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feat: M2 — GNOME/Mutter virtual-display backend (RecordVirtual) + preferred-mode negotiation

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Third compositor on the VirtualDisplay seam, via Mutter's direct D-Bus APIs (the
gnome-remote-desktop headless model, no portal grant): RemoteDesktop.CreateSession →
ScreenCast.CreateSession({remote-desktop-session-id}) → Session.RecordVirtual (creates a
virtual monitor) → Start → PipeWireStreamAdded(node_id). A keepalive thread owns the zbus
connection (sessions die with it — RAII teardown); select with LUMEN_COMPOSITOR=mutter or
XDG_CURRENT_DESKTOP=GNOME.

Mutter sizes its virtual monitor FROM the PipeWire format negotiation, so VirtualOutput
gains preferred_mode (w, h, refresh_hz), threaded into the consumer's format pods as the
default size/framerate. KWin/gamescope set it too (their outputs are already exact-size;
the preference just confirms it) — both regression-tested intact.

Compile/clippy/test clean; live validation needs gnome-shell installed (then
`gnome-shell --headless` + m0 --source kwin-virtual with LUMEN_COMPOSITOR=mutter).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
This commit is contained in:
Enrico Bühler
2026-06-09 22:48:53 +00:00
parent b6f00a3dc5
commit 31648d3e4f
5 changed files with 260 additions and 16 deletions
Download Patch File Download Diff File Expand all files Collapse all files
crates/lumen-host/src/capture/linux.rs
+24 -13
View File
@@ -64,7 +64,7 @@ impl PortalCapturer {
node_id,
"ScreenCast portal session started; connecting PipeWire"
);
let (frames, active) = spawn_pipewire(Some(fd), node_id)?;
let (frames, active) = spawn_pipewire(Some(fd), node_id, None)?;
Ok(PortalCapturer {
frames,
active,
@@ -81,7 +81,7 @@ impl PortalCapturer {
node_id = vout.node_id,
"connecting PipeWire to virtual output"
);
let (frames, active) = spawn_pipewire(vout.remote_fd, vout.node_id)?;
let (frames, active) = spawn_pipewire(vout.remote_fd, vout.node_id, vout.preferred_mode)?;
Ok(PortalCapturer {
frames,
active,
@@ -92,9 +92,12 @@ impl PortalCapturer {
/// Spawn the PipeWire consumer thread for `node_id` (fd `Some` = portal remote, `None` =
/// default daemon) and return the frame channel + the activation flag it gates on.
/// `preferred` seeds the format negotiation's default size/framerate — for Mutter virtual
/// monitors this is what actually sizes the monitor.
fn spawn_pipewire(
fd: Option<OwnedFd>,
node_id: u32,
preferred: Option<(u32, u32, u32)>,
) -> Result<(Receiver<CapturedFrame>, Arc<AtomicBool>)> {
// Frames flow from the pipewire thread over a small bounded channel.
let (frame_tx, frame_rx) = sync_channel::<CapturedFrame>(8);
@@ -104,7 +107,9 @@ fn spawn_pipewire(
thread::Builder::new()
.name("lumen-pipewire".into())
.spawn(move || {
if let Err(e) = pipewire::pipewire_thread(fd, node_id, frame_tx, active_cb, zerocopy) {
if let Err(e) =
pipewire::pipewire_thread(fd, node_id, frame_tx, active_cb, zerocopy, preferred)
{
tracing::error!(error = %format!("{e:#}"), "pipewire capture thread failed");
}
})
@@ -424,7 +429,11 @@ mod pipewire {
/// Build a BGRx dmabuf `EnumFormat` pod advertising the EGL-importable `modifiers` as a
/// mandatory enum Choice; the compositor fixates to one of them that it can allocate, which
/// we read back in `param_changed`.
fn build_dmabuf_format(modifiers: &[u64]) -> Result<Vec<u8>> {
fn build_dmabuf_format(
modifiers: &[u64],
preferred: Option<(u32, u32, u32)>,
) -> Result<Vec<u8>> {
let (dw, dh, dhz) = preferred.unwrap_or((1920, 1080, 60));
use pw::spa::param::format::{FormatProperties, MediaSubtype, MediaType};
let mut obj = pw::spa::pod::object!(
pw::spa::utils::SpaTypes::ObjectParamFormat,
@@ -438,8 +447,8 @@ mod pipewire {
Range,
Rectangle,
pw::spa::utils::Rectangle {
width: 1920,
height: 1080
width: dw,
height: dh
},
pw::spa::utils::Rectangle {
width: 1,
@@ -455,7 +464,7 @@ mod pipewire {
Choice,
Range,
Fraction,
pw::spa::utils::Fraction { num: 60, denom: 1 },
pw::spa::utils::Fraction { num: dhz, denom: 1 },
pw::spa::utils::Fraction { num: 0, denom: 1 },
pw::spa::utils::Fraction { num: 240, denom: 1 }
),
@@ -478,7 +487,8 @@ mod pipewire {
/// The default (shm/CPU-path) format offer: raw video in any encoder-mappable layout, any
/// size, any framerate (0/1 = variable allowed — gamescope fixates exactly that).
fn build_default_format_obj() -> pw::spa::pod::Object {
fn build_default_format_obj(preferred: Option<(u32, u32, u32)>) -> pw::spa::pod::Object {
let (dw, dh, dhz) = preferred.unwrap_or((1920, 1080, 60));
pw::spa::pod::object!(
pw::spa::utils::SpaTypes::ObjectParamFormat,
pw::spa::param::ParamType::EnumFormat,
@@ -515,8 +525,8 @@ mod pipewire {
Range,
Rectangle,
pw::spa::utils::Rectangle {
width: 1920,
height: 1080
width: dw,
height: dh
},
pw::spa::utils::Rectangle {
width: 1,
@@ -532,7 +542,7 @@ mod pipewire {
Choice,
Range,
Fraction,
pw::spa::utils::Fraction { num: 60, denom: 1 },
pw::spa::utils::Fraction { num: dhz, denom: 1 },
pw::spa::utils::Fraction { num: 0, denom: 1 },
pw::spa::utils::Fraction { num: 240, denom: 1 }
),
@@ -579,6 +589,7 @@ mod pipewire {
tx: SyncSender<CapturedFrame>,
active: Arc<AtomicBool>,
zerocopy: bool,
preferred: Option<(u32, u32, u32)>,
) -> Result<()> {
crate::pwinit::ensure_init();
@@ -903,7 +914,7 @@ mod pipewire {
),
)
} else {
build_default_format_obj()
build_default_format_obj(preferred)
};
// When zero-copy is on, offer ONLY a BGRx dmabuf format with our EGL-importable modifiers
@@ -914,7 +925,7 @@ mod pipewire {
let shm_values = serialize_pod(obj)?;
let (dmabuf_values, buffers_values) = if want_dmabuf {
(
Some(build_dmabuf_format(&modifiers)?),
Some(build_dmabuf_format(&modifiers, preferred)?),
Some(build_dmabuf_buffers()?),
)
} else {