Page 227 - DCAP408_WEB_PROGRAMMING

Unit 14: Text and Graphics Output

WPARAM wParam, Notes
LPARAM lParam
);
Parameters

wParam: This parameter is not used.

lParam: This parameter is not used.
Return Value

An application returns zero if it processes this message.
The WM_PAINT message is generated by the system and should not be sent by an application.
To force a window to draw into a specific device context, use the WM_PRINT or
WM_PRINTCLIENT message. Most common controls support the WM_PRINTCLIENT
message.

!
Caution This requires the target window to support the WM_PRINTCLIENT message.
The DefWindowProc function validates the update region. The function may also send the
WM_NCPAINT message to the window procedure if the window frame must be painted and
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.

Notes 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 GetUpdateRectfunction to determine whether
the window has an update region. If GetUpdateRect returns zero, the application should
not call the BeginPaint and EndPaint functions.

Task What does dispatchMessage signify?

Self Assessment

Fill in the blanks:
7. The ......................... message is sent when the system or another application makes a request
to paint a portion of an application’s window.
8. ......................... determines where to send the message.

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