[Interest] QThread and QPixmap::grabWindow()

[Rainer Wiesenfarth]

Am 08.08.2013 00:11, schrieb Alexander Syvak:
> [...]
>     auto const this_thread = this->thread ();
>     moveToThread (QApplication::instance()->thread());
>     screenshot = QPixmap::grabWindow( QApplication::desktop()->winId() );
>     moveToThread(this_thread);
> [...]

I think you might have a problem in understanding threads and the thread 
context as used in Qt. moveToThread() does NOT change the thread the 
current code runs in! It only changes the target for events sent to this 
object.

In your example, the thread that executes this->thread() is identical to 
the one that executes QPixmap::grabWindow().

You will have to implement synchronization between the main (GUI) thread 
and your workers. The workers send an event to the main thread each time 
they need a screenshot, the main thread picks up the event, takes the 
screenshot and sends an event back to the "caller". The addressed worker 
thread then picks up this event and processes the screenshot.

If you have only one worker, you might wrap up your processing in a 
single method and use QtConcurrent::run().

Best Regards / Mit freundlichen Grüßen
Rainer Wiesenfarth

-- 
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