Processing the WM_SIZE Message

// This is example assumes, that we have a valid LEAD paint handle and a valid 
// LEAD bitmap handle, and the user has set the bitmap handle in the paint handle 
// ( through the L_PntSetMetrics function ). And also assumes that user has initialized the 
// current horizontal and vertical scrolling position variables 
BITMAPHANDLE g_PaintBitmap ; 
RECT g_rcBitmapView ; 
int g_nHScrollPos ; 
int g_nVScrollPos ; 
L_VOID OnSize ( HWND hWnd, L_UINT nState, L_INT nCx, L_INT nCy ) 
{ 
   SCROLLINFO si ; 
   UNREFERENCED_PARAMETER ( nState ) ; 
    
   if ( g_PaintBitmap.Flags.Allocated ) 
   { 
      si.cbSize = sizeof ( SCROLLINFO ) ; 
      si.fMask  = SIF_ALL ; 
       
      // vertical scroll. 
      GetScrollInfo ( hWnd, SB_VERT, &si ) ; 
       
      si.nMin  = 0 ; 
      si.nMax  = BITMAPHEIGHT ( &g_PaintBitmap ) ; 
      si.nPage = nCy ; 
       
      SetScrollInfo ( hWnd, SB_VERT, &si, TRUE ) ; 
       
      GetScrollInfo ( hWnd, SB_VERT, &si ) ; 
       
      g_nVScrollPos = si.nPos ; 
       
      // horizontal scroll 
      GetScrollInfo ( hWnd, SB_HORZ, &si ) ; 
       
      si.nMin  = 0 ; 
      si.nMax  = BITMAPWIDTH ( &g_PaintBitmap ) ; 
      si.nPage = nCx ; 
       
      SetScrollInfo ( hWnd, SB_HORZ, &si, TRUE ) ; 
       
      GetScrollInfo ( hWnd, SB_HORZ, &si ) ; 
       
      g_nHScrollPos = si.nPos ; 
       
      // set the painting rectangel. 
      SetRect ( &g_rcBitmapView, 0, 0, BITMAPWIDTH ( &g_PaintBitmap ), BITMAPHEIGHT ( &g_PaintBitmap ) ) ; 
       
      OffsetRect ( &g_rcBitmapView, - g_nHScrollPos, - g_nVScrollPos ) ; 
   } 
   else 
   { 
      si.cbSize = sizeof ( SCROLLINFO ) ; 
      si.fMask  = SIF_RANGE ; 
      si.nMin   = 0 ; 
      si.nMax   = 0 ; 
       
      SetScrollInfo ( hWnd, SB_VERT, &si, TRUE ) ; 
      SetScrollInfo ( hWnd, SB_HORZ, &si, TRUE ) ; 
       
      SetRectEmpty ( &g_rcBitmapView ) ; 
   } 
    
   if ( GetFocus ( ) == hWnd ) 
   { 
      PAINTXFORM  PntXForm ; 
      RECT        rcDCRect ; 
       
       
      // set the paint tools DC extents. 
      SetRect ( &rcDCRect, 0, 0, nCx, nCy ) ; 
       
      L_PntSetDCExtents ( pPaint, &rcDCRect ) ; 
       
      // set Painting Transformation. 
      PntXForm.nZoom    = 100 ; 
      PntXForm.nXOffset = - g_rcBitmapView.left ; 
      PntXForm.nYOffset = - g_rcBitmapView.top ; 
       
      L_PntSetTransformation ( g_pPaintHandle, &PntXForm ) ; 
   } 
}