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GetUpdateRect info  Overview  Group

The GetUpdateRect function retrieves the coordinates of the smallest rectangle that completely encloses the update region of the specified window. If the window was created with the CS_OWNDC style and the mapping mode is not MM_TEXT, GetUpdateRect retrieves the rectangle in logical coordinates. Otherwise, it retrieves the rectangle in client coordinates. If there is no update region, GetUpdateRect retrieves an empty rectangle (sets all coordinates to zero).

BOOL GetUpdateRect(

    HWND hWnd,

// handle of window

    LPRECT lpRect,

// address of update rectangle coordinates

    BOOL bErase 

// erase flag



Identifies the window with an update region that is to be retrieved.
Points to the RECT structure that receives the coordinates of the enclosing rectangle.

An application can set this parameter to NULL to determine whether an update region exists for the window. If this parameter is NULL, GetUpdateRect returns nonzero if an update region exists, and zero if one does not. This provides a simple and efficient means of determining whether a WM_PAINT message resulted from an invalid area.

Specifies whether the background in the update region is to be erased. If this parameter is TRUE and the update region is not empty, GetUpdateRect sends a WM_ERASEBKGND message to the specified window to erase the background.

Return Values

If the update region is not empty, the return value is nonzero.

If there is no update region, the return value is zero. To get extended error information, call GetLastError.


The update rectangle retrieved by the BeginPaint function is identical to that retrieved by GetUpdateRect.

BeginPaint automatically validates the update region, so any call to GetUpdateRect made immediately after the call to BeginPaint retrieves an empty update region.

See Also

BeginPaint, GetUpdateRgn, InvalidateRect, RECT, UpdateWindow, ValidateRect

file: /Techref/os/win/api/win32/func/src/f42.htm, 3KB, , updated: 2000/4/7 12:19, local time: 2024/6/18 11:16,

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