Prevent black frames during startup

crates/bevy_app/src/app.rs

@@ -288,6 +288,14 @@ impl App {
             panic!("App::run() was called from within Plugin::build(), which is not allowed.");
         }
 
+        if app.ready() {
+            // If we're already ready, we finish up now and advance one frame.
+            // This prevents black frames during the launch transition on iOS.
+            app.finish();
+            app.cleanup();
+            app.update();
+        }
+
         let runner = std::mem::replace(&mut app.runner, Box::new(run_once));
         (runner)(app);
     }

crates/bevy_app/src/schedule_runner.rs

@@ -71,12 +71,14 @@ impl Plugin for ScheduleRunnerPlugin {
     fn build(&self, app: &mut App) {
         let run_mode = self.run_mode;
         app.set_runner(move |mut app: App| {
-            while !app.ready() {
-                #[cfg(not(target_arch = "wasm32"))]
-                bevy_tasks::tick_global_task_pools_on_main_thread();
+            if !app.ready() {
+                while !app.ready() {
+                    #[cfg(not(target_arch = "wasm32"))]
+                    bevy_tasks::tick_global_task_pools_on_main_thread();
+                }
+                app.finish();
+                app.cleanup();
             }
-            app.finish();
-            app.cleanup();
 
             let mut app_exit_event_reader = ManualEventReader::<AppExit>::default();
             match run_mode {

crates/bevy_winit/src/lib.rs

@@ -378,7 +378,7 @@ pub fn winit_runner(mut app: App) {
         ResMut<CanvasParentResizeEventChannel>,
     )> = SystemState::from_world(&mut app.world);
 
-    let mut finished_and_setup_done = false;
+    let mut finished_and_setup_done = app.ready();
 
     // setup up the event loop
     let event_handler = move |event: Event<()>,