Updated: March 15, 2021
I love buying new hardware. Apart from the obvious joy of having a new toy, there's an almost certainty that I'm going to face some fresh problems, related to this or that operating system. Karma definitely did not disappoint when I recently got meself a Lenovo IdeaPad 3, which I loaded with three operating systems, Kubuntu 20.10 included.In this Plasma-powered Groovy instance, I also set the HD scaling to 1.25, in order to be able to use the system comfortably on the 14-inch FHD screen. If you've followed my adventures with Plasma, specifically the good, the bad and the ugly of desktop scaling on my Slimbook, and then the fine results in Plasma 5.20, then you know things have improved massively, and there should be no issues. And yet there were. Some. Small ones. Weird ones. In Konsole specifically. I noticed white - or black - lines showing in the terminal output, whenever I'd move the cursor up and down. An issue that my sweet OCD demons cannot abide.
Problem in a little more detail & solution
Well, there's isn't too much more to say. The annoying thing was, if I tried to screenshot these, the lines would often disappear. Similarly, moving the cursor up and down would also often erase the lines as it would create them. Feels like some weird visual buffer thing. I was inclined to suspect the laptop's graphics, as my experience with AMD GPU is quite limited, but then, everything else was smooth and perfect. So I narrowed my anger and focus down on Konsole.
And then I found a bug - and old and recurring bug, because regressions are so hot right now, with fractional HiDPI scaling in the Plasma desktop. Anyway, there are two solutions - one, upgrade to a new version of Plasma, which might not be possible, two, a workaround with the Konsole profile.
Konsole > Settings > Edit Profile. Click on Appearance > Miscellaneous. Here, change the line spacing from the default value of 0px to something higher. I tried with 1px initially and this helped, but not entirely. 2px, still better, but not fully resolved. The 3px spacing fixed it for good. No more horizontal white or black lines. The laptop's scaling remains at 1.25, and everything is cool and smooth again.
Conclusion
I don't mind problems and challenges - but I gravely dislike regressions. Why should an old 2016 bug have to resurface four or five years later? But then, fighting and fixing this was ever so mildly fun, and I got me a nice little guide out of it, so it ain't all bad.
Anyway, Plasma users, if you're facing the issue of horizontal lines across the terminal window output in Konsole, either black or white, and you happen to be using fractional scaling, then changing the line spacing should help work around the problem until you have the option to update or upgrade to a version of the desktop that fixes the bug. And thus are the OCD demons pacified. Take care, and see you soon.
Cheers.