let user run a function on a scene entities

Cargo.toml

@@ -106,6 +106,10 @@ path = "examples/2d/contributors.rs"
 name = "text2d"
 path = "examples/2d/text2d.rs"
 
+[[example]]
+name = "3d_scene"
+path = "examples/3d/3d_scene.rs"
+
 [[example]]
 name = "load_gltf"
 path = "examples/3d/load_gltf.rs"
@@ -118,10 +122,6 @@ path = "examples/3d/msaa.rs"
 name = "parenting"
 path = "examples/3d/parenting.rs"
 
-[[example]]
-name = "3d_scene"
-path = "examples/3d/3d_scene.rs"
-
 [[example]]
 name = "spawner"
 path = "examples/3d/spawner.rs"
@@ -130,6 +130,10 @@ path = "examples/3d/spawner.rs"
 name = "texture"
 path = "examples/3d/texture.rs"
 
+[[example]]
+name = "update_gltf_scene"
+path = "examples/3d/update_gltf_scene.rs"
+
 [[example]]
 name = "z_sort_debug"
 path = "examples/3d/z_sort_debug.rs"

crates/bevy_scene/src/scene_spawner.rs

@@ -14,10 +14,10 @@ struct InstanceInfo {
 }
 
 #[derive(Copy, Clone, Debug, Eq, PartialEq, Hash)]
-struct InstanceId(Uuid);
+pub struct InstanceId(Uuid);
 
 impl InstanceId {
-    pub fn new() -> Self {
+    fn new() -> Self {
         InstanceId(Uuid::new_v4())
     }
 }
@@ -51,15 +51,17 @@ impl SceneSpawner {
         self.dynamic_scenes_to_spawn.push(scene_handle);
     }
 
-    pub fn spawn(&mut self, scene_handle: Handle<Scene>) {
+    pub fn spawn(&mut self, scene_handle: Handle<Scene>) -> InstanceId {
         let instance_id = InstanceId::new();
         self.scenes_to_spawn.push((scene_handle, instance_id));
+        instance_id
     }
 
-    pub fn spawn_as_child(&mut self, scene_handle: Handle<Scene>, parent: Entity) {
+    pub fn spawn_as_child(&mut self, scene_handle: Handle<Scene>, parent: Entity) -> InstanceId {
         let instance_id = InstanceId::new();
         self.scenes_to_spawn.push((scene_handle, instance_id));
         self.scenes_with_parent.push((instance_id, parent));
+        instance_id
     }
 
     pub fn despawn(&mut self, scene_handle: Handle<DynamicScene>) {
@@ -155,7 +157,7 @@ impl SceneSpawner {
         world: &mut World,
         resources: &Resources,
         scene_handle: Handle<Scene>,
-    ) -> Result<(), SceneSpawnError> {
+    ) -> Result<InstanceId, SceneSpawnError> {
         self.spawn_sync_internal(world, resources, scene_handle, InstanceId::new())
     }
 
@@ -165,7 +167,7 @@ impl SceneSpawner {
         resources: &Resources,
         scene_handle: Handle<Scene>,
         instance_id: InstanceId,
-    ) -> Result<(), SceneSpawnError> {
+    ) -> Result<InstanceId, SceneSpawnError> {
         let mut instance_info = InstanceInfo {
             entity_map: EntityMap::default(),
         };
@@ -220,7 +222,7 @@ impl SceneSpawner {
             .entry(scene_handle)
             .or_insert_with(Vec::new);
         spawned.push(instance_id);
-        Ok(())
+        Ok(instance_id)
     }
 
     pub fn update_spawned_scenes(
@@ -304,6 +306,21 @@ impl SceneSpawner {
             }
         }
     }
+
+    /// Check that an scene instance spawned previously is ready to use
+    pub fn instance_is_ready(&self, instance_id: InstanceId) -> bool {
+        self.spawned_instances.contains_key(&instance_id)
+    }
+
+    /// Get an iterator over the entities in an instance, once it's spawned
+    pub fn iter_instance_entities(
+        &'_ self,
+        instance_id: InstanceId,
+    ) -> Option<impl Iterator<Item = Entity> + '_> {
+        self.spawned_instances
+            .get(&instance_id)
+            .map(|instance| instance.entity_map.values())
+    }
 }
 
 pub fn scene_spawner_system(world: &mut World, resources: &mut Resources) {

examples/3d/update_gltf_scene.rs

@@ -0,0 +1,93 @@
+use bevy::{prelude::*, scene::InstanceId};
+
+fn main() {
+    App::build()
+        .add_resource(Msaa { samples: 4 })
+        .add_plugins(DefaultPlugins)
+        .add_resource(SceneInstance::default())
+        .add_startup_system(setup.system())
+        .add_system(scene_update.system())
+        .add_system(move_scene_entities.system())
+        .run();
+}
+
+// Resource to hold the scene `instance_id` until it is loaded
+#[derive(Default)]
+struct SceneInstance(Option<InstanceId>);
+
+// Component that will be used to tag entities in the scene
+struct EntityInMyScene;
+
+fn setup(
+    commands: &mut Commands,
+    asset_server: Res<AssetServer>,
+    mut scene_spawner: ResMut<SceneSpawner>,
+    mut scene_instance: ResMut<SceneInstance>,
+) {
+    commands
+        .spawn(LightBundle {
+            transform: Transform::from_translation(Vec3::new(4.0, 5.0, 4.0)),
+            ..Default::default()
+        })
+        .spawn(Camera3dBundle {
+            transform: Transform::from_translation(Vec3::new(1.05, 0.9, 1.5))
+                .looking_at(Vec3::new(0.0, 0.3, 0.0), Vec3::unit_y()),
+            ..Default::default()
+        });
+
+    // Spawn the scene as a child of another entity. This first scene will be translated backward
+    // with its parent
+    commands
+        .spawn((
+            Transform::from_translation(Vec3::new(0.0, 0.0, -1.0)),
+            GlobalTransform::default(),
+        ))
+        .with_children(|parent| {
+            parent.spawn_scene(asset_server.load("models/FlightHelmet/FlightHelmet.gltf"));
+        });
+
+    // Spawn a second scene, and keep its `instance_id`
+    let instance_id =
+        scene_spawner.spawn(asset_server.load("models/FlightHelmet/FlightHelmet.gltf"));
+    scene_instance.0 = Some(instance_id);
+}
+
+// This system will wait for the scene to be ready, and then tag entities from
+// the scene with `EntityInMyScene`. All entities from the second scene will be
+// tagged
+fn scene_update(
+    commands: &mut Commands,
+    scene_spawner: Res<SceneSpawner>,
+    scene_instance: Res<SceneInstance>,
+    mut done: Local<bool>,
+) {
+    if !*done {
+        if let Some(instance_id) = scene_instance.0 {
+            if let Some(entity_iter) = scene_spawner.iter_instance_entities(instance_id) {
+                entity_iter.for_each(|entity| {
+                    commands.insert_one(entity, EntityInMyScene);
+                });
+                *done = true;
+            }
+        }
+    }
+}
+
+// This system will move all entities with component `EntityInMyScene`, so all
+// entities from the second scene
+fn move_scene_entities(
+    time: Res<Time>,
+    mut scene_entities: Query<&mut Transform, With<EntityInMyScene>>,
+) {
+    let mut direction = 1.;
+    let mut scale = 1.;
+    for mut transform in scene_entities.iter_mut() {
+        transform.translation = Vec3::new(
+            scale * direction * time.seconds_since_startup().sin() as f32 / 20.,
+            0.,
+            time.seconds_since_startup().cos() as f32 / 20.,
+        );
+        direction *= -1.;
+        scale += 0.5;
+    }
+}

examples/README.md

@@ -73,6 +73,7 @@ Example | File | Description
 `parenting` | [`3d/parenting.rs`](./3d/parenting.rs) | Demonstrates parent->child relationships and relative transformations
 `spawner` | [`3d/spawner.rs`](./3d/spawner.rs) | Renders a large number of cubes with changing position and material
 `texture` | [`3d/texture.rs`](./3d/texture.rs) | Shows configuration of texture materials
+`update_gltf_scene` | [`3d/update_gltf_scene.rs`](./3d/update_gltf_scene.rs) | Update a scene from a gltf file, either by spawning the scene as a child of another entity, or by accessing the entities of the scene
 `z_sort_debug` | [`3d/z_sort_debug.rs`](./3d/z_sort_debug.rs) | Visualizes camera Z-ordering
 
 ## Application