Limit rewind to some static number (currently 5s)

src/bin/flappy/main.rs

@@ -128,13 +128,57 @@ enum PlayerState {
 }
 
 // A tape tracking the bird's state every frame
-#[derive(Component, Default)]
+#[derive(Component)]
 struct Tape {
-    linear_velocities: Vec<LinearVelocity>,
-    angular_velocities: Vec<AngularVelocity>,
-    external_impulses: Vec<ExternalImpulse>,
-    positions: Vec<Position>,
-    rotations: Vec<Rotation>,
+    capacity: usize,
+    linear_velocities: VecDeque<LinearVelocity>,
+    angular_velocities: VecDeque<AngularVelocity>,
+    external_impulses: VecDeque<ExternalImpulse>,
+    positions: VecDeque<Position>,
+    rotations: VecDeque<Rotation>,
+}
+
+impl Tape {
+    fn new_with_capacity(capacity: usize) -> Self {
+        Tape {
+            capacity,
+            linear_velocities: VecDeque::with_capacity(capacity),
+            angular_velocities: VecDeque::with_capacity(capacity),
+            external_impulses: VecDeque::with_capacity(capacity),
+            positions: VecDeque::with_capacity(capacity),
+            rotations: VecDeque::with_capacity(capacity),
+        }
+    }
+
+    fn push(&mut self, lv: LinearVelocity, av: AngularVelocity, ei: ExternalImpulse, p: Position, r: Rotation) {
+        // If we are at capacity, make room
+        if self.linear_velocities.len() == self.capacity {
+            self.linear_velocities.pop_front().unwrap();
+            self.angular_velocities.pop_front().unwrap();
+            self.external_impulses.pop_front().unwrap();
+            self.positions.pop_front().unwrap();
+            self.rotations.pop_front().unwrap();
+        }
+
+        self.linear_velocities.push_back(lv);
+        self.angular_velocities.push_back(av);
+        self.external_impulses.push_back(ei);
+        self.positions.push_back(p);
+        self.rotations.push_back(r);
+    }
+
+    fn pop(&mut self) -> Option<(LinearVelocity, AngularVelocity, ExternalImpulse, Position, Rotation)> {
+        if self.linear_velocities.is_empty() {
+            None
+        } else {
+            let lv = self.linear_velocities.pop_back().unwrap();
+            let av = self.angular_velocities.pop_back().unwrap();
+            let ei = self.external_impulses.pop_back().unwrap();
+            let p = self.positions.pop_back().unwrap();
+            let r = self.rotations.pop_back().unwrap();
+            Some((lv, av, ei, p, r))
+        }
+    }
 }
 
 fn init_bird(mut commands: Commands, bird_assets: Res<BirdAssets>) {
@@ -150,7 +194,10 @@ fn init_bird(mut commands: Commands, bird_assets: Res<BirdAssets>) {
         MaxLinearSpeed(500.0),
     );
 
-    let tape = Tape::default();
+    // 60fps * 60 seconds
+    // let tape = Tape::new_with_capacity(60 * 60);
+    const REWIND_SECONDS: usize = 5;
+    let tape = Tape::new_with_capacity(60 * REWIND_SECONDS);
 
     commands.spawn((
         name,
@@ -749,11 +796,7 @@ fn record(
     birds
         .iter_mut()
         .for_each(|(lv, av, ei, p, r, mut tape)| {
-            tape.linear_velocities.push(*lv);
-            tape.angular_velocities.push(*av);
-            tape.external_impulses.push(*ei);
-            tape.positions.push(*p);
-            tape.rotations.push(*r);
+            tape.push(*lv, *av, *ei, *p, *r);
         });
 }
 
@@ -781,15 +824,15 @@ fn rewind(
 
     birds.iter_mut().for_each(
         |(mut lv, mut av, mut ei, mut p, mut r, mut tape)| {
-            if tape.positions.is_empty() {
-                next.set(PlayerState::Pause);
-            } else {
-                lv.0 = tape.linear_velocities.pop().unwrap().0;
-                av.0 = tape.angular_velocities.pop().unwrap().0;
-                ei.set_impulse(tape.external_impulses.pop().unwrap().impulse());
-                p.0 = tape.positions.pop().unwrap().0;
-                *r = tape.rotations.pop().unwrap();
+            if let Some((new_lv, new_av, new_ei, new_p, new_r)) = tape.pop() {
+                lv.0 = new_lv.0;
+                av.0 = new_av.0;
+                ei.set_impulse(new_ei.impulse());
+                p.0 = new_p.0;
+                *r = new_r;
                 frames.0 += 1;
+            } else {
+                next.set(PlayerState::Pause);
             }
         },
     );