Find index of particular function in COM Interface's Vtable

Question

I'm trying to hook the SetCooperativeLevel function in the DirectDraw object. My goal is very similar to the one in this question API Hook on a COM object function? however the only problem is that I don't know the exact offset in IDirectDraw's vtable for SetCooperativeLevel. Is there anyway to glean this from perhaps <ddraw.h> or programatically?

Here's the interface declaration for IDirectDraw, however I'm unsure how this corresponds to the vtable.

DECLARE_INTERFACE_( IDirectDraw, IUnknown )
{
    STDMETHOD(QueryInterface) (THIS_ REFIID riid, LPVOID FAR * ppvObj) PURE;
    STDMETHOD_(ULONG,AddRef) (THIS)  PURE;
    STDMETHOD_(ULONG,Release) (THIS) PURE;
    STDMETHOD(Compact)(THIS) PURE;
    STDMETHOD(CreateClipper)(THIS_ DWORD, LPDIRECTDRAWCLIPPER FAR*, IUnknown FAR * ) PURE;
    STDMETHOD(CreatePalette)(THIS_ DWORD, LPPALETTEENTRY, LPDIRECTDRAWPALETTE FAR*, IUnknown FAR * ) PURE;
    STDMETHOD(CreateSurface)(THIS_  LPDDSURFACEDESC, LPDIRECTDRAWSURFACE FAR *, IUnknown FAR *) PURE;
    STDMETHOD(DuplicateSurface)( THIS_ LPDIRECTDRAWSURFACE, LPDIRECTDRAWSURFACE FAR * ) PURE;
    STDMETHOD(EnumDisplayModes)( THIS_ DWORD, LPDDSURFACEDESC, LPVOID, LPDDENUMMODESCALLBACK ) PURE;
    STDMETHOD(EnumSurfaces)(THIS_ DWORD, LPDDSURFACEDESC, LPVOID,LPDDENUMSURFACESCALLBACK ) PURE;
    STDMETHOD(FlipToGDISurface)(THIS) PURE;
    STDMETHOD(GetCaps)( THIS_ LPDDCAPS, LPDDCAPS) PURE;
    STDMETHOD(GetDisplayMode)( THIS_ LPDDSURFACEDESC) PURE;
    STDMETHOD(GetFourCCCodes)(THIS_  LPDWORD, LPDWORD ) PURE;
    STDMETHOD(GetGDISurface)(THIS_ LPDIRECTDRAWSURFACE FAR *) PURE;
    STDMETHOD(GetMonitorFrequency)(THIS_ LPDWORD) PURE;
    STDMETHOD(GetScanLine)(THIS_ LPDWORD) PURE;
    STDMETHOD(GetVerticalBlankStatus)(THIS_ LPBOOL ) PURE;
    STDMETHOD(Initialize)(THIS_ GUID FAR *) PURE;
    STDMETHOD(RestoreDisplayMode)(THIS) PURE;
    STDMETHOD(SetCooperativeLevel)(THIS_ HWND, DWORD) PURE;    // I'm trying to hook this
    STDMETHOD(SetDisplayMode)(THIS_ DWORD, DWORD,DWORD) PURE;
    STDMETHOD(WaitForVerticalBlank)(THIS_ DWORD, HANDLE ) PURE;
};

Answer 1

Answering my own question: The vtable is laid out in exactly the same order the interface functions are declared.