screencast: Emit MonitorsChanged

src/backend/tty.rs

@@ -710,13 +710,8 @@ impl Tty {
         let sequence_delta_plot_name =
             tracy_client::PlotName::new_leak(format!("{output_name} sequence delta"));
 
-        self.enabled_outputs
-            .lock()
-            .unwrap()
-            .insert(output_name.clone(), output.clone());
-
         let surface = Surface {
-            name: output_name,
+            name: output_name.clone(),
             compositor,
             dmabuf_feedback,
             vblank_frame: None,
@@ -730,6 +725,13 @@ impl Tty {
 
         niri.add_output(output.clone(), Some(refresh_interval(mode)));
 
+        self.enabled_outputs
+            .lock()
+            .unwrap()
+            .insert(output_name, output.clone());
+        #[cfg(feature = "dbus")]
+        niri.on_enabled_outputs_changed();
+
         // Power on all monitors if necessary and queue a redraw on the new one.
         niri.event_loop.insert_idle(move |state| {
             state.niri.activate_monitors(&state.backend);
@@ -769,6 +771,8 @@ impl Tty {
         };
 
         self.enabled_outputs.lock().unwrap().remove(&surface.name);
+        #[cfg(feature = "dbus")]
+        niri.on_enabled_outputs_changed();
     }
 
     fn on_vblank(

src/dbus/mutter_display_config.rs

@@ -5,7 +5,7 @@ use serde::Serialize;
 use smithay::output::Output;
 use zbus::fdo::RequestNameFlags;
 use zbus::zvariant::{self, OwnedValue, Type};
-use zbus::{dbus_interface, fdo};
+use zbus::{dbus_interface, fdo, SignalContext};
 
 use super::Start;
 
@@ -112,7 +112,8 @@ impl DisplayConfig {
         Ok((0, monitors, logical_monitors, HashMap::new()))
     }
 
-    // FIXME: monitors-changed signal.
+    #[dbus_interface(signal)]
+    pub async fn monitors_changed(ctxt: &SignalContext<'_>) -> zbus::Result<()>;
 }
 
 impl DisplayConfig {

src/niri.rs

@@ -2759,6 +2759,44 @@ impl Niri {
             constraint.activate();
         });
     }
+
+    #[cfg(feature = "dbus")]
+    pub fn on_enabled_outputs_changed(&self) {
+        let _span = tracy_client::span!("Niri::on_enabled_outputs_changed");
+
+        let Some(dbus) = &self.dbus else { return };
+        let Some(conn_display_config) = dbus.conn_display_config.clone() else {
+            return;
+        };
+
+        let res = thread::Builder::new()
+            .name("DisplayConfig MonitorsChanged Emitter".to_owned())
+            .spawn(move || {
+                use crate::dbus::mutter_display_config::DisplayConfig;
+                let _span = tracy_client::span!("MonitorsChanged");
+                let iface = match conn_display_config
+                    .object_server()
+                    .interface::<_, DisplayConfig>("/org/gnome/Mutter/DisplayConfig")
+                {
+                    Ok(iface) => iface,
+                    Err(err) => {
+                        warn!("error getting DisplayConfig interface: {err:?}");
+                        return;
+                    }
+                };
+
+                async_io::block_on(async move {
+                    if let Err(err) = DisplayConfig::monitors_changed(iface.signal_context()).await
+                    {
+                        warn!("error emitting MonitorsChanged: {err:?}");
+                    }
+                });
+            });
+
+        if let Err(err) = res {
+            warn!("error spawning a thread to send MonitorsChanged: {err:?}");
+        }
+    }
 }
 
 pub struct ClientState {