punktfunk/docs-site/content/docs/gamescope.md

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Steam / gamescope	Configure a gamescope/Steam host — attach vs managed, session following, and limits.

gamescope is the compositor behind Steam Gaming Mode — the couch/handheld game UI on Bazzite, SteamOS, or any distro running a gamescope session. The host auto-detects gamescope from your live session, so you rarely need to set anything here. It also follows a Gaming ↔ Desktop switch mid-stream — flip between Gaming Mode and the desktop with Steam's normal UI and the host re-targets whatever's running without a reconnect.

This page covers the gamescope-specific choices. To get a host running on an appliance box, start from the install guide for your OS: Bazzite or SteamOS (Host).

New here? Read Security & Safe Use first — a streaming host is remote control of the machine, so keep it on a trusted LAN or VPN and require pairing.

Attach vs managed

There are two mutually-exclusive models for a gamescope box; pick one. With nothing set, a box that has gamescope session infrastructure (Bazzite, SteamOS, Nobara) gets managed; the Bazzite template ships with attach chosen instead.

• Attach (PUNKTFUNK_GAMESCOPE_ATTACH=1) — the box owns its gamescope session and decides Gaming vs Desktop via the normal Steam UI. Game Mode stays on the box's own (physical) display; the host attaches to whatever's live and never tears it down, so switching Desktop ↔ Game is rock-solid and disconnecting leaves the box where it was. When the box is headless (no display connected) and the session is its own autologin unit, the host restarts it at the client's resolution on a mismatch; a box driving a physical display — and any foreign or bare gamescope — is streamed at its own mode.
• Managed (the infra-detected default; force with PUNKTFUNK_GAMESCOPE_MANAGED=1) — the host takes the box's gamescope session over and relaunches it headless at the client's exact resolution and refresh — Game Mode runs on the virtual screen, physical displays drop out of it — restoring the box on idle after disconnect.

Nobara and other autologin display managers

The managed takeover has to stop the box's Gaming Mode session to free Steam. How it does that depends on the display manager driving the autologin:

• SDDM (Bazzite, SteamOS): handled automatically — no setup.

• plasmalogin (Nobara) and other display managers: the host must stop the display manager itself for the length of the stream and restart it afterwards, which needs privilege. The packages ship that privilege: a root helper (/usr/libexec/punktfunk/pf-dm-helper) behind its own polkit action (io.unom.punktfunk.dm-helper), invoked automatically when the plain systemctl verbs are denied — no setup. The helper only stops/restores the unit the display-manager.service symlink points at, the same class of local-seat operation these distros already authorize for their own session switcher (Nobara's os-session-select).

  Installed from a tarball, or prefer not to ship the allow_any action? Remove the .policy file and use a polkit rule scoped to your user instead (adjust the unit and user names to your box) — the host tries the plain verbs first, so the rule takes precedence:

  // /etc/polkit-1/rules.d/49-punktfunk-dm.rules
  polkit.addRule(function(action, subject) {
      if (action.id == "org.freedesktop.systemd1.manage-units" &&
          action.lookup("unit") == "plasmalogin.service" &&
          subject.user == "YOUR_USER") {
          return polkit.Result.YES;
      }
  });
  

  With no privilege path at all the host degrades safely: it attaches to the live Gaming Mode session instead (Game Mode stays on the box's display at the box's own resolution, mirrored to the client — if your monitor stays on and the stream runs at the desktop's resolution, this is what happened; check the host log for "managed takeover unavailable"). If the display-manager restart ever loses its privilege mid-restore, PUNKTFUNK_RECOVER_SESSION_CMD (see Configuration) is fired as the fallback.

  Lingering is required here, and the host turns it on for you the first time it takes the box over. Stopping the display manager ends your last login session, and without loginctl enable-linger logind stops your systemd --user manager about ten seconds later — taking the host with it, mid-stream, with the display manager down and nothing left to bring it back. If lingering can't be enabled the host refuses the takeover and degrades to attach instead (above) rather than risk that. Run sudo loginctl enable-linger "$USER" once, as the setup guides ask; loginctl disable-linger "$USER" reverts it.

  With the takeover authorized the in-stream session switch round-trips in managed mode: Steam's "Switch to Desktop" inside the streamed Game Mode returns the box to its desktop session and the stream follows it there; the desktop's "Return to Gaming Mode" switches it forward again.

Session following

PUNKTFUNK_SESSION_WATCH follows a Gaming ↔ Desktop switch mid-stream — the host rebuilds the backend in place, with no reconnect. It is on by default on Bazzite/SteamOS; set 0 to disable. One host service covers both faces of the box: it streams Gaming Mode over gamescope and the desktop over its own compositor, and re-targets whichever is live on each switch.

Start the host

On an appliance box (Bazzite, SteamOS) the install guide already enables the host service for you. On any other distro running a gamescope session, just start it — the host auto-detects the live gamescope session and picks the model for it:

systemctl --user enable --now punktfunk-host

Then bring up The Web Console to arm pairing.

gamescope knobs

The gamescope-specific settings in host.env. Leave them unset to auto-detect; set one only to force a model. See the full Configuration reference for every other knob.

Setting	Values	Meaning
PUNKTFUNK_GAMESCOPE_ATTACH	1	Attach model: the box owns its gamescope session (on its own display); the host captures whatever's live and never tears it down. On a headless box the box-owned autologin session is restarted at the client's resolution on a mismatch; a box driving a physical display, and any foreign/bare gamescope, streams at its own mode.
PUNKTFUNK_GAMESCOPE_MANAGED	1	Managed model (the default where session infra is detected): the host takes the box's gamescope over and relaunches it headless at the client's exact mode, restoring on idle.
PUNKTFUNK_GAMESCOPE_SESSION	steam	The host owns a gamescope-session-plus (Steam) session at the client's mode — a headless appliance with no physical session running.
PUNKTFUNK_GAMESCOPE_NODE	auto · node id	Discover and capture a running gamescope's PipeWire node at a fixed mode. Do not combine with SESSION.
PUNKTFUNK_GAMESCOPE_APP	command	For an ad-hoc bare-gamescope session, the nested command to run (e.g. vkcube).
PUNKTFUNK_SESSION_WATCH	1 · 0	Follow a Gaming ↔ Desktop switch mid-stream (rebuild in place, no reconnect). On by default on Bazzite/SteamOS; set 0 to disable.
PUNKTFUNK_GAMESCOPE_HDR	1 · 0 (default off)	Allow HDR (10-bit BT.2020 PQ) sessions. Needs punktfunk-gamescope — see below.
PUNKTFUNK_GAMESCOPE_SDR_NITS	e.g. 400	On an HDR session, how bright SDR content (the desktop, the Steam overlay, an SDR game) is inside the PQ container. gamescope's default is 400.
PUNKTFUNK_GAMESCOPE_BIN	path	Force a specific gamescope binary. Otherwise the host prefers punktfunk-gamescope on PATH, then gamescope.

HDR on gamescope

Games can render HDR on a headless gamescope today, but a stock gamescope's capture output is 8-bit SDR: its PipeWire node offers only 8-bit formats, and it tone-maps the composite down before handing it over. So a stock setup streams SDR — correctly, including a correct SDR rendition of an HDR game — and there is nothing to configure.

To stream real HDR you need punktfunk-gamescope: gamescope plus a small patch that adds the 10-bit BT.2020 PQ formats to that node (offered upstream as gamescope#2126). It installs under its own name and does not replace your system gamescope — your Gaming Mode keeps using that one.

• Bazzite / Fedora Atomic — included in the punktfunk sysext; punktfunk-sysext update gets it.
• Arch / SteamOS — the punktfunk-gamescope package.
• NixOS — services.punktfunk.host.gamescopeHdr = true; (it also sets the env var below).
• Anything else — bash packaging/gamescope/build-punktfunk-gamescope.sh from the source tree.

Then turn it on:

PUNKTFUNK_GAMESCOPE_HDR=1

and check what the host thinks it can do:

punktfunk-host hdr-probe

A session goes HDR when all of: the host allows it (PUNKTFUNK_10BIT, on by default, plus the knob above), the resolved gamescope offers the 10-bit formats, the client advertises 10-bit decoding with HDR enabled in its settings, the codec is HEVC or AV1 (never H.264), and the GPU encodes Main10. Anything missing and the session streams 8-bit SDR — decided before the stream starts, so you never get a mislabelled picture. The client overlay shows 10-bit · HDR (BT.2020 PQ) when it worked.

Two things to know:

• SDR content rides the same PQ stream. The desktop, the Steam overlay and SDR games are mapped into the HDR container at PUNKTFUNK_GAMESCOPE_SDR_NITS (400 by default). If white looks too bright or too dim on your TV, that is the knob.
• On AMD and Intel, HDR follows what the GPU can encode. The host asks the driver whether it can encode your codec at 10 bits and picks the fast path when it can — which current AMD and Intel GPUs do for HEVC, and newer ones for AV1 too. On a GPU that declines, the session still streams HDR through a slower path. That slower path is also the only one that can draw a pointer back into the picture — so on a declining GPU, a stock gamescope would cost you the cursor. punktfunk-gamescope puts the pointer in the capture itself, which is why it is worth installing even on a box where you never turn HDR on. punktfunk-host hdr-probe reports what your box answered, including which side is drawing the cursor.

Known limits

These apply to the Gaming Mode (gamescope) path only; the desktop path is unaffected.

• gamescope 3.16.22 or newer is required. Older versions can deadlock during capture. Bazzite's and SteamOS's current gamescope is fine; this only bites if you've pinned an old one.
• gamescope leaves the mouse cursor out of its captured image. You still see a pointer: the host reads it separately and draws it into every frame. That costs a full pass over the picture, and on the fastest encode paths it cannot be done at all (see the AMD/Intel note above). punktfunk-gamescope fixes it at the source — that build paints the pointer straight into the capture, so the host stops redrawing it and the frame reaches the encoder untouched. Nothing to configure; installing the build is enough, HDR or not.
• Touch arrives as a single-finger pointer. gamescope's virtual input device has no touchscreen, so the host maps a client's touchscreen to an absolute pointer: taps click exactly where you touch and drags work, but multi-touch gestures (pinch) aren't available in Gaming Mode. The desktop path has full multi-touch.
• HDR needs the punktfunk gamescope build. A stock gamescope's capture output is 8-bit SDR, so sessions stream SDR — correctly, including SDR versions of HDR games. Install punktfunk-gamescope (gamescope plus a small patch that teaches its capture node the 10-bit BT.2020 PQ formats) and set PUNKTFUNK_GAMESCOPE_HDR=1, and a 10-bit-capable client streams true HDR10. See HDR on gamescope below.

To stream the KDE Plasma desktop of a Steam box instead, see KDE Plasma. To bring up the web console and pair a client, see The Web Console.