Open Poseidon Engine

Open Poseidon Engine brings modern engine features to Operation Flashpoint / Arma: Cold War Assault: WGPU/Vulkan rendering, a whole-Earth world you can fly from the ground into space, volumetric fire, smoke, fog and clouds, an FFT ocean with underwater life, Box3D physics with ragdolls, new infantry animations, experimental Arma 1, 2 and 3 missions with their own menus, and squad mates you can talk to through a language model. It is a community continuation of the original engine, with expanded gameplay, terrain editing and content support. It requires your own game data and is not a complete game or an official Bohemia Interactive product.

Tip

Don't want to compile? Ready-to-play Windows builds are waiting for you. Sponsors get access to our private builds repository, OpenPoseidon-Builds, with tested, precompiled releases. Become a member through GitHub Sponsors for a small monthly contribution: you get the builds and directly help fund the project's development, testing and build distribution. Building from source stays free, and your rights under the software licences are the same either way.

Playing a precompiled build

1. You need the original game. Open Poseidon runs on top of your own copy of Arma: Cold War Assault (Steam or GOG) or Operation Flashpoint. It does not include the game's data, so the game must be installed first.
2. Unpack the download and drag its contents into the game's installation folder, next to the game's own .exe: OpenPoseidon.exe, wgpu_renderer.dll and the assets folder. Nothing of the original game is overwritten, and the original game still starts as before.
3. Start OpenPoseidon.exe from that folder. If Windows reports a missing MSVCP140 or VCRUNTIME140 file, install Microsoft's Visual C++ Redistributable (x64).
4. Optional, for the modern main and options menus: install the free Arma: Cold War Assault Remastered Demo from Steam, then run assets\Install-Menus.cmd once. It copies the Demo's menu resources into the assets folder. Without it the game uses the classic menus.

To play Arma 1, 2, 3, DayZ or Reforger content you also need those games installed; their files are loaded in place from their own folders.

Engine features

The screenshots below are development captures using locally installed game content; imported maps and assets are not included with the engine.

Worlds and content

No conversion, no copying. Arma 1, 2, 3, DayZ and Reforger content loads straight from the original game's own installation folder. Point the engine at your installed game and play it in place: nothing is converted into a separate copy beforehand, and none of those games' files ship with Open Poseidon.

Arma 3 mission with its own pause menu · Whole-world rendering

• Arma 1, 2 and 3 missions (experimental): missions and campaigns from your own Arma installations start from their native main menus, pause screens and mission dialogs, with their own weapons, sounds, voices, animals, scripted state machines and conversations. Arma 1 support is the furthest along: its missions bring their own weapons, sights, magazines, shot sounds, vehicles with their own sounds and gun points, the Arma 1 equipment slots and its stringtables, and Arma 1 units, vehicles and objects can be placed in the mission editor. Many missions play from start to finish; others still stop at missing script commands or content.
• Whole-world rendering: fly from the ground to orbit over the whole Earth, built from real elevation and imagery streamed at runtime. Mountains cast shadows across the ground, the sea is drawn out to the horizon, valleys fill with fog and snowlines follow the season. A real-time Moon has its own relief and craters, and the Earth hangs in its sky. A scripted ICBM can be flown across the globe with a follow camera.
• Arma 1, 2, 3, Reforger and DayZ terrains: locally installed worlds load with their own buildings, vegetation, roads, materials and far-distance trees. Reforger worlds stream natively. Imported terrain opens in the native OFP mission editor with OFP units.
• Island Editor and OFP Fusion: a terrain editor with no object limit, and an archipelago built from all five locally installed classic islands.

The Moon, with the Earth in its sky · Arma Reforger terrain

Rendering

GTAO and interior shading · Night lighting and shadows

• Vulkan rendering through WGPU: Vulkan support on Windows and Linux, alongside Direct3D 12 on Windows. The active API depends on the platform, GPU and driver.
• GTAO: screen-space ambient occlusion and bent-normal ambient shading, with live developer controls and diagnostic views.
• Global illumination (GI): a local irradiance probe grid combines indirect sky lighting with coloured sunlight bounced from nearby surfaces.
• Lighting and shadows: dynamic sun/local-light shadows, contact shadows, muzzle illumination, atmospheric light scattering and script-created lights (Arma 2/3 light commands).
• Vehicle paint and reflections: clear-coat paint that reflects the sky and the lit ground, with screen-space reflections; glass, chrome and instruments are told apart from paint.
• Volumetric clouds and procedural sky: overcast controls shared with Zeus, stars, the Milky Way and cloud shadows affecting terrain, objects, grass and water.
• Layered volumetric fog: adjustable lower/upper heights, density, patchiness, valley/mountain presets, live controls, reset and a legacy-fog option. Local light scattering supports night lights and the player's torch.
• GPU-driven trees: dense forests, including Arma 3 and DayZ vegetation, are culled and drawn on the GPU.
• Upscaling: AMD FSR 1 and an optional local NVIDIA DLSS integration. The proprietary NGX SDK/runtime is not bundled; distributable builds disable DLSS. Its availability depends on build configuration and compatible hardware.

Layered volumetric fog

Fire, smoke and destruction

Volumetric fire, smoke and an impact crater

• Volumetric fire and smoke: a new fire and smoke system. Explosions start with a fireball, wrecks burn with flames that lean in the wind, and black smoke columns rise, drift and linger long after the fire. Smoke has buoyancy and wind response, self-shadowing and scene shadows, and room/portal-aware containment against walls, floors and ceilings, with flow through doorways. Containment depends on the building geometry/topology available to the engine.
• Volumetric impact craters: explosions dig real craters into the terrain, with thrown-out earth around the rim.
• Holes in walls: bullets and explosions break physical holes into walls.
• Destructible terrain and editor: brush deformation, small cuts, horizontal caves/tunnels, sinkholes, straight and tank trenches, and excavation selection/rotation/deletion. This extends terrain holes; it is not a general voxel-world simulation.
• Combat effects: muzzle flashes that light the shooter and the surroundings, ground explosions, snow bullet tracks and helicopter ground downwash particles.

Destructible terrain

Water, weather and wildlife

Procedural fish schools · Tidewater ocean

• Tidewater ocean: FFT waves, shoreline wetness, reflections, foam, wakes, spray, underwater rendering and caustics; projectile/explosion and helicopter interactions. Boats are rigid bodies that float at a real draft on the drawn waves and leave ripples.
• Procedurally generated wildlife and coastline: schools of fish gather around you under water. The sea floor has real depth, rocks and corals, and beaches get rippled sand, stones and driftwood. Surf, gulls, terns and whales are heard around the coast.
• Procedural grass: travelling gust fronts, spatial wind variation, configurable coverage and player/vehicle/explosion/downwash interactions.
• Weather and puddles: rain collects in puddles with ripples and drains away again, with wet ground and clothing, surface snow and terrain contact depressions.
• Snow depth and deformation: compressed foot/vehicle tracks and projectile marks in depth-bearing ground snow, alongside roof and vegetation snow cover.
• Mud: MudRunner-style mud with ruts, rolling resistance and mud thrown from wheels and tank tracks.

Rain puddles, beach sand and driftwood · Snow depth and vehicle tracks · Wind-driven procedural grass

Soldiers, AI and gameplay

Box3D physics

• NPC chat (experimental): talk to your squad, nearby soldiers, civilians and HQ by typing or by voice. A language model of your choice answers in character, using a live picture of the situation and the mission briefing. Hosted providers and fully local models (Ollama or any OpenAI-compatible server) are supported. Replies are spoken in 3D at the speaker, or over the radio. Orders you give in plain words (follow, hold, move, cover, engage, get in and more) run through the game's own commands; model output is never run as script. API keys stay on your computer.
• New infantry animations: seamless reloading while walking, leaning around corners (Q/E), jumping with a soft landing, swimming, and diving and surfacing.
• Improved AI: gunfire hearing/reporting, immediate orders and near-miss suppression. Soldiers remember where danger came from and search there, turn on whoever is shooting at them, look out from cover, avoid cover where a squad mate was hit and run from live grenades. Optional gradual spotting and cover/flank/search behavior. Behavior switches are configuration-dependent; this is not a universal new navigation system or complete replacement AI.
• Physical inventory (single player): open with Tab ↹ on foot (O in vehicle control seats) for vicinity cargo, drag/drop, equipped slots and weight/volume budgets; K opens inventory settings, including optional bearing callouts, a bearing readout and grenade-launcher ground-range estimates. Includes 17 original realistic equipment icons; addon pictures and labelled tiles remain fallbacks. Multiplayer keeps classic Gear; Dev Tools and Zeus are disabled in multiplayer.
• Box3D physics and articulated ragdolls: jointed character bodies, death and explosion reactions, and bullet reactivation of supported runtime corpses. Automatic ragdolls default to on, with a Physics developer-tab toggle.
• Firing from vehicles (FFV): personal-rifle fire from configured passenger seats, aiming arcs, reload and action-menu Ready/Stow controls. Stock Jeep coverage is validated; other seats, weapon families and multiplayer are limited.
• Steam Audio (default audio backend): Valve's Steam Audio places every 3D sound around you with binaural (HRTF) spatialisation, so headphones tell you where a shot or an engine is. Sounds are muffled by terrain and buildings between you and the source, rooms and surroundings add their own reverb, and diving brings underwater sound. The sea has its own soundscape: surf wave by wave, gulls, terns, whales and boat engines. The classic OpenAL backend remains available.

Engine and tools

• Satellite terrain textures (satmaps): authored satellite layers and an automatic classic-world far-colour bake incorporating static roofs/vegetation. This is a ground colour representation, not a replacement for live object LODs.
• Local content browser and editor: terrain discovery for installed Arma 1/2/3, DayZ and Reforger content, partial format conversion and selected vehicle bridges.
• Streaming and developer tools: geometry/residency work, GPU timings, debug views, test harnesses and Zeus freefly/unit placement.
• Multithreading: enkiTS worker jobs for selected terrain/cache, texture conversion and audio work, plus asynchronous streaming and pipeline builds. This does not imply that every simulation/rendering operation runs on its own thread.

Current limitations

Features are at different stages of acceptance. Dense/aerial fog can still show patterns. Ragdoll tests cover 37 locally present stock models; two Camel pilot models retain post-hit settling issues. Posture, saved-corpse reactivation, network ownership and physics budgets also limit ragdoll admission. Arbitrary addon rigs are not universally supported. Weather materials and modern-game material/LOD conversion still need refinement. Soft-ground prototypes do not provide general soft-body vehicle physics. Arma 1, 2 and 3 missions are experimental: some still stop at missing script commands or content, and they need your own Arma installations. Whole-world rendering streams public elevation and imagery data and needs an internet connection. NPC chat needs a language-model provider or a local model server of your choice.

Content and building

To play Cold War Assault, use your own legally acquired installation. Game archives, maps, models, textures, sounds and animation addons are not supplied by this source release. Included project artwork and omitted binary test fixtures are documented in ASSETS.md. Original-game and modern-game compatibility remains subject to the limitations in COMPATIBILITY.md.

See BUILDING.md for the Windows build procedure and CONTRIBUTING.md for contributions. The current Windows WGPU path is the primary development target. Other platform presets exist but are not a promise of equivalent runtime support.

The source is governed by LICENSE, including its additional terms. Third-party components retain their own licenses and notices. See CREDITS.md, THIRD_PARTY_NOTICES.md and the notices shipped with individual components. Source availability does not grant rights to proprietary game content or trademarks.