Gets a pointer the the function DWORD stream.
HRESULT GetFunction( LPD3DXBUFFER * ppFunction );
If the method succeeds, the return value is D3D_OK. If the method fails, the return value can be one of the following: D3DERR_INVALIDCALL, D3DXERR_INVALIDDATA.
Header: Declared in D3dx9shader.h.