GetUpdateRgn function (winuser.h)

Article
02/22/2024

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).

Syntax

int GetUpdateRgn(
  [in] HWND hWnd,
  [in] HRGN hRgn,
  [in] BOOL bErase
);

Parameters

[in] hWnd

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

[in] hRgn

Handle to the region to receive the update region.

[in] 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 value

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.

Requirements

Requirement	Value
Minimum supported client	Windows 2000 Professional [desktop apps only]
Minimum supported server	Windows 2000 Server [desktop apps only]
Target Platform	Windows
Header	winuser.h (include Windows.h)
Library	User32.lib
DLL	User32.dll
API set	ext-ms-win-ntuser-draw-l1-1-0 (introduced in Windows 8)