[Interest] QPixmap and threads

maitai maitai at virtual-winds.org
Fri May 5 11:21:53 CEST 2017


Ok, thanks all for your comments.

I'll change them all then.

BTW what is the "right format for display? Format_ARGB32_Premultiplied 
maybe?

Philippe.

Le 05-05-2017 10:25, Giuseppe D'Angelo a écrit :
> Il 05/05/2017 09:05, maitai ha scritto:
>> But still, I have hundreds of other QPixmaps used in threads, with no
>> problem at all (creating, painting, etc). All is working fine for 
>> years,
>> without any warning or so from Qt.
> 
> Well, not having problems doesn't imply that what you were doing was 
> correct...
> 
>> Should I change also all these
>> QPixmaps to QImages (with a conversion cost at the end of the 
>> threads)?
> 
> Yes. Note that the conversion cost may be extremely small: QPixmap
> these days is simply holding a QImage in the "right format" for
> display. If your QImage is already in that format, only a cheap
> refcount increase is needed, not a full format conversion.
> 
>> 
>> If QPixmaps are forbidden outside the main GUI thread, why is it not
>> written in the documentation?
> 
> It is implied by the lack of "This class is reentrant" note in QPixmap
> documentation. It's also documented that way in other places, like
> 
> http://doc.qt.io/qt-5/thread-basics.html
> 
> See also slides 27+
> 
>> https://conf.qtcon.org/system/attachments/104/original/multithreading-with-qt.pdf?1473018682
> 
> Cheers,
> 
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