enricobuehler
c8f9032dec
Deep investigation (gdb + daemon traces) proved the gamescope capture stall is a gamescope
3.16.20 bug, not ours: it calls pw_loop_iterate() without pw_loop_enter()/leave(), and under
PipeWire 1.6's loop locking its main thread permanently holds the loop mutex — the pw thread
deadlocks, gamescope never acks the daemon's port_set_param(Format), and the link parks in
"negotiating" silently. Stock gst pipewiresrc fails identically. Fixed upstream by gamescope
commit e3ed1ea7 ("pipewire: Fix pipewire loop locking", pipewire#5148); first release 3.16.22.
Ubuntu 26.04 ships 3.16.20 (built ten days before the fix) — patch/upgrade required.
Consumer-side improvements from the investigation (all verified correct vs gamescope's pods,
and needed once the producer is fixed):
- discover the node from gamescope's own "stream available on node ID: N" log line (its
node.name appears on two objects; the advertised id is authoritative); pw-dump fallback
- CPU path accepts mappable dmabufs: Buffers param now offers MemPtr|MemFd|DmaBuf (gamescope
counter-offers exactly DmaBuf when its modifier pod wins, never MemPtr), mmap the fd
ourselves when MAP_BUFFERS didn't (Vulkan-exported dmabufs aren't flagged mappable), and
treat chunk.size==0 as the computed span
- warn_once on every silent frame-drop path in the process callback
- node.dont-reconnect on our capture streams: an orphaned stream re-targeted by wireplumber
onto a fresh node wedges it — and a stuck link head-blocks the daemon's shared work queue,
stalling ALL new link negotiation system-wide (this poisoned whole test sessions)
- LUMEN_GAMESCOPE_NODE (attach to an existing gamescope) + LUMEN_PW_FIXED_POD (negotiation
bisection) debug knobs
KWin path regression-tested (zero-copy intact). gamescope end-to-end validation pending the
patched gamescope build.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
lumen
A ground-up low-latency desktop streaming stack, built Linux-first, with a shared Rust protocol core and native clients per platform.
lumen is a placeholder codename. The bet: ship a Linux virtual-display streaming
host that speaks the existing Moonlight protocol (every Moonlight/Artemis client works
day one), then break the ~1 Gbps FEC wall with a GF(2¹⁶) Leopard-RS transport as a
negotiated extension. See docs/implementation-plan.md.
Status
| Milestone | State |
|---|---|
M1 — lumen-core + C ABI |
✅ done & tested (FEC, packetization, crypto, session, lumen_core.h) |
M0 — pipeline spike (wlroots→PipeWire→NVENC→file→lumen-core) |
✅ done & verified on NVIDIA (RTX 5070 Ti / driver 595) |
| M2 — P1 host → stock Moonlight | 🟡 capture+encode landed in M0; pairing/RTSP/vdisplay pending |
| M3 — measurement harness | 🟡 tools/loss-harness runs; latency-probe scaffolded |
| M4 — P2 transport + Rust client | 🟡 GF(2¹⁶) core done; lumen-client-rs scaffolded |
| M5 — Apple client | ⬜ scaffolded (clients/apple) |
lumen-core is complete and verified: it builds and its full test suite (FEC recovery,
loopback round-trip under loss, property tests, and a C ABI harness) passes on
macOS/aarch64. M0 is done: lumen-host captures a headless wlroots output via the
ScreenCast portal + PipeWire, encodes it with NVENC, writes a playable H.265 file, and
round-trips every access unit through a lumen_core host→client session (see
docs/linux-setup.md). The remaining Linux host backends (KWin/Mutter virtual displays,
libei input, web/pairing) are #[cfg(target_os = "linux")] seams — defined and compiling,
implementations pending (M2).
Layout
crates/
lumen-core/ protocol · FEC · pacing · crypto — the C ABI (lib + cdylib + staticlib)
lumen-host/ Linux host: vdisplay · capture · encode · inject · web (cfg-gated)
lumen-client-rs/ reference client (M4): VAAPI decode + wgpu present
clients/{apple,android}/ native client scaffolds (import lumen_core.h)
include/lumen_core.h cbindgen-generated C header (checked in)
tools/{latency-probe,loss-harness}/ measurement (plan §10)
docs/implementation-plan.md
Build & test
cargo build --workspace # green on Linux and macOS
cargo test --workspace # unit + loopback + proptest + C ABI harness
cargo clippy --workspace --all-targets
cargo run -p loss-harness # FEC loss-resilience sweep (no network needed)
bash crates/lumen-core/tests/c/run.sh # standalone C-ABI link+round-trip proof
The C header regenerates from crates/lumen-core/src/abi.rs on every build (cbindgen via
build.rs) into include/lumen_core.h.
Design invariants
- One core, linked everywhere. Protocol/FEC/crypto/pacing live in
lumen-coreexactly once, exposed over a stable, versioned C ABI (lumen_abi_version(),LumenConfigcarries its ownstruct_size). - No async on the hot path. The per-frame pipeline uses native threads only;
tokio/quinnare gated behind the off-by-defaultquicfeature (control plane only). - FEC is the wall-breaker. GF(2⁸) (≤255 shards/block) for Moonlight compat; GF(2¹⁶) (≤65535 shards/block, SIMD, O(n log n)) to push past ~1 Gbps.
License
MIT OR Apache-2.0.