For multiplayer and simulationPhysics persona
Same inputs, same bits, on every machine.
A fixed 60 Hz tick, a digest per tick, recording of inputs only with the network included, replay and rollback — determinism as an engine guarantee you can verify, not a discipline you have to enforce.
What you get
A fixed tick, and proof
Physics and animation step on one 60 Hz accumulator, never the frame delta. Every tick has a digest, and balaur replay --verify stops at the first tick two runs disagree on.
Record inputs only
A session is each tick's input, network arrivals and events — not the world they produced — so it is small, and it replays by re-running the game against the same input.
Rollback
The rollback module decides each tick's inputs before the tick runs: the real one where it has arrived, a prediction where it has not, and re-simulates when the truth lands.
Networking that replays
HTTP, websockets and QUIC complete on worker threads and enter the simulation once per tick, at its start, recorded in the snapshot; a Gamend backend adds login, rooms and server hooks.
How it works
Three commands: trace, record, verify.
The engine measures its own determinism rather than asserting it: Rapier's enhanced-determinism feature in both worlds, transcendentals on the libm crate instead of the platform's math library, a fixed step, and a per-tick digest of every node and component.
Record a session on one machine, replay it on another, and the digests either match or the replay names the tick and the node that differ.
balaur run my-game --fixed-tick --trace-digest run-a.txt
balaur run my-game --fixed-tick --record session.blr
balaur replay session.blr --verify # stops at the first tick that disagrees
balaur replay session.blr --entries-at 25 # that tick, one digest per node and componentIn the editor
The Physics persona draws what the simulation sees; the Session dock records it.
Physics persona
Every body's collider and centre of mass drawn over the scene; show colliders, sleep bodies, step.
Session dock
Record and replay from the editor; its own recordings listed, replayable with the network included.
Once per tick
Input and network are one snapshot per tick; the Input overlay shows what the tick saw.
Next to Photon Quantum
Quantum is the deterministic multiplayer engine people know; Balaur makes the same promise at the engine level, without the platform around it.
Record a session, replay it, watch the digests agree.
angrynerds records itself from the Session dock; balaur replay --verify does the rest.