[Qgis-developer] Map canvas flickers

[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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