Monday, December 5, 2011

Make your Engine more dynamic!

When I started to program my Engine, I wanted to create a somewhat portable Engine.
I wanted to support different libraries like OpenGL, OpenAL or DirectX to make my Engine run under Windows and other platforms.

My first attempt was to differentiate with the Preprocessor variables given by the OS
(For example _WIN32 under Windows).

That worked, but was somewhat ugly...

It was indeed so ugly that I decided to give it another try.
So I split everything into separate dynamic libraries.

At the end I had one library for every replaceable feature of my engine.
Here are some of them:

K15_GraphicModule.dll /
K15_SoundModule.dll /
K15_InputQueueModule.dll /
They were implement as subsystems.

I'll try to explain the idea behind the subsystems by the example of the GraphicModule.

The GraphicModule is, for example, a subsystem of the Engine's GraphicManager.
The GraphicManager will try to find a "K15_GraphicModule.dll" or "" (depends on the OS) in it's initialize function. When it finds the dynamic library, it loads it and tries to perform the function "createGraphicModule()" within the library.

The function createGraphicModule will return an implementation of a GraphicModule interface that is declared inside the Engine's library file.

Here's some code to clarify my example.

      typedef createGraphicModule IGraphicManagerModule* (*createGraphicModule)(void);  
      DynLib graphicLib("K15_GraphicModule") // load library (without extension...Determined by the current OS)  
      if(graphicLib.loadedSuccessful()){ //Check if library has been loaded.  
           createGraphicModule func = (createGraphicModule)graphiclib.getFuction("createGraphicModule");  
           if(func != NULL){ // function loaded?  
                this->m_subsystem = func(); //get Subsystem from dynamic library.  

This system allows me to switch between OpenGL and DirectX just by replacing the dynamic library files...Or to switch from Windows File Manager to some Unix File Manager just by replacing the library file.

I just implemented this system about a few days ago, so I don't know how well that will work in an actual game...But it's only a matter of time 'till I know it ;-)