add language gives unusable flickering window

[jlittle]

wonder reported this in pre-release testing. As that thread was in a forum now closed, I'm starting a new one here.

I've got this in two fresh installs of focal. It's like the sub-window with the language choice is displayed and erased continuously, I estimate at 20 times a second. If I click on it repeatedly, one of clicks hits the window and it clears away. But one needs to choose a language and click "add", so I can't add a language. It does not occur on the focal install release upgraded from eoan. All on the same system.

In the thread started by wonder the focus was on the driver for his radeon graphics card, and installing packages for it seemed to be the solution. My desktop has only the integrated Intel HD graphics:

inxi -Gx                                                                ~
Graphics:
Device-1: Intel HD Graphics 530 vendor: Gigabyte driver: i915 v: kernel
bus ID: 00:02.0
Display: x11 server: X.Org 1.20.8 driver: modesetting unloaded: fbdev,vesa
resolution: 1920x1080~60Hz
OpenGL: renderer: Mesa Intel HD Graphics 530 (SKL GT2) v: 4.6 Mesa 20.0.4
direct render: Yes

There's scattered reports of something like this over the years, but now also this on bugs.kde.org

[Snowhog]

No issues like that on my 20.04, and I've been running it since it was Beta. What Rendering backend are you using? Here, it's OpenGL 2.0. All settings there are:

Scale method: Accurate
Rendering backend: OpenGL 2.0
Tearing prevention ("vsync"): Automatic
Keep windo thumbnails: Only for Shown Windows
Allow applications to block compositing (checked)

[Iangh]

I have this when the screen is maximised. Whilst it's flickering reduce the size of the screen and hey-presto! A strange one.

[Schwarzer Kater]

Same effect here: extreme flickering of the language choice window in KDE System Settings - with four different computers / GPUs since 20.04 beta.

As langh already said: a temporary solution is to resize the window of KDE System Settings - the flickering stops immediately (afterwards I can also maximise the screen again, the flickering stays away for now).

[jlittle]

I have this when the screen is maximized. Whilst it's flickering reduce the size of the screen and hey-presto! A strange one.

Thank you, I'd just discovered this myself, and have added British English . (The woe of American spellings.)
@snowhog, does it still not happen with the settings window maximized? I'll try in my release upgraded focal.[Edit] Now in my release upgraded focal, and if I make the window too tall, the flickering sets in. Running it as kcmshell5 translations &, the flickering occurs if the window is more that 799 pixels tall. I can stop the flickering by resizing the window below the threshold, and it doesn't come back if then resized large again.

Funny how on other distros the workaround is to maximize, but here to "minimalize".

[Snowhog]

@snowhog, does it still not happen with the settings window maximized?

Correct. On my laptop, even with the System Settings window maximized, I don't experience what everyone else here is reporting.