🔒 Locked

COM & DirectX References

Started by Shannon Barber Jun 26, 2000 at 9:48 PM 2 replies 350+ views

Original Post

Shannon Barber

Mod

368

Shannon Barber

Jun 26, 2000 at 9:48 PM

Is it possible to create a reference to a DirectX object? (or any COM object for that matter...) This appears to work...

        
class CFrame
{
public:
CFrame(hInstance newInst, int newShowCmd, IDirectDraw7* lpDD7): DD7(*lpDD7)
{
//WinAPI stuff..

}
private:
IDirectDraw7& DD7;
};

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nShowCmd)
{
IDirectDraw7* lpDD7;
HRESULT hr;
hr = DirectDrawCreateEx(NULL, (VOID**)&lpDD7, IID_IDirectDraw7, NULL);

CFrame* Capsule;

Capsule = new CFrame(hInstance, nShowCmn, lpDD7);

}

Yes it works! Object.Method(); is faster than pObject->Method(); right? I'm not missing something that makes them same, am I? If there's a single other person out there who does not think I am delusional, I'd be happy to hammer out some object designs that take advantage of this... Edited by - Magmai Kai Holmlor on 6/26/00 10:08:32 PM

Kylotan

Mod

3,487

Kylotan

Jun 27, 2000 at 7:00 AM

quote:

Object.Method();
is faster than
pObject->Method();
right?

Wrong

For 2 reasons. Here''s 3 variable declarations:

Object LocalObject;
Object* HeapObjectPtr = new Object;
Object& HeapObjectRef = *HeapObjectPtr;

First issue: A reference is not the same as a local object. It is merely a nicely-disguised pointer. So, just because:
LocalObject.Method()
and
HeapObjectRef.Method()
look similar, it doesn''t mean that the second one is not dereferencing a pointer. Behind the scenes, it is the same as HeapObjectPtr->Method().

Second issue: All calls to Method(), since it is a member function, will be translated internally to something like this:

Method(Object* aPtr, any other parameters);

For LocalObject, it will just pass its address (which will correspond to a position on the stack) as the ''this'' pointer. For HeapObjectPtr, it will just pass HeapObjectPtr in directly. For HeapObjectRef, it will pass in HeapObjectRef as a pointer, as they are fundamentally the same thing to the underlying system.

So the actual call itself is almost exactly the same. And accessing member variables from within Method() will be the same, as they will all be accessed through the ''this'' pointer, ie. dereferenced. The fact that all 3 forms translate to pretty much the same thing means that the misconception in the first issue is irrelevant... but I wanted to point it out anyway