It also depends on the "level" of the Engine.
What I mean with that, is how abstract the Engine is from a certain gamestyle. There might be small things like a engine that is focused on a FPS might be built to be optimized for indoor areas, outdoor areas, that you fly at high speed. So even if a Engine might not be locked to a game, certain game types will be easier to implement certain Engines.
But as stated above, the game won't inherit the engine, it will more probably draw on it's functionality, and you will probably attach components to it's existing components. Or expand the components that are part of the engine.
class CoolDiscoLight : public Engine::Light
{
};
...
//and somewhere in the source
"CoolDiscoLight cdl = new CoolDiscoLight etc..."
EngineInstance.AddLight(cdl);
...
Even more probible is the fact that just by extending from light and overloading the correct functions the light will be accessible to a level editor etc so you won't actually create them trough the source at all.
