Installation and features

Add bevy_arbor to your Cargo.toml. The guard needs trees and perception:

[dependencies]
bevy_arbor = { version = "0.1", features = ["perception"] }

It needs Bevy 0.20 and Rust 1.99 or later, edition 2024.

Behavior trees (bt) are on by default. Everything else is a feature.

Feature flags has the full list, including each crate’s own features.

Adding the plugins

Add ArborPlugins. It adds the plugin of every part you turned on:

use bevy::prelude::*;
use bevy_arbor::prelude::*;
fn main() {
    App::new()
        .add_plugins((DefaultPlugins, ArborPlugins))
        .run();
}

Trees and perception run in FixedUpdate. Perception works in 3D by default. The guard lives in a side-scroller, so switch it to 2D with with_space:

use bevy::prelude::*;
use bevy_arbor::prelude::*;
fn main() {
    App::new()
        .add_plugins((
            DefaultPlugins,
            ArborPlugins.with_space(Space::Planar),
        ))
        .run();
}

To change a plugin, use set, as with Bevy’s own plugin groups. To run trees in another schedule, set TreePlugin::new: ArborPlugins.with_space(Space::Planar).set(TreePlugin::new(Update)). with_space sets PerceptionPlugin, so to change perception’s schedule as well, set that one with both: ArborPlugins.set(PerceptionPlugin::new(Update).with_space(Space::Planar)).

Using one part alone

The parts don’t depend on each other. Perception writes components on the agent, and trees read them. To use one part alone, depend on its crate, such as bevy_arbor_bt or bevy_arbor_perception, and add its plugin.

If you add the plugins one by one, also add ArborSystemsPlugin. It runs the parts in the right order. How it fits together explains that order.

Pitfalls

• Time. Trees need Bevy’s TimePlugin for waits, timeouts and cooldowns. DefaultPlugins and MinimalPlugins both include it. TreePlugin warns if it’s missing.
• Gizmos. ArborGizmosPlugin isn’t in ArborPlugins, because it needs a renderer. Add it yourself. Debugging shows how.
• Both avian features. With avian2d and avian3d both on, neither is in the prelude, since their names clash. Use bevy_arbor::avian2d::... or bevy_arbor::avian3d::... instead.