Organizing an entity system with external component managers?
- by Gustav
I'm designing a game engine for a top-down multiplayer 2D shooter game, which I want to be reasonably reuseable for other top-down shooter games. At the moment I'm thinking about how something like an entity system in it should be designed. First I thought about this:
I have a class called EntityManager. It should implement a method called Update and another one called Draw. The reason for me separating Logic and Rendering is because then I can omit the Draw method if running a standalone server.
EntityManager owns a list of objects of type BaseEntity. Each entity owns a list of components such as EntityModel (the drawable representation of an entity), EntityNetworkInterface, and EntityPhysicalBody.
EntityManager also owns a list of component managers like EntityRenderManager, EntityNetworkManager and EntityPhysicsManager. Each component manager keeps references to the entity components. There are various reasons for moving this code out of the entity's own class and do it collectively instead. For example, I'm using an external physics library, Box2D, for the game. In Box2D, you first add the bodies and shapes to a world (owned by the EntityPhysicsManager in this case) and add collision callbacks (which would be dispatched to the entity object itself in my system). Then you run a function which simulates everything in the system. I find it hard to find a better solution to do this than doing it in an external component manager like this.
Entity creation is done like this:
EntityManager implements the method RegisterEntity(entityClass, factory) which registers how to create an entity if that class.
It also implements the method CreateEntity(entityClass) which would return an object of type BaseEntity.
Well now comes my problem:
How would the reference to a component be registered to the component managers? I have no idea how I would reference the component managers from a factory/closure.
