You know, "painting into an off screen image is not GUI related"
__should__ be true. Haven't tried it since 4.8.x, but it certainly
wasn't true back then. Desperately wanted to thread off the generating
of many pixmaps which would be later BLITted onto the touch screen as
needed by application. Nope nope nope nope. (Please, don't suggest
alternatives to pre-loading. Embedded device, single core, no GPU trying
to achieve 10 days of run-time battery life. Last I heard, we did it and
we had a responsive GUI touchscreen.)
This "all things GUI in primary thread" philosophy has an awful lot of
real world fallout, especially in the embedded world where RAM is fast
but hardened storage is slooooooow. It also leads to some pretty
horrible database interfaces, in particular when using spreadsheet/table
models to scroll through networked/remote databases with millions of
records where the connection could require several seconds to respond.
Yes, I've had to do some hacks to thread that stuff off, but the primary
examples floating around out there show it all running in the GUI thread.
Roland
On 04/04/2017 01:47 AM, interest-requ...@qt-project.org wrote:
On 04/01/2017 09:48 AM, Dan Allen wrote:
Hi Bill,
I agree, however when the print is quite complex it makes the GUI very
unresponsive.
Painting into an off screen image is not GUI related. The print preview could
show something like "Generating Preview" while a background thread generates it
and then show it when it's ready for example. This would prevent the GUI from
seeming unresponsive to the user. I wasn't sure if there was a current method to
do something like this.
Yes. We agree that the actual printing is non GUI, but if you want
to show a print preview or progress meter, that is GUI and needs
to stay in the main thread.
So, something like:
- Create a progress meter dialog.
- Start your printing in a sub thread.
- The main thread waits, perhaps in a sub-QEventLoop, servicing events.
- After a few seconds, if printing has not completed, show the dialog.
- The sub-event loop monitors the printing process with a thread safe
communication mechanism, like signals and slots.
- When the printing completes, close the dialog.
- Exit your sub-event loop.
Thanks,
Dan Allen.
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Roland Hughes, President
Logikal Solutions
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