tree: make surface visibility tracking more robust

src/backends/metal.rs

@@ -196,7 +196,9 @@ impl Backend for MetalBackend {
                 return;
             }
         }
-        if !idle {
+        if idle {
+            self.state.set_backend_idle(true);
+        } else {
             for device in devices.values() {
                 for connector in device.connectors.lock().values() {
                     connector.schedule_present();

src/backends/metal/video.rs

@@ -389,8 +389,11 @@ impl MetalConnector {
     async fn present_loop(self: Rc<Self>) {
         loop {
             self.present_trigger.triggered().await;
-            if let Err(e) = self.present(true) {
-                log::error!("Could not present: {}", ErrorFmt(e));
+            match self.present(true) {
+                Ok(_) => self.state.set_backend_idle(false),
+                Err(e) => {
+                    log::error!("Could not present: {}", ErrorFmt(e));
+                }
             }
         }
     }

src/backends/x.rs

@@ -772,6 +772,8 @@ impl XBackend {
             log::error!("Could not present image: {:?}", e);
             return;
         }
+
+        self.state.set_backend_idle(false);
     }
 
     async fn handle_input_event(self: &Rc<Self>, event: &Event) -> Result<(), XBackendError> {