GetUpdateRgn

The GetUpdateRgn function retrieves the update region of a window by copying it into the specified region. The coordinates of the update region are relative to the upper-left corner of the window (that is, they are client coordinates). 

int GetUpdateRgn(
  HWND hWnd,    // handle of window
  HRGN hRgn,    // handle of region
  BOOL bErase   // erase background flag
);

Parameters

hWnd
Handle to the window with an update region that is to be retrieved.
hRgn
Handle to the region to receive the update region.
bErase
Specifies whether the window background should be erased and whether nonclient areas of child windows should be drawn. If this parameter is FALSE, no drawing is done.

Return Values

The return value indicates the complexity of the resulting region; it can be one of the following values.

Value Meaning
COMPLEXREGION Region consists of more than one rectangle.
ERROR An error occurred.
NULLREGION Region is empty.
SIMPLEREGION Region is a single rectangle.

Remarks

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

Windows CE: The bErase parameter is ignored, the window background is not erased and no drawing is done.

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