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hierarchy.rs
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hierarchy.rs
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//! Creates a hierarchy of parents and children entities.
use std::f32::consts::*;
use bevy::prelude::*;
fn main() {
App::new()
.add_plugins(DefaultPlugins)
.add_systems(Startup, setup)
.add_systems(Update, rotate)
.run();
}
fn setup(mut commands: Commands, asset_server: Res<AssetServer>) {
commands.spawn(Camera2dBundle::default());
let texture = asset_server.load("branding/icon.png");
// Spawn a root entity with no parent
let parent = commands
.spawn(SpriteBundle {
transform: Transform::from_scale(Vec3::splat(0.75)),
texture: texture.clone(),
..default()
})
// With that entity as a parent, run a lambda that spawns its children
.with_children(|parent| {
// parent is a ChildBuilder, which has a similar API to Commands
parent.spawn(SpriteBundle {
transform: Transform::from_xyz(250.0, 0.0, 0.0).with_scale(Vec3::splat(0.75)),
texture: texture.clone(),
sprite: Sprite {
color: Color::BLUE,
..default()
},
..default()
});
})
// Store parent entity for next sections
.id();
// Another way is to use the push_children function to add children after the parent
// entity has already been spawned.
let child = commands
.spawn(SpriteBundle {
transform: Transform::from_xyz(0.0, 250.0, 0.0).with_scale(Vec3::splat(0.75)),
texture,
sprite: Sprite {
color: Color::GREEN,
..default()
},
..default()
})
.id();
// Add child to the parent.
commands.entity(parent).add_child(child);
}
// A simple system to rotate the root entity, and rotate all its children separately
fn rotate(
mut commands: Commands,
time: Res<Time>,
mut parents_query: Query<(Entity, &Children), With<Sprite>>,
mut transform_query: Query<&mut Transform, With<Sprite>>,
) {
for (parent, children) in &mut parents_query {
if let Ok(mut transform) = transform_query.get_mut(parent) {
transform.rotate_z(-PI / 2. * time.delta_seconds());
}
// To iterate through the entities children, just treat the Children component as a Vec
// Alternatively, you could query entities that have a Parent component
for child in children {
if let Ok(mut transform) = transform_query.get_mut(*child) {
transform.rotate_z(PI * time.delta_seconds());
}
}
// To demonstrate removing children, we'll remove a child after a couple of seconds.
if time.elapsed_seconds() >= 2.0 && children.len() == 2 {
let child = children.last().unwrap();
commands.entity(*child).despawn_recursive();
}
if time.elapsed_seconds() >= 4.0 {
// This will remove the entity from its parent's list of children, as well as despawn
// any children the entity has.
commands.entity(parent).despawn_recursive();
}
}
}