C++/VB - Making userdefined messages like WM_PAINT or WM_QUIT

Asked By Faisal

08-Feb-10 04:43 AM

Raymond Chen's blog says, messages like WM_PAINT, WM_QUIT messages are
treated in special way.
http://blogs.msdn.com/oldnewthing/archive/2005/11/04/489028.aspx

ie, even if more than one message is posted, system combines the
messages only once the windowprocedure is called.
I need this behaviour for a WM_APP or registered message. Is it
possible?

08-Feb-10 05:21 AM

You'd need to roll it yourself - use PeekMessage to filter for your
specific message.

Dave

08-Feb-10 09:56 AM

04/489028.aspx

As David said, you can roll your own easily and I do not know of any
mechanics supported by the system either.

That said... it is a strange question. It seems to me that you are not
asking with an explanation of a problem, but with an explanation of a
solution. That's usually a wrong way to ask. What exactly are you
trying to do? If you explain your problem, someone could help much
better.

And finally, could it be that some OnIdle scheme could work for your
case, did you consider that?

Goran.

08-Feb-10 11:35 AM

See below...

****
I agree.  This is another "How do I implement this solution?" instead of "How do I solve
this problem?" question.

The answer is: you cannot implement this solution.  Don't even waste time trying.

BUT: if you state your problem, there might be a half-dozen different ways of handling it
effectively.  We would have to know what kind of information you want to combine and the
specification of what "combine" means.

THe OnIdle suggestion below is one of the many ways you can tackle this.  There are
others.  Questions include whether or not these messages are created in a single thread or
in multiple threads, and sent via SendMessage or PostMessage.

Note that WM_PAINT is not an official message, and in fact they are not "combined".  What
is combined is the collection of invalidated regions in your client area; when the
WM_PAINT is eventually generated it reports the clipping region as the union of all
invalidated regions.  This is only because the creation of the message is deferred.  In
your case, you either have to come up with a way of deferring the message, or a way of
joe
****
Joseph M. Newcomer [MVP]
email: newcomer@flounder.com
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08-Feb-10 01:16 PM

Just a clarification: I said WM_PAINT is not an official message.  This means it NEVER,
EVER appears in the message queue; it is never sent via SendMessage or PostMessage.  It is
an entirely synthetic message, created whenever the low-level GetMessage handler feels
like it, specifically, it feels like it if there are no other messages in the queue and
there are no timers pending.
joe


Joseph M. Newcomer [MVP]
email: newcomer@flounder.com
Web: http://www.flounder.com
MVP Tips: http://www.flounder.com/mvp_tips.htm