[Nel] Drivers interface pb

[Vincent Caron]

Hello,

I just implemented a portable class to portably manipulate DLLs at 
runtime (bad and non portable code is duplicated in several places of 
NeL). It's called CModule, goes in 'misc', and is straightforward.

  http://zerodeux.net/misc/nel/module.patch

I tried to port 3D/DRU, but ran in a design pb. There's currently no 
mean to properly unload/free a driver. And there's a curious 'OpenGL' 
tying interface countering your efforts to make a portable 3D driver 
interface. In more details :

- There should not but such a CDRU::createGlDriver()

- There should be a :

    static IDriver* IDriver::createDriver(const std::string& module);

  We would currently load NL3D_DLL_NAME, of course ...

- And if you want to be able to release the module handle by destroying 
the IDriver instance, you'll have to give the module ownership to the 
driver:
  * pass it to the instance at init time
  * store it (use a CModule IDriver::_module member)
  * destroy it when needed (in ~IDriver())

--

It would be a little less ackward to have a CDriverHost class, holding 
the module reference, loading/instanciating/unloading the real driver. 
Example :

class CDriverHost
{
public:
  CDriverHost()
  {
    _module = NULL;
    _driver = NULL;
  }

  virtual ~CDriverHost()
  {
    if (_driver) delete _driver;
    if (_module) delete _module;
   }

  bool load(const std::string& moduleName)
  {
    if (_module) return false;
    nlassert(_driver == NULL);

    CModule* module = new CModule(moduleName);
    if (module->load() && onLoad(module))
      _module = module;
    else
      delete module;
  }

  IDriver* getDriver() const { return _driver; }

protected:
  void setDriver(IDriver* driver) { _driver = driver; }

  virtual bool onLoad(CModule* module) = 0;

private:
  CModule* _module;
  IDriver* _driver;
};

You can easily implement a 3D driver host by overloading the onLoad() 
method and doing the specific DLL and entry point discovery here.

I'd be interested in implementing the last solution, at least for the 3D 
and audio drivers.