GetUpdateRect

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
);
 

Parameters

hWnd

Handle to the window with an update region that is to be retrieved.

lpRect

Pointer 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.

bErase

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.

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

Remarks

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.

QuickInfo

  Windows NT: Requires version 3.1 or later.
  Windows: Requires Windows 95 or later.
  Windows CE: Requires version 1.0 or later.
  Header: Declared in winuser.h.
  Import Library: Use user32.lib.

See Also

Painting and Drawing Overview, Painting and Drawing Functions, BeginPaint, GetUpdateRgn, InvalidateRect, RECT, UpdateWindow, ValidateRect