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lass.pds.lassul.us/superconfig
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tablet-screen: android tablet as external screen via sunshine
Streams a sway headless output to Moonlight with Sunshine, so an Android
tablet works as a wireless second screen with its touchscreen acting as a
touchpad on the shared cursor.
The output is created once per session and stays disabled until a client
streams: sunshine's prep-cmd enables it at exactly the resolution and
refresh rate the client asks for, and disables it afterwards so sway moves
the workspace back to the real screens. wlroots never reuses a headless
output name, so the name is discovered at creation time, remembered in
$XDG_RUNTIME_DIR and handed to sunshine as an output_name command line
override instead of being hardcoded.
Replaces 2configs/sunshine.nix, which only shipped a manual launcher
script.
author
lassulus
date
(Sep 17, 2026, 4:17 PM CEST)
commit
1953a3f1
1953a3f152a9dd888fb6f2c61d602e54d1ac3799
parent
97fc9be5
97fc9be5e8ef9723e2c203d89745612cd8a7eaf5
+241
-29
-28
2configs/sunshine.nix
-28
2configs/sunshine.nix
···
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{ pkgs, ... }:
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{
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networking.firewall.allowedTCPPorts = [
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47984
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47989
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48010
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];
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networking.firewall.allowedUDPPorts = [
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47998
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47999
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48000
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];
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boot.kernelModules = [ "uinput" ];
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services.udev.extraRules = ''
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KERNEL=="uinput", SUBSYSTEM=="misc", OPTIONS+="static_node=uinput", TAG+="uaccess"
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'';
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environment.systemPackages = [
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(pkgs.writers.writeDashBin "sun" ''
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${pkgs.sunshine}/bin/sunshine --creds sun sun
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${pkgs.sunshine}/bin/sunshine -0 ${pkgs.writeText "sunshine.conf" ''
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channels = 15
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address_family = both
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''} "$@"
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'')
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];
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}
+240
2configs/tablet-screen.nix
+240
2configs/tablet-screen.nix
···
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# Android tablet as a wireless external screen.
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#
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# A sway headless output is streamed to Moonlight by Sunshine: hardware H.264/
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# HEVC/AV1 over UDP, i.e. the game streaming path, ~1 frame of latency on LAN.
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# The output exists but stays disabled until a client streams: Sunshine's
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# prep-cmd enables it at exactly the resolution/refresh rate the client asks
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# for (so pixels map 1:1) and disables it afterwards, which makes sway evacuate
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# its workspace back to the real screens.
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#
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# Touch as a touchpad: Moonlight's "Use the touchscreen as a trackpad" sends
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# relative mouse motion, which Sunshine injects through uinput, so dragging
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# anywhere on the tablet moves the (single, shared) cursor like a touchpad.
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# native_pen_touch is disabled below so absolute touch is never negotiated
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# instead.
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#
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# One-time setup per host:
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# sunshine --creds <user> <password> # or set them in the web UI
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# open https://<host>:47990, "PIN" page, enter the PIN Moonlight shows
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#
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# For the least judder, use 5 GHz, keep tablet and host on the same AP, and in
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# Moonlight pick HEVC with frame pacing on "Prefer lowest latency". Streaming
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# jitter is dominated by the tablet's radio, not by which host NIC is used.
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{
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config,
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lib,
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pkgs,
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...
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}:
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let
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workspace = "tablet";
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tablet-screen = pkgs.writeShellApplication {
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name = "tablet-screen";
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runtimeInputs = [
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pkgs.sway
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pkgs.jq
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];
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text = ''
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# wlroots names headless outputs HEADLESS-<n> in creation order and never
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# reuses a name, so the name we get depends on what else created one
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# first. Reserve one per session and remember which it is; the state lives
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# in the runtime dir, so it disappears together with the sway session that
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# owns the output.
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state=''${XDG_RUNTIME_DIR:-/run/user/$(id -u)}/tablet-screen.output
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# sway >=1.11 creates a per-pid IPC socket, and the systemd user manager
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# has not necessarily imported SWAYSOCK yet when sunshine starts or runs a
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# prep-cmd, so find the live socket ourselves.
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if ! swaymsg -t get_version >/dev/null 2>&1; then
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for sock in /run/user/"$(id -u)"/sway-ipc.*.sock; do
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if SWAYSOCK=$sock swaymsg -t get_version >/dev/null 2>&1; then
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export SWAYSOCK=$sock
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break
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fi
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done
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fi
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names() {
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swaymsg -r -t get_outputs | jq -c '[.[].name]'
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}
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exists() {
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names | jq -e --arg o "$1" 'index($o)' >/dev/null
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}
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reserve() {
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if [ -s "$state" ] && exists "$(cat "$state")"; then
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return 0
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fi
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before=$(names)
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swaymsg -- create_output >/dev/null
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output=$(names | jq -r --argjson before "$before" '(. - $before)[0] // empty')
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if [ -z "$output" ]; then
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echo "tablet-screen: sway created no headless output" >&2
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return 1
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fi
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printf '%s\n' "$output" > "$state"
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# Keep the tablet on its own workspace so it never steals a numbered one.
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swaymsg "workspace ${workspace} output $output" >/dev/null
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swaymsg "output $output disable" >/dev/null
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}
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target() {
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reserve
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cat "$state"
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}
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case "''${1-}" in
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reserve)
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reserve
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;;
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name)
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target
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;;
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on)
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shift
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# Sunshine exports the client's stream request; a resolution given on
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# the command line wins so the screen can also be used by hand.
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res=''${SUNSHINE_CLIENT_WIDTH:-1920}x''${SUNSHINE_CLIENT_HEIGHT:-1200}
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fps=''${SUNSHINE_CLIENT_FPS:-60}
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scale=1
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while [ $# -gt 0 ]; do
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case $1 in
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--mode)
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res=''${2%%@*}
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[ "''${2#*@}" = "$2" ] || fps=''${2#*@}
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shift 2
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;;
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--scale)
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scale=$2
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shift 2
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;;
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*)
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echo "tablet-screen: unknown option $1" >&2
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exit 1
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;;
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esac
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done
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output=$(target)
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# No position: sway appends an unpositioned output to the right of
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# every other one, which keeps the existing screens (and the order
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# sway-screen-switch counts in) exactly where they are.
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swaymsg "output $output enable mode ''${res}@''${fps}Hz scale $scale" >/dev/null
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;;
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off)
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# Disable instead of unplug: sway moves the workspace back to a real
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# screen, and the output keeps its name for the next stream.
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if [ -s "$state" ] && exists "$(cat "$state")"; then
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swaymsg "output $(cat "$state") disable" >/dev/null
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fi
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;;
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status)
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if ! { [ -s "$state" ] && exists "$(cat "$state")"; }; then
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echo "no virtual screen reserved"
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exit 0
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fi
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swaymsg -r -t get_outputs | jq -r --arg o "$(cat "$state")" '
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.[] | select(.name == $o)
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| if .active then
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"\(.name) active \(.current_mode.width)x\(.current_mode.height)@\((.current_mode.refresh / 1000) | floor) scale=\(.scale) position=\(.rect.x),\(.rect.y)"
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else
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"\(.name) disabled"
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end
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'
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;;
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*)
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echo "usage: tablet-screen reserve|name|on [--mode WxH[@FPS]] [--scale S]|off|status" >&2
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exit 1
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;;
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esac
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'';
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};
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appsFile = (pkgs.formats.json { }).generate "sunshine-apps.json" {
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env = { };
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apps = [
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{
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name = "Tablet screen";
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prep-cmd = [
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{
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do = "${lib.getExe tablet-screen} on";
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undo = "${lib.getExe tablet-screen} off";
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}
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];
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auto-detach = "true";
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}
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{
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# Same screen rendered at 1.5x, for reading size on a ~10" panel while
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# still encoding (and displaying) native pixels.
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name = "Tablet screen (HiDPI)";
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prep-cmd = [
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{
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do = "${lib.getExe tablet-screen} on --scale 1.5";
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undo = "${lib.getExe tablet-screen} off";
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}
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];
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auto-detach = "true";
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}
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];
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};
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settingsFile = (pkgs.formats.keyValue { }).generate "sunshine.conf" {
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sunshine_name = config.networking.hostName;
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# wlr-screencopy, unlike the kms backend, can also capture an output that
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# has no CRTC behind it - which is exactly what a headless output is.
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capture = "wlr";
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# Make Moonlight emulate a mouse rather than negotiating absolute touch,
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# so the touchscreen acts as a touchpad on the shared cursor.
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native_pen_touch = "disabled";
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file_apps = "${appsFile}";
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};
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+
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# output_name has to be known when sunshine starts, but the headless output's
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# name is only decided when it is created, so reserve it here and pass the
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# name as a command line override (any config key can be overridden that way).
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# Running through the capability wrapper gives sunshine CAP_SYS_NICE for its
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# EGL capture context.
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sunshine-tablet-screen = pkgs.writeShellApplication {
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name = "sunshine-tablet-screen";
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runtimeInputs = [ tablet-screen ];
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text = ''
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output=$(tablet-screen name)
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exec ${config.security.wrapperDir}/sunshine ${settingsFile} "output_name=$output"
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'';
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};
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in
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{
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environment.systemPackages = [ tablet-screen ];
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services.sunshine = {
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enable = true;
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openFirewall = true;
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# Started with sway-session.target below instead, which sway only reaches
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# after importing WAYLAND_DISPLAY/SWAYSOCK into the user manager.
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autoStart = false;
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# Not for KMS capture (unused): this is what makes the module build a
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# capability wrapper, whose capability set is replaced below.
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capSysAdmin = true;
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};
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+
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# CAP_SYS_NICE lets sunshine put its EGL capture context on a high priority
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# GPU queue; CAP_SYS_ADMIN would only be needed for KMS capture.
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security.wrappers.sunshine.capabilities = lib.mkForce "cap_sys_nice+p";
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systemd.user.services.sunshine = {
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wantedBy = [ "sway-session.target" ];
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partOf = [ "sway-session.target" ];
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after = [ "sway-session.target" ];
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# Fails while sway is not up yet (no IPC socket to create the output on);
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# the module's Restart=on-failure retries until the session exists.
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serviceConfig.ExecStart = lib.mkForce (lib.getExe sunshine-tablet-screen);
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};
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+
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# Mouse/keyboard injection goes through /dev/uinput; hand it to the user of
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# the active session (hardware.uinput, pulled in by services.sunshine, only
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# sets up the uinput group).
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services.udev.extraRules = ''
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KERNEL=="uinput", SUBSYSTEM=="misc", OPTIONS+="static_node=uinput", TAG+="uaccess"
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'';
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}