Wake the event loop when wallpaper decoding completes

compositor/src/main.rs

@@ -90,12 +90,6 @@ fn main() -> Result<(), Box<dyn Error>> {
     event_loop.handle().insert_source(
         Timer::from_duration(Duration::from_millis(150)),
         move |_, _, state: &mut Ferese| {
-            // Decoders finish on a worker even when an idle DRM output has no
-            // pending frame. Wake rendering once, never continuously for wallpaper.
-            if state.wallpaper.poll() {
-                state.backdrop_generation = state.backdrop_generation.wrapping_add(1);
-                backends::direct::render_all(state);
-            }
             if let Some(result) = monitor
                 .as_mut()
                 .and_then(|monitor| monitor.poll(std::time::Instant::now()))
@@ -124,9 +118,15 @@ fn main() -> Result<(), Box<dyn Error>> {
         },
     )?;
     let result = event_loop.run(None, &mut state, |state| {
+        // The decoder wakes the loop after publishing its result, including
+        // when no output has a pending frame.
+        let wallpaper_changed = state.wallpaper.poll();
+        if wallpaper_changed {
+            state.backdrop_generation = state.backdrop_generation.wrapping_add(1);
+        }
         // All input/Wayland callbacks have returned, releasing seat locks.
         // Coalesce cursor changes and redraw here, never inside cursor_image.
-        if std::mem::take(&mut state.cursor_redraw_pending) {
+        if std::mem::take(&mut state.cursor_redraw_pending) || wallpaper_changed {
             backends::direct::render_all(state);
         }
         // Registry/sync/configure replies must not depend on a submitted

compositor/src/state.rs

@@ -602,7 +602,10 @@ impl Ferese {
             resize_transactions: HashMap::new(),
             resize_snapshots: HashMap::new(),
             nested_backend: None,
-            wallpaper: crate::wallpaper::WallpaperState::new(config.wallpaper),
+            wallpaper: crate::wallpaper::WallpaperState::with_wakeup(
+                config.wallpaper,
+                Some(event_loop.get_signal()),
+            ),
             maximized_windows: HashSet::new(),
             maximized_column_widths: HashMap::new(),
             window_stack: crate::stacking::WindowStack::default(),

compositor/src/wallpaper.rs

@@ -67,15 +67,25 @@ pub(crate) struct WallpaperState {
     pixels: Option<image::RgbaImage>,
     textures: HashMap<ErasedContextId, WallpaperTexture>,
     upload_retries: HashMap<ErasedContextId, Instant>,
+    wakeup: Option<smithay::reexports::calloop::LoopSignal>,
 }
 
 impl WallpaperState {
+    #[cfg(test)]
     pub fn new(config: WallpaperConfig) -> Self {
+        Self::with_wakeup(config, None)
+    }
+
+    pub fn with_wakeup(
+        config: WallpaperConfig,
+        wakeup: Option<smithay::reexports::calloop::LoopSignal>,
+    ) -> Self {
         let retained = config.clone();
         let (sender, receiver) = mpsc::channel();
         let owned = config.path.as_ref().is_some_and(|path| path.is_file());
         if owned {
             let path = config.path.unwrap();
+            let wakeup = wakeup.clone();
             std::thread::spawn(move || {
                 let load = || -> Result<image::RgbaImage, String> {
                     let (width, height) =
@@ -88,6 +98,9 @@ impl WallpaperState {
                         .map_err(|e| e.to_string())
                 };
                 let _ = sender.send(load());
+                if let Some(wakeup) = wakeup {
+                    wakeup.wakeup();
+                }
             });
         }
         Self {
@@ -100,6 +113,7 @@ impl WallpaperState {
             pixels: None,
             textures: HashMap::new(),
             upload_retries: HashMap::new(),
+            wakeup,
         }
     }
 
@@ -126,7 +140,7 @@ impl WallpaperState {
             tracing::warn!("new wallpaper is unavailable; retaining previous image");
             return;
         }
-        let mut replacement = Self::new(config);
+        let mut replacement = Self::with_wakeup(config, self.wakeup.clone());
         self.config = replacement.config;
         self.mode = replacement.mode;
         self.owned = replacement.owned;
@@ -296,6 +310,29 @@ fn image_geometry(
 mod tests {
     use super::*;
 
+    #[test]
+    fn decoder_wakes_an_idle_event_loop() {
+        use smithay::reexports::calloop::{EventLoop, timer::Timer};
+        let mut event_loop = EventLoop::<WallpaperState>::try_new().unwrap();
+        event_loop
+            .handle()
+            .insert_source(Timer::from_duration(Duration::from_secs(5)), |_, _, _| {
+                panic!("wallpaper decoder failed to wake the idle event loop");
+            })
+            .unwrap();
+        let signal = event_loop.get_signal();
+        let mut state =
+            WallpaperState::with_wakeup(WallpaperConfig::default(), Some(signal.clone()));
+        event_loop
+            .run(None, &mut state, |state| {
+                if state.poll() {
+                    assert!(state.pixels.is_some());
+                    signal.stop();
+                }
+            })
+            .unwrap();
+    }
+
     #[test]
     fn failed_uploads_back_off_per_context_and_reset_for_new_pixels() {
         use smithay::backend::renderer::ContextId;

compositor/src/winit.rs

@@ -1068,9 +1068,6 @@ fn output_elements(
         );
         return elements;
     }
-    if state.wallpaper.poll() {
-        state.backdrop_generation = state.backdrop_generation.wrapping_add(1);
-    }
     let Some(output_geometry) = state.space.output_geometry(output) else {
         return Vec::new();
     };