// Outer most class
public class GameScreen {
    GameRenderer renderer;
    GameWorld world;
    // Called every frame. delta is the time since last frame.
    public void render(float delta) {
        float dt = world.update(delta);
        renderer.render(dt);
    }
}

public class GameRenderer {
    // Interpolation code (smooth states)
        static void interpolate(Vector2 newPosition, Vector2 oldPosition, float fraction, Vector2 vertex) {
                vertex.x = (1 - fraction) * oldPosition.x + fraction * newPosition.x;
                vertex.y = (1 - fraction) * oldPosition.y + fraction * newPosition.y;
        }
    // Main render method
    public void render(float delta) {
        batcher.begin();
        for (int i = 0; i < world.bodies.size(); i++) {
            GameCircle body = world.bodies.get(i);
            renderCircle(body, delta / GameWorld.timeDelta);
        }
        batcher.end();
    }
        private void renderCircle(GameCircle circle, float fraction) {
                tmpVertex3.x = circle.getX();
                tmpVertex3.y = circle.getY();
                GameRenderer.interpolate(tmpVertex3, circle._lastPosition, fraction, tmpVertex1);
                mapCoordinate(tmpVertex1.x, tmpVertex1.y, tmpVertex2);
                float radius = scale(circle.getRadius());
                sprite.setBounds(tmpVertex2.x - radius, tmpVertex2.y - radius, radius * 2, radius * 2);
                sprite.draw(batcher);
        }
}

// Physics updates
public class GameWorld {
        // delta is time elapsed since last frame.
        // this is called every frame.
        // It returns the accumulator
        public float update(float delta) {
                physicsDelta += Math.min(delta, 0.25f);
                while (physicsDelta >= GameWorld.timeDelta) {
                        rememberWorld();
                        protagonist.body.applyForceToCenter(force, true);
                        world.step(GameWorld.timeDelta, 8, 3);
                        physicsDelta -= GameWorld.timeDelta;
                }
                return physicsDelta;
        }
    // Remembers the current state of the world
        public void rememberWorld() {
                for (int i = bodies.size() - 1; i >= 0; i--) {
                        GameCircle body = bodies.get(i);
                        body._lastPosition.x = body.getX();
                        body._lastPosition.y = body.getY();
                }
        }
}