fixed-tick-gameplay

name	fixed-tick-gameplay
description	Keep all gameplay logic independent from render FPS. Use for any work on player input, movement, combat, abilities, cooldowns, enemy AI, projectiles, damage, loot, encounter state, animation timing, cameras, `useFrame`, frame-rate caps, fixed ticks, simulation clocks, replay, interpolation, or multiplayer snapshots in this project. Applies to system designers and programmers.

Fixed-tick gameplay

Gameplay is never driven by the render-frame delta or by the selected FPS cap. Rendering is presentation only. The canonical project contract is docs/system-design/TECHNICAL_ARCHITECTURE.md, ADR-01.

Non-negotiable boundary

input commands → fixed simulation tick → state/snapshots → render interpolation

• Run authoritative gameplay at a named fixed timestep (currently 30 Hz).
• Keep simulation state framework-free: no React, Three, camera, animation mixer, DOM event or Photon object in domain state.
• Treat useFrame delta and maxFps only as elapsed presentation time. They must never directly advance movement, cooldowns, casts, AI, projectiles, damage, rewards or encounter progression.
• Interpolate only continuous presentation fields between previous/current snapshots. Treat casts, deaths, teleports, target changes and event IDs as discrete boundaries.

System designer responsibilities

Before implementation, specify:

1. the fixed rate, tick order, authoritative state and command schema;
2. the input, simulation, snapshot and presentation module boundaries;
3. behaviour after focus loss, a long frame, hidden tab or authority loss — never leave a local player in a permanent unobservable input freeze;
4. which values interpolate and which are events; and
5. replay and real-browser acceptance criteria at 30, 45, 60 and uncapped FPS.

Do not approve a design that says "multiply by delta" as its gameplay-timing model. Do not use FPS as a game rule, timeout, cadence, cooldown or movement unit.

Programmer responsibilities

• Sample DOM/touch input into ordered commands; consume each edge exactly once in a fixed tick. Held input is sampled separately.
• Run every gameplay writer through one fixed-tick owner. Do not add a second independent useFrame gameplay loop.
• Keep rendering hooks read-only over snapshots. VFX, audio, animation and camera may observe events but may not create hits, cooldowns, rewards or movement.
• Put pure clock, command, replay and interpolation rules in systems/ with unit tests. Keep React/Three adapters in components/ or entities/.
• Do not make a long visual frame permanently disable input. If authority handoff is not implemented, define and visibly verify a safe local recovery policy before enabling the runner.

Required verification

• Replay one command stream under 30, 45, 60, uncapped and jittered rendering; gameplay outcome must match.
• Cover quick clicks, held buttons, several inputs between rendered frames, blur/refocus, long frames and death/evade/cast boundaries.
• Verify the real playable route in a headed browser. Send actual pointer and key input, then confirm both gameplay response and live simulation diagnostics.
• A reduced FPS cap may reduce smoothness only; it must not alter controls, animation state, movement, attack cadence, camera, damage, cooldowns, projectiles or encounter outcome.