4. Interfaces
The interfaces are the means of communication between the framework, the managers, and the systems. The framework and the managers reside within the engine and therefore the framework has direct access to the managers. The systems, however, reside outside of the engine and have different functionality from each other making it necessary to have a common method for accessing them. Also, the systems do not have direct access to the managers so they also need a method for accessing the managers but not necessarily the full functionality as certain items should only be accessible to the framework.
The interfaces provide a set functionality that needs to be implemented in order to have a common method of access. This makes it unnecessary for the framework to know the details about a specific system as it can communicate to it through a known set of calls.
4.1. Subject and Observer Interfaces
The subject and observer interfaces are used for the registration of the observer with the subject and for passing of change notifications from the subject to the observer. A default subject implementation is also provided as the functionality to handle observer registration/de-registration is common to all subjects.
4.2. Manager Interfaces
The managers, even though they are singletons, are only directly available to the framework which means that the different systems do not have access to them. In order to provide access, each manager would have an interface that exposes a subset of its functionality. The interface would then be passed to the system when it gets initialized and the systems would then have access to a subset of the manager.
The interface defined is dependent upon the manager and therefore is not a common interface but specific to that manager.
4.3. System Interfaces
The systems need to implement interfaces in order for the framework to get access to its components. Without it the framework would have to implement a specific implementation of each new system that gets added to the engine.
There are four components to a system so there are four interfaces a system must implement. They are: System, Scene, Object, and Task. These different components are covered in section 5, "Systems". The interfaces are the means of getting these components. The System interface provides methods for creating and destroying scenes. Scene interfaces provide methods for creating and destroying objects and a method for retrieving the primary task. The Task interface is used by the task manager when issuing tasks within its thread pool.
The scene and object interfaces also derive from the subject and observer interfaces as these are the pieces of the system that need to communicate with one another, and with the universal scene and object they are attached to.
4.4. Change Interfaces
There are also some special interfaces that are used for passing data between the systems. Any systems that make these specific modifications must also implement the interface. An example of this kind of interface is geometry. The geometry interface would have methods for retrieving the position, orientation, and scale for a certain item. Any systems that make modifications to geometry would need to implement this interface so that a different system would be able to access the geometry changes without needing to know about the other system.
