Component based game engine design [closed]

Question

Update 2013-01-07: If you want to see a good mix of component-based game engine with the (in my opinion) superior approach of reactive programming take a look at the V-Play engine. It very well integrates QTs QML property binding functionality.

We did some research on CBSE in games at our university and I collected some material over the years:

CBSE in games literature:

• Game Engine Architecture
• Game Programming Gems 4: A System for Managin Game Entities Game
• Game Programming Gems 5: Component Based Object Management
• Game Programming Gems 5: A Generic Component Library
• Game Programming Gems 6: Game Object Component System
• Object-Oriented Game Development
• Architektur des Kerns einer Game-Engine und Implementierung mit Java (german)

A very good and clean example of a component-based game-engine in C# is the Elephant game framework.

If you really want to know what components are read: Component-based Software Engineering! They define a component as:

A software component is a software element that conforms to a component model and can be independently deployed and composed without modification according to a composition standard.

A component model defines specific interaction and composition standards. A component model implementation is the dedicated set of executable software elements required to support the execution of components that conform to the model.

A software component infrastructure is a set of interacting software components designed to ensure that a software system or subsystem constructed using those components and interfaces will satisfy clearly defined performance specifications.

My opinions after 2 years of experience with CBSE in games thought are that object-oriented programming is simply a dead-end. Remember my warning as you watch your components become smaller and smaller, and more like functions packed in components with a lot of useless overhead. Use functional-reactive programming instead. Also take a look at my fresh blog post (which lead me to this question while writing it :)) about Why I switched from component-based game engine architecture to FRP.

CBSE in games papers:

• Component Based Game Development – A Solution to Escalating Costs and Expanding Deadlines?
• A Flexible And Expandable Architecture For Computer Games (404)
• A Software Architecture for Games
• A Generic Framework For Game Development (WebArchive)
• Smart Composition Of Game Objects Using Dependency Injection

CBSE in games web-links (sorted by relevancy):

• Component based objects Wiki (Empty wiki)
• Evolve Your Hierachy
• Game Object Structure: Inheritance vs. Aggregation
• A Data-Driven Game Object System (PDF)
• A Data-Driven Game Object System (PPT)
• Component-based prototyping tool for flash
• Theory and Practice of Game Object Component Architecture (404)
• Entity Systems are the Future of MMOs
• ogre3d.org forum: Component Based Objects
• gamedev.net: Outboard component-based entity system architecture
• gamedev.net: Entity System question
• Brainfold entity-system blog (WebArchive)

There does seem to be a lack of information on the subject. I recently implemented this system, and I found a really good GDC Powerpoint that explained the details that are often left behind quite well. That document is here: Theory and Practice of Game Object Component Architecture

In addition to that Powerpoint, there are some good resources and various blogs. PurplePwny has a good discussion and links to some other resources. Ugly Baby Studios has a bit of a discussion around the idea of how components interact with each other. Good luck!

While not a complete tutorial on the subject of game engine design, I have found that this page has some good detail and examples on use of the component architecture for games.

It is open-source, and available at http://codeplex.com/elephant

Some one’s made a working example of the gpg6-code, you can find it here: http://www.unseen-academy.de/componentSystem.html

or here: http://www.mcshaffry.com/GameCode/thread.php?threadid=732

regards

I am currently researching this exact topic in the many (MANY) threads at GameDev.net and found the following two solutions to be good candidates on what I will develop for my game:

• Critique my component-based entity system
• Outboard component-based entity system architecture -> Lord_Evil's proposal

I researched and implemented this last semester for a game development course. Hopefully this sample code can point you in the right direction of how you might approach this.

class Entity {
public:
    Entity(const unsigned int id, const std::string& enttype);
    ~Entity();

    //Component Interface
    const Component* GetComponent(const std::string& family) const;
    void SetComponent(Component* newComp);
    void RemoveComponent(const std::string& family);
    void ClearComponents();

    //Property Interface
    bool HasProperty(const std::string& propName) const;
    template<class T> T& GetPropertyDataPtr(const std::string& propName);
    template<class T> const T& GetPropertyDataPtr(const std::string& propName) const;

    //Entity Interface
    const unsigned int GetID() const;
    void Update(float dt);

private:
    void RemoveProperty(const std::string& propName);
    void ClearProperties();
    template<class T> void AddProperty(const std::string& propName);
    template<class T> Property<T>* GetProperty(const std::string& propName);
    template<class T> const Property<T>* GetProperty(const std::string& propName) const;

    unsigned int m_Id;
    std::map<const string, IProperty*> m_Properties;
    std::map<const string, Component*> m_Components;
};

Components specify behavior and operate on properties. Properties are shared between all components by a reference and get updates for free. This means no large overhead for message passing. If there's any questions I'll try to answer as best I can.