snippets of code

gistfile1.txt

..in on_start 
world.exec(
            |(loader, mut scene, mut scene_map): (PrefabLoader<'_, ScenePrefabData>, Write<'_, Scene>, Write<'_, SceneMap>)| {
                scene_map.insert(0,
                    loader.load(
                        Path::new("prefab")
                            .join("lightroom_0.ron")
                            .to_string_lossy(),
                        RonFormat,
                        self.progress.as_mut().unwrap(),
                    ),
                );
                scene_map.insert(1,
                    loader.load(
                        Path::new("prefab")
                            .join("lightroom_1.ron")
                            .to_string_lossy(),
                        RonFormat,
                        self.progress.as_mut().unwrap(),
                    ),
                );

                scene.handle = Some(scene_map.get(&0).unwrap().clone());
            },
        );
        
...
        
        
        
#[derive(Derivative)]
#[derivative(Default(bound = ""))]
pub struct Scene {
    pub handle: Option<Handle<Prefab<ScenePrefabData>>>,
    pub scene: Option<usize>,
    pub entity: Option<Entity>,
    pub animation_index: usize,
}        
        
#[derive(Debug, SystemDesc, new)]
#[system_desc(name(SceneChangeSystemDesc))]
pub struct SceneChangeSystem;

impl<'a> System<'a> for SceneChangeSystem {
    type SystemData = (
        Entities<'a>,
        Read<'a, UIState>,
        Write<'a, Scene>,
        Read<'a, SceneMap>,
        WriteStorage<'a, Handle<Prefab<ScenePrefabData>>>,
    );

    fn run(&mut self, (entities, ui_state, mut scene, scene_map, mut prefabs): Self::SystemData) {
        if scene.scene.is_none() || scene.scene.unwrap() != ui_state.scene {
            scene.scene = Some(ui_state.scene);
            let scene_handle = scene_map.get(&ui_state.scene).unwrap().clone();
            if scene.entity.is_some() {
                entities.delete(scene.entity.unwrap());
            }
            println!("Creating new parent entity for scene {}.", scene.scene.unwrap());
            scene.entity = Some(entities.build_entity().with(scene_handle, &mut prefabs).build());
        }
    }
}