enricobuehler
d6818263ce
gamescope's built-in PipeWire node has always been SDR-only: it offers BGRx and NV12, and `paint_pipewire()` hardcodes a Gamma-2.2 composite with the SDR screenshot LUT set. So an HDR game reaches punktfunk already tone-mapped down, and the whole gamescope backend streams 8-bit no matter what the client can decode. Games CAN render HDR on a headless gamescope today — only the capture half is missing. Carry the two patches that close it (packaging/gamescope/patches): the node additionally offers `xRGB_210LE`/`xBGR_210LE` with MANDATORY SMPTE ST.2084 + BT.2020 props, mapped to the same 10-bit capture texture the HDR AVIF screenshot path already allocates, and `paint_pipewire()` composites into them with the HDR screenshot LUTs + `EOTF_PQ` — which is exactly the in-tree `bHDRScreenshot` branch. The new formats are listed LAST, so every existing consumer keeps negotiating the 8-bit stream bit-for-bit. Offered upstream against ValveSoftware/gamescope#2126. Ship it as `punktfunk-gamescope`, beside the distro's own binary rather than replacing it: a Bazzite sysext payload (`build-sysext.sh --gamescope`, which refuses a binary without the marker), an Arch package, a nix derivation + `services.punktfunk.host.gamescopeHdr`, and one distro-agnostic build script the rest call. The second patch stamps `+pfhdr1` into the `--version` banner. That is not cosmetic: punktfunk fixes a session's bit depth in the Welcome, before the display exists and with no way to take it back, so its capability answer has to be a static property of the binary it will spawn.
3.9 KiB
punktfunk-gamescope — gamescope with 10-bit HDR PipeWire capture
Upstream gamescope's built-in PipeWire node is SDR-only: build_format_params() offers BGRx
and NV12, and paint_pipewire() hardcodes a Gamma-2.2 composite with the SDR screenshot LUT
set. An HDR game therefore reaches every capture consumer already tone-mapped down — which is
why the punktfunk gamescope backend has always streamed 8-bit, even though games can render
HDR on a headless gamescope today (--hdr-enabled --hdr-debug-force-support).
The patches here add the missing half, and nothing else. See
punktfunk-planning/design/gamescope-hdr-virtual-output.md for the full design.
| Patch | What | Upstream? |
|---|---|---|
0001-pipewire-offer-10-bit-BT.2020-PQ-capture-formats-HDR.patch |
Offer SPA xRGB_210LE/xBGR_210LE with MANDATORY SMPTE ST.2084 + BT.2020 props, map them to DRM_FORMAT_XRGB2101010/XBGR2101010, and composite them with g_ScreenshotColorMgmtLutsHDR + EOTF_PQ |
Yes — offered against gamescope#2126 |
0002-punktfunk-stamp-the-version-banner-with-pfhdr1.patch |
Append +pfhdr1 to the --version banner |
No — ours only, retired when patch 1 lands upstream |
Why the marker exists
punktfunk decides a session's bit depth at handshake time, before the virtual display
exists, and the Welcome is irrevocable (a PQ stream handed to an 8-bit encoder is a deliberate
hard error). The capability answer must therefore be a static property of the resolved binary,
not an optimistic negotiation. The host runs <gamescope> --version once per boot and looks for
+pfhdr in the banner — see gamescope_hdr_capable() in
crates/pf-vdisplay/src/vdisplay/linux/gamescope/discovery.rs.
Bump the number (+pfhdr2, …) only if the patch's wire behaviour changes; the host's probe
accepts any +pfhdr<N>.
Which binary the host runs
Resolution order, applied identically by the bare spawn, the GAMESCOPE_BIN wrapper
(gamescope-session-plus) and the SteamOS PATH shim:
PUNKTFUNK_GAMESCOPE_BIN— absolute path overridepunktfunk-gamescopeonPATHgamescope
So installing this build under the name punktfunk-gamescope is enough; nothing replaces the
distro's gamescope.
Building
Pinned upstream: 8c676c39 (master, 2026-07-27 — tags through 3.16.25). The patches apply
cleanly to that commit; they touch src/pipewire.cpp, src/steamcompmgr.cpp and
src/meson.build only.
git clone https://github.com/ValveSoftware/gamescope.git
cd gamescope
git checkout 8c676c39
git submodule update --init --recursive # or let meson fetch the subprojects
git am /path/to/punktfunk/packaging/gamescope/patches/*.patch
meson setup build/ --prefix=/usr -Dpipewire=enabled
ninja -C build/
# install as punktfunk-gamescope, NOT as gamescope
install -Dm755 build/src/gamescope /usr/bin/punktfunk-gamescope
gamescope needs CAP_SYS_NICE for its realtime priority; the distro packages set it on their
own binary. Mirror it if you install ours system-wide:
setcap 'CAP_SYS_NICE=eip' /usr/bin/punktfunk-gamescope
Verifying the patch on a box (P0 exit)
punktfunk-gamescope --version # must contain +pfhdr1
punktfunk-gamescope --backend headless -W 1920 -H 1080 -r 60 \
--hdr-enabled --hdr-debug-force-support -- vkcube &
pw-dump | grep -A40 '"gamescope"' # node offers xRGB_210LE / xBGR_210LE
The stream is only 10-bit once a consumer asks for it: the formats are listed last, so any consumer that negotiates the 8-bit stream today keeps negotiating it bit-for-bit.
Rebase policy
The functional patch is two files and mirrors code that already exists in-tree (the HDR AVIF screenshot path), so it rebases cheaply. We pin the gamescope commit we ship; when upstream takes it, both patches are dropped and the host's capability probe becomes a plain version floor.