Technology

I use KDE Plasma on my Arch desktop and I’ve had some issues with getting my dual-monitor, mixed DPI setup to work properly as mentioned in my previous post.

I nuked and paved my existing installation a few weeks ago and set up Arch afresh on the same computer on a new SSD. On the previous install, I had set up the root filesystem on a hard drive with LVM and the system startup was very slow – ~45 seconds to reach SDDM, an additional ~30 seconds to drop to a usable desktop, and then ~5 seconds to run my xrandr script.

The boot time and the time taken to reach a usable desktop was significantly lesser with the SSD – ~8 seconds to start SDDM, ~5 seconds to the desktop, ~3 seconds to run the xrandr script. So I was happy.

As exciting as that was, I still had many rough edges and paper cuts, most of them persisting across multiple re-installations. Thanks to the posts by various posts by fellow Plasma users, I was able to solve them 🙂

SDDM

Monitor layout

When SDDM started, it always did with my monitor layout and DPI configured wrong. My secondary 1080p monitor is placed to the left of my primary 4K monitor and SDDM always placed the former to the right of the latter.

Thanks to this useful post, I was able to create a custom Xsetup script by adding the xrandr command from my previous post and configuring SDDM to run it when starting the display server.

# /etc/sddm.conf
[XDisplay]
DisplayCommand=/usr/share/sddm/scripts/Xsetup

Theme

I don’t like the default theme used by SDDM, maui. Since Arch is a DIY distro, it doesn’t automatically set up the default Plasma theme, breeze, like many other distros do when Plasma is installed.

Previously, I was using the Chili login theme to make the SDDM greeter look nice. I was unsure why and how, the Manjaro installation on my laptop, had a nice Plasma theme for SDDM. But I didn’t spend any time investigating at all till now.

I checked the Arch wiki page on SDDM theming to check if there are nice themes listed there that I could use and found that it is possible to configure the SDDM theme using the Plasma System Settings application after installing the sddm-kcm package. I found the default Breeze theme which I liked very much and set it as the theme. But that didn’t work. So I went ahead and configured it manually in sddm.conf and voilà, it worked! 😀

# /etc/sddm.conf
[XDisplay]
DisplayCommand=/usr/share/sddm/scripts/Xsetup

[Theme]
Current=breeze

Desktop scaling

I was pleasantly surprised to see that Plasma automatically scaled my 4K monitor without having to configure scaling manually via the Display settings application. Everything in the secondary monitor looked large as expected and I had to run my xrandr command from the previous post, with some changes to restart Plasma shell for making the wallpaper fit the scaled display, manually every time due to something in the Plasma startup process resetting the screen configuration irrespective of when my xrandr auto-start script ran.

Thanks to this post on Reddit by a fellow Plasma user, I found that the kscreen2 service was the culprit and disabling it ensured that the display configuration set up by the SDDM Xsetup script persisted and as a result, I didn’t have to manually run my xrandr script 😀 😌

There could be some side-effects caused by disabling the kscreen2 service, but I haven’t run into any till now 🙂

Emoji picker

The built-in emoji picker, introduced in Plasma 5.18, is very convenient and something that Plasma was sorely missing before. However, in spite of installing an appropriate emoji font, the emoji picker had a lot of missing emoji with blank squares and the color/gender variants of some emoji looked broken with those showing up as two separate symbols (one for the emoji and the other for the color/gender variant) overlapping each other.

Thanks to this Reddit post, I was able to solve the issue by creating a custom fontconfig configuration file, ~/.config/fontconfig/fonts.conf, with the configuration below and by forcefully rebuilding the font info cache files by running fc-cache -f.

<?xml version='1.0'?>
<!DOCTYPE fontconfig SYSTEM 'fonts.dtd'>
<fontconfig>
	<match target="font">
		<edit mode="assign" name="rgba">
		<const>rgb</const>
		</edit>
	</match>
	<match target="font">
		<edit mode="assign" name="hinting">
		<bool>true</bool>
		</edit>
	</match>
	<match target="font">
		<edit mode="assign" name="hintstyle">
		<const>hintfull</const>
		</edit>
	</match>
	<match target="font">
		<edit mode="assign" name="antialias">
		<bool>true</bool>
		</edit>
	</match>
	<match target="font">
		<edit mode="assign" name="lcdfilter">
		<const>lcddefault</const>
		</edit>
	</match>
	<match target="font">
		<edit name="autohint" mode="assign">
		<bool>false</bool>
		</edit>
	</match>
	<match target="pattern"> 
		<edit name="family" mode="prepend"> 
		<string>Noto Color Emoji</string> 
		</edit> 
	</match> 
</fontconfig>

It looks nice after the fix 👌🏼

Last year, I purchased a new 4K monitor to use as my primary display in addition to my existing 1080p monitor. Like with most 4K monitors, this one required scaling to display text and interface elements in a readable size. While the dual monitor setup worked okay out of the box on Windows 10, it didn’t on my Arch install running an up-to-date KDE Plasma.

1.5x scaling in the Display settings on Plasma made everything look okay on the primary 4K monitor but look large and ugly on the 1080p monitor. I was aware that Wayland supports mixed DPI environments very well but I was stuck on Xorg due to having an Nvidia GPU and Plasma’s support for EGLStreams still being a work in progress.

I read multiple recommendations on the internet to scale (mentioned correctly in a few places as “upscaling”) the 1080p display using xrandr to compensate for the scaling done by the desktop environment so that everything looks okay on both displays. What confused me a long time is that “scaling” meant different things when it came to xrandr and the desktop environment. Scaling in the desktop environment translated to zooming in the desktop by 1.5x (“downscaling”) to make everything look larger and (up)scaling the display using xrandr meant zooming out the Xorg display for the monitor 1.5x to make everything look smaller.

A lot of different xrandr commands were given as examples. However, all of those were for setups different from mine and used a lot of parameters and flags without a general explanation of what they do and how to adapt them for other scenarios. This was very important for someone like me who isn’t familiar with the terminology. So for a while, I had to resort using just konsole on the secondary 1080p monitor with the font size reduced to make it look okay and the interface elements still looking large and ugly.

Eventually, I found out the solution that I needed – scale the desktop environment 1.5x which reduced the effective resolution of the 4K (3840×2160) monitor to 1440p (2560×1440) and that of the 1080p (1920×1080) monitor by 1.5x to 720p (1280×720). That made everything on the 4K monitor look properly sized and large on the 1080p monitor. To fix that, I had to use xrandr to upscale the 1080p display by 1.5x (2880×1620) to compensate for the desktop environment’s 1.5x scaling. With that, everything looked good on both monitors. Below is the xrandr command that I used.

xrandr --fbmm 6720x3780 --output DP-0 --pos 2880x0 --mode 3840x2160 --scale 1x1 --primary --output HDMI-0 --pos 0x0 --mode 1920x1080 --scale 1.5x1.5

The fbmm flag sets the reported physical size of the X screen as a whole. In this case it is (3840+2880)x(2160+1620), which is the sum of the resolutions of both monitors after running the xrandr command. The --pos flag is used to position the monitors in the 6720x3780 display. Since the 1080p monitor is present to the left of the primary 4K monitor, its position is at 0x0. The starting position of the 4K monitor is 2880x0, where 2880 is the horizontal resolution of the 1080p monitor, so that it is positioned right after the latter ends.

This still caused an issue on the 1080p monitor where the Plasma desktop screen was reduced in size by 1.5x and was not filling the whole display. This also meant that the wallpaper was not filling the whole display. The unfilled area in that display was black in color. (Update May 2020: this can be fixed by restarting the Plasma Shell) To work around this issue, I used black color as the wallpaper for that screen and removed all the elements on that desktop. Till very recently, I continued using black color as the wallpaper and when I found that this was fixed in a recent Plasma update (not sure when and which version), I was able to use a proper wallpaper on the 1080p monitor as well.

While this solved the major problem with mixed DPIs, the GUI toolkits (Qt 5, GTK 3) and some applications like Firefox needed some additional scaling tweaks to get them looking okay. For this I used the excellent documentation on HiDPI in the Arch wiki which covered almost everything. Steam and VirtualBox were a couple of notable exceptions that didn’t work okay. The former didn’t support fractional scaling and only worked with 2x scaling which makes everything noticeably larger. The latter was broken and had a lot of issues with the menus appearing in the wrong places and the guest VMs unable to use a proper resolution. Fixing this issue required setting QT_SCREEN_SCALE_FACTORS to 1.0.