InvalidateRgn function (winuser.h)

Article
10/13/2021

The InvalidateRgn function invalidates the client area within the specified region by adding it to the current update region of a window. The invalidated region, along with all other areas in the update region, is marked for painting when the next WM_PAINT message occurs.

Syntax

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

Parameters

[in] hWnd

A handle to the window with an update region that is to be modified.

[in] hRgn

A handle to the region to be added to the update region. The region is assumed to have client coordinates. If this parameter is NULL, the entire client area is added to the update region.

[in] bErase

Specifies whether the background within the update region should be erased when the update region is processed. If this parameter is TRUE, the background is erased when the BeginPaint function is called. If the parameter is FALSE, the background remains unchanged.

Return value

The return value is always nonzero.

Remarks

Invalidated areas accumulate in the update region until the next WM_PAINT message is processed or until the region is validated by using the ValidateRect or ValidateRgn function.

The system 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.

The specified region must have been created by using one of the region functions.

If the bErase parameter is TRUE for any part of the update region, the background in the entire region is erased, not just in the specified part.

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)