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InvalidateRect info  Overview  Group

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 of window with changed update region

    CONST RECT *lpRect,

// address of rectangle coordinates

    BOOL bErase

// erase-background flag



Identifies the window whose update region has changed. If this parameter is NULL, Windows invalidates and redraws all windows, and sends the WM_ERASEBKGND and WM_NCPAINT messages to the window procedure before the function returns.
Points 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.
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. To get extended error information, call GetLastError.


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.

Windows 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 given part.

See Also

BeginPaint, InvalidateRgn, RECT, ValidateRect, ValidateRgn, WM_ERASEBKGND, WM_NCPAINT, WM_PAINT 

file: /Techref/os/win/api/win32/func/src/f50_6.htm, 3KB, , updated: 2000/4/7 12:19, local time: 2024/6/22 14:46,

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