A free, open-source real-time strategy game spanning six epochs — from clubmen to nuclear submarines — that runs in your browser. The whole simulation is written in Rust and compiled to a 170 KB WebAssembly module with zero dependencies. 3D rendering, sound and peer-to-peer multiplayer are plain browser APIs: no engine, no bundler, no asset files.
Epoch-spanning RTS games of the early 2000s were wonderful, but big late-game battles — fleets, submarines, air wings — tended to stutter no matter how fast the PC was. OpenEpoch is a from-scratch take on that genre built around one goal: thousands of units with flat frame times.
Measured on the built-in stress test (node tools/smoke.mjs, one desktop core):
| Entities | Simulation cost per tick (20 ticks/s) |
|---|---|
| 2 000 | ~0.9 ms |
| 4 000 | ~2.4 ms |
| 7 000 | ~5.6 ms |
A complete 3D frame with 4 000 units (simulation tick, instance upload, GPU) took 4–13 ms depending on zoom on an integrated AMD Radeon at 1400×850, i.e. about 60 fps without a dedicated graphics card.
How it stays smooth:
- Fixed 20 Hz simulation, interpolated rendering. The display rate never drives game logic, and a slow frame drops time instead of spiralling.
- Shared flow fields instead of per-unit pathfinding. A move order runs one BFS over the map; every unit heading there reads the same field. 500 units cost the same as 5.
- No allocation in the tick. Rust, fixed pools, no garbage collector — nothing to pause.
- Uniform spatial grid rebuilt by counting sort each tick for collision, targeting and splash damage; target searches are staggered across ticks.
- One draw call per model type. Rust writes a flat instance buffer, sorted by model, straight into WASM memory; JavaScript hands it to the GPU. No per-object JS calls, about 50 draw calls for any army size.
- Multiplayer sends commands, not state. Both browsers run the same deterministic simulation in lockstep, so a 4 000-unit battle needs the same few bytes per second as an empty map.
- Six epochs: Stone Age → Bronze Age → Middle Ages → Industrial Age → Modern Age → Atomic Age
- 43 units and buildings across land, sea, air and underwater, all as procedurally generated low-poly 3D models on height-mapped terrain
- Territories: the map is divided into regions. A Town Center claims a free one; everything else can only be built on land you hold.
- 12 technologies researched at the Town Center, Barracks, Workshop, Dock and Airfield (gathering, weapons and armour per unit class)
- Transport ships carry ten land units across the sea: right-click the ship to board, right-click a shore to land
- Multiplayer 1 vs 1 (plus optional AI), peer to peer over WebRTC with no server
- Save games in the browser (Ctrl+S, autosave every three minutes, Continue in the menu)
- Sound effects synthesised at run time with WebAudio
- Submarines are invisible until a detector (destroyer, cruiser, gunship, tower, another sub) is nearby or they fire. Nuclear submarines torpedo ships and launch cruise missiles at targets far inland.
- Aircraft really fly: fixed-wing planes can't stop, make strafing and bombing runs, and loiter in circles; helicopters hover and hunt subs.
- Economy: food, wood, metal; workers gather, build, and go back to work afterwards; farms give endless food.
- Fog of war, minimap, control groups, attack-move, rally points, production queues, formations.
- AI opponents (1–3) that build an economy, advance through the epochs and attack in waves.
- Procedural maps from a seed — continents, lakes, forests, ore fields.
| Input | Action |
|---|---|
| Left click / drag | Select · double-click selects all of a type · Shift adds |
| Right click | Move · attack · gather · build · set rally point |
A + click |
Attack-move |
S / Del |
Stop / destroy selected |
| Arrow keys, screen edge, middle-drag | Scroll |
| Mouse wheel | Zoom |
Q W E R T / Z X C V B |
Command buttons |
Ctrl+1…9 / 1…9 |
Set / recall control group (tap twice to jump) |
F · H · Space |
Idle worker · home · jump to selection |
U |
Unload selected transport ships |
P · + · - · M |
Pause · game speed · sound on/off |
Ctrl+S |
Save (single player) |
Open the game in two browsers, choose Multiplayer… in the menu:
- The host clicks Host a game and sends the invite code to the other player (chat, mail, anything).
- The guest clicks Join a game, pastes it, presses Create reply code and sends that code back.
- The host pastes the reply and presses Connect. The game starts on both sides.
There is no server in between, which also means the codes contain your network addresses (as with any WebRTC connection): only exchange them with the person you want to play with. Very strict firewalls or carrier-grade NAT can prevent a direct connection, because there is no relay.
rustup target add wasm32-unknown-unknown
./build.sh # or .\build.ps1 on Windows
python -m http.server --directory docs 8123Then open http://localhost:8123. No bundler, no npm install, no wasm-bindgen.
src/defs.rs unit & building data
src/map.rs map generation, passability, flow fields
src/game.rs entities, orders, movement, combat, economy
src/ai.rs scripted opponent
src/cmd.rs player commands as data (the only way input reaches the simulation)
src/save.rs save games
src/render.rs instance buffer, minimap, HUD state
src/lib.rs C-ABI exports called from the page
docs/main.js 3D WebGL2 renderer, camera, input, HUD, lobby
docs/models.js procedural low-poly 3D models
docs/atlas.js procedural 2D icons for the HUD
docs/audio.js synthesised sound effects
docs/net.js lockstep scheduler and WebRTC connection
tools/ headless tests and benchmark (Node)
URL parameters: ?seed=42 starts a skirmish on that map, ?ai=3 sets opponents, ?bench=2000 starts the stress test with 2 000 units per side.
node tools/smoke.mjs # AI game, build/research flow, save & load, lockstep determinism, benchmark
node tools/transport.mjs # dock -> transport ship -> board -> unloadThe lockstep test runs two copies of the simulation against each other over a simulated laggy link with random commands from both seats and checks that they never diverge.
Playable skirmish against AI and 1 vs 1 multiplayer. Not there yet: music, more than two human players, a relay for networks that block direct connections, rejoining or saving multiplayer games, camera rotation, unit animation, upgrading existing units between epochs, AI use of transport ships, touch controls. Contributions welcome.
OpenEpoch is an independent, original work. All code was written from scratch and every model, icon and sound is generated procedurally at start-up (docs/models.js, docs/atlas.js, docs/audio.js) — the repository contains no art, audio, data, names or code from any commercial game, and it is not affiliated with or endorsed by any game publisher.