Updated: December 29, 2018
Here's a story for you - you need it to understand the reasoning for this article slash guide. Got meself a new laptop, one Slimbook Pro2 and installed Kubuntu Beaver on it, right. Encountered HD scaling issues all over the place, which I fixed. So far so cushty.
Now, I also started reporting my daily slash weekly experience with this machine, used on full thrusters in a production environment, no restraint and no detail glossed over. If it's good, it's good, and if it's not, then hopefully, stuff will be fixed in future versions of Plasma, like the 5.14 release, for instance. I found out that the default KDE image viewer GwenView and the text editor Kate aren't quite as slick and efficient as their Windows counterparts by the names of IrfanView and Notepad++, respectively. So I installed these, and noticed they looked mighty tiny on Slimbook's 1920x1080px display. No scaling. Aha! The reason why we're here. Let's fix that, then, shall we?
So this is what the WINE applications look like - notice the difference between the window title and the application menu. The font seems tiny - and it would look quite all right on a very large screen and/or a lesser resolution, but the combo of a small physical display (14 inches) and high resolution means WINE apps do not render that well, it's hard to read text, and none of the overrides in the system seem to help.
The answer actually hides inside the WINE configuration itself. You wouldn't necessarily think about it, but you do need the settings menu. You can access it through the UI menu or by running winecfg on the command line. Once the program launches, you will notice the tiny font and the old-school Windows 2000 theme.
We need the tab labeled Graphics. Here, you can change the Screen resolution DPI settings. By default, the value will be set to either 72 or 96. You need to change this to a higher value. If you're using Plasma display scaling, match this to the scaling factor, e.g. use a multiplier of 1.2 or 1.5 or whatever. If you're using a hard-coded DPI value, which you can govern through font settings, then match this one, as this will help get the most optimal visual effect. In my case, 128 or 144 DPI seem to do a really nice job. Most importantly, the fonts are clear and smooth, so we don't need any additional changes or fixes. Boom!
Of course, you can do still more. You can install additional fonts, use themes - but all these are not really necessary to get a consistent font look & feel for your desktop (Plasma in this case). This Ask Ubuntu thread has a lot more information on the other aspects of visual tweaking. However, those are mostly perks.
What the Linux desktop has always lacked is good integration, especially what I consider second-order integration. Some things are obvious and trivial, but then you get to things like Gtk software on Plasma and vice versa, the icons and fonts in various programs, WINE software, and more. These often fall under the radar, and are not covered by default tools and utilities provided in this or that desktop environment. My dream is to see a super-cohesive Linux experience on all fronts one day.
Well, with the combination of my HD scaling tutorial, the Slimbook reports (so far), and this little guide, if you happen to be running Linux on a smaller device with a high-quality screen and lots of pixels, then you probably have enough ammo to make the experience elegant and consistent across the board. Hopefully, this was useful, and see you around.