Processing Window Scrolling Messages

// This is example asumes, that we have a valid LEAD paint handle and a valid 
// LEAD bitmap handle, and the user has initialzied the current horizontal 
// and vertical scrolling position variables 
BITMAPHANDLE g_PaintBitmap ; 
RECT                       g_rcBitmapView ; 
int                             g_nHScrollPos ; 
int                             g_nVScrollPos ; 
L_VOID OnHScroll ( HWND hWnd, HWND hWndCtl, L_UINT nCode, L_INT nPos ) 
{ 
   SCROLLINFO si ; 
   PAINTXFORM PntXForm ; 
   UNREFERENCED_PARAMETER ( nPos ) ; 
   UNREFERENCED_PARAMETER ( hWndCtl ) ; 
   si.cbSize = sizeof ( SCROLLINFO ) ; 
   si.fMask  = SIF_ALL ; 
   GetScrollInfo ( hWnd, SB_HORZ, &si ) ; 
    
   g_nHScrollPos = si.nPos ; 
   switch ( nCode ) 
   { 
      case SB_LINELEFT: 
      si.nPos -= 1 ; 
      break ; 
       
      case SB_LINERIGHT: 
      si.nPos += 1 ; 
      break ; 
       
      case SB_PAGELEFT: 
      si.nPos -= si.nPage ; 
      break ; 
       
      case SB_PAGERIGHT: 
      si.nPos += si.nPage ; 
      break ; 
       
      case SB_THUMBTRACK: 
      si.nPos = si.nTrackPos ; 
      break ; 
       
default: 
      break ; 
   } 
   si.fMask = SIF_POS ; 
   SetScrollInfo ( hWnd, SB_HORZ, &si, TRUE ) ; 
   GetScrollInfo ( hWnd, SB_HORZ, &si ) ; 
    
   if ( si.nPos != g_nHScrollPos ) 
   { 
      // update screen. 
      OffsetRect ( &g_rcBitmapView, ( g_nHScrollPos - si.nPos ), 0 ) ; 
      ScrollWindow ( hWnd, ( g_nHScrollPos - si.nPos ), 0, NULL, NULL ) ; 
      g_nHScrollPos = si.nPos ; 
      UpdateWindow ( hWnd ) ; 
       
      // set Painting Transformation. 
      PntXForm.nZoom    = 100 ; 
      PntXForm.nXOffset = - g_rcBitmapView.left ; 
      PntXForm.nYOffset = - g_rcBitmapView.top ; 
      L_PntSetTransformation ( g_pPaintHandle, &PntXForm ) ; 
   } 
}