Comments on: Component Oriented Entities

By: Michael

Michael — Sat, 25 Apr 2009 20:03:36 +0000

As of April 25, 2009 the above code has been updated. It’s recommended to update your code if you’re using the above code.

By: Nick

Nick — Sat, 11 Apr 2009 13:56:40 +0000

Well, in OOP objects can be other objects (a circle is a shape) and objects can have other objects (shapes have vertices). An object is defined but what it has and can do. Attaching 4 wheels to an engine does not make it a car, unless the engine’s power can be transferred to the wheels in some way.

With components, the separation between data (4 wheels, engine) and function (transfer power) is lost. I don’t know if that’s bad good or does not matter, but composition is something quit different from inheritance in C++, and maybe for a good reason.

By: Michael

Michael — Sat, 11 Apr 2009 06:50:38 +0000

I’m trying to decipher what you meant with a has-a and is-a relationship. If you mean that an entity and its components should recognize each other, that’s already possible. An entity can access it’s components through the vector or the method getComponent(…). And components can access their parent entity through the parent pointer. This enables code like this:

AnimatedComponent::onUpdate() { Entity *entity = pParent; EntityComponent *comp = entity->getComponent("CameraComponent"); // ^ You might want to do a cast there to access the specific code of the component. }

By the way, I saw your post at DaniWeb. Looked pretty interesting. You might want to cross-post that here.

By: Nick

Nick — Sat, 11 Apr 2009 00:43:14 +0000

Getting pretty late, but what the heck.

Multiple Virtual Inheritance seems a good way to go with C++ and still doing this, but I still have to inherit from more than 2 classes and with some more complex ways. I dislike the components stuff because you can’t really tell the difference anymore between has-a and is-a relationships, a fundamental part of OOP I reckon. But hey, maybe that’s not that important. Or maybe it’s as simple as having two vectors, one for is-a relationships and one for has-a relationships.

Bedtime! Finally.