How State Interpolation Reduces Rubber-Banding

In competitive multiplayer game development, network latency frequently causes high-ping clients to experience "rubber-banding"—the jarring effect where a character rapidly snaps or teleports back to an authoritative position. State interpolation mitigates this issue by rendering remote entities slightly in the past, allowing the client to smoothly blend between confirmed server snapshots rather than guessing where entities should be in real time. This article explores the mechanics of state interpolation, why high-ping players suffer from synchronization errors, and how buffering and smoothing techniques eliminate erratic position corrections.

The Mechanics of Rubber-Banding

In authoritative server architectures, the server remains the ultimate source of truth for all player positions, velocities, and game events. To ensure gameplay feels responsive locally, clients utilize Client-Side Prediction, immediately updating local movement before waiting for the server's acknowledgment.

When a player has high latency or packet jitter, the client's predicted position may diverge significantly from the server's simulated position by the time the acknowledgment returns. If the discrepancy exceeds a defined error threshold, the client must reconcile its state by snapping the player back to the server-verified position. For remote entities (other players), missing or delayed packets leave the client without up-to-date trajectory data, causing sudden teleportation when a delayed packet finally arrives.

How State Interpolation Works

State interpolation resolves discontinuous movement by delaying the rendering of other players by a fixed duration—often referred to as the interpolation buffer or interpolation delay (typically 50ms to 100ms, or 2–3 server ticks).

Instead of attempting to extrapolate where a player will be (which easily leads to prediction errors), the client waits until it possesses at least two authoritative snapshots from the past:

  1. Snapshot A (Older position at time \(t_0\))
  2. Snapshot B (Newer position at time \(t_1\))

The client then calculates the entity’s visual position at render time \(t\) (where \(t_0 \le t \le t_1\)) using interpolation formulas such as linear interpolation (Lerp) or cubic splines (Hermite/Catmull-Rom) for smoother curves:

\[\text{Position}(t) = \text{Lerp}(\text{Snapshot A}, \text{Snapshot B}, \alpha)\]

\[\text{where } \alpha = \frac{t - t_0}{t_1 - t_0}\]

Key Ways Interpolation Reduces Visual Artifacts

  • Buffers Against Packet Jitter: Network packets rarely arrive at uniform intervals. By maintaining a buffer of past states, state interpolation provides a cushion. If a packet arrives slightly late due to jitter, the client is still interpolating between older received states, preventing the entity from freezing and then snapping forward.
  • Transforms Discrete Ticks into Continuous Motion: Servers typically tick at 30Hz, 60Hz, or 128Hz, while client displays often refresh at 144Hz or higher. Interpolation calculates intermediate frames, providing fluid animation between coarse network updates.
  • Eliminates Extrapolation Over-Shooting: Without interpolation, a client must use dead reckoning (extrapolation) to guess an opponent's trajectory when packets lag. If an opponent changes direction during a lag spike, extrapolation sends them in the wrong direction, requiring a violent visual snap-back once the real data arrives. Interpolation looks backward, entirely bypassing trajectory mispredictions for remote players.

Balancing Latency and Competitive Integrity

While state interpolation creates fluid visual movement, it introduces a necessary trade-off: players observe remote entities slightly in the past.

To maintain competitive fairness, modern engines pair state interpolation with Server-Side Lag Compensation. When a player shoots at an interpolated target, the client sends the timestamp of the shot to the server. The server then rolls back its game state to that exact historical timestamp, verifying whether the crosshair was aligned with the target as it appeared on the shooter's screen. This ensures that the visual smoothness gained from interpolation does not compromise hit registration accuracy in high-stakes competitive environments.