@Override
    public void update(float deltaTime) {
      List<TouchEvent> touchEvents = game.getInput().getTouchEvents();
      game.getInput().getKeyEvents();

      int len = touchEvents.size();
      for (int i = 0; i < len; i++) {
        TouchEvent event = touchEvents.get(i);

        camera.touchToWorld(touchPos.set(event.x, event.y));

        cannon.angle = touchPos.sub(cannon.position).angle();

        if (event.type == TouchEvent.TOUCH_UP) {
          float radians = cannon.angle * Vector2.TO_RADIANS;
          float ballSpeed = touchPos.len() * 2;
          ball.position.set(cannon.position);

          ball.velocity.x = FloatMath.cos(radians) * ballSpeed;
          ball.velocity.y = FloatMath.sin(radians) * ballSpeed;

          ball.bounds.lowerLeft.set(ball.position.x - 0.1f, ball.position.y - 0.1f);
        }
      }

      ball.velocity.add(gravity.x * deltaTime, gravity.y * deltaTime);
      ball.position.add(ball.velocity.x * deltaTime, ball.velocity.y * deltaTime);
      ball.bounds.lowerLeft.add(ball.velocity.x * deltaTime, ball.velocity.y * deltaTime);

      List<GameObject> colliders = grid.getPotentialColliders(ball);
      len = colliders.size();

      for (int i = 0; i < len; i++) {
        GameObject collider = colliders.get(i);
        if (OverlapTester.overlapRectangle(ball.bounds, collider.bounds)) {
          grid.removeObject(collider);
          targets.remove(collider);
        }
      }

      if (ball.position.y > 0) {
        camera.position.set(ball.position);
        camera.zoom = 1 + ball.position.y / WORLD_HEIGHT;
      } else {
        camera.position.set(WORLD_WIDTH / 2, WORLD_HEIGHT / 2);
        camera.zoom = 1;
      }
    }
    public Camera2DScreen(Game game) {
      super(game);
      GLGraphics glGraphics = ((GLGame) game).getGLGraphics();
      gl = glGraphics.getGL();

      camera = new Camera2D(glGraphics, WORLD_WIDTH, WORLD_HEIGHT);
      cannon = new Cannon(0, 0, 1, 1);
      ball = new DynamicGameObject(0, 0, 0.2f, 0.2f);
      targets = new ArrayList<GameObject>(NUM_TARGETS);
      grid = new SpatialHashGrid(WORLD_WIDTH, WORLD_HEIGHT, 2.5f);
      for (int i = 0; i < NUM_TARGETS; i++) {
        GameObject target =
            new GameObject(
                (float) Math.random() * WORLD_WIDTH,
                (float) Math.random() * WORLD_HEIGHT,
                0.5f,
                0.5f);
        grid.insertStaticObject(target);
        targets.add(target);
      }

      cannonVertices = new Vertices(gl, 3, 0, false, false);
      cannonVertices.setVertices(new float[] {-0.5f, -0.5f, 0.5f, 0.0f, -0.5f, 0.5f}, 0, 6);

      ballVertices = new Vertices(gl, 4, 6, false, false);
      ballVertices.setVertices(
          new float[] {-0.1f, -0.1f, 0.1f, -0.1f, 0.1f, 0.1f, -0.1f, 0.1f}, 0, 8);
      ballVertices.setIndices(new short[] {0, 1, 2, 2, 3, 0}, 0, 6);

      targetVertices = new Vertices(gl, 4, 6, false, false);
      targetVertices.setVertices(
          new float[] {-0.25f, -0.25f, 0.25f, -0.25f, 0.25f, 0.25f, -0.25f, 0.25f}, 0, 8);
      targetVertices.setIndices(new short[] {0, 1, 2, 2, 3, 0}, 0, 6);
    }