`state_tree`

AI & gameplay Experimental

Author StateTree assets: evaluators, tasks, conditions, transitions.

What it's for

StateTree is Unreal's hierarchical state machine for AI and gameplay logic. This namespace lets your assistant author those assets directly: attach native task, evaluator, and condition nodes to states, wire up transitions, and bind one node's property to another. Every node type is addressed by its UScriptStruct name or path, so you describe the behavior you want and the assistant drops in the right FStateTreeTaskBase, FStateTreeEvaluatorBase, or FStateTreeConditionBase child.

Reach for it when you are building or editing StateTree logic and want the structure filled in from a description instead of clicking through the StateTree editor: adding a task to a state, gating a state's entry with a condition, or setting what triggers a transition (a tick, a gameplay event, or a completed child state).

This is a sibling to the behavior_tree namespace. Use state_tree when your project drives its AI or gameplay through StateTree assets, and behavior_tree when the logic lives in classic Behavior Tree assets instead.

This area is experimental and still improving. The node set and parameter shapes may change between releases, so verify what the assistant authored before you rely on it.

Examples

Add a task to a state

Attach a native task node to an existing state so it runs while that state is active.

You: In ST_Guard, make the Patrol state run a MoveTo task.

  call("state_tree.add_task", {stateTreePath:"/Game/AI/ST_Guard",
        stateName:"Patrol", taskClass:"StateTreeMoveToTask", save:true})
    → {ok:true, nodeId:"A1F3..."}

Done. Patrol now runs a MoveTo task.

Gate a state with an enter condition

Add a condition to a state's enter conditions so it is only selected when the condition passes.

You: Only let ST_Guard enter Chase when the alert tag is set.

  call("state_tree.add_condition", {stateTreePath:"/Game/AI/ST_Guard",
        stateName:"Chase", conditionClass:"StateTreeGameplayTagMatchCondition",
        target:"enter", save:true})
    → {ok:true, nodeId:"7C2B..."}

Done. Chase now requires the alert condition to enter.

Trigger a transition on a gameplay event

Set an existing transition to fire on a specific event tag rather than every tick.

You: In ST_Guard, make Chase go back to Patrol when it hears the lost-target event.

  call("state_tree.set_transition_trigger", {stateTreePath:"/Game/AI/ST_Guard",
        fromState:"Chase", toState:"Patrol", trigger:"OnEvent",
        gameplayEventTag:"AI.Event.LostTarget", save:true})
    → {ok:true}

Done. Chase transitions to Patrol on the LostTarget event.

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