Interpolation
Interpolation smooths the movement of other players between server updates rather than snapping them to each new position. The client renders slightly in the past and draws the path between two known states. It costs a little added delay on remote players in exchange for motion that looks continuous.
Also called
entity interpolation
,
What Does Interpolation Cost, and What Does It Buy?
Interpolation trades time for certainty. An interpolated player only moves through positions the server actually sent, so there is nothing to mispredict and nothing to snap back. It is also cheap: the client runs no game logic for that player, only the blend between two states (SnapNet).
The price is the delay. Valve's Source engine defaults to 100 ms, so that one lost update still leaves two to blend between (Valve). Newer libraries adjust the delay as conditions change instead of fixing it. SnapNet aims for each entity to reach its latest update just as the next one arrives, and Unity's Netcode for Entities takes measured jitter into account when it sizes the buffer (Unity documentation).
In Practices - Insights from Edgegap's Blog
Article's key insights
Desync is a disagreement, not a delay: Lag means information arrives late. Desync means two machines hold different versions of the same world, which is a separate failure with separate fixes.
There are two distinct kinds: Replication desync, where an authoritative server corrects a client that guessed wrong, and determinism desync, where peer simulations diverge and the session stops outright.
Rubberbanding has two levers: How often the client mispredicts, which latency drives, and how visible each correction is, which netcode drives. Pull either one and players see less of it.
Tick rate is neither lever: Raising it does not make predictions more accurate, and on a connection already dropping packets it makes the artifacts worse.
"A desync has occurred" is a checksum failing: Lockstep games compare state hashes every turn, so one divergent float or one unsynchronized random call ends the session.
When Do Games Predict Instead of Interpolate?
When an interpolated object has to line up with a predicted one. A player's own character is usually predicted, so it runs slightly ahead of the server, while interpolated objects run slightly behind it. SnapNet's example is a ball in a sports game: a predicted player chasing an interpolated ball reaches the right spot too late. An interpolated object also cannot react to the local player's input until at least a full round trip has passed, because only the server can change it (SnapNet).
For mechanics built on contact between players, such as grabs, throws or a shared ball, that gap can rule interpolation out, which is why fighting and sports games often predict everything. Shooters usually predict only what the player controls and interpolate the rest. Client-side prediction covers the predicted side.
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