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Creating holes in a window

, 6 Feb 2000 CPOL
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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" Wink | ;-) .

    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

    Comments and Discussions

    GeneralNice! PinmemberAbu Mami1-May-10 9:53 
    Questioncan i use SetWindowrgn to create hoels on the desktop Pinmemberudayt24-Feb-05 0:35 
    GeneralChild Windows PinmemberJohn Ulvr9-Mar-03 6:58 
    QuestionRegular Windows? PinsussWayne Fuller8-Feb-00 5:43 
    AnswerRe: Regular Windows? PinsussWayne Fuller8-Feb-00 5:50 

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