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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--
Dr. Marco Hugentobler
Sourcepole - Linux & Open Source Solutions
Weberstrasse 5, CH-8004 Zürich, Switzerland
marco.hugentob...@sourcepole.ch http://www.sourcepole.ch
Technical Advisor QGIS Project Steering Committee
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