QGIS » QGIS Application

Just wanted to update this issue as it is still a big problem on Ubuntu. The MapCanvas still flickers constantly as the map is panned. It also constantly flickers in the 'dirty' rectangle while creating or editing shapes. The flicker is bad enough that QGIS is not usable for editing vectors. The problem is apparent in the master version (27/Oct/2011) and also in the final_1-7-1 tag, built on Kubuntu 11.10. The flickering is not apparent if you check out the commit before the one indicated above.

Roland

I can replicate on ubuntu 11.10 running xfce4

see

http://www.youtube.com/watch?v=w3xO21xXxeI

I see it too... but I am almost sure that until a few days ago (qgis master on Ubuntu) it wasn't doing it.

Tim Sutton wrote:

I can replicate on ubuntu 11.10 running xfce4

see

http://www.youtube.com/watch?v=w3xO21xXxeI

See also #3771

I reverted patch f4d26d6211830a866030a333236dcfbf15e077aa and the flicker disappeared. (This makes sense, as this patch disabled back-buffering)

I then tried to reproduce bug #2714 but QGis wouldn't crash (Qt version 4.8.1). Maybe this issue is solved in qt meanwhile?

Matthias Kuhn wrote:

I reverted patch f4d26d6211830a866030a333236dcfbf15e077aa and the flicker disappeared. (This makes sense, as this patch disabled back-buffering)

I then tried to reproduce bug #2714 but QGis wouldn't crash (Qt version 4.8.1). Maybe this issue is solved in qt meanwhile?

Can anyone of the main developers leave feedback on this? If we can get rid of flickering it would be great... Thanks.

It would be helpful to find out which versions of Qt produce the crashed from #2714 - for those ones the workaround could be kept (checking qVersion) and for the rest there would be flicker-free dragging.

Martin Dobias wrote:

It would be helpful to find out which versions of Qt produce the crashed from #2714 - for those ones the workaround could be kept (checking qVersion) and for the rest there would be flicker-free dragging.

can anyone help give an answer to Martin question?

I also have this problem, both in Debian squeeze, wheezy, Xubuntu and Lubuntu 12.04, and on different machines.

I leave here another screencast that shows the problem - http://goo.gl/URAVh

QGIS 1.7.4 and 1.8.

Looking at Marcos update for Issue #2714 it could be reproduced with at least Qt 4.6.2 and 4.7.

Regarding the fact that upcoming releases probably only in very rare cases will run with affected Qt versions I'd propose to use this fix with a pre-compiler switch. This would prevent the (admittedly small) overhead of asking the Qt version on every repaint. A warning could be thrown if one tries to compile on a system with [Qt < 4.8 && OS != Linux] without the fix.

Matthias Kuhn wrote:

Looking at Marcos update for Issue #2714 it could be reproduced with at least Qt 4.6.2 and 4.7.

Regarding the fact that upcoming releases probably only in very rare cases will run with affected Qt versions I'd propose to use this fix with a pre-compiler switch. This would prevent the (admittedly small) overhead of asking the Qt version on every repaint. A warning could be thrown if one tries to compile on a system with [Qt < 4.8 && OS != Linux] without the fix.

please raise this issue/discussion/proposal in the developer mailing list. It is a pretty serious issue and nobody seems to care much.

Qt 4.8.1 is also still affected (see ![Qgis-developer] Map canvas flickers)

Anyone affected by this issue please give a try to this fork/branch

https://github.com/matthias-kuhn/Quantum-GIS/tree/release-1_8

it includes a patch that adds an option to enable/disable backbuffer.

Fixed on master

New config option in Settings=>Options=>Rendering=>Enable backbuffer
(Only X11 / Linux )

If enabled, drawing is flickerfree, but rendering can't be cancelled (by clicking esc and no incremental feature drawing is possible)

A good fix will be available as soon as threading branch is merged

487879df520e74fed0e0cd06a909b6025ae00c43

Hello,

I am using the QGIS 1.8 debian wheezy build from 'http://qgis.org/debian/ wheezy main' repository, the flickering bug remains on Debian Wheezy stable using KDE, and there is no 'enable backbuffer' option at all anywhere in the settings that I can find.

I would have reported this problem a few months ago but instead began using the 1.9 nightly builds until the dependencies broke over the weekend (not complaining about this -- it is a nightly after all). That coupled with some other problems in 1.9 makes it necessary to use 1.8, but the flicker is so pronounced it is unusable.

Thank you.

there is no 'enable backbuffer' option at all anywhere in the settings that I can find.

there are no backports.

I got the flickering to go away in KDE by changing some settings in System Settings > Qt Graphics System > Configure the default graphics system of Qt appliations > Default (X11/XRender)

It was set to Raster before - switching to X11/XRender might help for users on KDE for now.

Everything renders smooth now, no flickers for my KDE desktops anymore.

Giovanni Manghi wrote:

Alexander Bruy wrote:

Fix from 487879df52 introduces another problem. When backbuffer enabled and layers loaded into map then any docked windows like MessageLog or SEXTANTE toolbox are opened with artifacts, e.g. some GUI elements are not rendered. To reproduce:

1. enable backbuffer
2. load any wms layer
3. open MessageLog

does not happen here/anymore, can you check again?

If we can't reproduce it, I think that we can close this issue.
If it's reproducible, I think that will be a good idea close this issue and open a new ticket, citing this one.

Good catch! Thank you very much.
The easiest thing is to start with the environment variable QT_GRAPHICSSYSTEM=X11, so it leaves the rest of your system untouched.
I'm acutally considering a last-minute patch to remove the "Enable Backbuffer" option and instead use QApplication::setGraphicsSystem().
Will do some in-depth testing on that.

Donovan Cameron wrote:

I got the flickering to go away in KDE by changing some settings in System Settings > Qt Graphics System > Configure the default graphics system of Qt appliations > Default (X11/XRender)

It was set to Raster before - switching to X11/XRender might help for users on KDE for now.

Everything renders smooth now, no flickers for my KDE desktops anymore.

Giovanni Manghi wrote:

on what platform are you seeing this? also on master?

This is on QGIS 2.2, I haven't been able to test on master.
Do you think this is specific to desktops running KDE?

$ uname -a
Linux archasus 3.13.6-1-ARCH #1 SMP PREEMPT Fri Mar 7 22:47:48 CET 2014 x86_64 GNU/Linux

Do you think this is specific to desktops running KDE?

cannot see it on Mint using Cinnamon or Mate.