WM_PAINT

This message is sent by an application when Windows or another application makes a request to paint a portion of an application's window. The message is sent when the UpdateWindow function is called, or by the DispatchMessage function when the application obtains a WM_PAINT message by using the GetMessage or PeekMessage function.

WM_PAINT hdc = (HDC) wParam;

Parameters

• hdc
  Handle to the device context to draw in. If this parameter is NULL, use the default device context. This parameter is used by some common controls to enable drawing in a device context other than the default device context. Other windows can safely ignore this parameter.

Return Values

An application should return zero if it processes this message.

Remarks

The DefWindowProc function validates the update region. The function may send the WM_ERASEBKGND message if the window background must be erased.

The system sends this message when there are no other messages in the application's message queue. DispatchMessage determines where to send the message; GetMessage determines which message to dispatch. GetMessage returns the WM_PAINT message when there are no other messages in the application's message queue, and DispatchMessage sends the message to the appropriate window procedure.

A window may receive internal paint messages as a result of calling RedrawWindow with the RDW_INTERNALPAINT flag set. In this case, the window may not have an update region. An application should call the GetUpdateRect function to determine whether the window has an update region. If GetUpdateRect returns zero, the application should not call the BeginPaint and EndPaint functions.

An application must check for any necessary internal painting by looking at its internal data structures for each WM_PAINT message, because a WM_PAINT message may have been caused by both a non-NULL update region and a call to RedrawWindow with the RDW_INTERNALPAINT flag set.

The system sends an internal WM_PAINT message only once. After an internal WM_PAINT message is returned from GetMessage or PeekMessage or is sent to a window by UpdateWindow, the system does not post or send further WM_PAINT messages until the window is invalidated or until RedrawWindow is called again with the RDW_INTERNALPAINT flag set.

For some common controls, the default WM_PAINT message processing checks the wParam parameter. If wParam is non-NULL, the control assumes that the value is an HDC and paints using that device context.

Requirements

Note   This API is part of the complete Windows CE OS package as provided by Microsoft. The functionality of a particular platform is determined by the original equipment manufacturer (OEM) and some devices may not support this API.

See Also

BeginPaint, DefWindowProc, DispatchMessage, EndPaint, GetMessage, GetUpdateRect, PeekMessage, UpdateWindow, WM_ERASEBKGND

 Last updated on Tuesday, July 13, 2004

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