120 lines
3.9 KiB
Markdown
120 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_systems(Startup, 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_systems(Startup, 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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