Re: How many msg loop cycles to paint a button?

"Heinz Ozwirk" <>
Tue, 4 Jul 2006 12:57:45 +0200
"KMA" <> schrieb im Newsbeitrag

OK, OK, the question is a bit vague, but there's only so much room in the
subject line. So here's the real question.

For reasons beyond my immediate control I have a program that is designed
so that it continously posts itself messages to do some lengthy (+-30ms )
processing. So it goes:

long HandleUserMessage()
// do lengthy stuff


Clearly, for the 30ms of lengthy stuff, the UI is dead. This much I know.
But the other undesirable effect is that the controls repaint themselves a
l0 windows 3.1 on a 386, i.e. they repaint their borders, then a bit of
text, then a highlight etc. This happens, I assume, because painting of
controls doesn't happen in one msg loop cycle because the button (or
whatever other control) has to post/send messages in order to get the
right text/font whatever, and that these messages are delayed because of
the intermediate UWM_DO_USER_STUFF.

WM_PAINT (and IIRC WM_TIMER) messages are not written to the message queue.
They are kept apart and only returned by GetMessage when there are no other
messages in the queue. So whenever you post another message, updating the UI
will be delayed. The easiest solution would be not to send messages to
trigger your function. Implement OnIdle in your CWinApp derived class and do
your lengthy stuff there. If you cannot do that for whatever reason you
could read and dispatch all messages in the queue before posting your own
message. Somethink like

    while (PeekMessage(... WM_REMOVE))
        if (message is not UWM_DO_USER_STUFF)

So, what I would like to find out is how many msg loop cycles does it take
to paint particular controls. I would like a method that doesn't interfere
with the normal flow of events.

That's not a good idea. That number may change if the number of controls in
your windows changes, or even if the number of items in a list control
changes. Not to mention different Windows versions.

BTW I'm quite aware that I could maybe help things by putting "lengthy
processing" into a thread, but like I said, things aren't entirely within
my control as yet. first I've got to drag an anvil to the top of a cliff
and get my colleague to walk underneath........

Take care to aim well...


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