Joining a match in progress, in a few kilobytes
Late-join used to mean shipping the whole world. With compressed snapshots and reconnect deltas, a player slots into a live match almost for free.
Lockstep is wonderfully cheap while everyone’s been in the room since tick zero — you only ever send inputs. The interesting question is what happens when someone shows up late: a spectator, a reconnect, a drop-in co-op partner. They’ve missed thousands of ticks of history.
Send the state once, compressed
For a late-joiner we hand over a single world snapshot — and snapshots compress beautifully. Game worlds are sparse and repetitive, so a general-purpose pass gets us very large reductions on real states. The joiner decompresses, adopts the state, and from that tick on they’re back to sending nothing but inputs.
Reconnects are even cheaper
A player who just dropped already has most of the world. So instead of a full snapshot we send a delta against what they last knew — often a tiny fraction of the size. The determinism guarantee holds throughout: the reconstructed state is byte-identical to everyone else’s.