Client-Side Prediction for Responsive Movement

In this lesson, you will learn how to mask network latency by predicting movement locally before the server confirms your new position.

When building an authoritative multiplayer game, the server is the ultimate source of truth. However, waiting for a "round trip" packet (the time it takes for your input to reach the server and the confirmation to return) makes movement feel sluggish and unresponsive. Client-Side Prediction solves this by letting the client move the player immediately, assuming the server will eventually agree with the result.

How it Works

The client maintains its own state and applies input locally, rendering the movement instantly. Simultaneously, the client sends that input to the server. When the server eventually broadcasts the "authoritative" position back, the client compares it to its predicted position. If there is a discrepancy—perhaps due to a collision or a latency spike—the client must "reconcile" by snapping to or smoothly interpolating toward the server's version of the truth.

Consider this simplified logic loop:

void Update() {
    // 1. Local Prediction: Move instantly
    Vector3 input = GetPlayerInput();
    transform.position += input * moveSpeed * Time.deltaTime;

    // 2. Send input to server
    SendInputToServer(input);

    // 3. Reconciliation (on receiving server state)
    if (serverDataReceived) {
        float distance = Vector3.Distance(transform.position, serverPosition);
        if (distance > toleranceThreshold) {
            // Correct the position to match the server
            transform.position = serverPosition;
        }
    }
}

The Reconciliation Challenge

The trickiest part is handling the gap between your local simulation and the server's delayed state. If the server tells you where you were 100ms ago, you cannot simply snap back to that position, or your character will stutter backward. Advanced implementations keep a buffer of recent inputs. When the server provides a correction, the client "replays" all inputs that occurred after the timestamp of that server packet to arrive at the current, corrected position. This hides the correction from the player, keeping the experience fluid despite high latency.

Key Takeaway: Client-Side Prediction allows players to experience zero-latency movement by simulating inputs immediately and reconciling the game state only when the authoritative server provides a correction.