[Qgis-developer] Map canvas flickers

[Marco Hugentobler]

Hi Matthias

I still have the resize crash with Qt 4.8.1. To reproduce, load a layer 
with many objects. Go with the mouse to the right corner and resize 
several times without releasing the mouse. After the mouse release, the 
crash occures.
Note: this problem (and the flicker with the workaround) is X11 only. 
But still, Linux is the most important platform.
Btw, the threading branch would be the clean solution for the issue. But 
if you have another workaround in the short-term, let me know.

Regards,
Marco


Am 27.07.2012 13:08, schrieb Matthias Kuhn:
> 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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-- 
Dr. Marco Hugentobler
Sourcepole -  Linux & Open Source Solutions
Weberstrasse 5, CH-8004 Zürich, Switzerland
marco.hugentobler at sourcepole.ch http://www.sourcepole.ch
Technical Advisor QGIS Project Steering Committee