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//! This example illustrates loading scenes from files.
use bevy::{prelude::*, tasks::IoTaskPool, utils::Duration};
use std::{fs::File, io::Write};
fn main() {
App::new()
.add_plugins(DefaultPlugins)
.register_type::<ComponentA>()
.register_type::<ComponentB>()
.register_type::<ResourceA>()
.add_systems(
Startup,
(save_scene_system, load_scene_system, infotext_system),
)
.add_systems(Update, log_system)
.run();
}
// Registered components must implement the `Reflect` and `FromWorld` traits.
// The `Reflect` trait enables serialization, deserialization, and dynamic property access.
// `Reflect` enable a bunch of cool behaviors, so its worth checking out the dedicated `reflect.rs`
// example. The `FromWorld` trait determines how your component is constructed when it loads.
// For simple use cases you can just implement the `Default` trait (which automatically implements
// `FromWorld`). The simplest registered component just needs these three derives:
#[derive(Component, Reflect, Default)]
#[reflect(Component)] // this tells the reflect derive to also reflect component behaviors
struct ComponentA {
pub x: f32,
pub y: f32,
}
// Some components have fields that cannot (or should not) be written to scene files. These can be
// ignored with the #[reflect(skip_serializing)] attribute. This is also generally where the `FromWorld`
// trait comes into play. `FromWorld` gives you access to your App's current ECS `Resources`
// when you construct your component.
#[derive(Component, Reflect)]
#[reflect(Component, FromWorld)]
struct ComponentB {
pub value: String,
#[reflect(skip_serializing)]
pub _time_since_startup: Duration,
}
impl FromWorld for ComponentB {
fn from_world(world: &mut World) -> Self {
let time = world.resource::<Time>();
ComponentB {
_time_since_startup: time.elapsed(),
value: "Default Value".to_string(),
}
}
}
// Resources can be serialized in scenes as well, with the same requirements `Component`s have.
#[derive(Resource, Reflect, Default)]
#[reflect(Resource)]
struct ResourceA {
pub score: u32,
}
// The initial scene file will be loaded below and not change when the scene is saved
const SCENE_FILE_PATH: &str = "scenes/load_scene_example.scn.ron";
// The new, updated scene data will be saved here so that you can see the changes
const NEW_SCENE_FILE_PATH: &str = "scenes/load_scene_example-new.scn.ron";
fn load_scene_system(mut commands: Commands, asset_server: Res<AssetServer>) {
// "Spawning" a scene bundle creates a new entity and spawns new instances
// of the given scene's entities as children of that entity.
commands.spawn(DynamicSceneBundle {
// Scenes are loaded just like any other asset.
scene: asset_server.load(SCENE_FILE_PATH),
..default()
});
}
// This system logs all ComponentA components in our world. Try making a change to a ComponentA in
// load_scene_example.scn. If you enable the `file_watcher` cargo feature you should immediately see
// the changes appear in the console whenever you make a change.
fn log_system(
query: Query<(Entity, &ComponentA), Changed<ComponentA>>,
res: Option<Res<ResourceA>>,
) {
for (entity, component_a) in &query {
info!(" Entity({})", entity.index());
info!(
" ComponentA: {{ x: {} y: {} }}\n",
component_a.x, component_a.y
);
}
if let Some(res) = res {
if res.is_added() {
info!(" New ResourceA: {{ score: {} }}\n", res.score);
}
}
}
fn save_scene_system(world: &mut World) {
// Scenes can be created from any ECS World.
// You can either create a new one for the scene or use the current World.
// For demonstration purposes, we'll create a new one.
let mut scene_world = World::new();
// The `TypeRegistry` resource contains information about all registered types (including components).
// This is used to construct scenes, so we'll want to ensure that our previous type registrations
// exist in this new scene world as well.
// To do this, we can simply clone the `AppTypeRegistry` resource.
let type_registry = world.resource::<AppTypeRegistry>().clone();
scene_world.insert_resource(type_registry);
let mut component_b = ComponentB::from_world(world);
component_b.value = "hello".to_string();
scene_world.spawn((
component_b,
ComponentA { x: 1.0, y: 2.0 },
Transform::IDENTITY,
Name::new("joe"),
));
scene_world.spawn(ComponentA { x: 3.0, y: 4.0 });
scene_world.insert_resource(ResourceA { score: 1 });
// With our sample world ready to go, we can now create our scene using DynamicScene or DynamicSceneBuilder.
// For simplicity, we will create our scene using DynamicScene:
let scene = DynamicScene::from_world(&scene_world);
// Scenes can be serialized like this:
let type_registry = world.resource::<AppTypeRegistry>();
let serialized_scene = scene.serialize_ron(type_registry).unwrap();
// Showing the scene in the console
info!("{}", serialized_scene);
// Writing the scene to a new file. Using a task to avoid calling the filesystem APIs in a system
// as they are blocking
// This can't work in WASM as there is no filesystem access
#[cfg(not(target_arch = "wasm32"))]
IoTaskPool::get()
.spawn(async move {
// Write the scene RON data to file
File::create(format!("assets/{NEW_SCENE_FILE_PATH}"))
.and_then(|mut file| file.write(serialized_scene.as_bytes()))
.expect("Error while writing scene to file");
})
.detach();
}
// This is only necessary for the info message in the UI. See examples/ui/text.rs for a standalone
// text example.
fn infotext_system(mut commands: Commands) {
commands.spawn(Camera2dBundle::default());
commands.spawn(
TextBundle::from_section(
"Nothing to see in this window! Check the console output!",
TextStyle {
font_size: 50.0,
..default()
},
)
.with_style(Style {
align_self: AlignSelf::FlexEnd,
..default()
}),
);
}