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 InvalidateRect

The InvalidateRect function adds a rectangle to the specified window's update region. The update region represents the portion of the window's client area that must be redrawn.

    BOOL InvalidateRect(
      HWND hWnd,           // handle to window
      CONST RECT* lpRect,  // rectangle coordinates
      BOOL bErase          // erase state
    );

Parameters

• 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.
• lpRect
  [in] Pointer to a RECT structure that contains the client coordinates of the rectangle to be added to the update region. If this parameter is NULL, the entire client area is added to the update region.
• bErase
  [in] Specifies whether the background within the update region is to be erased when the update region is processed. If this parameter is TRUE, the background is erased when the BeginPaint function is called. If this parameter is FALSE, the background remains unchanged.

Return Values

If the function succeeds, the return value is nonzero.

If the function fails, the return value is zero.

Windows NT/2000/XP: To get extended error information, call GetLastError.

Remarks

The invalidated areas accumulate in the update region until the region is processed when the next WM_PAINT message occurs or until the region is validated by using the ValidateRect or ValidateRgn function.

The system sends a WM_PAINT message to a window whenever its update region is not empty and there are no other messages in the application queue for that window.

If the bErase parameter is TRUE for any part of the update region, the background is erased in the entire region, not just in the specified part.

Requirements

• Windows NT/2000/XP/Vista: Included in Windows NT 3.1 and later.
• Windows 95/98/Me: Included in Windows 95 and later.
• Header: Declared in Winuser.h; include Windows.h.
• Library: Use User32.lib.

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Notebook exported on Monday, 7 July 2008, 18:56:50 PM Eastern Daylight Time