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Posted 6 Feb 2000

Creating holes in a window

, 6 Feb 2000
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How to create a window with holes in it
  • Download source files - 12 Kb

    Sample Image - holes.gif

    Lets say you have to create a window inside a window or a hole, just to look outsite and say: "Hi" ;-).

    It's not so diffcult to accomplish - actually it's pretty easy. The keyword is SetWindowRgn - which sets the window border to the specified CRgn. You can also invert the CRgn (RGN_XOR) and create a hole inside the window. I've created 2 functions for this:

    • void CreateHole(CRgn& rgn) - creates the hole in the shape of CRgn.
    • void ClearHoles() - clear the holes and return the window to it's usual shape.
    void CHolesDlg::CreateHole(CRgn& rgn)
        CRgn WindowRgn;
        CRgn HoleRgn;
        static CRgn ThisRgn;
        CRect WindowRect;
        static bool Start = true;
        GetWindowRect (WindowRect);   // Get the Window rect
        WindowRgn.CreateRectRgn (0,0,WindowRect.Width (), WindowRect.Height());
        // initialize the hole region
        HoleRgn.CreateRectRgn (0,0,0,0);
        if (Start)
           // initialize ThisRgn
           ThisRgn.CreateRectRgn (0,0,0,0);
           // First copy the region himself in ThisRgn
           ThisRgn.CopyRgn (&rgn);
           // Other times, Add the new region to ThisRgn
           ThisRgn.CombineRgn (&ThisRgn, &rgn, RGN_OR);
        Start = false;
        // create the border of the hole(s) with ThisRgn and set it in that
        // border by reversing it
        HoleRgn.CombineRgn (&ThisRgn, &WindowRgn, RGN_XOR);
        SetWindowRgn ((HRGN__*)HoleRgn.m_hObject, TRUE);
    void CMyControl::ClearHoles()
        CRect WindowRect;
        CRgn WindowRgn;
        GetWindowRect (WindowRect);
        WindowRgn.CreateRectRgn (0,0,WindowRect.Width (), WindowRect.Height());
        // Get back to the classic border
        SetWindowRgn ((HRGN__*)WindowRgn.m_hObject, TRUE);
    void CMyControl::OnClear()
        // TODO: Add your control notification handler code here
        CString s;
        GetDlgItem (IDC_CLEAR)->GetWindowText (s);
        if (s == "Clear Holes")
           GetDlgItem (IDC_CLEAR)->SetWindowText ("Show Holes");
        if (s == "Show Holes")
           GetDlgItem (IDC_CLEAR)->SetWindowText ("Clear Holes");

    In my example I show 4 shaped holes in a dialog-based application (VC++ 6.0, Windows 98). It should work well for other controls as well.

  • License

    This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


    About the Author

    Amir Zalzberg
    Israel Israel
    No Biography provided

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    Comments and Discussions

    Questioncan i use SetWindowrgn to create hoels on the desktop Pin
    udayt23-Feb-05 23:35
    memberudayt23-Feb-05 23:35 

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