The Ruleset Cells: Overview

V5 makes a promise that sounds impossible the moment you say it out loud: one Unreal Engine 5.5 open-world game that has to feel like six different games. A Hong Kong triad brawl in a fish-market corridor, a 1947 noir interrogation where a witness's eyes betray the lie, a 1899 outlaw chase across open frontier, a Witcher-style contract hunt that starts at a posted notice and ends with the right oil on the right blade, a Mass-Effect squad firefight resolved by a dialogue-wheel interrupt, and a Newtonian two-ship duel that flips under thrust to bring its torpedoes to bear — all in one executable, sharing one roster, one perception model, and one cross-cell deduction graph. The unit that makes that shippable instead of a marketing fantasy is the ruleset cell: a self-contained gameplay framework with its own pacing, control scheme, camera discipline, AI personality, HUD vocabulary, and audio identity, standing on a shared engine spine it specializes rather than forks. This page is the orientation door to that model — what a cell is, how the six are built, how they share the foundation, and exactly where the real code stops and the production art begins. For the full per-cell feature catalogue it summarizes, start at the hub: ../V5_features.md.

What ships, honestly#

The cell skeleton is real, in-tree C++, and tested — the dressing is not. The engine's join key is one tiny enum, EV5Cell (V5/ue/Source/V5Core/Public/V5Types.h), carrying seven values: Urban, Period, Frontier, Hunter, SciFi, Steampunk, MindPalace. Every cell is realized as a family of statically compiled Source/ modules: the campaign module (V5UrbanHeistCity, V5PeriodMadeMan, V5FrontierOutlawTrail, V5HunterWitchersPath, V5SciFiGalacticSquad, V5SciFiHardVacuum, and a dozen more) plus the shared per-cell systems it leans on. Each campaign module is a catalog-builder + validator pair — a real, domain-specific pattern, not CRUD — and each ships its own colocated Private/Tests/ spec that asserts the catalog's exact invariants.

Two honest qualifications run through everything below. First, the architecture prose frames each cell as a hot-swappable GameFeatures plugin; on disk the cell code is a compiled Source module instead, and the matching Plugins/V5Mode_* directories are content/manifest shells — all 29 carry zero .cpp, declare "EnabledByDefault": false, and there are zero GameFeatureData.uasset binaries in the tree. The cells are modular by source module, not yet by runtime feature. Second, V5 is a logic-and-manifest skeleton: V5/ue/Content/ holds 0 .uasset and 1 .umap against 393 JSON authoring sidecars. So a cell's missions, districts, ships, and monsters exist as validated data and the systems that consume them are real C++ — but the meshes, MetaHumans, mocap, VO, and cinematics that would dress them are production-gated and absent. The honest posture, traced in full by the architecture companion ../architecture/promise-and-glossary.md, is: the systems are real; the content is described, not baked.

The ruleset-cell model#

One enum is the join key#

The whole architecture turns on EV5Cell. It is the value that the save document, the progression ledger, the perception tuning table, the mode registry, and the deduction graph all carry, so that "which game am I in right now" is a single typed answer the entire engine agrees on. V5Core exposes GetAllV5Cells() (returning all seven values from V5Types.cpp), LexToString(EV5Cell), and TryParseV5Cell — and the seven-count matters, because a per-cell dataset that sizes against a literal 5 or 6 desynchronizes from the enum (the 2026-05-31 audit traced four automation failures to exactly that mismatch). The save spine is cell-tagged at the seam: FV5SaveDocument carries an ActiveCell field and a CellSlots map keyed per cell, and FV5BureauXPLedger holds a PerCellXP map fed by AddXP(EV5Cell, int32). Cell identity is not a label on a menu — it is the primary key threaded through persistence and progression.

A cell is a catalog plus a validator#

Open any campaign module and you find the same disciplined shape, not a renamed shell. V5UrbanHeistCity exposes UV5_UrbanHeistCity_Catalog (Public/V5UrbanHeistCitySystems.h), a UBlueprintFunctionLibrary whose Build* methods author the cell as structured data — BuildProtagonists, BuildMainStoryMissions, BuildMainHeists, BuildDistricts, BuildRadioStations, BuildAmbientEncounters — and whose ValidateCampaignCatalog enforces the cell's contract. That validator (Private/V5UrbanHeistCitySystems.cpp) is where "real" lives: it fails unless there are exactly 3 protagonists, 32 main-story missions, 12 main heists each with 4–6 setup missions and 3 ending bands, 90 rep-gated side missions, 16 districts whose PlayableAreaKm2 sums to 140.0, 18 radio stations, 140 TV channels, 240 ambient encounters, 1200 talk-radio lines, a 5-tier wanted escalation, and a switch cinematic of 1.5 s. The colocated V5UrbanHeistCityTests.cpp asserts every one of those numbers with TestEqual — a spec that would collapse instantly against a placeholder list. This is the pattern in every cell: real catalogs, real invariants, real per-module automation. Honestly labelled: the campaign modules are intentionally thin — six files each (catalog, systems, types, two headers, one spec) — because the verbs live one tier down in the shared systems they depend on.

How a cell specializes the engine#

A cell does not re-implement gunplay or AI; it composes shared modules and contributes its narrow slice. The dependency edges are declared explicitly in each *.Build.cs and they are real and one-way:

• V5UrbanHeistCity → V5Core, V5Wanted
• V5PeriodMadeMan → V5Core, V5Audio, V5PeriodAuth, V5Vehicles
• V5FrontierOutlawTrail → V5Core, V5DeadEye, V5Honor, V5HorseAI, V5Hunting, V5Squad
• V5HunterWitchersPath → V5Core, V5Alchemy, V5Melee, V5MonsterHunt, V5Signs, V5Squad
• V5SciFiGalacticSquad → V5Core, V5Dialogue, V5Spaceship, V5Squad, V5StarMap
• V5SciFiHardVacuum → V5Spaceship

Which cell's ruleset and HUD are actually live is the job of V5Modes: UV5_Mode_RulesetGate::EvaluateModeForTarget(ModePlugin, Target) gates a mode against the build target, BuildHUDRoute(EV5Cell, ActiveModePlugin) routes the right HUD vocabulary, and FV5ModeDefinition carries an EV5Cell Cell so the registry always knows which cell a mode belongs to. To stand up a cell you supply: one EV5Cell value, one campaign catalog + validator, the cell's shared system dependencies, one mode entry, and a feel test — and inherit the spine.

A tour of the six cells#

The prompt frames V5 as six ruleset cells — urban crime, period drama, frontier, monster hunter, and two sci-fi flavours — and the disk bears that out. Each is a distinct experience with its own inspiration, camera, and pacing, yet all six descend from the same enum and the same shared modules.

Urban Crime carries the largest authored-content footprint of any cell — its validator alone pins a 140 km² playable surface across 16 districts, three switchable protagonists with simulated downtime, and an 18-station radio dial. Its campaign module even encodes its roadmap as validated data: BuildYear1NewDistrictExpansionCatalog and a forward-looking BuildFullVisionCyberpunkSubCellCatalog are real catalog builders with their own validators, honestly labelled as future-content definitions, not shipped levels. For the deep dive, see ./urban-crime-cell.md.

Period Drama trades open chaos for paced authenticity: it depends on V5PeriodAuth (per-era vehicle, font, prop, and slang bundles) and V5Vehicles for period-correct driving, and its sister module V5PeriodViceSquad rides V5Interrogation and V5FaceCapture for the LA-Noire truth/doubt/lie tells.

Frontier is the widest shared-system fan-out on the open-world side — its Build.cs pulls in V5HorseAI (gait library, bonding, saddle inventory), V5DeadEye (painted-shot slow-mo), V5Honor (persistent reputation/bounty), and V5Hunting (the perfect-pelt skinning economy) — a frontier cell assembled almost entirely from reusable parts.

Monster Hunter is the densest systems composition: V5HunterWitchersPath depends on five shared modules at once — V5Alchemy, V5Melee, V5MonsterHunt, V5Signs, and V5Squad. V5Alchemy is itself a real 13-file module (UV5_Alchemy_ToxicitySystem::ApplyConsumableToxicity and DecayToxicity, AV5_Alchemy_BrewingStation::BrewRecipe), so the Witcher contract loop — read the notice, investigate, brew the oil, fight the monster — is wired through real toxicity and brewing math, not a façade.

Sci-Fi (Squad RPG) is V5SciFiGalacticSquad, leaning on V5Dialogue (paragon/renegade wheel), V5Squad (companions and loyalty), and V5StarMap (galaxy navigation). Sci-Fi (Hard Vacuum) is the standout for systems depth: V5SciFiHardVacuum depends only on V5Spaceship, a 20-file module that ships a real AV5_Ship_NewtonianPawn : APawn with ConfigureShip and SetNewtonianState, an FV5ShipClassDefinition whose RCSTorqueDegPerSecond defaults to 18.0f, and UV5_Ship_FlipAndBurn::StepFlipAndBurn — genuine Newtonian flight, not a renamed CRUD shell.

Three honest cell counts#

The "how many cells" question has three answers that are all correct in their own frame, and the architecture companion is careful about this:

• Five is the marketing/promise count: Urban, Period, Frontier, Hunter, Sci-Fi.
• Six is what you get counting the two distinct sci-fi gameplay modules as separate experiences — V5SciFiGalacticSquad (squad RPG) and V5SciFiHardVacuum (Newtonian sim) — which is the framing this tour uses.
• Seven is the canonical engine count baked into EV5Cell: the five launch cells plus the Steampunk Brave New World Detective DLC cell (V5SteampunkDetective, [P3]) and the cross-cell MindPalace meta-layer.

The seventh enum value, MindPalace, is the important subtlety: it is not a sixth playable cell but a meta-layer every cell feeds. V5MindPalace (the deepest module in the tree at 36 files) exposes AddEvidenceNode, AttemptDeduction(Graph, NodeA, NodeB, FV5BureauXPLedger), BuildHypothesisChain, MakeAccusation, and a CrossEraGate — and the fact that AttemptDeduction takes the shared FV5BureauXPLedger is the cross-cell link made literal: evidence picked up by an outlaw in 1899 and a witness in 1947 can pair into one deduction, credited against the same roster's progression. That cross-cell plumbing, plus the unified roster, perception, crowd, and animation, is the subject of its own page: ./shared-cross-cell-systems.md.

Sharing the engine, honestly#

The reason six genres can cohabit one build is that the expensive, correctness-critical machinery is written once and tuned per cell rather than duplicated. The clearest example is perception. A triad goon, a noir witness, an outlaw, a drowner, and a station guard all read stimuli through the same V5Perception state machine: EV5PerceptionState runs Idle → Curious → Alert → Hostile, and a single FV5PerceptionTuning carries the thresholds (CuriousThreshold = 20.0, AlertThreshold = 55.0, HostileThreshold = 90.0, in V5PerceptionTypes.h). What differs per cell is tuning, not the model: UV5_Perception_*::FindTuning(EV5Cell, EV5PerceptionNPCClass, ...) resolves a cell-and-class-specific tuning over the one shared brain, so a 1947 beat cop and a frontier marshal escalate on the same curve with different sensitivities. The same write-once-tune-per-cell discipline governs the roster, the crowd and schedule subsystems, the animation rig, and the save spine — each detailed in the shared cross-cell systems page.

What the engine does not yet do is hot-activate a cell at runtime. The 29 V5Mode_* plugins that the architecture imagined as toggleable GameFeatures are manifest shells today; the cell code compiles into the monolith and is gated by V5Modes logic, but the binary GameFeatureData.uasset that would let a cell be DLC-dropped or platform-stripped without a rebuild is unauthored. That gap is named, not hidden — it is the single biggest honest correction the architecture companion makes.

Cell feel tests#

Each cell ships a feel test — a curated in-game scenario that confirms the cell hits its inspiration's hallmark — and these exist on disk as structured fixtures, not prose. Under V5/ue/Source/V5Tests/FeelTests/ are six cell folders (urban, period, frontier, hunter, scifi, mindpalace), each holding *.feeltest.json files with a cell, a plugin, a runtimePath, a sourceFeature, and a list of successCriteria. The urban urban-heist-chase-swap.feeltest.json, for instance, requires that a two-protagonist control swap completes mid-chase "without visible streamed-world hitch," that the wanted response escalates through its five bands, and that passenger lean-out shooting holds aim across the swap. The feature catalogue wires these into the nightly Gauntlet run so a failing feel test blocks the affected cell's release — the per-cell quality gate, expressed as data the same way the cells themselves are.

Related#

• The feature hub: ../V5_features.md
• The Urban Crime cell — the deepest authored-content cell, Heist City + Street Triad over the shared open-world spine
• Shared cross-cell systems — the roster, perception, crowd/schedule, and Mind Palace plumbing every cell rides
• Architecture companion: ../architecture/promise-and-glossary.md — the 74-module split, the EV5Cell enum, the three cell counts, and the GameFeatures gap in full