OpenRA Engine — Comprehensive Feature Reference

Purpose: Exhaustive catalog of every feature the OpenRA engine provides to modders and game developers. Sourced directly from the OpenRA/OpenRA GitHub repository (C#/.NET). Organized by category for Iron Curtain design reference.

1. Trait System (Actor Component Architecture)

OpenRA’s core architecture uses a trait system — essentially a component-entity model. Every actor (unit, building, prop) is defined by composing traits in YAML. Each trait is a C# class implementing one or more interfaces. Traits attach to actors, players, or the world.

Core Trait Infrastructure

TraitsInterfaces — Master file defining all trait interfaces (ITraitInfo, IOccupySpace, IPositionable, IMove, IFacing, IHealth, INotifyCreated, INotifyDamage, INotifyKilled, IWorldLoaded, ITick, IRender, IResolveOrder, IOrderVoice, etc.)
ConditionalTrait — Base class enabling traits to be enabled/disabled by conditions
PausableConditionalTrait — Conditional trait that can also be paused
Target — Represents a target for orders/attacks (actor, terrain position, frozen actor)
ActivityUtils — Utilities for the activity (action queue) system
LintAttributes — Compile-time validation attributes for trait definitions

General Actor Traits (~130+ traits)

Trait	Purpose
`Health`	Hit points (current, max), damage state tracking
`Armor`	Armor type for damage calculation
`Mobile`	Movement capability, speed, locomotor reference
`Immobile`	Cannot move (buildings, props)
`Selectable`	Can be selected by player
`IsometricSelectable`	Selection for isometric maps
`Interactable`	Can be interacted with
`Tooltip`	Name shown on hover
`TooltipDescription`	Extended description text
`Valued`	Cost in credits
`Voiced`	Has voice lines
`Buildable`	Can be produced (cost, time, prerequisites)
`Encyclopedia`	In-game encyclopedia entry
`MapEditorData`	Data for map editor display
`ScriptTags`	Tags for Lua scripting identification

Combat Traits

Trait	Purpose
`Armament`	Weapon mount (weapon, cooldown, barrel)
`AttackBase`	Base attack logic
`AttackFollow`	Attack while following target
`AttackFrontal`	Attack only from front arc
`AttackOmni`	Attack in any direction
`AttackTurreted`	Attack using turret
`AttackCharges`	Attack with charge mechanic
`AttackGarrisoned`	Attack from inside garrison
`AutoTarget`	Automatic target acquisition
`AutoTargetPriority`	Priority for auto-targeting
`Turreted`	Has rotatable turret
`AmmoPool`	Ammunition system
`ReloadAmmoPool`	Ammo reload behavior
`Rearmable`	Can rearm at specific buildings
`BlocksProjectiles`	Blocks projectile passage
`JamsMissiles`	Missile jamming capability
`HitShape`	Collision shape for hit detection
`Targetable`	Can be targeted by weapons
`RevealOnFire`	Reveals when firing

Movement & Positioning

Trait	Purpose
`Mobile`	Ground movement (speed, locomotor)
`Aircraft`	Air movement (altitude, VTOL, speed, turn)
`AttackAircraft`	Air-to-ground attack patterns
`AttackBomber`	Bombing run behavior
`FallsToEarth`	Crash behavior when killed
`BodyOrientation`	Physical orientation of actor
`QuantizeFacingsFromSequence`	Snap facings to sprite frames
`Wanders`	Random wandering movement
`AttackMove`	Attack-move command support
`AttackWander`	Attack while wandering
`TurnOnIdle`	Turn to face direction when idle
`Husk`	Wreck/corpse behavior

Transport & Cargo

Trait	Purpose
`Cargo`	Can carry passengers
`Passenger`	Can be carried
`Carryall`	Air transport (pick up & carry)
`Carryable`	Can be picked up by carryall
`AutoCarryall`	Automatic carryall dispatch
`AutoCarryable`	Can be auto-carried
`CarryableHarvester`	Harvester carryall integration
`ParaDrop`	Paradrop passengers
`Parachutable`	Can use parachute
`EjectOnDeath`	Eject pilot on destruction
`EntersTunnels`	Can use tunnel network
`TunnelEntrance`	Tunnel entry point

Economy & Harvesting

Trait	Purpose
`Harvester`	Resource gathering (capacity, resource type)
`StoresResources`	Local resource storage
`StoresPlayerResources`	Player-wide resource storage
`SeedsResource`	Creates resources on map
`CashTrickler`	Periodic cash generation
`AcceptsDeliveredCash`	Receives cash deliveries
`DeliversCash`	Delivers cash to target
`AcceptsDeliveredExperience`	Receives experience deliveries
`DeliversExperience`	Delivers experience to target
`GivesBounty`	Awards cash on kill
`GivesCashOnCapture`	Awards cash when captured
`CustomSellValue`	Override sell price

Stealth & Detection

Trait	Purpose
`Cloak`	Invisibility system
`DetectCloaked`	Reveals cloaked units
`IgnoresCloak`	Can target cloaked units
`IgnoresDisguise`	Sees through disguises
`AffectsShroud`	Base for shroud/fog traits
`CreatesShroud`	Creates shroud around actor
`RevealsShroud`	Reveals shroud (sight range)
`RevealsMap`	Reveals entire map
`RevealOnDeath`	Reveals area on death

Capture & Ownership

Trait	Purpose
`Capturable`	Can be captured
`CapturableProgressBar`	Shows capture progress
`CapturableProgressBlink`	Blinks during capture
`CaptureManager`	Manages capture state
`CaptureProgressBar`	Progress bar for capturer
`Captures`	Can capture targets
`ProximityCapturable`	Captured by proximity
`ProximityCaptor`	Captures by proximity
`RegionProximityCapturable`	Region-based proximity capture
`TemporaryOwnerManager`	Temporary ownership changes
`TransformOnCapture`	Transform when captured

Destruction & Death

Trait	Purpose
`KillsSelf`	Self-destruct timer
`SpawnActorOnDeath`	Spawn actor when killed
`SpawnActorsOnSell`	Spawn actors when sold
`ShakeOnDeath`	Screen shake on death
`ExplosionOnDamageTransition`	Explode at damage thresholds
`FireWarheadsOnDeath`	Apply warheads on death
`FireProjectilesOnDeath`	Fire projectiles on death
`FireWarheads`	General warhead application
`MustBeDestroyed`	Must be destroyed for victory
`OwnerLostAction`	Behavior when owner loses

Miscellaneous Actor Traits

Trait	Purpose
`AutoCrusher`	Automatically crushes crushable actors
`Crushable`	Can be crushed by vehicles
`TransformCrusherOnCrush`	Transform crusher on crush
`DamagedByTerrain`	Takes terrain damage
`ChangesHealth`	Health change over time
`ChangesTerrain`	Modifies terrain type
`Demolishable`	Can be demolished
`Demolition`	Can demolish buildings
`Guard`	Guard command support
`Guardable`	Can be guarded
`Huntable`	Can be hunted by AI
`InstantlyRepairable`	Can be instantly repaired
`InstantlyRepairs`	Can instantly repair
`Mine`	Land mine
`Minelayer`	Can lay mines
`Plug`	Plugs into pluggable (e.g., bio-reactor)
`Pluggable`	Accepts plug actors
`Replaceable`	Can be replaced by Replacement
`Replacement`	Replaces a Replaceable actor
`RejectsOrders`	Ignores player commands
`Sellable`	Can be sold
`Transforms`	Can transform into another actor
`ThrowsParticle`	Emits particle effects
`CommandBarBlacklist`	Excluded from command bar
`AppearsOnMapPreview`	Visible in map preview
`Repairable`	Can be sent for repair
`RepairableNear`	Can be repaired when nearby
`RepairsUnits`	Repairs nearby units
`RepairsBridges`	Can repair bridges
`UpdatesDerrickCount`	Tracks oil derrick count
`CombatDebugOverlay`	Debug combat visualization
`ProducibleWithLevel`	Produced with veterancy level
`RequiresSpecificOwners`	Only specific owners can use

2. Building System

Building Traits

Trait	Purpose
`Building`	Base building trait (footprint, dimensions)
`BuildingInfluence`	Building cell occupation tracking
`BaseBuilding`	Base expansion flag
`BaseProvider`	Provides base build radius
`GivesBuildableArea`	Enables building placement nearby
`RequiresBuildableArea`	Requires buildable area for placement
`PrimaryBuilding`	Can be set as primary
`RallyPoint`	Production rally point
`Exit`	Unit exit points
`Reservable`	Landing pad reservation
`Refinery`	Resource delivery point
`RepairableBuilding`	Can be repaired by player
`Gate`	Openable gate

Building Placement

Trait	Purpose
`ActorPreviewPlaceBuildingPreview`	Actor preview during placement
`FootprintPlaceBuildingPreview`	Footprint overlay during placement
`SequencePlaceBuildingPreview`	Sequence-based placement preview
`PlaceBuildingVariants`	Multiple placement variants
`LineBuild`	Line-building (walls)
`LineBuildNode`	Node for line-building
`MapBuildRadius`	Controls build radius rules

Bridge System

Trait	Purpose
`Bridge`	Bridge segment
`BridgeHut`	Bridge repair hut
`BridgePlaceholder`	Bridge placeholder
`BridgeLayer`	World bridge management
`GroundLevelBridge`	Ground-level bridge
`LegacyBridgeHut`	Legacy bridge support
`LegacyBridgeLayer`	Legacy bridge management
`ElevatedBridgeLayer`	Elevated bridge system
`ElevatedBridgePlaceholder`	Elevated bridge placeholder

Building Transforms

Trait	Purpose
`TransformsIntoAircraft`	Building → aircraft
`TransformsIntoDockClientManager`	Building → dock client
`TransformsIntoEntersTunnels`	Building → tunnel user
`TransformsIntoMobile`	Building → mobile unit
`TransformsIntoPassenger`	Building → passenger
`TransformsIntoRepairable`	Building → repairable
`TransformsIntoTransforms`	Building → transformable

Docking System

Trait	Purpose
`DockClientBase`	Base for dock clients (harvesters, etc.)
`DockClientManager`	Manages dock client behavior
`DockHost`	Building that accepts docks (refinery, repair pad)

3. Production System

Production Traits

Trait	Purpose
`Production`	Base production capability
`ProductionQueue`	Standard production queue (base class, 25KB)
`ClassicProductionQueue`	C&C-style single queue per type
`ClassicParallelProductionQueue`	Parallel production (RA2 style)
`ParallelProductionQueue`	Modern parallel production
`BulkProductionQueue`	Bulk production variant
`ProductionQueueFromSelection`	Queue from selected factory
`ProductionAirdrop`	Air-delivered production
`ProductionBulkAirDrop`	Bulk airdrop production
`ProductionFromMapEdge`	Units arrive from map edge
`ProductionParadrop`	Paradrop production
`FreeActor`	Spawns free actors
`FreeActorWithDelivery`	Spawns free actors with delivery animation

Production model diversity across mods: Analysis of six major OpenRA community mods (see research/openra-mod-architecture-analysis.md) reveals that production is one of the most varied mechanics across RTS games — even the 13 traits above only cover the C&C family. Community mods demonstrate at least five fundamentally different production models:

Model	Mod	IC Implication
Global sidebar queue	RA1, TD (OpenRA core)	`ClassicProductionQueue` — IC’s RA1 default
Tabbed parallel queue	RA2, Romanovs-Vengeance	`ClassicParallelProductionQueue` — one queue per factory
Per-building on-site	OpenKrush (KKnD)	Replaced `ProductionQueue` entirely with custom `SelfConstructing` + per-building rally points
Single-unit selection	d2 (Dune II)	No queue at all — select building, click one unit, wait
Colony-based	OpenSA (Swarm Assault)	Capture colony buildings for production; no construction yard, no sidebar

IC must treat production as a game-module concern, not an engine assumption. The ProductionQueue component is defined by the game module, not the engine core (see 02-ARCHITECTURE.md § “Production Model Diversity”).

Prerequisite System

Trait	Purpose
`TechTree`	Tech tree management
`ProvidesPrerequisite`	Building provides prerequisite
`ProvidesTechPrerequisite`	Provides named tech prerequisite
`GrantConditionOnPrerequisiteManager`	Manager for prerequisite conditions
`LobbyPrerequisiteCheckbox`	Lobby toggle for prerequisites

4. Condition System (~34 traits)

The condition system is OpenRA’s primary mechanism for dynamic behavior modification. Conditions are boolean flags that enable/disable conditional traits.

Trait	Purpose
`ExternalCondition`	Receives conditions from external sources
`GrantCondition`	Always grants a condition
`GrantConditionOnAttack`	Condition on attacking
`GrantConditionOnBotOwner`	Condition when AI-owned
`GrantConditionOnClientDock`	Condition when docked (client)
`GrantConditionOnCombatantOwner`	Condition when combatant owns
`GrantConditionOnDamageState`	Condition at damage thresholds
`GrantConditionOnDeploy`	Condition when deployed
`GrantConditionOnFaction`	Condition for specific factions
`GrantConditionOnHealth`	Condition at health thresholds
`GrantConditionOnHostDock`	Condition when docked (host)
`GrantConditionOnLayer`	Condition on specific layer
`GrantConditionOnLineBuildDirection`	Condition by wall direction
`GrantConditionOnMinelaying`	Condition while laying mines
`GrantConditionOnMovement`	Condition while moving
`GrantConditionOnPlayerResources`	Condition based on resources
`GrantConditionOnPowerState`	Condition based on power
`GrantConditionOnPrerequisite`	Condition when prereq met
`GrantConditionOnProduction`	Condition during production
`GrantConditionOnSubterraneanLayer`	Condition when underground
`GrantConditionOnTerrain`	Condition on terrain type
`GrantConditionOnTileSet`	Condition on tile set
`GrantConditionOnTunnelLayer`	Condition in tunnel
`GrantConditionWhileAiming`	Condition while aiming
`GrantChargedConditionOnToggle`	Charged toggle condition
`GrantExternalConditionToCrusher`	Grant condition to crusher
`GrantExternalConditionToProduced`	Grant condition to produced unit
`GrantRandomCondition`	Random condition selection
`LineBuildSegmentExternalCondition`	Line build segment condition
`ProximityExternalCondition`	Proximity-based condition
`SpreadsCondition`	Condition that spreads to neighbors
`ToggleConditionOnOrder`	Toggle condition via order

5. Multiplier System (~20 traits)

Multipliers modify numeric values on actors. All are conditional traits.

Multiplier	Affects
`DamageMultiplier`	Incoming damage
`FirepowerMultiplier`	Outgoing damage
`SpeedMultiplier`	Movement speed
`RangeMultiplier`	Weapon range
`InaccuracyMultiplier`	Weapon spread
`ReloadDelayMultiplier`	Weapon reload time
`ReloadAmmoDelayMultiplier`	Ammo reload time
`ProductionCostMultiplier`	Build cost
`ProductionTimeMultiplier`	Build time
`PowerMultiplier`	Power consumption/production
`RevealsShroudMultiplier`	Sight range
`CreatesShroudMultiplier`	Shroud creation range
`DetectCloakedMultiplier`	Cloak detection range
`CashTricklerMultiplier`	Cash trickle rate
`ResourceValueMultiplier`	Resource gather value
`GainsExperienceMultiplier`	XP gain rate
`GivesExperienceMultiplier`	XP given on death
`HandicapDamageMultiplier`	Handicap damage received
`HandicapFirepowerMultiplier`	Handicap firepower
`HandicapProductionTimeMultiplier`	Handicap build time

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Iron Curtain — Design Documentation