RedrawWindow function

The RedrawWindow function updates the specified rectangle or region in a window's client area.

Syntax

BOOL RedrawWindow(
  HWND       hWnd,
  const RECT *lprcUpdate,
  HRGN       hrgnUpdate,
  UINT       flags
);

Parameters

hWnd

A handle to the window to be redrawn. If this parameter is NULL, the desktop window is updated.

lprcUpdate

A pointer to a RECT structure containing the coordinates, in device units, of the update rectangle. This parameter is ignored if the hrgnUpdate parameter identifies a region.

hrgnUpdate

A handle to the update region. If both the hrgnUpdate and lprcUpdate parameters are NULL, the entire client area is added to the update region.

flags

One or more redraw flags. This parameter can be used to invalidate or validate a window, control repainting, and control which windows are affected by RedrawWindow.

The following flags are used to invalidate the window.

Flag (invalidation) Description
RDW_ERASE
Causes the window to receive a WM_ERASEBKGND message when the window is repainted. The RDW_INVALIDATE flag must also be specified; otherwise, RDW_ERASE has no effect.
RDW_FRAME
Causes any part of the nonclient area of the window that intersects the update region to receive a WM_NCPAINT message. The RDW_INVALIDATE flag must also be specified; otherwise, RDW_FRAME has no effect. The WM_NCPAINT message is typically not sent during the execution of RedrawWindow unless either RDW_UPDATENOW or RDW_ERASENOW is specified.
RDW_INTERNALPAINT
Causes a WM_PAINT message to be posted to the window regardless of whether any portion of the window is invalid.
RDW_INVALIDATE
Invalidates lprcUpdate or hrgnUpdate (only one may be non-NULL). If both are NULL, the entire window is invalidated.
 

The following flags are used to validate the window.

Flag (validation) Description
RDW_NOERASE
Suppresses any pending WM_ERASEBKGND messages.
RDW_NOFRAME
Suppresses any pending WM_NCPAINT messages. This flag must be used with RDW_VALIDATE and is typically used with RDW_NOCHILDREN. RDW_NOFRAME should be used with care, as it could cause parts of a window to be painted improperly.
RDW_NOINTERNALPAINT
Suppresses any pending internal WM_PAINT messages. This flag does not affect WM_PAINT messages resulting from a non-NULL update area.
RDW_VALIDATE
Validates lprcUpdate or hrgnUpdate (only one may be non-NULL). If both are NULL, the entire window is validated. This flag does not affect internal WM_PAINT messages.
 

The following flags control when repainting occurs. RedrawWindow will not repaint unless one of these flags is specified.

Flag Description
RDW_ERASENOW
Causes the affected windows (as specified by the RDW_ALLCHILDREN and RDW_NOCHILDREN flags) to receive WM_NCPAINT and WM_ERASEBKGND messages, if necessary, before the function returns. WM_PAINT messages are received at the ordinary time.
RDW_UPDATENOW
Causes the affected windows (as specified by the RDW_ALLCHILDREN and RDW_NOCHILDREN flags) to receive WM_NCPAINT, WM_ERASEBKGND, and WM_PAINT messages, if necessary, before the function returns.
 

By default, the windows affected by RedrawWindow depend on whether the specified window has the WS_CLIPCHILDREN style. Child windows that are not the WS_CLIPCHILDREN style are unaffected; non-WS_CLIPCHILDREN windows are recursively validated or invalidated until a WS_CLIPCHILDREN window is encountered. The following flags control which windows are affected by the RedrawWindow function.

Flag Description
RDW_ALLCHILDREN
Includes child windows, if any, in the repainting operation.
RDW_NOCHILDREN
Excludes child windows, if any, from the repainting operation.

Return value

If the function succeeds, the return value is nonzero.

If the function fails, the return value is zero.

Remarks

When RedrawWindow is used to invalidate part of the desktop window, the desktop window does not receive a WM_PAINT message. To repaint the desktop, an application uses the RDW_ERASE flag to generate a WM_ERASEBKGND message.

Requirements

   
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

See also

GetUpdateRect

GetUpdateRgn

InvalidateRect

InvalidateRgn

Painting and Drawing Functions

Painting and Drawing Overview

RECT

UpdateWindow