AI for Bevy: reactive behavior trees, perception, environment queries, smart objects and navigation.
Behavior trees that sleep until something they wait on changes, with tasks as entities your own systems tick.
The bevy_arbor book · docs.rs/bevy_arbor · crates.io/crates/bevy_arbor
An agent carries its behavior tree as a component. Each task the tree reaches is an entity of its own, with a component of yours on it, ticked by your systems; the tree despawns it when it's done or no longer wanted. Between ticks a tree sleeps, until a component its decorators read changes, a timer runs out, or its task reports. Perception writes what an agent senses to it, changing only when something is noticed, lost or forgotten, so trees reading it sleep in between.
Warning
Early development. The API may change at any time.
- Reactive behavior trees: composites, modifiers and decorators, built
with the
behavior_tree!macro, that sleep until something they wait on changes. - Tasks as entities: each task a tree starts is an entity with a component of yours, ticked by your own systems and despawned when it's no longer wanted.
- Perception: sight, hearing, touch and sharing between allies, in 2D or 3D, with memory, sensors and senses of your own.
- Environment queries: generate places and things round an agent, filter and score them, and pick the best: cover, a target, a place to flank.
- Smart objects: slots on things in the world that agents find, claim and use, running behavior the object brings.
- Navigation, your way: a
MoveTotask and path costs for queries, over whatever pathfinding and movement your game has. - Physics with avian: line of sight through colliders, and touch from contacts.
- Debug drawing: sight cones, what's perceived, how queries scored, slots, and where agents are going, with Bevy's gizmos.
- Rust + Cargo: 1.99+, Edition 2024
- Bevy: 0.20
Add bevy_arbor with perception:
[dependencies]
bevy_arbor = { version = "0.1", features = ["perception"] }A guard that patrols, and chases what it sees:
use bevy::prelude::*;
use bevy_arbor::prelude::*;
/// A task is a component of yours: the tree spawns an entity with it, and
/// your systems tick it.
#[derive(Component, Clone)]
struct Patrol;
#[derive(Component, Clone)]
struct Chase;
/// A condition: the tree wakes only when what the guard sees changes.
fn sees_intruder(seen: &Perceived<Sight>) -> bool {
seen.active().any(Percept::is_hostile)
}
fn spawn(mut commands: Commands) {
commands.spawn((
Sight::new(12.0).with_lose_range(15.0),
Team(1),
Transform::default(),
BehaviorTree::new(behavior_tree! {
Forever => {
Select => {
when(sees_intruder) => task(Chase),
task(Patrol),
}
}
}),
));
}
/// Moves each chasing guard toward what it sees; `patrol` is alike.
fn chase(
mut tasks: Tasks<&Chase, (&Perceived<Sight>, &mut Transform)>,
targets: Query<&GlobalTransform>,
) {
tasks.for_each(|_, _, (seen, mut at)| {
let target = seen.active().find(|percept| percept.is_hostile());
if let Some(target) = target.and_then(|percept| targets.get(percept.entity()).ok()) {
let toward = target.translation() - at.translation;
at.translation += toward.clamp_length_max(0.1);
}
});
}
fn main() {
App::new()
.add_plugins((
DefaultPlugins,
ArborPlugins.with_space(Space::Planar),
))
.add_systems(Startup, spawn)
.add_systems(FixedUpdate, chase.after(ArborSystems))
.run();
}The bevy_arbor book is the guide: building trees, tasks and interruption, perception, environment queries, smart objects and navigation, one guard built up chapter by chapter. See its Installation and Feature flags pages for configuration.
See CONTRIBUTING.md for development setup and guidelines, and CHANGELOG.md for release notes.
Licensed under either of Apache License, Version 2.0 or MIT license at your option.