A game loop is the simulation step of a realm — a realm is, by definition, the region served by a single one. Each iteration turns the realm’s input streams into its output streams:

  • Record the current position of every input stream, so the whole iteration reads a consistent snapshot of its inputs.
  • Run AI.
  • Move objects.
  • Generate sounds.
  • Compute output deltas and append them to the output streams.
  • Repeat.

Why the shape matters#

Reading inputs at a recorded stream position, and emitting deltas appended to a stream, is what makes the loop a state machine over the log: two nodes that begin in the same state and consume the same inputs in the same order end in the same state. That is the property the peer-to-peer network leans on in place of an authoritative server — convergence follows from determinism rather than from anyone being in charge.

Determinism is demanding in practice. It rules out reading a wall clock or un-seeded randomness mid-iteration, and it requires that floating-point results agree across machines and browsers. A fixed timestep for simulation, decoupled from a variable-rate render, is the standard way to keep the loop reproducible while still drawing as fast as the display allows.

Similar concepts and prior art:

See also#

Backward Bounding Volume Hierarchy Gargantis Architecture Forward