BEHAVIOR See video link in URL field for example. When I enable the screen tearing prevention in the Compositor settings, click apply, then drag & move a window around, screen tearing seems fixed for a few seconds, but the tearing returns after that. Changing the settings again produces the same result: tearing is fixed for a few seconds, but dragging and moving a window across the screen will show that screen tearing returns. EXPECTED BEHAVIOR When tearing prevention is applied (regardless of the setting), the settings stick after you click APPLY or OK, and the tearing is gone, period. BUG DISCOVERED USING Kubuntu 17.04 x64 KDE Plasma 5.10.4 (via ppa:kubuntu-ppa/backports) KDE Frameworks 5.36.0 Qt 5.7.1 Linux kernel 4.10.0-28-generic Nvidia GTX 1080 graphics card Nvidia 384.59 proprietary driver (via ppa:graphics-drivers/ppa)
This is an old and known issue with NVIDIA driver and kwin. By the way, screen tearing will not show in your screencast (recheck your video please). This is the (original?) bug entry with a lengthy discussion: https://bugs.kde.org/show_bug.cgi?id=322060 There's a workaround in the last comment.
*** This bug has been marked as a duplicate of bug 322060 ***
@Pablo, sorry about that -- didn't realize the screen-tearing wasn't evident in the video. I'll do better to re-check those before posting, next time. I'll continue the discussion at the bug that my bug was marked a duplicate of. Thanks for your responses.