NetworkUpdateFlags

The Thing.NetworkUpdateFlags 16-bit bitmask and how vanilla serialization uses the low 12 bits, leaving a small band of free bits that mods can piggyback on to add custom per-thing sync data.

Bitmask semantics

Thing.NetworkUpdateFlags is a bitmask. Setting a bit causes the game's next network tick to include that object in the update broadcast. SprayPaintPlus uses bit 12 (0x1000, GenericFlag2) for spray can color updates. This piggybacks on the existing Consumable.BuildUpdate/ProcessUpdate serialization.

Vanilla bit usage

16-bit bitmask. Values through 0x0800 are used by Thing/DynamicThing/Item for standard state (position, rotation, damage, color, access, etc.). EquipmentPlus uses 0x4000 for active-sensor sync. BuildUpdate and ProcessUpdate are called by the network layer; each flag bit causes the corresponding data block to be written/read.

Thing-level bit map and the transform bit (bit 1)

The Thing base class owns the low bits; subclasses (Structure, Cable/logic units, Item, DynamicThing, devices, etc.) add their own bits above the Thing range, each handled in that subclass's BuildUpdate/ProcessUpdate override (which calls base.BuildUpdate/base.ProcessUpdate first). From Assembly-CSharp (0.2.6228.27061) — Thing.BuildUpdate (:303247), Thing.ProcessUpdate (:303329), Thing.SerializeDeltaState (:303187), and the various property setters:

Bit (decimal)	Owner	Meaning / serialized block	Set by
1	Thing	transform delta — BuildUpdateTransform (:303381) writes WriteVector3(Position); WriteQuaternion(Rotation) (the Position/Rotation mirror fields, kept synced by the ThingTransformPosition/ThingTransformRotation setters at :298397/:298426); client ProcessUpdateTransform (:303387) reads them and does if (!HasAuthority) ThingTransform.SetPositionAndRotation(...)	never set automatically by a transform write. Set explicitly by Slot.Take for DynamicThing slot occupants (~Slot.cs:292640/:292644) and a handful of other special cases (a CursorManager-area site :56523, vehicle/rocket classes :141801/:202841); also SerializeOnJoin sets NetworkUpdateFlags |= ushort.MaxValue (:303033) so the join package includes everything
2	Thing	interactable-state delta — BuildInteractableUpdate (:303291) writes the dirty Interactables	Interactable.IsDirty machinery
4	Thing	indestructable DamageState	damage code
8	Thing	ReagentMixture	reagent code (VerifyUpdateType at :303230 clears this bit if ReagentMixture == null)
16	Thing	IsBurning flag	IsBurning setter (:298530)
32	Thing	CustomColor index + CustomName	CustomName setter (:298559) and color setters
64	Structure	CurrentBuildStateIndex (sbyte) — Structure.BuildUpdate (:295569)	CurrentBuildStateIndex setter (:295484, server only)
128	Thing	EnergyConvected + EnergyRadiated	thermal code
0x1000 (4096 / GenericFlag2)	free	—	SprayPaintPlus piggybacks here on Consumable.BuildUpdate (see below)
0x4000 (16384)	free in vanilla	—	EquipmentPlus active-sensor sync

(Subclasses such as CircuitHousing/logic units reuse bits 512/1024–32768 for their own device lists — those overlap the "free" range above only for prefab families that don't carry that subclass's serialization, which is exactly why SprayPaintPlus / EquipmentPlus picked bits unused by Consumable / their target type.)

Two distinct transform-serialization paths exist and use different fields: - Per-tick delta (bit 1): BuildUpdateTransform → Position / Rotation (the live-transform mirror fields). Neither Structure nor Cable overrides BuildUpdateTransform/ProcessUpdateTransform. - Join package (full state): Thing.SerializeOnJoin (:303031) calls WriteTransform(writer). Thing.WriteTransform (:303025) writes ThingTransformPosition / ThingTransform.rotation; Structure.WriteTransform (:295588) overrides it to write RegisteredPosition / RegisteredRotation instead. The joining client applies these via Thing.DeserializeNew (:303168) → Create<Thing>(...) + SnapTransform(transformPosition, transformRotation) (:303176/:303179). Structure.SerializeOnJoin (:295594) additionally writes RegisteredLocalGrid + WriteQuaternion(Direction), read back by Structure.DeserializeOnJoin (:295602).

Consequence for a mod that moves/rotates a placed Structure server-side: the visible mesh follows ThingTransform.rotation immediately, but for the change to (a) save it must update Structure.RegisteredRotation (the save reads RegisteredRotation, not the live transform — Structure.InitialiseSaveData :295797), (b) reach already-connected clients it must set NetworkUpdateFlags |= 1 server-side, and © reach late-joiners correctly it relies on RegisteredRotation (the join-package transform) — and Structure.Direction should be set too for the join-package Direction field. See ../GameSystems/PlacementOrientation.md ("Changing a placed Structure's rotation at runtime") for the full recipe and the option comparison; MoveToWorld is not usable for this (it is DynamicThing's inventory-eject op, a no-op for a non-slotted Structure).

GenericFlag2 (bit 12) for SprayPaintPlus color sync

Bit 12 of NetworkUpdateFlags (GenericFlag2) was chosen because it is unused by Consumable's vanilla serialization. Setting this flag triggers a network update that includes the spray can's data, and the postfix patches append the color index to that data.

From SprayPaintHelpers.cs:

// Network flag for custom spray can color sync (bit 12 = GenericFlag2).

Verification history

• 2026-04-20: page created from the Research migration; verbatim content lifted from F0029a (primary), F0026, F0126a, and F0387.
• 2026-05-12: added "Thing-level bit map and the transform bit (bit 1)" section after a decompile pass on Thing.NetworkUpdateFlags/BuildUpdate/ProcessUpdate/BuildUpdateTransform/ProcessUpdateTransform/WriteTransform/SerializeDeltaState/SerializeOnJoin/DeserializeNew and Structure.WriteTransform/SerializeOnJoin/DeserializeOnJoin/BuildUpdate in Assembly-CSharp.decompiled.cs (0.2.6228.27061), plus a whole-file grep of NetworkUpdateFlags |= 1 sites. Findings: enumerates the Thing-owned bits (1 transform, 2 interactables, 4 damage, 8 reagent, 16 burning, 32 colour/name, 128 thermal), Structure's 64 (build state); documents that bit 1 is never set automatically by a transform write (only by Slot.Take for slot occupants and a few special cases) and that two distinct transform-serialization paths exist (per-tick delta via BuildUpdateTransform → Position/Rotation; join package via WriteTransform → for Structure, RegisteredPosition/RegisteredRotation). Additive; cross-linked to PlacementOrientation.md (which carries the "re-roll a placed structure at runtime" recipe and option comparison). Found via investigating runtime re-rolling of a placed straight Cable; full dump in .work/2026-05-12-cable-rotation/notes/mutation-findings.md.

Open questions

None.