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::*;
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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_systems(Startup, setup)
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.add_systems(Update, 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.elapsed_seconds() >= 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.elapsed_seconds() >= 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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