[Qt-interest] QTimer on Windows in Unreliable for Small (16ms- 30ms) Delays

[Scott Aron Bloom]

But integrating win32 message events into QT can be daunting..

Some hints on doing it
1) Custom qcoreapplication
2) Implement your own winEventFilter

Scott
-----Original Message-----
From: qt-interest-bounces at trolltech.com [mailto:qt-interest-bounces at trolltech.com] On Behalf Of Malyushytsky, Alex
Sent: Friday, September 18, 2009 5:56 PM
To: qt-interest at trolltech.com
Subject: Re: [Qt-interest] QTimer on Windows in Unreliable for Small (16ms- 30ms) Delays

Wouldn't msdn help?

http://msdn.microsoft.com/en-us/library/dd757664%28VS.85%29.aspx

Regards,
 Alex

-----Original Message-----
From: qt-interest-bounces at trolltech.com [mailto:qt-interest-bounces at trolltech.com] On Behalf Of Josiah Bryan
Sent: Friday, September 18, 2009 5:28 PM
To: Thiago Macieira
Cc: qt-interest at trolltech.com
Subject: Re: [Qt-interest] QTimer on Windows in Unreliable for Small (16ms - 30ms) Delays

Thiago Macieira wrote:
> Em Segunda-feira 7. Setembro 2009, às 02.48.17, você escreveu:
>> I'm a bit confused - the description for QTimer says:
>>
>> "Note that QTimer's accuracy depends on the underlying operating system and
>>  hardware." "Most platforms support an accuracy of 1 millisecond, but
>>  Windows 98 supports only 55." "If Qt is unable to deliver the requested
>>  number of timer clicks, it will silently discard some"
>>
>> while you said:
>>> That said, QTimer uses the system timer which is unreliable and
>>> inaccurate. You should use the Windows Multimedia Timers if you
>>> something accurate. In fact, QTimer uses multimedia timers for interval
>>> < 10ms (maybe it's <= 10ms, not sure). You can either use 8ms timer and
>>> process every alternate one or use the Windows MM Timer Api directly.
>> so with Win XP, what is the accuracy of QTimer for periods of greater than
>> 10 msecs - is it 1 millisecond or is it more?  Why doesn't QTimer use the
>> Multimedia Timers for all periods?
>
> Because QTimer isn't a precise timer. It's not guaranteed to be and it doesn't
> pretend to be.
>
> If you need high-precision timers, you'll have to find a way of getting them
> yourself. QTimer is meant for normal-priority tasks where being a few
> milliseconds late is ok. Conserving power (reducing the number of CPU wakeups)
> is more important than precision.
>

Thiago - thanks for replying. Sorry for getting to this so late.

I have no problem with a few milliseconds - heck, even 100 or 200ms is
fine once in a while. But averaging 1000ms delays every 5 - 10 seconds -
thats simply unacceptable. I dont need high-precision, but some
resemblance of reliability would be nice. A jump from 33ms to 1000ms is
not just a few milliseconds, thats several orders of magnitude larger.

If theres no way around the 1000ms jump - would you or anyone else at
trolltech be able to offer any code samples on using Win32 multimedia
timers in a Qt app? I havn't been able to dig up any examples of win32
MM timers + Qt since this thread started - and I've been persistent at
google. I've even tried parsing the Qt source tree for how you folks do
it - but I can't seem to separate the MM-specific parts from the rest of
the core. Anything you can offer would be greatly appreciated.

Thanks!
-josiah


--
Josiah Bryan
Productive Concepts, Inc.
jbryan at pciint.com
(765) 964-6009, ext. 224

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