01aedc8431
# Objective Now that we can consolidate Bundles and Components under a single insert (thanks to #2975 and #6039), almost 100% of world spawns now look like `world.spawn().insert((Some, Tuple, Here))`. Spawning an entity without any components is an extremely uncommon pattern, so it makes sense to give spawn the "first class" ergonomic api. This consolidated api should be made consistent across all spawn apis (such as World and Commands). ## Solution All `spawn` apis (`World::spawn`, `Commands:;spawn`, `ChildBuilder::spawn`, and `WorldChildBuilder::spawn`) now accept a bundle as input: ```rust // before: commands .spawn() .insert((A, B, C)); world .spawn() .insert((A, B, C); // after commands.spawn((A, B, C)); world.spawn((A, B, C)); ``` All existing instances of `spawn_bundle` have been deprecated in favor of the new `spawn` api. A new `spawn_empty` has been added, replacing the old `spawn` api. By allowing `world.spawn(some_bundle)` to replace `world.spawn().insert(some_bundle)`, this opened the door to removing the initial entity allocation in the "empty" archetype / table done in `spawn()` (and subsequent move to the actual archetype in `.insert(some_bundle)`). This improves spawn performance by over 10%:  To take this measurement, I added a new `world_spawn` benchmark. Unfortunately, optimizing `Commands::spawn` is slightly less trivial, as Commands expose the Entity id of spawned entities prior to actually spawning. Doing the optimization would (naively) require assurances that the `spawn(some_bundle)` command is applied before all other commands involving the entity (which would not necessarily be true, if memory serves). Optimizing `Commands::spawn` this way does feel possible, but it will require careful thought (and maybe some additional checks), which deserves its own PR. For now, it has the same performance characteristics of the current `Commands::spawn_bundle` on main. **Note that 99% of this PR is simple renames and refactors. The only code that needs careful scrutiny is the new `World::spawn()` impl, which is relatively straightforward, but it has some new unsafe code (which re-uses battle tested BundlerSpawner code path).** --- ## Changelog - All `spawn` apis (`World::spawn`, `Commands:;spawn`, `ChildBuilder::spawn`, and `WorldChildBuilder::spawn`) now accept a bundle as input - All instances of `spawn_bundle` have been deprecated in favor of the new `spawn` api - World and Commands now have `spawn_empty()`, which is equivalent to the old `spawn()` behavior. ## Migration Guide ```rust // Old (0.8): commands .spawn() .insert_bundle((A, B, C)); // New (0.9) commands.spawn((A, B, C)); // Old (0.8): commands.spawn_bundle((A, B, C)); // New (0.9) commands.spawn((A, B, C)); // Old (0.8): let entity = commands.spawn().id(); // New (0.9) let entity = commands.spawn_empty().id(); // Old (0.8) let entity = world.spawn().id(); // New (0.9) let entity = world.spawn_empty(); ```
93 lines
3.1 KiB
Rust
93 lines
3.1 KiB
Rust
//! Creates a hierarchy of parents and children entities.
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use std::f32::consts::PI;
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use bevy::prelude::*;
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fn main() {
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App::new()
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.add_plugins(DefaultPlugins)
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.add_startup_system(setup)
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.add_system(rotate)
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.run();
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}
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fn setup(mut commands: Commands, asset_server: Res<AssetServer>) {
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commands.spawn(Camera2dBundle::default());
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let texture = asset_server.load("branding/icon.png");
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// Spawn a root entity with no parent
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let parent = commands
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.spawn(SpriteBundle {
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transform: Transform::from_scale(Vec3::splat(0.75)),
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texture: texture.clone(),
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..default()
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})
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// With that entity as a parent, run a lambda that spawns its children
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.with_children(|parent| {
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// parent is a ChildBuilder, which has a similar API to Commands
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parent.spawn(SpriteBundle {
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transform: Transform::from_xyz(250.0, 0.0, 0.0).with_scale(Vec3::splat(0.75)),
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texture: texture.clone(),
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sprite: Sprite {
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color: Color::BLUE,
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..default()
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},
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..default()
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});
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})
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// Store parent entity for next sections
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.id();
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// Another way is to use the push_children function to add children after the parent
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// entity has already been spawned.
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let child = commands
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.spawn(SpriteBundle {
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transform: Transform::from_xyz(0.0, 250.0, 0.0).with_scale(Vec3::splat(0.75)),
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texture,
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sprite: Sprite {
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color: Color::GREEN,
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..default()
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},
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..default()
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})
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.id();
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// Add child to the parent.
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commands.entity(parent).add_child(child);
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}
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// A simple system to rotate the root entity, and rotate all its children separately
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fn rotate(
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mut commands: Commands,
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time: Res<Time>,
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mut parents_query: Query<(Entity, &Children), With<Sprite>>,
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mut transform_query: Query<&mut Transform, With<Sprite>>,
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) {
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for (parent, children) in &mut parents_query {
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if let Ok(mut transform) = transform_query.get_mut(parent) {
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transform.rotate_z(-PI / 2. * time.delta_seconds());
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}
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// To iterate through the entities children, just treat the Children component as a Vec
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// Alternatively, you could query entities that have a Parent component
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for child in children {
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if let Ok(mut transform) = transform_query.get_mut(*child) {
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transform.rotate_z(PI * time.delta_seconds());
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}
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}
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// To demonstrate removing children, we'll remove a child after a couple of seconds.
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if time.seconds_since_startup() >= 2.0 && children.len() == 2 {
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let child = children.last().unwrap();
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commands.entity(*child).despawn_recursive();
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}
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if time.seconds_since_startup() >= 4.0 {
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// This will remove the entity from its parent's list of children, as well as despawn
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// any children the entity has.
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commands.entity(parent).despawn_recursive();
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}
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}
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}
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