Aero effect Shadow, and transparency goes away if Rgn APIs are used

[Deepak_Sharma]

hello,

i have a Default MFC Application, and i have an imaginary Rectangle(larger then MFC Apps) in the Desktops,
i want to clip the MFC applications when it moves beyond that rectangle. here is what i have been doing
i used SetWindowRgn() with the offset rects, and i am able to clip it.

if ( pRect->right > 800)
	{
		
		int delta = pRect->right - 800;

		HRGN  hgn = CreateRectRgn(0,0, rc.Width() -delta, rc.Height());

		HRGN hrgntemp = CreateRectRgn(0,0,0,0);
		int regionType = GetWindowRgn(hrgntemp);
		if (regionType != ERROR)
		{
			DeleteObject(hrgntemp);
			SetWindowRgn(hgn, TRUE);
		}
		else
		{
			SetWindowRgn(hgn, TRUE);
		}
		

	}

but for some unknown reason, the tranperency and shadow effect goes away when i am using SetWindowRgn, is there any way to keep transperance and Shodow effect.

then i dug more that found that there is a message(WM_DWMNCRENDERINGCHANGED fRenderingEnabled:False) that is sent to my widnow when i apply region API, and when i delete it same message with true (WM_DWMNCRENDERINGCHANGED fRenderingEnabled:True) is sent. looks windows itself is doing it, is there any way to prevent it?

i added a message handle on WM_DWMNCRENDERINGCHANGED message and then try to re-enable it, but strangly for the first time it works multiple tries it does not work.

LRESULT CMonitorTestAppDlg::OndwmncRenderingChanged(WPARAM wp, LPARAM lp)
{
	if(wp == TRUE)
	{
		OutputDebugString(L"Nc Rendereing Enabled\n");
	}
	else
	{
		OutputDebugString(L"Nc Rendereing disabled\n");
		EnableNCRendering(m_hWnd);
	}

	return 0;
}

HRESULT EnableNCRendering(HWND hwnd)
{
   HRESULT hr = S_OK;
   DWMNCRENDERINGPOLICY ncrp = DWMNCRP_ENABLED;

   // Disable non-client area rendering on the window.
   hr = DwmSetWindowAttribute(hwnd, DWMWA_NCRENDERING_POLICY, &ncrp, sizeof(ncrp));

   if (SUCCEEDED(hr))
   {
      // Do work here. 
   }
 
   return hr;
}

Any clue when using region deactivates Aero Effects, is there any way to fix it

regards
Deepak