refactor: simplify the main update loop

core/src/game_state.rs

@@ -16,19 +16,18 @@ pub struct GameState {
 }
 
 impl GameState {
-    pub fn new() -> Self {
+    pub fn new(timestamp: Timestamp) -> Self {
         let mut world = World::new();
         let mut schedule = Schedule::default();
-        let timestamp = Timestamp::now();
         world.insert_resource::<Time<Real>>(Time::at(timestamp));
         world.insert_resource(Credits::new());
         schedule.add_systems((update_credits, update_ui).chain());
         Self { world, schedule }
     }
 
-    pub fn update(&mut self, timestamp: f64) {
+    pub fn update(&mut self, timestamp: Timestamp) {
         let mut real_time: Mut<Time<Real>> = self.world.resource_mut();
-        real_time.advance_to(Timestamp::at(timestamp));
+        real_time.advance_to(timestamp);
         self.schedule.run(&mut self.world);
     }
 }

core/src/lib.rs

@@ -8,30 +8,28 @@ mod time;
 mod ui;
 
 use game_state::GameState;
-use std::{
-    cell::RefCell,
-    rc::Rc,
-    sync::{Mutex, OnceLock},
-};
+use std::sync::{Mutex, OnceLock};
+use time::Timestamp;
 use wasm_bindgen::prelude::*;
 
 static GAME_STATE: OnceLock<Mutex<GameState>> = OnceLock::new();
 
-fn request_animation_frame(f: &Closure<dyn Fn(f64)>) {
+fn request_animation_frame(f: impl 'static + Fn(f64)) {
+    let update_cb: Closure<dyn Fn(f64)> = Closure::new(f);
     let window = web_sys::window().unwrap();
     let _ = window
-        .request_animation_frame(f.as_ref().unchecked_ref())
+        .request_animation_frame(update_cb.into_js_value().unchecked_ref())
         .unwrap();
 }
 
+fn update(timestamp: f64) {
+    let timestamp = Timestamp::at(timestamp);
+    let game_state = GAME_STATE.get_or_init(|| Mutex::new(GameState::new(timestamp)));
+    game_state.lock().unwrap().update(timestamp);
+    request_animation_frame(update);
+}
+
 #[wasm_bindgen(start)]
 fn run() {
-    GAME_STATE.set(Mutex::new(GameState::new())).unwrap();
-    let update_cb = Rc::new(RefCell::new(None));
-    let ucb_clone = update_cb.clone();
-    *ucb_clone.borrow_mut() = Some(Closure::new(move |timestamp| {
-        GAME_STATE.get().unwrap().lock().unwrap().update(timestamp);
-        request_animation_frame(update_cb.borrow().as_ref().unwrap());
-    }));
-    request_animation_frame(ucb_clone.borrow().as_ref().unwrap());
+    request_animation_frame(update);
 }