vincentbernat.i3wm-configuration/bin/xsettingsd-setup

#!/bin/sh

DISPLAY=${DISPLAY%.0}

# Compute DPI of each screens
dpis=""
for info in $(xrandr --current \
                  | sed -n 's/^\([^ ]\{1,\}\)* connected.* \([0-9]\{1,\}\)x.* \([0-9]\{1,\}\)mm x .*/\1,\2,\3/p'); do
    output=${info%%,*}
    pixels=${info#*,}
    pixels=${pixels%%,*}
    mm=${info##*,}
    dpi=$(($pixels * 254 / 10 / $mm))
    # For laptop screens, we need to apply a correction factor
    case $output in
        eDP-1|eDP1) corrected=$(($dpi * 96/144)) ;;
        *) corrected=$dpi ;;
    esac
    # Authorized factors: 1, 1.5, 2, 3, 4, ...
    rounded=$(((corrected + 24) / 48 * 48))
    [ $rounded -gt 192 ] && rounded=$(((corrected + 48) / 96 * 96))
    [ $rounded -lt 96 ] && rounded=96
    dpis="$dpis$rounded "
    echo "$output: ${dpi}dpi (corrected to ${corrected}dpi, rounded to ${rounded}dpi)" >&2
done

# Use first screen DPI
dpi=${dpis%% *}
dpi=${dpi:-96}

echo "using ${dpi}dpi" >&2
xrandr --dpi $dpi

# Build xsettingsd
{
    cat  ~/.config/awesome/xsettingsd
    echo Xft/DPI $(( $dpi*1024 ))
    echo Xft/RGBA \"$( [ $dpi -gt 144 ] && echo none || echo rgb )\"
    echo Gdk/WindowScalingFactor $(( $dpi/96 ))
    echo Gdk/UnscaledDPI $(( $dpi*1024/($dpi/96) ))
} > ~/.xsettingsd

# Signal xsettingsd
systemctl --user reload xsettingsd@$(systemd-escape -- "$DISPLAY").service

# Also use xrdb for very old stuff (you know, LibreOffice)
echo Xft.dpi: $dpi | xrdb -merge