feat: initialize direct session backend

compositor/src/backends/direct.rs

@@ -0,0 +1,65 @@
+use std::{error::Error, io};
+
+use smithay::{
+    backend::{
+        libinput::{LibinputInputBackend, LibinputSessionInterface},
+        session::{Event as SessionEvent, Session, libseat::LibSeatSession},
+        udev::{UdevBackend, UdevEvent},
+    },
+    reexports::{calloop::EventLoop, input::Libinput},
+};
+
+use crate::Ferese;
+
+pub fn init(event_loop: &mut EventLoop<Ferese>, state: &mut Ferese) -> Result<(), Box<dyn Error>> {
+    let (session, notifier) = LibSeatSession::new()?;
+    let seat_name = session.seat();
+    let udev_backend = UdevBackend::new(&seat_name)?;
+    let mut libinput_context =
+        Libinput::new_with_udev::<LibinputSessionInterface<LibSeatSession>>(session.clone().into());
+    libinput_context
+        .udev_assign_seat(&seat_name)
+        .map_err(|()| io::Error::other(format!("failed to assign libinput seat {seat_name}")))?;
+    let libinput_backend = LibinputInputBackend::new(libinput_context.clone());
+
+    state.direct_session = Some(session);
+    state.session_active = true;
+
+    event_loop
+        .handle()
+        .insert_source(libinput_backend, |event, _, state| {
+            state.process_input_event(event);
+        })?;
+    event_loop
+        .handle()
+        .insert_source(notifier, move |event, _, state| match event {
+            SessionEvent::PauseSession => {
+                state.session_active = false;
+                libinput_context.suspend();
+                tracing::info!("direct session paused");
+            }
+            SessionEvent::ActivateSession => {
+                if libinput_context.resume().is_err() {
+                    tracing::error!("failed to resume libinput");
+                }
+                state.session_active = true;
+                tracing::info!("direct session activated");
+            }
+        })?;
+    event_loop
+        .handle()
+        .insert_source(udev_backend, |event, _, _state| match event {
+            UdevEvent::Added { device_id, path } => {
+                tracing::info!(?device_id, ?path, "DRM device added");
+            }
+            UdevEvent::Changed { device_id } => {
+                tracing::debug!(?device_id, "DRM device changed");
+            }
+            UdevEvent::Removed { device_id } => {
+                tracing::info!(?device_id, "DRM device removed");
+            }
+        })?;
+
+    tracing::info!(seat = %seat_name, "initialized direct session input and device discovery");
+    Ok(())
+}

compositor/src/backends/mod.rs

@@ -0,0 +1,143 @@
+mod direct;
+
+use std::ffi::OsString;
+
+use smithay::reexports::calloop::EventLoop;
+
+use crate::Ferese;
+
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+pub enum BackendKind {
+    Nested,
+    Drm,
+}
+
+#[derive(Debug, Eq, PartialEq)]
+pub struct LaunchConfig {
+    pub backend: BackendKind,
+    pub client: Vec<OsString>,
+}
+
+impl LaunchConfig {
+    pub fn from_environment() -> Result<Self, String> {
+        let graphical_session =
+            std::env::var_os("WAYLAND_DISPLAY").is_some() || std::env::var_os("DISPLAY").is_some();
+
+        Self::parse(std::env::args_os().skip(1), graphical_session)
+    }
+
+    fn parse(
+        args: impl IntoIterator<Item = OsString>,
+        graphical_session: bool,
+    ) -> Result<Self, String> {
+        let mut args = args.into_iter().peekable();
+        let mut requested_backend = None;
+        let mut client = Vec::new();
+
+        while let Some(argument) = args.next() {
+            if argument == "--" {
+                client.extend(args);
+                break;
+            }
+            if argument == "--backend" {
+                let value = args
+                    .next()
+                    .ok_or_else(|| "--backend requires auto, nested, or drm".to_owned())?;
+                requested_backend = Some(parse_backend(&value)?);
+                continue;
+            }
+            if let Some(value) = argument
+                .to_str()
+                .and_then(|argument| argument.strip_prefix("--backend="))
+            {
+                requested_backend = Some(parse_backend(&OsString::from(value))?);
+                continue;
+            }
+
+            client.push(argument);
+            client.extend(args);
+            break;
+        }
+
+        let backend = requested_backend.flatten().unwrap_or(if graphical_session {
+            BackendKind::Nested
+        } else {
+            BackendKind::Drm
+        });
+
+        Ok(Self { backend, client })
+    }
+}
+
+pub fn init(
+    backend: BackendKind,
+    event_loop: &mut EventLoop<Ferese>,
+    state: &mut Ferese,
+) -> Result<(), Box<dyn std::error::Error>> {
+    match backend {
+        BackendKind::Nested => crate::winit::init(event_loop, state),
+        BackendKind::Drm => direct::init(event_loop, state),
+    }
+}
+
+fn parse_backend(value: &OsString) -> Result<Option<BackendKind>, String> {
+    match value.to_str() {
+        Some("auto") => Ok(None),
+        Some("nested") => Ok(Some(BackendKind::Nested)),
+        Some("drm") => Ok(Some(BackendKind::Drm)),
+        _ => Err(format!(
+            "unknown backend {:?}; expected auto, nested, or drm",
+            value
+        )),
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn auto_selects_nested_inside_a_graphical_session() {
+        let config = LaunchConfig::parse([OsString::from("foot")], true).unwrap();
+
+        assert_eq!(config.backend, BackendKind::Nested);
+        assert_eq!(config.client, [OsString::from("foot")]);
+    }
+
+    #[test]
+    fn auto_selects_drm_without_a_graphical_session() {
+        let config = LaunchConfig::parse(Vec::<OsString>::new(), false).unwrap();
+
+        assert_eq!(config.backend, BackendKind::Drm);
+        assert!(config.client.is_empty());
+    }
+
+    #[test]
+    fn explicit_backend_and_separator_are_consumed() {
+        let config = LaunchConfig::parse(
+            [
+                OsString::from("--backend=drm"),
+                OsString::from("--"),
+                OsString::from("foot"),
+                OsString::from("--title=Ferese"),
+            ],
+            true,
+        )
+        .unwrap();
+
+        assert_eq!(config.backend, BackendKind::Drm);
+        assert_eq!(
+            config.client,
+            [OsString::from("foot"), OsString::from("--title=Ferese")]
+        );
+    }
+
+    #[test]
+    fn rejects_an_unknown_backend() {
+        let error =
+            LaunchConfig::parse([OsString::from("--backend"), OsString::from("other")], true)
+                .unwrap_err();
+
+        assert!(error.contains("unknown backend"));
+    }
+}

compositor/src/main.rs

@@ -1,31 +1,36 @@
 #![allow(irrefutable_let_patterns)]
 
+mod backends;
 mod grabs;
 mod handlers;
 mod input;
 mod state;
 mod winit;
 
-use std::{error::Error, process::Command};
+use std::{error::Error, io, process::Command};
 
 use smithay::reexports::{calloop::EventLoop, wayland_server::Display};
 pub use state::Ferese;
 use tracing::{info, warn};
 
+use crate::backends::LaunchConfig;
+
 fn main() -> Result<(), Box<dyn Error>> {
     init_logging();
 
+    let launch = LaunchConfig::from_environment()
+        .map_err(|error| io::Error::new(io::ErrorKind::InvalidInput, error))?;
     let mut event_loop = EventLoop::try_new()?;
     let display = Display::new()?;
     let mut state = Ferese::new(&mut event_loop, display)?;
-    winit::init(&mut event_loop, &mut state)?;
+    backends::init(launch.backend, &mut event_loop, &mut state)?;
 
     // SAFETY: the backend has already read the host display and Ferese is
     // single-threaded before the event loop and optional child start.
     unsafe { std::env::set_var("WAYLAND_DISPLAY", &state.socket_name) };
 
-    info!(socket = ?state.socket_name, "Ferese is accepting Wayland clients");
-    spawn_client_from_args();
+    info!(socket = ?state.socket_name, backend = ?launch.backend, "Ferese is accepting Wayland clients");
+    spawn_client(launch.client);
     event_loop.run(None, &mut state, |_| {})?;
     Ok(())
 }
@@ -36,12 +41,12 @@ fn init_logging() {
     tracing_subscriber::fmt().with_env_filter(filter).init();
 }
 
-fn spawn_client_from_args() {
-    let mut args = std::env::args_os().skip(1);
-    let Some(program) = args.next() else {
+fn spawn_client(mut args: Vec<std::ffi::OsString>) {
+    if args.is_empty() {
         info!("no client requested; pass one after `--`, for example `-- foot`");
         return;
-    };
+    }
+    let program = args.remove(0);
 
     match Command::new(&program).args(args).spawn() {
         Ok(child) => info!(program = ?program, pid = child.id(), "spawned nested client"),

compositor/src/state.rs

@@ -11,6 +11,7 @@ use ferese_core::{WindowPlacement, WorkspaceSet};
 use ferese_layout::{Axis, Direction, GapConfig, LayoutResult, Rect, SizeConstraints, WindowId};
 
 use smithay::{
+    backend::session::libseat::LibSeatSession,
     desktop::{PopupManager, Space, Window, WindowSurfaceType},
     input::{Seat, SeatState},
     reexports::{
@@ -51,6 +52,8 @@ pub struct Ferese {
     pub window_geometry: HashMap<WindowId, WindowGeometry>,
     pub focused_window: Option<WindowId>,
     pub intercepted_keys: HashSet<smithay::input::keyboard::Keycode>,
+    pub direct_session: Option<LibSeatSession>,
+    pub session_active: bool,
     next_window_id: u64,
     last_animation_tick: Instant,
     pub popups: PopupManager,
@@ -110,6 +113,8 @@ impl Ferese {
             window_geometry: HashMap::new(),
             focused_window: None,
             intercepted_keys: HashSet::new(),
+            direct_session: None,
+            session_active: true,
             next_window_id: 1,
             last_animation_tick: start_time,
             popups: PopupManager::default(),