game
• Ensures update() and paint() happen at the right time

public class MyGame implements Game {

  public void init() {
    // initialize game.
  }

  public void update(float delta) {
    // update world:
    //   delta indicates the time-step
  }

  public void paint(float alpha) {
    // render world:
    //   alpha indicates time in the range [0, 1) between world frames
  }
}
        

• Simple abstractions for input devices
  • Pointer, Mouse, Touch
  • Keyboard

pointer().setListener(new Pointer.Adapter() {
  public void onPointerStart(Pointer.Event event) {
    // Handle mouse down event.
  }
});

keyboard().setListener(new Keyboard.Adapter() {
  public void onKeyDown(Event event) {
    // Handle key down event.
  }
});
        

• Two main concepts
  • Layers: retained structures (similar to DOM)
  • Surfaces: immediate rendering (similar to Canvas)
• Implemented using a combination of DOM, Canvas, and WebGL

public void init() {
  bg = graphics().createSurfaceLayer();
  graphics.rootLayer().add(bg);

  Layer catGirl = graphics().createImageLayer('catGirl.png');
  graphics.rootLayer().add(catGirl);
}

public void paint(float alpha) {
  Surface surf = bg.surf();
  surf.clear();
  surf.drawImage(cloud, cloudX, cloudY);
}
        

• Simple audio API

public void init() {
  Sound music = assetManager().getSound('ambient.mp3');
  music.setLooping(true);
  music.play();

  squawk = assetManager().getSound('squawk.mp3');
}

public void somethingHappened() {
  squawk.play();
}
        

• Simple loading methods for images, sounds, and text

public void init() {
  Image image = assetManager().getImage('bird.png');
  Sound sound = assetManager().getSound('squawk.mp3');

  // Completion callbacks are available
  image.addCallback(new ResourceCallback<Image>() {
    public void done(Image resource) { imageReady = true; }
    public void error(Throwable err) { imageFailed(); }
  });

  // Text is necessarily async
  assetManager().getText('level.json', new ResourceCallback<String>() {
    public void done(String resource) { loadLevel(json().parse(resource)); }
    public void error(Throwable err) { gameOver(); }
  });
}
        

• Some network access already handled by AssetManager
• You can also make direct HTTP requests

public void saveState() {
  Writer json = json().newWriter();
  json.key('id');    json.value(playerId);
  json.key('score'); json.value(playerScore);

  net().post('/saveState', json.write(), new Callback<String>() {
    public void onSuccess(String result) { }
    public void onFailure(Throwable cause) { tryAgain();}
  });
}
        

• Box2D baked into the library
• Why embedded?
  • Somewhat tricky to do it yourself with JBox2D
  • We can do some platform-specific optimizations

public void init() {
  world = new World(gravity, true);

  Body ground = world.createBody(new BodyDef());
  PolygonShape groundShape = new PolygonShape();
  groundShape.setAsEdge(new Vec2(0, height), new Vec2(width, height));
  ground.createFixture(groundShape, 0.0f);

  world.setContactListener(new ContactListener() {
    public void beginContact(Contact contact) { ... }
    public void endContact(Contact contact) { ... }
    // ...
  }
}

public void update(float delta) {
  // Fix physics at 30f/s for stability.
  world.step(0.033f, 10, 10);
}
        

• Input
  • Game pads and other input devices
• Rendering
  • 3d graphics API
• Audio
  • Audio effects and spatialization
• Network
  • Streaming sockets
• C (or possibly LLVM) backend
  • Support for iOS and other platforms