How to structure game states in an entity/component-based system
- by Eva
I'm making a game designed with the entity-component paradigm that uses systems to communicate between components as explained here. I've reached the point in my development that I need to add game states (such as paused, playing, level start, round start, game over, etc.), but I'm not sure how to do it with my framework. I've looked at this code example on game states which everyone seems to reference, but I don't think it fits with my framework. It seems to have each state handling its own drawing and updating. My framework has a SystemManager that handles all the updating using systems. For example, here's my RenderingSystem class:
public class RenderingSystem extends GameSystem {
private GameView gameView_;
/**
* Constructor
* Creates a new RenderingSystem.
* @param gameManager The game manager. Used to get the game components.
*/
public RenderingSystem(GameManager gameManager) {
super(gameManager);
}
/**
* Method: registerGameView
* Registers gameView into the RenderingSystem.
* @param gameView The game view registered.
*/
public void registerGameView(GameView gameView) {
gameView_ = gameView;
}
/**
* Method: triggerRender
* Adds a repaint call to the event queue for the dirty rectangle.
*/
public void triggerRender() {
Rectangle dirtyRect = new Rectangle();
for (GameObject object : getRenderableObjects()) {
GraphicsComponent graphicsComponent =
object.getComponent(GraphicsComponent.class);
dirtyRect.add(graphicsComponent.getDirtyRect());
}
gameView_.repaint(dirtyRect);
}
/**
* Method: renderGameView
* Renders the game objects onto the game view.
* @param g The graphics object that draws the game objects.
*/
public void renderGameView(Graphics g) {
for (GameObject object : getRenderableObjects()) {
GraphicsComponent graphicsComponent =
object.getComponent(GraphicsComponent.class);
if (!graphicsComponent.isVisible()) continue;
GraphicsComponent.Shape shape = graphicsComponent.getShape();
BoundsComponent boundsComponent =
object.getComponent(BoundsComponent.class);
Rectangle bounds = boundsComponent.getBounds();
g.setColor(graphicsComponent.getColor());
if (shape == GraphicsComponent.Shape.RECTANGULAR) {
g.fill3DRect(bounds.x, bounds.y, bounds.width, bounds.height,
true);
} else if (shape == GraphicsComponent.Shape.CIRCULAR) {
g.fillOval(bounds.x, bounds.y, bounds.width, bounds.height);
}
}
}
/**
* Method: getRenderableObjects
* @return The renderable game objects.
*/
private HashSet<GameObject> getRenderableObjects() {
return gameManager.getGameObjectManager().getRelevantObjects(
getClass());
}
}
Also all the updating in my game is event-driven. I don't have a loop like theirs that simply updates everything at the same time.
I like my framework because it makes it easy to add new GameObjects, but doesn't have the problems some component-based designs encounter when communicating between components. I would hate to chuck it just to get pause to work. Is there a way I can add game states to my game without removing the entity-component design? Does the game state example actually fit my framework, and I'm just missing something?
EDIT:
I might not have explained my framework well enough. My components are just data. If I was coding in C++, they'd probably be structs. Here's an example of one:
public class BoundsComponent implements GameComponent {
/**
* The position of the game object.
*/
private Point pos_;
/**
* The size of the game object.
*/
private Dimension size_;
/**
* Constructor
* Creates a new BoundsComponent for a game object with initial position
* initialPos and initial size initialSize. The position and size combine
* to make up the bounds.
* @param initialPos The initial position of the game object.
* @param initialSize The initial size of the game object.
*/
public BoundsComponent(Point initialPos, Dimension initialSize) {
pos_ = initialPos;
size_ = initialSize;
}
/**
* Method: getBounds
* @return The bounds of the game object.
*/
public Rectangle getBounds() {
return new Rectangle(pos_, size_);
}
/**
* Method: setPos
* Sets the position of the game object to newPos.
* @param newPos The value to which the position of the game object is
* set.
*/
public void setPos(Point newPos) {
pos_ = newPos;
}
}
My components do not communicate with each other. Systems handle inter-component communication. My systems also do not communicate with each other. They have separate functionality and can easily be kept separate. The MovementSystem doesn't need to know what the RenderingSystem is rendering to move the game objects correctly; it just need to set the right values on the components, so that when the RenderingSystem renders the game objects, it has accurate data.
The game state could not be a system, because it needs to interact with the systems rather than the components. It's not setting data; it's determining which functions need to be called.
A GameStateComponent wouldn't make sense because all the game objects share one game state. Components are what make up objects and each one is different for each different object. For example, the game objects cannot have the same bounds. They can have overlapping bounds, but if they share a BoundsComponent, they're really the same object. Hopefully, this explanation makes my framework less confusing.
