Guide

Multiplayer#

Perception runs on the server only. Clients get an optional, compact summary for their UI: a detection meter, a "being watched" indicator, a spectator view.

The 30-second version

The APS Core goes on the Pawn, and the Pawn must have Replicates on.
Profile › Replication › Replicate Perception State on.
On clients: On Replicated State Changed → Get Replicated Perception State → update the widget.

How it works#

On a client, APS does nothing at all: no traces, no evaluation, no cost. Clients can't be tricked into reporting a detection, and there is nothing to desync. Everything that changes perception (Emit Sound, Report Pain from Definition, Set Target Confidence, Add Target Evidence, squads) must run on the server: a sound emitted only on a client is heard by nobody.

Perception events (On AI Detect and the rest) fire on the server. Replicate their consequences (an animation, a state on your character), not the perception.

The APS Core goes on the Pawn#

The APS Core must be on the Pawn or Character it perceives for, never on the AI Controller:

It perceives from the body: eye position and facing, mesh sockets, the collision touch listens to, the damage it feels. A controller stays where it spawned and never takes damage.
It replicates with the Pawn. A component reaches clients only through an actor that replicates. Pawns do; AI Controllers never do.

On a controller it logs an error naming the controller (also in the Message Log after Play) and stays off. Your Behavior Tree and Blackboard stay on the controller: reach the core with Get Controlled Pawn → Get Component by Class (APS Core).

Turn on the summary#

Profile › Replication:

Setting	Default	What it does
`Replicate Perception State`	Off	Send a compact summary of this AI's targets to clients
`Max Replicated Targets`	3	How many targets go in (1 to 8), the best first. Every AI with replication pays for this.
`Replication Interval`	0.25	Seconds between updates
`Use Replication Relevance`	On	Leave out targets nobody is near or that it barely suspects (the next two)
`Replication Relevance Range`	15000	A target whose believed position is further than this (cm) from every player's camera is left out; 0 turns the distance test off
`Replication Min Confidence`	0.1	Below this confidence a target is left out
`Skip Unchanged Replication`	On	Send nothing when nothing changed
`Replication Confidence Delta`	0.02	How much confidence must move to count as a change

Only targets that are Suspected, Detected, Tracked or Lost go in. Turn Replicates on in the Pawn's Class Defaults too: if it's off, the summary can't reach anyone, and APS logs a warning once.

Read it on clients#

On Replicated State Changed
  └─► Get Replicated Perception State
        ├─ Out Targets   (array of APSReplicated Target State)
        └─ Out Awareness (the AI's awareness)
              └─► update the detection meter

Each APSReplicated Target State has Target, Confidence, State, Threat Level and Last Known Position; Out Awareness is also on the APS Core as the variable Replicated Awareness. Bind the event instead of polling on Tick.

On Replicated State Changed is raised when new data arrives, which happens only on clients. On a listen server's host (and in single player) it never fires: there, read Get Replicated Perception State on a short timer, or use the server's own events.

Bandwidth#

The most it can cost is **AI × Max Replicated Targets ÷ Replication Interval** target states a second: 50 AI × 3 ÷ 0.25 s is 600. Relevance and skipping unchanged updates usually send far less.

Most games only need this on the few AI near the player. Keep replication off in the base profile and on in a close-range child profile, and switch with Set Profile when an AI comes near (Profiles). Or set Max Replicated Targets to 1 and Replication Interval to 0.5.

Debugging in multiplayer#

The Visualizer, Explain Perception and the recording read what the AI believes, which exists only where perception runs: the server. Debug with a listen server (or play as the host), not from a pure client.

Checklist#

APS Core on the Pawn, the Pawn set to Replicates
Replicate Perception State on, if clients show perception in their UI
Max Replicated Targets as small as your UI needs
Client UI reads Get Replicated Perception State, driven by On Replicated State Changed (a timer on a listen-server host)
Emit Sound, pain, evidence and confidence calls run on the server (Has Authority)

When something's wrong#

Symptom	Cause
The client's target array is empty	`Replicate Perception State` is off, the Pawn doesn't replicate (look for the APS warning), or no target passes relevance
The AI perceives nothing and the log says the APS Core is on a controller	Move it to the Pawn or Character Blueprint
The meter never updates on the host	On a listen-server host the event doesn't fire: read the state on a timer
A sound is never heard	Emit Sound ran only on a client: call it from server code or through a server RPC
Perception events never fire on clients	By design: perception runs on the server
Bandwidth spikes with many AI	Lower `Max Replicated Targets`, raise `Replication Interval`, and replicate only the AI near players