Prefab cloning (Mirrored Devices template)

Full recipe for cloning a vanilla prefab, registering it with the game's prefab system, wiring multi-constructor kits, and preserving multiplayer/save-load compatibility. Lifted verbatim from RepairPrototype's reverse-engineering of the Mirrored Devices mod.

Problem

A mod that wants to add a new device whose behavior matches an existing one does NOT need to hand-build the prefab. Clone the vanilla prefab, override identity (name, hash), register with WorldManager.SourcePrefabs, and the game treats the clone as any other device. Multiplayer save/load "just works" because the clone shares all original components.

The recipe has three Harmony entry points, each serving a distinct phase of the prefab lifecycle, plus helpers for constructor conversion, localization, and crafting recipes.

Solution / recipe

Three Harmony patches

F0225 (Plans/RepairPrototype/plan.md:479-484):

1. Prefab.LoadAll Prefix (line 499): Runs before game loads prefabs. This is where cloning happens.
2. Localization.LanguageFolder.LoadAll Prefix (line 828): Registers display names.
3. InventoryManager.SetupConstructionCursors Postfix (line 455): Fixes placement cursor arrows.

HiddenParent setup

F0226 (Plans/RepairPrototype/plan.md:487-495):

// Static field (lives for entire game session)
private static readonly GameObject HiddenParent = new GameObject("~HiddenGameObject");

// In Prefab.LoadAll prefix:
UnityEngine.Object.DontDestroyOnLoad(HiddenParent.gameObject);
HiddenParent.SetActive(value: false);

The hidden parent prevents clones from being visible. DontDestroyOnLoad survives scene loads.

CreateMirroredThing core

F0227 (Plans/RepairPrototype/plan.md:521-545):

// (1) Clone the entire GameObject hierarchy
GameObject mirroredGameObject = GameObject.Instantiate(source, HiddenParent.transform);
mirroredGameObject.name = mirrorDef.mirrorName;

// (2) Override identity
Thing mirroredThing = mirroredGameObject.GetComponent<Thing>();
mirroredThing.PrefabName = mirrorDef.mirrorName;
mirroredThing.PrefabHash = mirrorDef.mirrorHash;

// (3) [Mirror-specific: flip transform -- NOT NEEDED for repair mod]
FlipTransform(mirroredGameObject.transform);

// (4) Clone and process blueprint (placement ghost)
if (mirroredThing.Blueprint != null)
{
    mirroredThing.Blueprint = GameObject.Instantiate(mirroredThing.Blueprint, HiddenParent.transform);
    FlipTransform(mirroredThing.Blueprint.transform);
    Wireframe blueprintWireframe = mirroredThing.Blueprint.GetComponent<Wireframe>();
    FlipWireframe(blueprintWireframe);
}

// (5) REGISTER with the game
WorldManager.Instance.SourcePrefabs.Add(mirroredThing);

FindMirrorInfos + ConvertConstructorToMultiConstructor

F0229n (Plans/RepairPrototype/plan.md:497-514):

FindMirrorInfos() scans WorldManager.Instance.SourcePrefabs: if prefab is MultiConstructor with matching Constructable, store constructor reference; if plain Constructor, queue for upgrade; if matches by name, store as deviceToMirror. Walks all prefabs' BuildStates to find Tool.ToolEntry/ToolEntry2 references pointing at old Constructor. ConvertConstructorToMultiConstructor (line 526): var mctor = ctor.gameObject.AddComponent<MultiConstructor>(); mctor.Constructables = new List<Structure>() { buildStructure }; CopySharedFields((Stackable)ctor, (Stackable)mctor); WorldManager.Instance.SourcePrefabs[prefabIndex] = mctor; UnityEngine.Object.DestroyImmediate(ctor); CopySharedFields uses reflection to copy every field from Stackable up through Item/DynamicThing/Thing, with special handling for self-references and IList with Parent refs pointing to source.

AddToConstructor + MirrorDefinition class

F0229o (Plans/RepairPrototype/plan.md:547-560):

AddToConstructor: int insertIndex = mirrorDef.constructor.Constructables.FindIndex(p => p.name == mirrorDef.deviceName); mirrorDef.constructor.Constructables.Insert(insertIndex + 1, mirroredDevice as Structure); Inserts clone right after original in kit's constructable list. MirrorDefinition class: deviceName, mirrorName (= deviceName + "Mirrored"), mirrorHash (= Animator.StringToHash(mirrorName)), mirrorDescription, connectionsToFlip, deviceToMirror, constructor, postfix delegate. Per-device postfix delegate runs device-specific tweaks.

Localization + free crafting recipes

F0229p (Plans/RepairPrototype/plan.md:583-610):

Localization registration via [HarmonyPatch(typeof(Localization.LanguageFolder), nameof(Localization.LanguageFolder.LoadAll))] Prefix: finds original name in __instance.LanguagePages[0].Things, then adds new Localization.RecordThing { Key = mirrorDef.mirrorName, Value = originalName + " (Mirrored)", ThingDescription = mirrorDef.mirrorDescription }. No XML needed. Crafting recipes FREE: GameObject.Instantiate() copies entire BuildStates chain. Clone inherits exact same recipe as original. No XML, no recipe code needed.

Save-load stability

F0229h (Plans/RepairPrototype/plan.md:452-459):

Stationeers saves use PrefabHash (integer) to identify things. Animator.StringToHash(name) is deterministic - same name always produces same hash. Cloned prefabs with stable names survive save/load automatically. If mod removed, things with unknown PrefabHash fail to load (silently disappear or cause errors). No custom save data types needed if clone doesn't add new state fields.

Key takeaways

F0228 (Plans/RepairPrototype/plan.md:612-620):

1. The actual cloning is ~30 lines. Everything else is bookkeeping.
2. Prefab.LoadAll prefix is the universal hook for prefab manipulation.
3. Animator.StringToHash(name) is the hash function; deterministic, stable across saves.
4. Hidden parent with DontDestroyOnLoad + inactive is essential.
5. The Constructor/MultiConstructor distinction is the trickiest bookkeeping.
6. Multiplayer and save/load "just work" because the clone shares all original components.
7. This breaks the moment you add custom state or behavior; then all clients need the mod.

Cited verifications

Eight findings, all from RepairPrototype's plan, fit together as one template:

Finding	Subject
F0225	Three Harmony patches (Prefab.LoadAll, Localization.LoadAll, SetupConstructionCursors)
F0226	HiddenParent + DontDestroyOnLoad setup
F0227	CreateMirroredThing core (Instantiate + rename + register)
F0228	Key-takeaways summary
F0229h	PrefabHash stability via Animator.StringToHash
F0229n	FindMirrorInfos + ConvertConstructorToMultiConstructor + CopySharedFields
F0229o	AddToConstructor + MirrorDefinition
F0229p	Localization registration + free crafting recipes

Verification history

• 2026-04-20: page created from the Research migration; eight findings combined verbatim into one coherent template.

Open questions

None at creation.