BOOL CMainWindow::OnMouseWheel(UINT nFlags,

                              short zDelta,

                              CPoint point)

{

     BOOL bUp = TRUE;

     int nDelta = zDelta;

     if(zDelta < 0) {

         bUp = FALSE;

         nDelta = -nDelta;

     }

     UINT nWheelScrollLines;

     ::SystemParametersInfo(SPI_GETWHEELSCROLLLINES, 0,

         &nWheelScrollLines, 0);

     int nLines = (nDelta * nWheelScrollLines) / WHEEL_DELTA;

     while(nLines--)

         SendMessage(WM_VSCROLL, MAKEWPARAM(bUp ? SB_LINEUP : SB_LINEDOWN, 0), 0);

     return TRUE;

}