SteamOS Nested Desktop script with fixes for ValveSoftware/SteamOS#2063 and ValveSoftware/SteamOS#1820

custom-nested-desktop.sh

#!/bin/sh -eu

# Remove the performance overlay, it meddles with some tasks.
unset LD_PRELOAD

# Unset various XDG variables set by gamescope; allows portals to work.
unset XDG_DESKTOP_PORTAL_DIR XDG_SEAT_PATH XDG_SESSION_PATH

# Use the home directory as the starting directory instead of the default
# of `./`, which resolves to one of Steam's data directories.
cd "$HOME"

cleanup () {
    # Flush fuse mounts beneath here.
    umount --recursive "$NEW_XDG_RUNTIME_DIR" || true
    rm -Rf "$NEW_XDG_RUNTIME_DIR"
}

# Create a new XDG_RUNTIME_DIR.
NEW_XDG_RUNTIME_DIR=$XDG_RUNTIME_DIR/nested_plasma
trap cleanup EXIT

cleanup
mkdir "$NEW_XDG_RUNTIME_DIR" --mode 0700

# Some things are (currently) shared, pulseaudio socket needs to be
# connected to the main session.
mkdir "$NEW_XDG_RUNTIME_DIR/pulse" --mode 0700
ln -s "$XDG_RUNTIME_DIR/pulse/native" "$NEW_XDG_RUNTIME_DIR/pulse/native"
ln -s "$XDG_RUNTIME_DIR/pipewire"* "$NEW_XDG_RUNTIME_DIR/."

# Grab the resolution that gamescope sets up.
res=$(xdpyinfo -display :0 | awk '/dimensions/{print $2}')
width=${res%x*}; height=${res#*x}

# Shadow kwin_wayland_wrapper so that we can pass args to kwin wrapper
# whilst being launched by plasma-session.
mkdir "$NEW_XDG_RUNTIME_DIR/bin"
cat <<EOF > "$NEW_XDG_RUNTIME_DIR/bin/kwin_wayland_wrapper"
#!/bin/sh
/usr/bin/kwin_wayland_wrapper \
 --width="$width" --height="$height" \
 --no-lockscreen "\$@"
EOF
chmod a+x "$NEW_XDG_RUNTIME_DIR/bin/kwin_wayland_wrapper"
export PATH="$NEW_XDG_RUNTIME_DIR/bin:$PATH"

export XDG_RUNTIME_DIR="$NEW_XDG_RUNTIME_DIR"

dbus-run-session startplasma-wayland