In this lesson, you will learn how to mathematically adjust movement calculations to account for the Round-Trip Time (RTT) and variance in packet arrival, ensuring smooth gameplay despite network instability.
Understanding the Latency Gap
When a client sends a move command, it must travel across the network, be processed by the server, and then a response must travel back. This delay, known as RTT, means that by the time the client receives the server’s "corrective" state, the server’s view of the world is already outdated.
Jitter compounds this issue: if packets arrive at inconsistent intervals, movement appears to "teleport" or "hitch" because your client-side prediction and server-side reconciliation are fighting over a moving timeline.
Compensating with Timestamp Offsets
To bridge this gap, we don't just snap to the server's position. Instead, we use the ServerPing (or RTT) to adjust our interpolation logic. When the server sends a state update, it includes a timestamp of when that state was calculated. The client calculates the discrepancy:
float NetworkLatency = PlayerController->PlayerState->ExactPing / 1000.f;
float TargetTime = ServerTimestamp - NetworkLatency;
// We interpolate toward the state the server was in
// at the exact moment the client initiated the move.
SmoothPosition = FMath::InterpEaseInOut(CurrentPos, ServerPos, DeltaTime * JitterSmoothingFactor, 2.0f);
Smoothing the Jitter
To prevent jitter, we avoid hard-setting the actor’s location. Instead, we maintain a "Correction Buffer." When the server sends a correction that conflicts with our locally predicted position, we calculate the error vector. Rather than snapping to the server's location, we apply a small, frame-rate independent adjustment over several frames. This "softens" the correction, making the movement feel fluid even if the network is dropping frames or fluctuating in latency.
We essentially treat the incoming server data as a "suggestion" to be smoothly blended into our current movement path, effectively masking the latency gaps that would otherwise cause visual snapping.
Key Takeaway: Use the calculated RTT to offset server timestamps and apply error corrections over time rather than snapping, effectively hiding network jitter behind smooth interpolation.