[Qgis-developer] Map canvas flickers

[Matthias Kuhn]

Thanks for the review and good point.

I'll disable this option and remove it from the dialog on any other than
Q_WS_X11 or do you think this can be useful for Mac as well? (You
diabled some code and mentioned resizing as cause for this)

Regards

On Die, 2012-08-07 at 17:37 +0200, Marco Hugentobler wrote:
> Hi Matthias
> 
> I didn't try it yet, but from a first look at the patch source, it seems 
> to me backbuffering is enabled by default:
> 
> settings.value( "/Map/enableBackbuffer", 1 ).toBool();
> 
> That would be ok on X11. But the windows users (who are not affected by 
> the flickering) would loose the paint update / esc key interrupt without 
> having an advantage. So either always execute processEvents() in vector 
> layer for windows or disable backbuffer by default.
> 
> Apart from that, the patch looks fine and I'm happy to apply it.
> 
> Regards,
> Marco
> 
> Am 07.08.2012 11:02, schrieb Matthias Kuhn:
> > Hi all,
> >
> > There is now a config option to turn this fix on and off
> > ( Setting=>Options=>Rendering: Enable backbuffer )
> >
> > The more people that test it, the better are the chances to get this
> > into the main code.
> >
> > Thanks to everybody who is participating in this discussion and testing!
> >
> > On Fre, 2012-07-27 at 13:08 +0200, Matthias Kuhn wrote:
> >> Hi all,
> >>
> >> there is this issue report #4011 "Map canvas flickers when content is
> >> dragged" which is actually pretty annoying and doesn't get much
> >> attention. ( http://hub.qgis.org/issues/4011 ) I think the solution
> >> would be pretty simple. Please read on.
> >>
> >> It was introduced by f4d26d6211830a866030a333236dcfbf15e077aa "Fix for
> >> resize crash, ticket #2714".
> >> This bugfix disables backbuffering, what fixes the crash but leads to
> >> the beforementioned flickering.
> >>
> >> The crash seems to be related to Qt versions (probably 4.6 and 4.7
> >> affected). When I tried to reproduce the crash in 4.8.1 (by reverting
> >> abovementioned patch) I couldn't reproduce the crash. So it is well
> >> possible that this problem has been fixed in Qt upstreams.
> >>
> >> But: I myself never could reproduce this crash (due to the lack of a
> >> system with old Qt libs). So, I would be happy if someone familiar with
> >> this problem could confirm that this is fixed with Qt 4.8.
> >>
> >> Then there are two possibilities (unless you come up with a third one):
> >>
> >> 1. Check for qVersion upon every repaint as suggested by Martin Dobias
> >> and then enable/disable the workaround accordingly.
> >>
> >> 2. Switch the workaround on/off by a pre-compiler constant. This way,
> >> any new distro with Qt>=4.8 could be shipped without the workaround-code
> >> being compiled into the binaries.
> >>
> >> Any comments on this issue are very welcome, as it makes QGIS look a lot
> >> sweeter :)
> >>
> >> Regards
> >>
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