Creating Holes in a Window






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Feb 7, 2000

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How to create a window with holes in it
Let's say you have to create a window inside a window or a hole, just to look outside and say: "Hi" ;-).
It's not so difficult 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 ofCRgn
void ClearHoles()
- clear the holes and return the window to its 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);
}
else
{
// 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");
ClearHoles();
}
if (s == "Show Holes")
{
GetDlgItem (IDC_CLEAR)->SetWindowText ("Clear Holes");
ShowHoles();
}
}
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.
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