Approach

Based on game build 714014 | Last updated: 2026-03-03

Overview

Approach is a behavior node used in the DST AI behavior tree system to move an entity toward a specified target until it comes within a defined distance threshold. It relies on the locomotor component to execute movement and integrates with the health component to detect target validity (e.g., whether the target is dead). The node transitions to SUCCESS when the target is within range or FAILED when the target becomes invalid or unreachable.

Usage example

local approach = inst.components.behaviourtree:GetNode("Approach")
    or inst.components.behaviourtree:AddNode("Approach", inst, target_entity, 3.0, true)
approach:EvaluateDistances()
-- In stategraph or behavior tree context:
if approach:Visit() == "SUCCESS" then
    -- Target reached within range
end

Dependencies & tags

Components used: locomotor, health Tags: Checks running (state tag) on the entity's stategraph; no custom tags added or removed.

Properties

Property	Type	Default Value	Description
inst	entity	nil	The entity instance that will move (owner of the component).
target	entity/function	nil	The target entity, or a function returning an entity.
dist	number/function	nil	The squared distance threshold (if number) or a function computing it.
canrun	boolean	true	Whether the entity is allowed to run (use GoToPoint(..., nil, true)).
currenttarget	entity	nil	The currently targeted entity (cached during evaluation).
dist_fn	function	nil	Optional function that computes distance dynamically (set if dist is a function).

Main functions

GetTarget()

• Description: Retrieves the target entity by evaluating self.target (which may be a function or direct reference) and validates it.
• Parameters: None.
• Returns: entity if valid and not destroyed, otherwise nil.

EvaluateDistances()

• Description: Updates the self.dist value if self.dist_fn is set. Called when the target changes to recompute dynamic distance thresholds.
• Parameters: None.
• Returns: Nothing.

DBString()

• Description: Returns a debug string containing the current target name and distance (in meters), useful for behavior tree visualization or logging.
• Parameters: None.
• Returns: string — formatted as "<target>, (xx.xx) ".

AreDifferentPlatforms(inst, target)

• Description: Determines whether the entity and target are on different platforms, respecting the allow_platform_hopping setting on locomotor.
• Parameters:
  • inst (entity) — the moving entity.
  • target (entity) — the target entity.
• Returns: boolean — true if platforms differ and platform hopping is disabled; otherwise false.

Visit()

• Description: The core method called by the behavior tree to execute the node's logic. Evaluates target validity, computes distances, and moves the entity toward the target if needed.
• Parameters: None.
• Returns: Implicitly returns nil, but sets self.status to "READY", "RUNNING", "SUCCESS", or "FAILED".
• Error states:
  • Returns early (sets status = FAILED) if self.currenttarget is nil or invalid.
  • Stops movement via locomotor:Stop() and returns nil if target becomes invalid during RUNNING.

Events & listeners

• Listens to: None (does not register event listeners directly).
• Pushes: None (does not fire events directly; relies on stategraph or behavior tree node handling).