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Most Qubes-native applications don't scale well in dom0 because they are made in Qt.

2023-04-08 12:18:37 -04:00

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DPI scaling

Qubes OS passes on dom0's screen resolution to VMs (this can be seen in the output of xrandr) but doesn't pass on dom0's dpi value. Recent distributions have automatic scaling depending on the screen's resolution (eg. in fedora if the screen resolution is at least 192dpi and the screen height is greater than 1200 pixels) but for a variety of reasons one may have to set a custom dpi scaling value.

Dom0

The simplest way to set dpi scaling in dom0 is to use the desktop environment's custom dpi feature:

Xfce: Qubes Menu → System Tools → Appearance → Fonts tab: Custom DPI setting: xxx
KDE: Qubes Menu → System Settings → Font → Force font dpi: xxx
i3: add Xft.dpi: xxx to `/home/user/.Xresources' in dom0

Replace xxx with a number that fits your setup and is a multiple of 6, as numbers that aren't sometimes result in annoying rounding errors that cause adjacent bitmap font sizes to not increment and decrement linearly.

Qubes Applications

Qubes applications (e.g. Qubes Create VM, etc.) don't scale automatically, to solve this issue it is possible to set the QT_SCALE_FACTOR variables as described here. To test these values first, open a terminal and type:

QT_SCALE_FACTOR=1.8 qubes-global-settings

You can try change the values for QT_SCALE_FACTOR to your liking.

Once you confirmed that this is working, you can make these settings permanent by creating a file /etc/profile.d/dpi_QT.sh (in dom0) with the following content and your own values:

#!/bin/sh

export QT_SCALE_FACTOR=1.8

Then make the script executable with

sudo chmod +x /etc/profile.d/dpi_QT.sh

And logout and login again to see the results.

VMs

The procedure for setting DPI scaling is different depending on whether gnome settings daemon is running or not:

if the daemon is stopped/not installed, applications honor the Xft.dpi X resource which we can then use for scaling.
if the daemon is running (/usr/libexec/gsd-xsettings process in Fedora), applications are prevented from using the Xft.dpi resource and dconf values have to set.

Notes:

the official fedora-xx template has the gnome-settings-daemon rpm installed by default while the fedora-xx-minimal template doesn't.
DPI scaling with xterm (or any glib apps) requires the use of a xft font:
- for xterm, ctrl - right click in the terminal's windows and select 'TrueType Fonts' (make sure you have such fonts installed).
- or more generally, set the faceName Xresource, eg.:
  
  *faceName: DejaVu Sans Mono:size=14:antialias=true
  
  You may do so temporarily with the xrdb -merge command, or permanently in a Xresources file (see section below).

VMs without gnome settings daemon

Get the current value of Xft.dpi:

xrdb -query | grep Xft.dpi

Test with a different dpi value: in a terminal issue the following command and then start an application to check that the menus/fonts' size is increased/decreased; replace '144' with the value set in dom0 (it's possible to set a different value in VMs though):

echo Xft.dpi: 144 | xrdb -merge

Once you found a value that fits your setup you'll likely want to permanently set the Xft.dpi resource. You can do so on a per-template (system-wide) or per-VM basis:

add (or modify) Xft.dpi: xxx in the TemplateVM's Xresource file (/etc/X11/Xresources or /etc/X11/Xresources/x11-common for whonix-ws-template).
or, add Xft.dpi: xxx to $HOME/.Xresources in each AppVM.

VMs with gnome settings daemon

We'll set the scaling-factor and text-scaling-factor dconf values in the org.gnome.desktop.interface schema.

Get the current values:

gsettings get org.gnome.desktop.interface scaling-factor
gsettings get org.gnome.desktop.interface text-scaling-factor

Test with different values; notes:

windows and menu/fonts should be resized dynamically
when running the commands below the values will be automatically written to $HOME/.config/dconf/user
replace 2 and 0.75 to suit your needs (scaling-factor must be an integer though)

gsettings set org.gnome.desktop.interface scaling-factor 2
gsettings set org.gnome.desktop.interface text-scaling-factor 0.75

If gsd-xsettings is running but nothing happens, examine the output of dconf dump /. If needed, reset any xsettings override:

gsettings reset org.gnome.settings-daemon.plugins.xsettings overrides

To store the dconf values system-wide - eg. when customizing templateVMs - copy the following text into /etc/dconf/db/local.d/dpi (replace 2 and 0.75 with your values):

[org/gnome/desktop/interface]
scaling-factor=uint32 2
text-scaling-factor=0.75

Then run dconf update.

Note: the scaling-factor and text-scaling-factor values might already be set in an AppVM's user profile, in which case they'll override the system-wide ones. To use system-wide values, reset the user values like so in the AppVM(s):

gsettings reset org.gnome.desktop.interface scaling-factor
gsettings reset org.gnome.desktop.interface text-scaling-factor

For more information on setting system-wide dconf values see this page.

Troubleshooting

Firefox and other GTK3 applications

Even when setting the correct dpi values, some applications might have very small icons or similar elements. This usually happens in Firefox for example.

To mitigate this issue it is possible to set the GDK_SCALE and GDK_DPI_SCALE variables as described [here](https://wiki.archlinux.org/title/HiDPI#GDK_3_(GTK_3). To test these values first, open a terminal and type:

export GDK_SCALE=2
export GDK_DPI_SCALE=0.5
firefox

You can try change the values for GDK_SCALE and GDK_DPI_SCALE to your liking, but GDK_SCALE needs to be an integer value.

Once you confirmed that this is working, you can make these settings permanent by creating a file /etc/profile.d/dpi_GDK.sh (ideally in the template VM) with the following content and your own values:

#!/bin/sh

export GDK_SCALE=2
export GDK_DPI_SCALE=0.5