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https://github.com/bevyengine/bevy
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# 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(); ```
119 lines
3.9 KiB
Markdown
119 lines
3.9 KiB
Markdown
# B0004
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A runtime warning.
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An [`Entity`] with a hierarchy-inherited component has a [`Parent`]
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without the hierarchy-inherited component in question.
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The hierarchy-inherited components defined in bevy include:
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- [`ComputedVisibility`]
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- [`GlobalTransform`]
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Third party plugins may also define their own hierarchy components, so
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read the warning message carefully and pay attention to the exact type
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of the missing component.
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To fix this warning, add the missing hierarchy component to all ancestors
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of entities with the hierarchy component you wish to use.
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The following code will cause a warning to be emitted:
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```rust,no_run
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use bevy::prelude::*;
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// WARNING: this code is buggy
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fn setup_cube(
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mut commands: Commands,
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mut meshes: ResMut<Assets<Mesh>>,
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mut materials: ResMut<Assets<StandardMaterial>>,
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) {
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commands
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.spawn(TransformBundle::default())
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.with_children(|parent| {
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// cube
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parent.spawn(PbrBundle {
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mesh: meshes.add(Mesh::from(shape::Cube { size: 1.0 })),
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material: materials.add(Color::rgb(0.8, 0.7, 0.6).into()),
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transform: Transform::from_xyz(0.0, 0.5, 0.0),
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..default()
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});
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});
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// camera
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commands.spawn(Camera3dBundle {
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transform: Transform::from_xyz(-2.0, 2.5, 5.0).looking_at(Vec3::ZERO, Vec3::Y),
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..default()
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});
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}
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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_cube)
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.run();
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}
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```
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This code **will not** show a cube on screen.
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This is because the entity spawned with `commands.spawn(…)`
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doesn't have a [`ComputedVisibility`] component.
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Since the cube is spawned as a child of an entity without the
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[`ComputedVisibility`] component, it will not be visible at all.
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To fix this, you must use [`SpatialBundle`] over [`TransformBundle`],
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as follows:
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```rust,no_run
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use bevy::prelude::*;
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fn setup_cube(
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mut commands: Commands,
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mut meshes: ResMut<Assets<Mesh>>,
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mut materials: ResMut<Assets<StandardMaterial>>,
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) {
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commands
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// We use SpatialBundle instead of TransformBundle, it contains the
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// ComputedVisibility component needed to display the cube,
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// In addition to the Transform and GlobalTransform components.
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.spawn(SpatialBundle::default())
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.with_children(|parent| {
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// cube
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parent.spawn(PbrBundle {
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mesh: meshes.add(Mesh::from(shape::Cube { size: 1.0 })),
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material: materials.add(Color::rgb(0.8, 0.7, 0.6).into()),
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transform: Transform::from_xyz(0.0, 0.5, 0.0),
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..default()
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});
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});
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// camera
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commands.spawn(Camera3dBundle {
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transform: Transform::from_xyz(-2.0, 2.5, 5.0).looking_at(Vec3::ZERO, Vec3::Y),
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..default()
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});
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}
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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_cube)
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.run();
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}
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```
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A similar problem occurs when the [`GlobalTransform`] component is missing.
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However, when a parent [`GlobalTransform`] is missing,
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it will simply prevent all transform propagation,
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including when updating the [`Transform`] component of the child.
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You will most likely encounter this warning when loading a scene
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as a child of a pre-existing [`Entity`] that does not have the proper components.
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[`ComputedVisibility`]: https://docs.rs/bevy/*/bevy/render/view/struct.ComputedVisibility.html
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[`GlobalTransform`]: https://docs.rs/bevy/*/bevy/transform/components/struct.GlobalTransform.html
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[`Transform`]: https://docs.rs/bevy/*/bevy/transform/components/struct.Transform.html
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[`Parent`]: https://docs.rs/bevy/*/bevy/hierarchy/struct.Parent.html
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[`Entity`]: https://docs.rs/bevy/*/bevy/ecs/entity/struct.Entity.html
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[`SpatialBundle`]: https://docs.rs/bevy/*/bevy/render/prelude/struct.SpatialBundle.html
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[`TransformBundle`]: https://docs.rs/bevy/*/bevy/transform/struct.TransformBundle.html
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