SUMMARY If QT_SCALE_FACTOR is set to 2, Kwin doesn't start and runs at 100% CPU forever. Running with QT_SCALE_FACTOR set to 1 works. STEPS TO REPRODUCE Start Kwin with "QT_SCALE_FACTOR" set to 2, for instance like so: "(export QT_SCALE_FACTOR=2; kwin --replace &)" OBSERVED RESULT Kwin kills the current window manager, but then doesn't start and runs at 100% CPU forever. Can only be killed with "kill -9". EXPECTED RESULT Kwin should start normally SOFTWARE/OS VERSIONS Linux/KDE Plasma: Xfce on Ubuntu Bionic KDE Plasma Version: 5.12.7 KDE Frameworks Version: 5.44.0 Qt Version: 5.9.5 ADDITIONAL INFORMATION This problem seems to be caused by a combination of environmental variables that I'm running. If I create a brand new user, Kwin can start correctly even with QT_SCALE_FACTOR set to 2. Which variables are causing the problem, I cannot figure out. I actually figured out that I had originally opened another bug at https://bugs.kde.org/show_bug.cgi?id=398965, but last time I failed to figure out how to get a backtrace of the process. This time, I'm also attaching backtrace (sorry, don't know how to output to file so it's an image).
Ops, nevermind--image was too big to attach. I uploaded it here: https://i.imgur.com/ElQEOe6.jpg
Why do you set this environment variable anyway?
Use this instead: QT_SCREEN_SCALE_FACTORS
Git commit 79ce5dac9a2af0823c16f80dfff19ef3494d08c3 by David Edmundson. Committed on 04/04/2019 at 01:03. Pushed by davidedmundson into branch 'Plasma/5.15'. Also unset QT_SCALE_FACTOR Summary: Qt scaling and kwin on X11 is never going to work so it is disabled. However, Qt uses multiple environment variables for subtly different internal things. We don't set QT_SCALE_FACTOR in Plasma, using different ones. An XFCE user was setting this, which kinda makes sense if your DE doesn't have an appropriate UI. I don't think it's relevant for main_wayland as wl_output.scale should trump the environment variable. Reviewers: zzag Reviewed By: zzag Subscribers: zzag, kwin Tags: #kwin Differential Revision: https://phabricator.kde.org/D20234 M +1 -0 main_x11.cpp https://commits.kde.org/kwin/79ce5dac9a2af0823c16f80dfff19ef3494d08c3
Thanks, guys!