C / C++ / MFC

TheRect.left    = 0;
TheRect.top     = 0;
TheRect.right   = 1023; // assuming a 1024x768 display
TheRect.bottomn = 767;

"Ideas are a dime a dozen. People who put them into action are priceless." - Unknown

	HWND	hWndDesktop = ::GetDesktopWindow();<br />
	HDC		hDcDesktop = ::GetDC(hWndDesktop);<br />
<br />
	int nX = BOUND(m_ptZoom.x, m_nxZoomed / 2, m_nxScreenMax - (m_nxZoomed / 2));<br />
	int nY = BOUND(m_ptZoom.y, m_nyZoomed / 2, m_nyScreenMax - (m_nyZoomed / 2));<br />
<br />
	RECT rBounding, rErase;<br />
	rBounding.left   = nX - m_nxZoomed / 2;<br />
	rBounding.top    = nY - m_nyZoomed / 2;<br />
	rBounding.right  = rBounding.left + m_nxZoomed;<br />
	rBounding.bottom = rBounding.top  + m_nyZoomed;<br />
	::InflateRect(&rBounding, 1, 1);<br />
<br />
	::CopyRect(&rErase, &rBounding);<br />
	::MapWindowPoints(NULL, hWndDesktop, (LPPOINT)&rErase, 2);<br />
	HRGN hRegion = ::CreateRectRgn(rErase.left, rErase.top, rErase.right, rErase.bottom);<br />
//	::ExtSelectClipRgn(hDcDesktop, hRegion, RGN_OR);<br />
	::InvalidateRgn(hWndDesktop, hRegion, TRUE);<br />
	::UpdateWindow(hWndDesktop);<br />
<br />
	::DeleteObject(hRegion);<br />
	::ReleaseDC(hWndDesktop, hDcDesktop);<br />

hWnd 
   [in] Handle to the window whose update region has changed. If this parameter is NULL, the   
   system invalidates and redraws all windows, and sends the WM_ERASEBKGND and WM_NCPAINT 
   messages to the window procedure before the function returns.

<br />
HWND	hWndDesktop = ::GetDesktopWindow();<br />
<br />
RECT rBounding;<br />
..set rBounding to rectangle in 'screen' coordinates that needs to be erased...<br />
<br />
// RDW_ERASE as per special note for the desktop window<br />
// we want children of desktop to repaint, if they are part of the rectangle.<br />
// seems to work even if area covers a caption, toolbar, <br />
// status bar, control bar, menu, etc. of a child window<br />
::RedrawWindow(hWndDesktop, &rBounding, NULL, RDW_INVALIDATE|RDW_ERASE|RDW_ALLCHILDREN);