InvalidateRect function (winuser.h)

Article
10/13/2021

The InvalidateRect function adds a rectangle to the specified window's update region. The update region represents the portion of the window's client area that must be redrawn.

Syntax

BOOL InvalidateRect(
  [in] HWND       hWnd,
  [in] const RECT *lpRect,
  [in] BOOL       bErase
);

Parameters

[in] hWnd

A handle to the window whose update region has changed. If this parameter is NULL, the system invalidates and redraws all windows, not just the windows for this application, and sends the WM_ERASEBKGND and WM_NCPAINT messages before the function returns. Setting this parameter to NULL is not recommended.

[in] lpRect

A pointer to a RECT structure that contains the client coordinates of the rectangle to be added to the update region. 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 is to be erased when the update region is processed. If this parameter is TRUE, the background is erased when the BeginPaint function is called. If this parameter is FALSE, the background remains unchanged.

Return value

If the function succeeds, the return value is nonzero.

If the function fails, the return value is zero.

Remarks

The invalidated areas accumulate in the update region until the region is processed when the next WM_PAINT message occurs 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.

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

Examples

For an example, see Invalidating the Client Area.

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)

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