8eb0440f1e
## Objective Implement absolute minimum viable product for the changes proposed in bevyengine/rfcs#53. ## Solution - Remove public mutative access to `Parent` (Children is already publicly read-only). This includes public construction methods like `Copy`, `Clone`, and `Default`. - Remove `PreviousParent` - Remove `parent_update_system` - Update all hierarchy related commands to immediately update both `Parent` and `Children` references. ## Remaining TODOs - [ ] Update documentation for both `Parent` and `Children`. Discourage using `EntityCommands::remove` - [x] Add `HierarchyEvent` to notify listeners of hierarchy updates. This is meant to replace listening on `PreviousParent` ## Followup - These changes should be best moved to the hooks mentioned in #3742. - Backing storage for both might be best moved to indexes mentioned in the same relations.
101 lines
3.4 KiB
Rust
101 lines
3.4 KiB
Rust
//! Creates a hierarchy of parents and children entities.
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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_bundle(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_bundle(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_bundle(SpriteBundle {
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transform: Transform {
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translation: Vec3::new(250.0, 0.0, 0.0),
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scale: Vec3::splat(0.75),
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..default()
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},
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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_bundle(SpriteBundle {
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transform: Transform {
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translation: Vec3::new(0.0, 250.0, 0.0),
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scale: Vec3::splat(0.75),
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..default()
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},
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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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// Pushing takes a slice of children to add:
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commands.entity(parent).push_children(&[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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let angle = std::f32::consts::PI / 2.0;
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for (parent, children) in parents_query.iter_mut() {
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if let Ok(mut transform) = transform_query.get_mut(parent) {
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transform.rotate_z(-angle * 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.iter() {
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if let Ok(mut transform) = transform_query.get_mut(*child) {
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transform.rotate_z(angle * 2.0 * time.delta_seconds());
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}
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}
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// To demonstrate removing children, we'll start to remove the children after a couple of
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// seconds
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if time.seconds_since_startup() >= 2.0 && children.len() == 3 {
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let child = children.last().copied().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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