[in, out] Pointer to a SCROLLINFO structure. Before calling GetScrollInfo, set the cbSize member to sizeof(SCROLLINFO), and set the fMask member to specify the scroll bar parameters to retrieve. Before returning, the function copies the specified parameters to the appropriate members of the structure.
The fMask member can be one or more of the following values.

SIF_PAGE
Copies the scroll page to the nPage member of the SCROLLINFO structure pointed to by lpsi.
SIF_POS
Copies the scroll position to the nPos member of the SCROLLINFO structure pointed to by lpsi.
SIF_RANGE
Copies the scroll range to the nMin and nMax members of the SCROLLINFO structure pointed to by lpsi.
SIF_TRACKPOS
Copies the current scroll box tracking position to the nTrackPos member of the SCROLLINFO structure pointed to by lpsi.