Add loading state handler, very rough

examples/sensors.rs

@@ -27,7 +27,7 @@ fn main() {
                 control_ball,
                 process_events,
                 sync_resource_to_ui::<InsideArea>.run_if(resource_changed::<InsideArea>),
-            ),
+            ).run_if(in_state(GameState::Main)),
         )
         .run();
 }

src/base_game.rs

@@ -9,10 +9,19 @@ impl Plugin for BaseGamePlugin {
             .add_plugins(DebuggingPlugin)
             .add_plugins(MeshPickingPlugin)
             .add_plugins(RapierPhysicsPlugin::<NoUserData>::default())
-            .add_systems(Startup, setup_camera);
+            .add_plugins(LoadingPlugin)
+            .add_systems(Startup, setup_camera)
+            .init_state::<GameState>();
     }
 }
 
+#[derive(States, Clone, PartialEq, Eq, Hash, Debug, Default)]
+pub enum GameState {
+    #[default]
+    Loading,
+    Main,
+}
+
 /// System to toggle the visibility of entities based on their state
 pub fn toggle_state_visibility<S: States + Component>(
     mut q: Query<(Entity, &mut Visibility, &S)>,

src/lib.rs

@@ -3,12 +3,14 @@
 
 mod base_game;
 mod debug;
+mod loading;
 mod scheduling;
 mod ui;
 
 pub use std::fmt::Display;
 
 pub use bevy::{
+    asset::LoadState,
     color::palettes::css::{BLACK, RED, WHITE},
     input::{ButtonState, keyboard::KeyboardInput, mouse::MouseMotion},
     prelude::*,
@@ -17,5 +19,6 @@ pub use bevy_rapier3d::prelude::*;
 
 pub use base_game::*;
 pub use debug::*;
+pub use loading::*;
 pub use scheduling::*;
 pub use ui::*;

src/loading.rs

@@ -0,0 +1,62 @@
+
+use super::*;
+
+/// Systems run during loading state
+pub struct LoadingPlugin;
+
+impl Plugin for LoadingPlugin {
+    fn build(&self, app: &mut App) {
+        // PERF: We check all asset classes every frame, should be event based
+        app
+            .init_resource::<TrackLoadingProgress>()
+            .add_systems(PreUpdate, reset_progress)
+            .add_systems(Update,
+                (
+                    track_loading::<AnimationClip>,
+                    track_loading::<AudioSource>,
+                    track_loading::<Font>,
+                    track_loading::<Gltf>,
+                    track_loading::<Image>,
+                    track_loading::<Shader>,
+                ).run_if(in_state(GameState::Loading)),
+            )
+            .add_systems(PostUpdate, check_progress);
+    }
+}
+
+/// Resource for tracking asset loading progress
+#[derive(Resource, Default)]
+struct TrackLoadingProgress(Vec<bool>);
+
+/// At the start of the update clear progress
+fn reset_progress(
+    mut progress: ResMut<TrackLoadingProgress>,
+) {
+    progress.0.clear()
+}
+
+/// Track the progress of all assets in this asset class
+fn track_loading<A: Asset>(
+    assets: Res<Assets<A>>,
+    server: Res<AssetServer>,
+    mut progress: ResMut<TrackLoadingProgress>,
+) {
+    let all_loaded = assets
+        .ids()
+        .map(|id| server.load_state(id))
+        .all(|load_state| {
+            !load_state.is_loading() && !load_state.is_failed()
+        });
+
+    progress.0.push(all_loaded);
+}
+
+/// At the end of the frame check if all asset classes are loaded
+fn check_progress(
+    progress: Res<TrackLoadingProgress>,
+    mut next_state: ResMut<NextState<GameState>>,
+) {
+    if progress.0.iter().all(|x| *x) {
+        next_state.set(GameState::Main);
+    }
+}