examples/game/lib/game_demo_world.dart - mirrors/engine - Git at Google

 part of game;

 const double _steeringThreshold = 0.0;
 const double _steeringMax = 150.0;

 // Random generator
 Math.Random _rand = new Math.Random();

 const double _gameSizeWidth = 1024.0;
 const double _gameSizeHeight = 1024.0;

 const double _shipRadius = 30.0;
 const double _lrgAsteroidRadius = 40.0;
 const double _medAsteroidRadius = 20.0;
 const double _smlAsteroidRadius = 10.0;
 const double _maxAsteroidSpeed = 1.0;

 const int _lifeTimeLaser = 50;

 const int _numStarsInStarField = 150;

 const int _numFramesShieldActive = 60 * 5;
 const int _numFramesShieldFlickers = 60;

 class GameDemoWorld extends NodeWithSize {
   // Images
   sky.Image _imgNebula;

   SpriteSheet _spriteSheet;
   SpriteSheet _spriteSheetUI;

   Map<String,SoundEffect> _sounds;
   SoundEffectPlayer _soundPool = SoundEffectPlayer.sharedInstance();

   Navigator _navigator;

   // Inputs
   double _joystickX = 0.0;
   double _joystickY = 0.0;

   Node _gameLayer;

   Ship _ship;
   Sprite _shield;
   List<Asteroid> _asteroids = [];
   List<Laser> _lasers = [];
   StarField _starField;
   Nebula _nebula;

   // Game state
   int _numFrames = 0;
   bool _isGameOver = false;
   int _gameOverFrame;
   int _currentLevel = 0;

   // Heads up display
   Hud _hud;

   Function _gameOverCallback;

   GameDemoWorld(App app, this._navigator, ImageMap images, this._spriteSheet, this._spriteSheetUI, this._sounds, this._gameOverCallback) : super(new Size(_gameSizeWidth, _gameSizeHeight)) {
     // Fetch images
     _imgNebula = images["assets/nebula.png"];

     _gameLayer = new Node();
     this.addChild(_gameLayer);
     // Add ship
     addShip();

     // Add background
     Sprite sprtBackground = new Sprite.fromImage(images["assets/starfield.png"]);
     sprtBackground.position = new Point(512.0, 512.0);
     sprtBackground.zPosition = -3.0;
     addChild(sprtBackground);

     // Add starfield
     _starField = new StarField(_spriteSheet, _numStarsInStarField);
     _starField.zPosition = -2.0;
     addChild(_starField);

     // Add nebula
     addNebula();

     userInteractionEnabled = true;
     handleMultiplePointers = true;

     _hud = new Hud(_spriteSheetUI);
     _hud.zPosition = 1000.0;
     addChild(_hud);

     // Setup level
     setupLevel(0);
   }

   void setupLevel(int level) {
     int numLargeAsteroids = 5 + level * 2;
     int numMediumAsteroids = 5 + level * 2;

     // Add some asteroids to the game world
     for (int i = 0; i < numLargeAsteroids; i++) {
       addAsteroid(AsteroidSize.large);
     }
     for (int i = 0; i < numMediumAsteroids; i++) {
       addAsteroid(AsteroidSize.medium);
     }

     _numFrames = 0;
     _shield.visible = true;
   }

   // Methods for adding game objects

   void addAsteroid(AsteroidSize size, [Point pos]) {
     Asteroid asteroid = new Asteroid(_spriteSheet, size);
     asteroid.zPosition = 1.0;
     if (pos != null) asteroid.position = pos;
     _gameLayer.addChild(asteroid);
     _asteroids.add(asteroid);

     // Animate asteroid into the scene
     Action action = new ActionTween((a) => asteroid.scale = a, 0.0, 1.0, 1.0, bounceOut);
     _gameLayer.actions.run(action);
   }

   void addShip() {
     Ship ship = new Ship(_spriteSheet["ship.png"]);
     ship.zPosition = 10.0;
     _gameLayer.addChild(ship);
     _ship = ship;

     _shield = new Sprite(_spriteSheet["shield.png"]);
     _shield.zPosition = 11.0;
     _shield.scale = 0.5;
     _shield.transferMode = sky.TransferMode.plus;
     _gameLayer.addChild(_shield);

     Action rotate = new ActionRepeatForever(new ActionTween((a) => _shield.rotation = a, 0.0, 360.0, 1.0));
     actions.run(rotate);
   }

   void addLaser() {
     Laser laser = new Laser(_spriteSheet["laser.png"], _ship);
     laser.zPosition = 8.0;
     laser.constrainProportions = true;
     _lasers.add(laser);
     _gameLayer.addChild(laser);

     _soundPool.play(_sounds["laser"]);
   }

   void addNebula() {
     _nebula = new Nebula.withImage(_imgNebula);
     _gameLayer.addChild(_nebula);
   }

   void addExplosion(AsteroidSize asteroidSize, Point position) {
     Node explosionNode = new Node();

     // Add particles
     ParticleSystem particlesDebris = new ParticleSystem(
         _spriteSheet["explosion_particle.png"],
         rotateToMovement: true,
         startRotation:90.0,
         startRotationVar: 0.0,
         endRotation: 90.0,
         startSize: 0.3,
         startSizeVar: 0.1,
         endSize: 0.3,
         endSizeVar: 0.1,
         numParticlesToEmit: 25,
         emissionRate:1000.0,
         greenVar: 127,
         redVar: 127
     );
     particlesDebris.zPosition = 1010.0;
     explosionNode.addChild(particlesDebris);

     ParticleSystem particlesFire = new ParticleSystem(
       _spriteSheet["fire_particle.png"],
       colorSequence: new ColorSequence([new Color(0xffffff33), new Color(0xffff3333), new Color(0x00ff3333)], [0.0, 0.5, 1.0]),
       numParticlesToEmit: 25,
       emissionRate: 1000.0,
       startSize: 0.5,
       startSizeVar: 0.1,
       endSize: 0.5,
       endSizeVar: 0.1,
       posVar: new Point(10.0, 10.0),
       speed: 10.0,
       speedVar: 5.0
     );
     particlesFire.zPosition = 1011.0;
     explosionNode.addChild(particlesFire);


     // Add ring
     Sprite sprtRing = new Sprite(_spriteSheet["explosion_ring.png"]);
     sprtRing.transferMode = sky.TransferMode.plus;
     explosionNode.addChild(sprtRing);

     Action scale = new ActionTween( (a) => sprtRing.scale = a, 0.2, 1.0, 1.5);
     Action scaleAndRemove = new ActionSequence([scale, new ActionRemoveNode(sprtRing)]);
     Action fade = new ActionTween( (a) => sprtRing.opacity = a, 1.0, 0.0, 1.5);
     actions.run(scaleAndRemove);
     actions.run(fade);

     // Add streaks
     for (int i = 0; i < 5; i++) {
       Sprite sprtFlare = new Sprite(_spriteSheet["explosion_flare.png"]);
       sprtFlare.pivot = new Point(0.3, 1.0);
       sprtFlare.scaleX = 0.3;
       sprtFlare.transferMode = sky.TransferMode.plus;
       sprtFlare.rotation = _rand.nextDouble() * 360.0;
       explosionNode.addChild(sprtFlare);

       double multiplier = _rand.nextDouble() * 0.3 + 1.0;

       Action scale = new ActionTween( (a) => sprtFlare.scaleY = a, 0.3 * multiplier, 0.8, 1.5 * multiplier);
       Action scaleAndRemove = new ActionSequence([scale, new ActionRemoveNode(sprtFlare)]);
       Action fadeIn = new ActionTween( (a) => sprtFlare.opacity = a, 0.0, 1.0, 0.5 * multiplier);
       Action fadeOut = new ActionTween( (a) => sprtFlare.opacity = a, 1.0, 0.0, 1.0 * multiplier);
       Action fadeInOut = new ActionSequence([fadeIn, fadeOut]);
       actions.run(scaleAndRemove);
       actions.run(fadeInOut);
     }

     explosionNode.position = position;
     explosionNode.zPosition = 1010.0;

     if (asteroidSize == AsteroidSize.large) {
       explosionNode.scale = 1.5;
     }

     _gameLayer.addChild(explosionNode);

     _soundPool.play(_sounds["explosion"]);
   }

   void update(double dt) {
     // Move asteroids
     for (Asteroid asteroid in _asteroids) {
       asteroid.position = pointAdd(asteroid.position, asteroid._movementVector);
     }

     // Move lasers and remove expired lasers
     for (int i = _lasers.length - 1; i >= 0; i--) {
       Laser laser = _lasers[i];
       laser.move();
       if (laser._frameCount > _lifeTimeLaser) {
         laser.removeFromParent();
         _lasers.removeAt(i);
       }
     }

     // Apply thrust to ship
     if (_joystickX != 0.0 || _joystickY != 0.0) {
       _ship.thrust(_joystickX, _joystickY);
     }

     // Move ship
     _ship.move();
     _shield.position = _ship.position;

     // Check collisions between asteroids and lasers
     for (int i = _lasers.length -1; i >= 0; i--) {
       // Iterate over all the lasers
       Laser laser = _lasers[i];

       for (int j = _asteroids.length - 1; j >= 0; j--) {
         // Iterate over all the asteroids
         Asteroid asteroid = _asteroids[j];

         // Check for collision
         if (pointQuickDist(laser.position, asteroid.position) < laser.radius + asteroid.radius) {
           // Remove laser
           laser.removeFromParent();
           _lasers.removeAt(i);

           // Add asteroids and explosions
           if (asteroid._asteroidSize == AsteroidSize.large) {
             for (int a = 0; a < 3; a++) addAsteroid(AsteroidSize.medium, asteroid.position);
           }
           else if (asteroid._asteroidSize == AsteroidSize.medium) {
             for (int a = 0; a < 5; a++) addAsteroid(AsteroidSize.small, asteroid.position);
           }

           addExplosion(asteroid._asteroidSize, asteroid.position);

           // Remove asteroid
           asteroid.removeFromParent();
           _asteroids.removeAt(j);

           // Scoring
           if (asteroid._asteroidSize == AsteroidSize.large)
             addScore(100);
           else if (asteroid._asteroidSize == AsteroidSize.medium)
             addScore(50);
           else
             addScore(10);
           break;
         }
       }
     }

     // Check collisions between asteroids and ship
     if (_numFrames > _numFramesShieldActive) {
       // Shield is no longer active

       for (int i = _asteroids.length - 1; i >= 0; i--) {
         // Iterate over all the asteroids
         Asteroid asteroid = _asteroids[i];

         if (pointQuickDist(asteroid.position, _ship.position) < asteroid.radius + _ship.radius) {
           killShip();
         }
       }
     }

     // Move objects to center camera and warp objects around the edges
     centerCamera();
     warpObjects();

     // Check for level up
     if (_asteroids.length == 0) {
       _currentLevel++;
       setupLevel(_currentLevel);
     }

     // Update shield
     if (_numFrames > _numFramesShieldActive) _shield.visible = false;
     else if (_numFrames > _numFramesShieldActive - _numFramesShieldFlickers) _shield.visible = !_shield.visible;

     // Check for exit back to main screen
     if (_isGameOver && _numFrames - _gameOverFrame == 60) {
       _navigator.pop();
     }

     _numFrames++;
   }

   void centerCamera() {
     const cameraDampening = 0.1;
     Point delta = new Point(_gameSizeWidth/2 - _ship.position.x, _gameSizeHeight/2 - _ship.position.y);
     delta = pointMult(delta, cameraDampening);

     for (Node child in _gameLayer.children) {
       child.position = pointAdd(child.position, delta);
     }

     // Update starfield
     _starField.move(delta.x, delta.y);
   }

   void warpObjects() {
     for (Node child in _gameLayer.children) {
       if (child.position.x < 0) child.position = pointAdd(child.position, new Point(_gameSizeWidth, 0.0));
       if (child.position.x >= _gameSizeWidth) child.position = pointAdd(child.position, new Point(-_gameSizeWidth, 0.0));
       if (child.position.y < 0) child.position = pointAdd(child.position, new Point(0.0, _gameSizeHeight));
       if (child.position.y >= _gameSizeHeight) child.position = pointAdd(child.position, new Point(0.0, -_gameSizeHeight));
     }
   }

   void killShip() {
     if (_isGameOver) return;

     // Set game over
     _isGameOver = true;
     _gameOverFrame = _numFrames;
     _gameOverCallback(_hud.score);

     // Remove the ship
     _ship.visible = false;

     // Add an explosion
     addExplosion(AsteroidSize.large, _ship.position);
   }

   // Handling controls

   void controlSteering(double x, double y) {
     // Reset controls if it's game over
     if (_isGameOver) {
       x = y = 0.0;
     }

     _joystickX = x;
     _joystickY = y;
   }

   void controlFire() {
     // Don't shoot if it's game over
     if (_isGameOver) return;

     addLaser();
   }

   // Handle pointer events

   int _firstPointer = -1;
   int _secondPointer = -1;
   Point _firstPointerDownPos;

   bool handleEvent(SpriteBoxEvent event) {

     Point pointerPos = convertPointToNodeSpace(event.boxPosition);
     int pointer = event.pointer;

     switch (event.type) {
       case 'pointerdown':
         if (_firstPointer == -1) {
           // Assign the first pointer
           _firstPointer = pointer;
           _firstPointerDownPos = pointerPos;
         }
         else if (_secondPointer == -1) {
           // Assign second pointer
           _secondPointer = pointer;
           controlFire();
         }
         else {
           // There is a pointer used for steering, let's fire instead
           controlFire();
         }
         break;
       case 'pointermove':
         if (pointer == _firstPointer) {
           // Handle turning control
           double joystickX = 0.0;
           double deltaX = pointerPos.x - _firstPointerDownPos.x;
           if (deltaX > _steeringThreshold || deltaX < -_steeringThreshold) {
             joystickX = (deltaX - _steeringThreshold)/(_steeringMax - _steeringThreshold);
             if (joystickX > 1.0) joystickX = 1.0;
             if (joystickX < -1.0) joystickX = -1.0;
           }

           double joystickY = 0.0;
           double deltaY = pointerPos.y - _firstPointerDownPos.y;
           if (deltaY > _steeringThreshold || deltaY < -_steeringThreshold) {
             joystickY = (deltaY - _steeringThreshold)/(_steeringMax - _steeringThreshold);
             if (joystickY > 1.0) joystickY = 1.0;
             if (joystickY < -1.0) joystickY = -1.0;
           }

           controlSteering(joystickX, joystickY);
         }
         break;
       case 'pointerup':
       case 'pointercancel':
         if (pointer == _firstPointer) {
           // Un-assign the first pointer
           _firstPointer = -1;
           _firstPointerDownPos = null;
           controlSteering(0.0, 0.0);
         }
         else if (pointer == _secondPointer) {
           _secondPointer = -1;
         }
         break;
       default:
         break;
     }
     return true;
   }

   // Scoring and HUD
   void addScore(int score) {
     _hud.score += score;
   }
 }

 // Game objects

 enum AsteroidSize {
   small,
   medium,
   large,
 }

 class Asteroid extends Sprite {
   Point _movementVector;
   AsteroidSize _asteroidSize;
   double _radius;

   double get radius {
     if (_radius != null) return _radius;
     if (_asteroidSize == AsteroidSize.small) _radius = _smlAsteroidRadius;
     else if (_asteroidSize == AsteroidSize.medium) _radius = _medAsteroidRadius;
     else if (_asteroidSize == AsteroidSize.large) _radius = _lrgAsteroidRadius;
     return _radius;
   }

   Asteroid(SpriteSheet spriteSheet, AsteroidSize this._asteroidSize) {
     size = new Size(radius * 2.0, radius * 2.0);
     position = new Point(_gameSizeWidth * _rand.nextDouble(), _gameSizeHeight * _rand.nextDouble());
     rotation = 360.0 * _rand.nextDouble();

     if (_asteroidSize == AsteroidSize.small) {
       texture = spriteSheet["asteroid_small_${_rand.nextInt(2)}.png"];
     } else {
       texture = spriteSheet["asteroid_big_${_rand.nextInt(2)}.png"];
     }

     _movementVector = new Point(_rand.nextDouble() * _maxAsteroidSpeed * 2 - _maxAsteroidSpeed,
                                 _rand.nextDouble() * _maxAsteroidSpeed * 2 - _maxAsteroidSpeed);

     userInteractionEnabled = true;

     // Rotate forever
     double direction = (_rand.nextBool()) ? 360.0 : -360.0;
     ActionTween rot = new ActionTween( (a) => rotation = a, 0.0, direction, 2.0 * _rand.nextDouble() + 2.0);
     ActionRepeatForever repeat = new ActionRepeatForever(rot);
     actions.run(repeat);
   }

   bool handleEvent(SpriteBoxEvent event) {
     if (event.type == "pointerdown") {
       actions.stopWithTag("fade");
       colorOverlay = new Color(0x99ffffff);
     }
     else if (event.type == "pointerup") {
       // Fade out the color overlay
       Action fadeOut = new ActionTween((a) => this.colorOverlay = a, new Color(0x99ffffff), new Color(0x00ffffff), 1.0);
       Action fadeOutAndRemove = new ActionSequence([fadeOut, new ActionCallFunction(() => this.colorOverlay = null)]);
       actions.run(fadeOutAndRemove, "fade");
     }
     return false;
   }
 }

 class Ship extends Sprite {
   Vector2 _movementVector;
   double _rotationTarget;
   double radius = _shipRadius;

   Ship(Texture img) : super(img) {
     _movementVector = new Vector2.zero();
     rotation = _rotationTarget = 270.0;

     // Create sprite
     size = new Size(_shipRadius * 2.0, _shipRadius * 2.0);
     position = new Point(_gameSizeWidth/2.0, _gameSizeHeight/2.0);
   }

   void thrust(double x, double y) {
     _rotationTarget = convertRadians2Degrees(Math.atan2(y, x));
     Vector2 directionVector = new Vector2(x, y).normalize();
     _movementVector.addScaled(directionVector, 1.0);
   }

   void move() {
     position = new Point(position.x + _movementVector[0], position.y + _movementVector[1]);
     _movementVector.scale(0.9);

     rotation = dampenRotation(rotation, _rotationTarget, 0.1);
   }
 }

 class Laser extends Sprite {
   int _frameCount = 0;
   Point _movementVector;
   double radius = 20.0;

   Laser(Texture img, Ship ship) : super(img) {
     size = new Size(30.0, 30.0);
     position = ship.position;
     rotation = ship.rotation + 90.0;
     transferMode = sky.TransferMode.plus;
     double rotRadians = convertDegrees2Radians(rotation);
     _movementVector = pointMult(new Point(Math.sin(rotRadians), -Math.cos(rotRadians)), 10.0);
     _movementVector = new Point(_movementVector.x + ship._movementVector[0], _movementVector.y + ship._movementVector[1]);
   }

   void move() {
     position = pointAdd(position, _movementVector);
     _frameCount++;
   }
 }

 // Background starfield

 class StarField extends NodeWithSize {
   sky.Image _image;
   int _numStars;
   bool _autoScroll;
   List<Point> _starPositions;
   List<double> _starScales;
   List<Rect> _rects;
   List<Color> _colors;
   Paint _paint = new Paint()
     ..setFilterQuality(sky.FilterQuality.low)
     ..isAntiAlias = false
     ..setTransferMode(sky.TransferMode.plus);

   StarField(SpriteSheet spriteSheet, this._numStars, [this._autoScroll = false]) : super(new Size(1024.0, 1024.0)) {
     _starPositions = [];
     _starScales = [];
     _colors = [];
     _rects = [];

     for (int i  = 0; i < _numStars; i++) {
       _starPositions.add(new Point(_rand.nextDouble() * _gameSizeWidth, _rand.nextDouble() * _gameSizeHeight));
       _starScales.add(_rand.nextDouble());
       _colors.add(new Color.fromARGB((255.0 * (_rand.nextDouble() * 0.5 + 0.5)).toInt(), 255, 255, 255));
       _rects.add(spriteSheet["star_${_rand.nextInt(2)}.png"].frame);
     }

     _image = spriteSheet.image;
   }

   void paint(PaintingCanvas canvas) {
     // Create a transform for each star
     List<sky.RSTransform> transforms = [];
     for (int i = 0; i < _numStars; i++) {
       sky.RSTransform transform = new sky.RSTransform(_starScales[i], 0.0, _starPositions[i].x, _starPositions[i].y);
       transforms.add(transform);
     }

     // Draw the stars
     canvas.drawAtlas(_image, transforms, _rects, _colors, sky.TransferMode.modulate, null, _paint);
   }

   void move(double dx, double dy) {
     for (int i  = 0; i < _numStars; i++) {
       double xPos = _starPositions[i].x;
       double yPos = _starPositions[i].y;
       double scale = _starScales[i];

       xPos += dx * scale;
       yPos += dy * scale;

       if (xPos >= _gameSizeWidth) xPos -= _gameSizeWidth;
       if (xPos < 0) xPos += _gameSizeWidth;
       if (yPos >= _gameSizeHeight) yPos -= _gameSizeHeight;
       if (yPos < 0) yPos += _gameSizeHeight;

       _starPositions[i] = new Point(xPos, yPos);
     }
   }

   void update(double dt) {
     if (_autoScroll) {
       move(dt * 100.0, 0.0);
     }
   }
 }

 class Hud extends NodeWithSize {
   SpriteSheet spriteSheetUI;
   Sprite sprtBgScore;
   Sprite sprtBgShield;
   bool _dirtyScore = true;

   int _score = 0;

   int get score => _score;

   set score(int score) {
     _score = score;
     _dirtyScore = true;
   }

   Hud(this.spriteSheetUI) : super(Size.zero) {
     pivot = Point.origin;

     sprtBgScore = new Sprite(spriteSheetUI["scoreboard.png"]);
     sprtBgScore.pivot = new Point(1.0, 0.0);
     sprtBgScore.scale = 0.6;
     addChild(sprtBgScore);

     sprtBgShield = new Sprite(spriteSheetUI["bar_shield.png"]);
     sprtBgShield.pivot = Point.origin;
     sprtBgShield.scale = 0.6;
     // TODO: Add shield
     //addChild(sprtBgShield);
   }

   void spriteBoxPerformedLayout() {
     // Set the size and position of HUD display
     position = spriteBox.visibleArea.topLeft;
     size = spriteBox.visibleArea.size;

     // Position hud objects
     sprtBgShield.position = new Point(20.0, 20.0);
     sprtBgScore.position = new Point(size.width - 20.0, 20.0);
   }

   void update(double dt) {
     // Update score
     if (_dirtyScore) {

       sprtBgScore.removeAllChildren();

       String scoreStr = _score.toString();
       double xPos = -50.0;
       for (int i = scoreStr.length - 1; i >= 0; i--) {
         String numStr = scoreStr.substring(i, i + 1);
         Sprite numSprt = new Sprite(spriteSheetUI["number_$numStr.png"]);
         numSprt.position = new Point(xPos, 49.0);
         sprtBgScore.addChild(numSprt);
         xPos -= 37.0;
       }
       _dirtyScore = false;
     }
     // Update power bar
   }
 }

 class Nebula extends Node {

   Nebula.withImage(sky.Image img) {
     for (int i = 0; i < 2; i++) {
       for (int j = 0; j < 2; j++) {
         Sprite sprt = new Sprite.fromImage(img);
         sprt.transferMode = sky.TransferMode.plus;
         sprt.pivot = Point.origin;
         sprt.position = new Point(i * _gameSizeWidth - _gameSizeWidth, j * _gameSizeHeight - _gameSizeHeight);
         addChild(sprt);
       }
     }
   }
 }

 // Convenience methods

 Point pointAdd(Point a, Point b) {
   return new Point(a.x+ b.x, a.y + b.y);
 }

 Point pointMult(Point a, double multiplier) {
   return new Point(a.x * multiplier, a.y * multiplier);
 }

 double dampenRotation(double src, double dst, double dampening) {
   double delta = dst - src;
   while (delta > 180.0) delta -= 360;
   while (delta < -180) delta += 360;
   delta *= dampening;

   return src + delta;
 }

 double pointQuickDist(Point a, Point b) {
   double dx = a.x - b.x;
   double dy = a.y - b.y;
   if (dx < 0.0) dx = -dx;
   if (dy < 0.0) dy = -dy;
   if (dx > dy) {
     return dx + dy/2.0;
   }
   else {
     return dy + dx/2.0;
   }
 }
	part of game;

	const double _steeringThreshold = 0.0;
	const double _steeringMax = 150.0;

	// Random generator
	Math.Random _rand = new Math.Random();

	const double _gameSizeWidth = 1024.0;
	const double _gameSizeHeight = 1024.0;

	const double _shipRadius = 30.0;
	const double _lrgAsteroidRadius = 40.0;
	const double _medAsteroidRadius = 20.0;
	const double _smlAsteroidRadius = 10.0;
	const double _maxAsteroidSpeed = 1.0;

	const int _lifeTimeLaser = 50;

	const int _numStarsInStarField = 150;

	const int _numFramesShieldActive = 60 * 5;
	const int _numFramesShieldFlickers = 60;

	class GameDemoWorld extends NodeWithSize {
	// Images
	sky.Image _imgNebula;

	SpriteSheet _spriteSheet;
	SpriteSheet _spriteSheetUI;

	Map<String,SoundEffect> _sounds;
	SoundEffectPlayer _soundPool = SoundEffectPlayer.sharedInstance();

	Navigator _navigator;

	// Inputs
	double _joystickX = 0.0;
	double _joystickY = 0.0;

	Node _gameLayer;

	Ship _ship;
	Sprite _shield;
	List<Asteroid> _asteroids = [];
	List<Laser> _lasers = [];
	StarField _starField;
	Nebula _nebula;

	// Game state
	int _numFrames = 0;
	bool _isGameOver = false;
	int _gameOverFrame;
	int _currentLevel = 0;

	// Heads up display
	Hud _hud;

	Function _gameOverCallback;

	GameDemoWorld(App app, this._navigator, ImageMap images, this._spriteSheet, this._spriteSheetUI, this._sounds, this._gameOverCallback) : super(new Size(_gameSizeWidth, _gameSizeHeight)) {
	// Fetch images
	_imgNebula = images["assets/nebula.png"];

	_gameLayer = new Node();
	this.addChild(_gameLayer);
	// Add ship
	addShip();

	// Add background
	Sprite sprtBackground = new Sprite.fromImage(images["assets/starfield.png"]);
	sprtBackground.position = new Point(512.0, 512.0);
	sprtBackground.zPosition = -3.0;
	addChild(sprtBackground);

	// Add starfield
	_starField = new StarField(_spriteSheet, _numStarsInStarField);
	_starField.zPosition = -2.0;
	addChild(_starField);

	// Add nebula
	addNebula();

	userInteractionEnabled = true;
	handleMultiplePointers = true;

	_hud = new Hud(_spriteSheetUI);
	_hud.zPosition = 1000.0;
	addChild(_hud);

	// Setup level
	setupLevel(0);
	}

	void setupLevel(int level) {
	int numLargeAsteroids = 5 + level * 2;
	int numMediumAsteroids = 5 + level * 2;

	// Add some asteroids to the game world
	for (int i = 0; i < numLargeAsteroids; i++) {
	addAsteroid(AsteroidSize.large);
	}
	for (int i = 0; i < numMediumAsteroids; i++) {
	addAsteroid(AsteroidSize.medium);
	}

	_numFrames = 0;
	_shield.visible = true;
	}

	// Methods for adding game objects

	void addAsteroid(AsteroidSize size, [Point pos]) {
	Asteroid asteroid = new Asteroid(_spriteSheet, size);
	asteroid.zPosition = 1.0;
	if (pos != null) asteroid.position = pos;
	_gameLayer.addChild(asteroid);
	_asteroids.add(asteroid);

	// Animate asteroid into the scene
	Action action = new ActionTween((a) => asteroid.scale = a, 0.0, 1.0, 1.0, bounceOut);
	_gameLayer.actions.run(action);
	}

	void addShip() {
	Ship ship = new Ship(_spriteSheet["ship.png"]);
	ship.zPosition = 10.0;
	_gameLayer.addChild(ship);
	_ship = ship;

	_shield = new Sprite(_spriteSheet["shield.png"]);
	_shield.zPosition = 11.0;
	_shield.scale = 0.5;
	_shield.transferMode = sky.TransferMode.plus;
	_gameLayer.addChild(_shield);

	Action rotate = new ActionRepeatForever(new ActionTween((a) => _shield.rotation = a, 0.0, 360.0, 1.0));
	actions.run(rotate);
	}

	void addLaser() {
	Laser laser = new Laser(_spriteSheet["laser.png"], _ship);
	laser.zPosition = 8.0;
	laser.constrainProportions = true;
	_lasers.add(laser);
	_gameLayer.addChild(laser);

	_soundPool.play(_sounds["laser"]);
	}

	void addNebula() {
	_nebula = new Nebula.withImage(_imgNebula);
	_gameLayer.addChild(_nebula);
	}

	void addExplosion(AsteroidSize asteroidSize, Point position) {
	Node explosionNode = new Node();

	// Add particles
	ParticleSystem particlesDebris = new ParticleSystem(
	_spriteSheet["explosion_particle.png"],
	rotateToMovement: true,
	startRotation:90.0,
	startRotationVar: 0.0,
	endRotation: 90.0,
	startSize: 0.3,
	startSizeVar: 0.1,
	endSize: 0.3,
	endSizeVar: 0.1,
	numParticlesToEmit: 25,
	emissionRate:1000.0,
	greenVar: 127,
	redVar: 127
	);
	particlesDebris.zPosition = 1010.0;
	explosionNode.addChild(particlesDebris);

	ParticleSystem particlesFire = new ParticleSystem(
	_spriteSheet["fire_particle.png"],
	colorSequence: new ColorSequence([new Color(0xffffff33), new Color(0xffff3333), new Color(0x00ff3333)], [0.0, 0.5, 1.0]),
	numParticlesToEmit: 25,
	emissionRate: 1000.0,
	startSize: 0.5,
	startSizeVar: 0.1,
	endSize: 0.5,
	endSizeVar: 0.1,
	posVar: new Point(10.0, 10.0),
	speed: 10.0,
	speedVar: 5.0
	);
	particlesFire.zPosition = 1011.0;
	explosionNode.addChild(particlesFire);


	// Add ring
	Sprite sprtRing = new Sprite(_spriteSheet["explosion_ring.png"]);
	sprtRing.transferMode = sky.TransferMode.plus;
	explosionNode.addChild(sprtRing);

	Action scale = new ActionTween( (a) => sprtRing.scale = a, 0.2, 1.0, 1.5);
	Action scaleAndRemove = new ActionSequence([scale, new ActionRemoveNode(sprtRing)]);
	Action fade = new ActionTween( (a) => sprtRing.opacity = a, 1.0, 0.0, 1.5);
	actions.run(scaleAndRemove);
	actions.run(fade);

	// Add streaks
	for (int i = 0; i < 5; i++) {
	Sprite sprtFlare = new Sprite(_spriteSheet["explosion_flare.png"]);
	sprtFlare.pivot = new Point(0.3, 1.0);
	sprtFlare.scaleX = 0.3;
	sprtFlare.transferMode = sky.TransferMode.plus;
	sprtFlare.rotation = _rand.nextDouble() * 360.0;
	explosionNode.addChild(sprtFlare);

	double multiplier = _rand.nextDouble() * 0.3 + 1.0;

	Action scale = new ActionTween( (a) => sprtFlare.scaleY = a, 0.3 * multiplier, 0.8, 1.5 * multiplier);
	Action scaleAndRemove = new ActionSequence([scale, new ActionRemoveNode(sprtFlare)]);
	Action fadeIn = new ActionTween( (a) => sprtFlare.opacity = a, 0.0, 1.0, 0.5 * multiplier);
	Action fadeOut = new ActionTween( (a) => sprtFlare.opacity = a, 1.0, 0.0, 1.0 * multiplier);
	Action fadeInOut = new ActionSequence([fadeIn, fadeOut]);
	actions.run(scaleAndRemove);
	actions.run(fadeInOut);
	}

	explosionNode.position = position;
	explosionNode.zPosition = 1010.0;

	if (asteroidSize == AsteroidSize.large) {
	explosionNode.scale = 1.5;
	}

	_gameLayer.addChild(explosionNode);

	_soundPool.play(_sounds["explosion"]);
	}

	void update(double dt) {
	// Move asteroids
	for (Asteroid asteroid in _asteroids) {
	asteroid.position = pointAdd(asteroid.position, asteroid._movementVector);
	}

	// Move lasers and remove expired lasers
	for (int i = _lasers.length - 1; i >= 0; i--) {
	Laser laser = _lasers[i];
	laser.move();
	if (laser._frameCount > _lifeTimeLaser) {
	laser.removeFromParent();
	_lasers.removeAt(i);
	}
	}

	// Apply thrust to ship
	if (_joystickX != 0.0 \|\| _joystickY != 0.0) {
	_ship.thrust(_joystickX, _joystickY);
	}

	// Move ship
	_ship.move();
	_shield.position = _ship.position;

	// Check collisions between asteroids and lasers
	for (int i = _lasers.length -1; i >= 0; i--) {
	// Iterate over all the lasers
	Laser laser = _lasers[i];

	for (int j = _asteroids.length - 1; j >= 0; j--) {
	// Iterate over all the asteroids
	Asteroid asteroid = _asteroids[j];

	// Check for collision
	if (pointQuickDist(laser.position, asteroid.position) < laser.radius + asteroid.radius) {
	// Remove laser
	laser.removeFromParent();
	_lasers.removeAt(i);

	// Add asteroids and explosions
	if (asteroid._asteroidSize == AsteroidSize.large) {
	for (int a = 0; a < 3; a++) addAsteroid(AsteroidSize.medium, asteroid.position);
	}
	else if (asteroid._asteroidSize == AsteroidSize.medium) {
	for (int a = 0; a < 5; a++) addAsteroid(AsteroidSize.small, asteroid.position);
	}

	addExplosion(asteroid._asteroidSize, asteroid.position);

	// Remove asteroid
	asteroid.removeFromParent();
	_asteroids.removeAt(j);

	// Scoring
	if (asteroid._asteroidSize == AsteroidSize.large)
	addScore(100);
	else if (asteroid._asteroidSize == AsteroidSize.medium)
	addScore(50);
	else
	addScore(10);
	break;
	}
	}
	}

	// Check collisions between asteroids and ship
	if (_numFrames > _numFramesShieldActive) {
	// Shield is no longer active

	for (int i = _asteroids.length - 1; i >= 0; i--) {
	// Iterate over all the asteroids
	Asteroid asteroid = _asteroids[i];

	if (pointQuickDist(asteroid.position, _ship.position) < asteroid.radius + _ship.radius) {
	killShip();
	}
	}
	}

	// Move objects to center camera and warp objects around the edges
	centerCamera();
	warpObjects();

	// Check for level up
	if (_asteroids.length == 0) {
	_currentLevel++;
	setupLevel(_currentLevel);
	}

	// Update shield
	if (_numFrames > _numFramesShieldActive) _shield.visible = false;
	else if (_numFrames > _numFramesShieldActive - _numFramesShieldFlickers) _shield.visible = !_shield.visible;

	// Check for exit back to main screen
	if (_isGameOver && _numFrames - _gameOverFrame == 60) {
	_navigator.pop();
	}

	_numFrames++;
	}

	void centerCamera() {
	const cameraDampening = 0.1;
	Point delta = new Point(_gameSizeWidth/2 - _ship.position.x, _gameSizeHeight/2 - _ship.position.y);
	delta = pointMult(delta, cameraDampening);

	for (Node child in _gameLayer.children) {
	child.position = pointAdd(child.position, delta);
	}

	// Update starfield
	_starField.move(delta.x, delta.y);
	}

	void warpObjects() {
	for (Node child in _gameLayer.children) {
	if (child.position.x < 0) child.position = pointAdd(child.position, new Point(_gameSizeWidth, 0.0));
	if (child.position.x >= _gameSizeWidth) child.position = pointAdd(child.position, new Point(-_gameSizeWidth, 0.0));
	if (child.position.y < 0) child.position = pointAdd(child.position, new Point(0.0, _gameSizeHeight));
	if (child.position.y >= _gameSizeHeight) child.position = pointAdd(child.position, new Point(0.0, -_gameSizeHeight));
	}
	}

	void killShip() {
	if (_isGameOver) return;

	// Set game over
	_isGameOver = true;
	_gameOverFrame = _numFrames;
	_gameOverCallback(_hud.score);

	// Remove the ship
	_ship.visible = false;

	// Add an explosion
	addExplosion(AsteroidSize.large, _ship.position);
	}

	// Handling controls

	void controlSteering(double x, double y) {
	// Reset controls if it's game over
	if (_isGameOver) {
	x = y = 0.0;
	}

	_joystickX = x;
	_joystickY = y;
	}

	void controlFire() {
	// Don't shoot if it's game over
	if (_isGameOver) return;

	addLaser();
	}

	// Handle pointer events

	int _firstPointer = -1;
	int _secondPointer = -1;
	Point _firstPointerDownPos;

	bool handleEvent(SpriteBoxEvent event) {

	Point pointerPos = convertPointToNodeSpace(event.boxPosition);
	int pointer = event.pointer;

	switch (event.type) {
	case 'pointerdown':
	if (_firstPointer == -1) {
	// Assign the first pointer
	_firstPointer = pointer;
	_firstPointerDownPos = pointerPos;
	}
	else if (_secondPointer == -1) {
	// Assign second pointer
	_secondPointer = pointer;
	controlFire();
	}
	else {
	// There is a pointer used for steering, let's fire instead
	controlFire();
	}
	break;
	case 'pointermove':
	if (pointer == _firstPointer) {
	// Handle turning control
	double joystickX = 0.0;
	double deltaX = pointerPos.x - _firstPointerDownPos.x;
	if (deltaX > _steeringThreshold \|\| deltaX < -_steeringThreshold) {
	joystickX = (deltaX - _steeringThreshold)/(_steeringMax - _steeringThreshold);
	if (joystickX > 1.0) joystickX = 1.0;
	if (joystickX < -1.0) joystickX = -1.0;
	}

	double joystickY = 0.0;
	double deltaY = pointerPos.y - _firstPointerDownPos.y;
	if (deltaY > _steeringThreshold \|\| deltaY < -_steeringThreshold) {
	joystickY = (deltaY - _steeringThreshold)/(_steeringMax - _steeringThreshold);
	if (joystickY > 1.0) joystickY = 1.0;
	if (joystickY < -1.0) joystickY = -1.0;
	}

	controlSteering(joystickX, joystickY);
	}
	break;
	case 'pointerup':
	case 'pointercancel':
	if (pointer == _firstPointer) {
	// Un-assign the first pointer
	_firstPointer = -1;
	_firstPointerDownPos = null;
	controlSteering(0.0, 0.0);
	}
	else if (pointer == _secondPointer) {
	_secondPointer = -1;
	}
	break;
	default:
	break;
	}
	return true;
	}

	// Scoring and HUD
	void addScore(int score) {
	_hud.score += score;
	}
	}

	// Game objects

	enum AsteroidSize {
	small,
	medium,
	large,
	}

	class Asteroid extends Sprite {
	Point _movementVector;
	AsteroidSize _asteroidSize;
	double _radius;

	double get radius {
	if (_radius != null) return _radius;
	if (_asteroidSize == AsteroidSize.small) _radius = _smlAsteroidRadius;
	else if (_asteroidSize == AsteroidSize.medium) _radius = _medAsteroidRadius;
	else if (_asteroidSize == AsteroidSize.large) _radius = _lrgAsteroidRadius;
	return _radius;
	}

	Asteroid(SpriteSheet spriteSheet, AsteroidSize this._asteroidSize) {
	size = new Size(radius * 2.0, radius * 2.0);
	position = new Point(_gameSizeWidth * _rand.nextDouble(), _gameSizeHeight * _rand.nextDouble());
	rotation = 360.0 * _rand.nextDouble();

	if (_asteroidSize == AsteroidSize.small) {
	texture = spriteSheet["asteroid_small_${_rand.nextInt(2)}.png"];
	} else {
	texture = spriteSheet["asteroid_big_${_rand.nextInt(2)}.png"];
	}

	_movementVector = new Point(_rand.nextDouble() * _maxAsteroidSpeed * 2 - _maxAsteroidSpeed,
	_rand.nextDouble() * _maxAsteroidSpeed * 2 - _maxAsteroidSpeed);

	userInteractionEnabled = true;

	// Rotate forever
	double direction = (_rand.nextBool()) ? 360.0 : -360.0;
	ActionTween rot = new ActionTween( (a) => rotation = a, 0.0, direction, 2.0 * _rand.nextDouble() + 2.0);
	ActionRepeatForever repeat = new ActionRepeatForever(rot);
	actions.run(repeat);
	}

	bool handleEvent(SpriteBoxEvent event) {
	if (event.type == "pointerdown") {
	actions.stopWithTag("fade");
	colorOverlay = new Color(0x99ffffff);
	}
	else if (event.type == "pointerup") {
	// Fade out the color overlay
	Action fadeOut = new ActionTween((a) => this.colorOverlay = a, new Color(0x99ffffff), new Color(0x00ffffff), 1.0);
	Action fadeOutAndRemove = new ActionSequence([fadeOut, new ActionCallFunction(() => this.colorOverlay = null)]);
	actions.run(fadeOutAndRemove, "fade");
	}
	return false;
	}
	}

	class Ship extends Sprite {
	Vector2 _movementVector;
	double _rotationTarget;
	double radius = _shipRadius;

	Ship(Texture img) : super(img) {
	_movementVector = new Vector2.zero();
	rotation = _rotationTarget = 270.0;

	// Create sprite
	size = new Size(_shipRadius * 2.0, _shipRadius * 2.0);
	position = new Point(_gameSizeWidth/2.0, _gameSizeHeight/2.0);
	}

	void thrust(double x, double y) {
	_rotationTarget = convertRadians2Degrees(Math.atan2(y, x));
	Vector2 directionVector = new Vector2(x, y).normalize();
	_movementVector.addScaled(directionVector, 1.0);
	}

	void move() {
	position = new Point(position.x + _movementVector[0], position.y + _movementVector[1]);
	_movementVector.scale(0.9);

	rotation = dampenRotation(rotation, _rotationTarget, 0.1);
	}
	}

	class Laser extends Sprite {
	int _frameCount = 0;
	Point _movementVector;
	double radius = 20.0;

	Laser(Texture img, Ship ship) : super(img) {
	size = new Size(30.0, 30.0);
	position = ship.position;
	rotation = ship.rotation + 90.0;
	transferMode = sky.TransferMode.plus;
	double rotRadians = convertDegrees2Radians(rotation);
	_movementVector = pointMult(new Point(Math.sin(rotRadians), -Math.cos(rotRadians)), 10.0);
	_movementVector = new Point(_movementVector.x + ship._movementVector[0], _movementVector.y + ship._movementVector[1]);
	}

	void move() {
	position = pointAdd(position, _movementVector);
	_frameCount++;
	}
	}

	// Background starfield

	class StarField extends NodeWithSize {
	sky.Image _image;
	int _numStars;
	bool _autoScroll;
	List<Point> _starPositions;
	List<double> _starScales;
	List<Rect> _rects;
	List<Color> _colors;
	Paint _paint = new Paint()
	..setFilterQuality(sky.FilterQuality.low)
	..isAntiAlias = false
	..setTransferMode(sky.TransferMode.plus);

	StarField(SpriteSheet spriteSheet, this._numStars, [this._autoScroll = false]) : super(new Size(1024.0, 1024.0)) {
	_starPositions = [];
	_starScales = [];
	_colors = [];
	_rects = [];

	for (int i = 0; i < _numStars; i++) {
	_starPositions.add(new Point(_rand.nextDouble() * _gameSizeWidth, _rand.nextDouble() * _gameSizeHeight));
	_starScales.add(_rand.nextDouble());
	_colors.add(new Color.fromARGB((255.0 * (_rand.nextDouble() * 0.5 + 0.5)).toInt(), 255, 255, 255));
	_rects.add(spriteSheet["star_${_rand.nextInt(2)}.png"].frame);
	}

	_image = spriteSheet.image;
	}

	void paint(PaintingCanvas canvas) {
	// Create a transform for each star
	List<sky.RSTransform> transforms = [];
	for (int i = 0; i < _numStars; i++) {
	sky.RSTransform transform = new sky.RSTransform(_starScales[i], 0.0, _starPositions[i].x, _starPositions[i].y);
	transforms.add(transform);
	}

	// Draw the stars
	canvas.drawAtlas(_image, transforms, _rects, _colors, sky.TransferMode.modulate, null, _paint);
	}

	void move(double dx, double dy) {
	for (int i = 0; i < _numStars; i++) {
	double xPos = _starPositions[i].x;
	double yPos = _starPositions[i].y;
	double scale = _starScales[i];

	xPos += dx * scale;
	yPos += dy * scale;

	if (xPos >= _gameSizeWidth) xPos -= _gameSizeWidth;
	if (xPos < 0) xPos += _gameSizeWidth;
	if (yPos >= _gameSizeHeight) yPos -= _gameSizeHeight;
	if (yPos < 0) yPos += _gameSizeHeight;

	_starPositions[i] = new Point(xPos, yPos);
	}
	}

	void update(double dt) {
	if (_autoScroll) {
	move(dt * 100.0, 0.0);
	}
	}
	}

	class Hud extends NodeWithSize {
	SpriteSheet spriteSheetUI;
	Sprite sprtBgScore;
	Sprite sprtBgShield;
	bool _dirtyScore = true;

	int _score = 0;

	int get score => _score;

	set score(int score) {
	_score = score;
	_dirtyScore = true;
	}

	Hud(this.spriteSheetUI) : super(Size.zero) {
	pivot = Point.origin;

	sprtBgScore = new Sprite(spriteSheetUI["scoreboard.png"]);
	sprtBgScore.pivot = new Point(1.0, 0.0);
	sprtBgScore.scale = 0.6;
	addChild(sprtBgScore);

	sprtBgShield = new Sprite(spriteSheetUI["bar_shield.png"]);
	sprtBgShield.pivot = Point.origin;
	sprtBgShield.scale = 0.6;
	// TODO: Add shield
	//addChild(sprtBgShield);
	}

	void spriteBoxPerformedLayout() {
	// Set the size and position of HUD display
	position = spriteBox.visibleArea.topLeft;
	size = spriteBox.visibleArea.size;

	// Position hud objects
	sprtBgShield.position = new Point(20.0, 20.0);
	sprtBgScore.position = new Point(size.width - 20.0, 20.0);
	}

	void update(double dt) {
	// Update score
	if (_dirtyScore) {

	sprtBgScore.removeAllChildren();

	String scoreStr = _score.toString();
	double xPos = -50.0;
	for (int i = scoreStr.length - 1; i >= 0; i--) {
	String numStr = scoreStr.substring(i, i + 1);
	Sprite numSprt = new Sprite(spriteSheetUI["number_$numStr.png"]);
	numSprt.position = new Point(xPos, 49.0);
	sprtBgScore.addChild(numSprt);
	xPos -= 37.0;
	}
	_dirtyScore = false;
	}
	// Update power bar
	}
	}

	class Nebula extends Node {

	Nebula.withImage(sky.Image img) {
	for (int i = 0; i < 2; i++) {
	for (int j = 0; j < 2; j++) {
	Sprite sprt = new Sprite.fromImage(img);
	sprt.transferMode = sky.TransferMode.plus;
	sprt.pivot = Point.origin;
	sprt.position = new Point(i * _gameSizeWidth - _gameSizeWidth, j * _gameSizeHeight - _gameSizeHeight);
	addChild(sprt);
	}
	}
	}
	}

	// Convenience methods

	Point pointAdd(Point a, Point b) {
	return new Point(a.x+ b.x, a.y + b.y);
	}

	Point pointMult(Point a, double multiplier) {
	return new Point(a.x * multiplier, a.y * multiplier);
	}

	double dampenRotation(double src, double dst, double dampening) {
	double delta = dst - src;
	while (delta > 180.0) delta -= 360;
	while (delta < -180) delta += 360;
	delta *= dampening;

	return src + delta;
	}

	double pointQuickDist(Point a, Point b) {
	double dx = a.x - b.x;
	double dy = a.y - b.y;
	if (dx < 0.0) dx = -dx;
	if (dy < 0.0) dy = -dy;
	if (dx > dy) {
	return dx + dy/2.0;
	}
	else {
	return dy + dx/2.0;
	}
	}