Bevy animation graph

When to use

Load this when clips must blend, add, or mask. Single-clip playback stays on bevy-animation.

ECS shape

• Assets: AnimationGraph describes how clips blend. add_clip parents a clip node. add_blend parents a blend node. add_clip_with_mask stores a u64 mask (bone groups you assign; 0 means no mask).
• Components: AnimationGraphHandle is a handle to the graph used by the AnimationPlayer on the same entity. AnimationTransitions crossfades between nodes.
• Weights: ActiveAnimation::set_weight on the player, after play, drives a node that is already in the graph.
• Systems: evaluation still runs through the animation player systems. Do not add a second player.

#[derive(Resource)]
struct LocomotionNodes {
    graph: Handle<AnimationGraph>,
    walk: AnimationNodeIndex,
    run: AnimationNodeIndex,
}

fn build_locomotion_graph(
    mut commands: Commands,
    asset_server: Res<AssetServer>,
    mut graphs: ResMut<Assets<AnimationGraph>>,
) {
    let mut graph = AnimationGraph::new();
    let blend = graph.add_blend(0.5, graph.root);
    let walk = graph.add_clip(
        asset_server.load(GltfAssetLabel::Animation(0).from_asset("models/fox.glb")),
        1.0,
        blend,
    );
    let run = graph.add_clip_with_mask(
        asset_server.load(GltfAssetLabel::Animation(1).from_asset("models/fox.glb")),
        0b0011,
        1.0,
        blend,
    );
    let handle = graphs.add(graph);
    commands.insert_resource(LocomotionNodes {
        graph: handle,
        walk,
        run,
    });
}

#[derive(Resource)]
struct LocomotionNodes {
    graph: Handle<AnimationGraph>,
    walk: AnimationNodeIndex,
    run: AnimationNodeIndex,
}

fn attach_player(
    mut commands: Commands,
    nodes: Res<LocomotionNodes>,
    mut players: Query<(Entity, &mut AnimationPlayer), Without<AnimationGraphHandle>>,
) {
    for (entity, mut player) in &mut players {
        commands.entity(entity).insert((
            AnimationGraphHandle(nodes.graph.clone()),
            AnimationTransitions::new(),
        ));
        player.play(nodes.walk).repeat();
        player.play(nodes.run).repeat();
    }
}

#[derive(Resource)]
struct LocomotionNodes {
    graph: Handle<AnimationGraph>,
    walk: AnimationNodeIndex,
    run: AnimationNodeIndex,
}

#[derive(Component)]
struct RunBlend(f32);

fn sync_blend(mut players: Query<(&mut AnimationPlayer, &RunBlend)>, nodes: Res<LocomotionNodes>) {
    for (mut player, blend) in &mut players {
        if let Some(active) = player.animation_mut(nodes.run) {
            active.set_weight(blend.0.clamp(0.0, 1.0));
        }
        if let Some(active) = player.animation_mut(nodes.walk) {
            active.set_weight(1.0 - blend.0.clamp(0.0, 1.0));
        }
    }
}

use std::time::Duration;

#[derive(Resource)]
struct LocomotionNodes {
    graph: Handle<AnimationGraph>,
    walk: AnimationNodeIndex,
    run: AnimationNodeIndex,
}

#[derive(Component)]
struct RunBlend(f32);

fn fade_to_run(
    nodes: Res<LocomotionNodes>,
    mut query: Query<(&mut AnimationPlayer, &mut AnimationTransitions, &RunBlend)>,
) {
    for (mut player, mut transitions, blend) in &mut query {
        if blend.0 > 0.5 {
            transitions.play(&mut player, nodes.run, Duration::from_millis(180));
        }
    }
}

[dependencies]
bevy = "0.20"

Graph choices

Need	Bevy approach
Blend clips	AnimationGraph plus AnimationGraphHandle
Gameplay mode	App or entity states stay on bevy-state-machines. The graph is not that state type.
Additive layer	AnimationGraph::add_additive_blend inserts AnimationNodeType::Add. Clip weights still go through ActiveAnimation::set_weight.

Scope

• Crossfades use AnimationTransitions::play with a Duration, as in fade_to_run.
• Persisting a graph is SerializedAnimationGraph plus ron. A 1D or 2D blend-space type is not part of AnimationGraph; blend with node weights.

Expert Knowledge Delta

Target: Bevy 0.20+.

Core ECS types: Component, Resource, Query, Commands, Startup, Update, Fixed / FixedMain (bevy::time), .chain(), Plugin, DefaultPlugins, MinimalPlugins. Messages and observers are an ownership slot. See bevy-events-messaging for their APIs. Systems run in parallel unless .chain() orders the ones that conflict.

Who owns state

Piece	Owner	Who may mutate	Schedule
Data on one entity	Component	One system via Query	Update or FixedMain
One value for the whole app	Resource	One system	Startup to insert, then the schedule that reads it
Spawn	Commands	The spawning system	Startup for the initial world; later schedules for runtime spawn
Order that must not race	.chain()	The chained systems only	Same schedule
Plugin boundary	Plugin	build registers systems and resources	Before the app runs

Borrow rule: two systems that both mutably query the same component must be ordered (.chain()) or split so only one writes. Unrelated systems stay parallel. That is the ECS page rule, not a guess at a system-set API.

Decision

If you need	Do this	Do not
Per-entity data	Component + Query	A script field copied onto the entity
App-wide config or clock	Resource	Copy the value onto every entity
Stable simulation step	FixedMain and the Fixed clock	Tie simulation to raw frame Update
Startup spawn	Commands in Startup	Spawn from a render system
Cross-system notice that is not shared state	Message or observer slot in bevy-events-messaging	A new event type invented in this file
An API outside the documented set	Check the official docs first	A made-up crate or API

Load references/ecs-ownership.md for the ownership table.

NEVER

• Do not pin /0.20.0/ in docs URLs. WHY: links stay on latest; the 0.20 target is stated once in prose.

• Do not mutably query the same component from two unordered systems. WHY: the schedule runs systems in parallel unless .chain() orders them.

• Do not invent a physics, navigation, networking, or XR crate here. WHY: this skill only names documented Bevy crates and modules.

• No AnimationTree, BlendSpace, or scene-tree state-machine types in Bevy code. WHY: AnimationGraph, AnimationGraphHandle, and AnimationTransitions are the documented Bevy pieces.

• No invented APIs or unnamed third-party crates as the chosen solver. WHY: Bevy code stays idiomatic ECS and uses only documented Bevy APIs.

Reference

Official links stay on bevy.org. The library pin on bevy-master stays 0.20.0.

Official Documentation

• Assets - Official asset catalog. No third-party crate was selected.
• Examples - Example tree on the latest branch.
• ECS - Component, systems, Query, Startup, Update, and .chain().
• Plugins - Plugin, DefaultPlugins, MinimalPlugins, and add_plugins.

Related Skills

Prerequisites

• bevy-master - Hub and schedules.
• bevy-ecs-composition - Components and systems.
• bevy-animation - Player and clips the graph drives.

Complements

• bevy-state-machines - Gameplay mode is not an animation graph.
• godot-animation-tree-mastery - Same topic on the Godot track.

Downstream / consumers

• None yet.

Master

• bevy-master - Bevy router.