RE: [Algorithms] Introducing COM into existing engine

[Tony C. <to...@mi...>]

>I just ported my little engine to DirectX8 and thought about converting
it
>into a dll (right now you have to include the source) but it seems to
make
>a lot of sense to implement it as COM objects. The thing I like most
about
>COM objects is that you only need to distribute one dll and an
interface
>definition file, whereas with an ordinary dll I would have to
distribute
>the dll plus all headers in the project (since they all include each
other
>somewhere).

That seems like a reasonable approach. It also gives you the advantage
of being easier to migrate to other languages (e.g. VB or C# for writing
tools) should you wish to do so in the future.

>However, I'm not certain which objects should become COM objects. Of
>course I would only want to expose some interface functionality, and I
>would likely hide stuff like CRenderstateNode. But I'm not sure about
>which level of abstraction would be usefull. My engine class is
probably a
>good COM candidate. Maybe the camera too. But what about my vector
class?
>I don't think it would make a good COM object, but it would be nice if
the
>client code could use calls like someObject.InitPosition(CMyVector(0,
0,
>0));

Tiny little data objects like individual vectors are not good candidates
for COM objects. COM is less fine-grained than that - think of supplying
*components* rather than individual data objects.

>As you may have guessed, I'm not too familiar with COM, so here is
another
>question: would you recommend to use ATL or should I write everything
>myself?

If you're not too familiar with COM, you could do a lot worse than read
Don Box's "Essential COM", which is pretty much *the* book on the
subject.

To answer your specific question, ATL is great, although it can take a
little bit of getting used to. Certainly there's no real reason to
endlessly rewrite boilerplate code for class factories, IUnknown
implementations and free-threaded marshaller aggregation when then ATL
just does it all for you.

Tony Cox - DirectX Luminary
Windows Gaming Developer Relations Group
http://msdn.microsoft.com/directx