HOWTO: Work With Invalid Rectangle When Window Is Resized

• The Microsoft Foundation Classes (MFC) included with:

      - Microsoft Visual C++, 32-bit Editions, versions 4.0, 4.1, 4.2, 5.0
      - Microsoft Visual C++ for Windows, 16-bit edition, version 1.52
  

SUMMARY

This article describes how to work with the invalidated rectangle that is created when a window is resized.

MORE INFORMATION

To optimize painting in an MFC program, you can usually call GetClipBox() in your view's OnDraw() function to get the invalid rectangle and paint only in this area. However, if the user resizes the window, GetClipBox() l always returns the whole client area. This happens because the "window class" used for CView and CFrameWnd has the styles CS_VREDRAW and CS_HREDRAW. These styles cause the whole window to be invalidated whenever the window is resized. To work around this problem, you have to register your own window class for the view and the frame which do not have the class styles of CS_VREDRAW and CS_HREDRAW. You can register the class name in InitApplication() and use the class name in PreCreateWindow().

Sample Code

   class CTestApp : public CWinApp
   {
   public:
      CString m_strMyClassName;
   ...
   }

   BOOL CTestApp::InitApplication()
   {
   // Register our own class with the same attributes as AfxFrameOrView"
   // refer to MFC Tech Note 1: Window Class Registration for more
   // information.
         m_strMyClassName = AfxRegisterWndClass (0, ::LoadCursor (NULL,
                            IDC_ARROW), (HBRUSH)(COLOR_WINDOW+1),
                            LoadIcon(AFX_IDI_STD_FRAME));

         return CWinApp::InitApplication();
   }


   BOOL CMainFrame::PreCreateWindow(CREATESTRUCT& cs)
   {
         CTestApp* pApp = (CTestApp*)AfxGetApp ();
         //  Change the class name to our own name.
         cs.lpszClass = (const char *)(pApp->m_strMyClassName);

         return CFrameWnd::PreCreateWindow(cs);
   }


   BOOL CTestView::PreCreateWindow(CREATESTRUCT& cs)
   {
         CTestApp* pApp = (CTestApp*)AfxGetApp ();
         //  Change the class name to our own name.
         cs.lpszClass = (const char *)(pApp->m_strMyClassName);

         return CView::PreCreateWindow(cs);
   }

Keywords          : MfcUI
Version           : WINDOWS:1.52; WINNT:4.0,4.1,4.2,5.0
Platform          : WINDOWS winnt
Issue type        : kbhowto