Re: What is the best way to drive (time) animations?

"Scott McPhillips [MVP]" <org-dot-mvps-at-scottmcp>
Mon, 8 Mar 2010 15:54:28 -0500
"dan" <> wrote in message

"Scott McPhillips [MVP]" <org-dot-mvps-at-scottmcp> wrote in message

There are a couple of possible ways to use timeSetEvent (which comes in
on a system thread) and still do your painting in your main thread. The
first is to call Invalidate on your window's HWND from the timer thread.
That will cause a WM_PAINT. It's debateable whether Invalidate accesses
the window from the thread, but in my experience this is thread safe.

Another possibility is to simply PostMessage or SendMessage a
user-defined message (WM_APP + n) to the HWND. The message handler in
the main thread (use ON_MESSAGE in the message map) can then do
Invalidate or even paint directly. The advantage here is that the
WM_APP+n message is not low priority like WM_TIMER, so you will get a
more consistent frame rate than WM_TIMER can give you.

Scott McPhillips [VC++ MVP]


Thanks for the reply.

I think that calling Invalidate() would be ideal but since I cannot be
absolutely sure that it is thread safe then I need to stay away from it.
If, for example, I get a report about the app locking up once a week (or
even month) I will always tend to think that Invalidate() is the cause.

I was also considering PostMessage() in the past but was afraid that this
would flood the message queue. Do you see any problems with posting ~30
WM_APPn messages a second?

As per my original post, is there a way that I could override CWinApp's
Run() method and use QueryPerformanceCounter() to drive animations? Or,
is this approach not recommended for mfc apps?


PostMessage at 30/second certainly won't flood the message queue if you are
processing the messages. And if the message handler does nothing except
Invalidate() then there's no harm done even if a number of messages build up
in the queue.

Overriding the Run() method with QueryPerformanceCounter-based timing would
be the way to go if you want really smooth animation. Gamers do it that way
(not that they use MFC much). You might have to rewrite the Run() method to
use PeekMessage instead of GetMessage to keep your animation running full
time. If you want that quality level then you should pretty much forget
about WM_PAINT and draw at regular intervals. The only downside is you
gobble up CPU cycles spinnning at QueryPerformanceCounter.

There is no issue of this being "not recommended" for MFC apps: Run() is
virtual so you can do this. But at some point down this road MFC stops being

Scott McPhillips [VC++ MVP]

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