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Device Port Geometry (power connection cells)

Which small-grid cells a device's power ports occupy and face, measured live per prefab. This is the data needed to place cables programmatically so they actually connect (fixture authoring, save editing, spawn tooling); hand-positioning cables without it fails silently because the connection law is cell-exact.

The connection law

From the decompile (connection cell math at lines 312730-312745, FillConnected at 312896-312941 of .work/decomp/0.2.6403.27689/Assembly-CSharp.decompiled.cs):

A device port connects to the cable occupying the port's LocalGrid cell only when that cable has an open end whose LocalGrid equals the port's FacingGrid. The relation is mutual: the cable end must sit in the cell the port occupies, AND point back at the cell the port faces. For every single-cell device probed below, the port's FacingGrid is the device's own body cell (facing offset (0,0,0) from ThingTransformPosition at identity rotation), so in practice the adjacent cable end must aim at the device body.

Connections register at structure COMPLETION, not at kit placement: a multi-build-state structure at CurrentBuildStateIndex 0 has not run its port registration, sits on no cable network, and is invisible to the power grid until the final build state lands (see Structure.md, "Construction completion" and the build-state completion boundary section). This is why a placed-but-unfinished device shows no power behavior of any kind.

How the data was captured

The ScenarioRunner scenario pgp-fresh-device-trace spawns each prefab at identity rotation on a fresh dedicated-server world and reads, for every entry of SmallGrid.OpenEnds whose ConnectionType includes NetworkType.Power:

  • ConnectionRole (None / Input / Output),
  • ConnectionType (Power / PowerAndData),
  • LocalGrid minus ThingTransformPosition (the port cell offset, printed as local=),
  • FacingGrid minus ThingTransformPosition (the faced cell offset, printed as facing=),
  • Structure.BuildStates.Count (printed as buildStates=).

Reproducible: set Scenario = pgp-fresh-device-trace in the ScenarioRunner config, start a fresh world, and grep the log for FDT PROBE. Offsets are in world meters on the small grid (0.5 m half-cell steps); a rotated placement rotates the offsets with the body.

Measured port geometry (verbatim capture, 2026-07-17)

FDT PROBE StructureRTG body=(440,400,400) buildStates=1 ports=[None:Power local=(0,0.5,0) facing=(0,0,0)]
FDT PROBE StructureTransformerSmall body=(440,400,404) buildStates=1 ports=[Input:PowerAndData local=(-0.5,0,0) facing=(0,0,0) | Output:Power local=(0.5,0,0) facing=(0,0,0)]
FDT PROBE StructureWallLight body=(440,400,408) buildStates=1 ports=[None:PowerAndData local=(0,-0.5,0) facing=(0,0,0)]
FDT PROBE StructureGrowLight body=(440,400,412) buildStates=1 ports=[None:Power local=(0,-0.5,0) facing=(0,0,0)]
FDT PROBE StructureConsole body=(440,400,416) buildStates=2 ports=[None:PowerAndData local=(0,-0.5,0) facing=(0,0,0)]
FDT PROBE StructureWallCooler body=(440,400,420) buildStates=1 ports=[None:PowerAndData local=(0,0.5,0) facing=(0,0,0)]
FDT PROBE StructureWallHeater body=(440,400,424) buildStates=1 ports=[None:PowerAndData local=(0,0.5,0) facing=(0,0,0)]
FDT PROBE StructureCableCorner body=(444,400,428) buildStates=1 ports=[None:PowerAndData local=(-0.5,0,0) facing=(0,0,0) | None:PowerAndData local=(0,0,0.5) facing=(0,0,0)]
FDT PROBE StructureCableCornerH body=(444,400,432) buildStates=1 ports=[None:PowerAndData local=(0,0,-0.5) facing=(0,0,0) | None:PowerAndData local=(-0.5,0,0) facing=(0,0,0)]
FDT PROBE StructureCableJunction body=(444,400,436) buildStates=1 ports=[None:PowerAndData local=(0,0,-0.5) facing=(0,0,0) | None:PowerAndData local=(0,0,0.5) facing=(0,0,0) | None:PowerAndData local=(-0.5,0,0) facing=(0,0,0)]
FDT PROBE StructureCableJunctionH body=(444,400,440) buildStates=1 ports=[None:PowerAndData local=(0.5,0,0) facing=(0,0,0) | None:PowerAndData local=(-0.5,0,0) facing=(0,0,0) | None:PowerAndData local=(0,0,-0.5) facing=(0,0,0)]
FDT PROBE StructureCableJunction4 body=(444,400,444) buildStates=1 ports=[None:PowerAndData local=(0,0,-0.5) facing=(0,0,0) | None:PowerAndData local=(0,0,0.5) facing=(0,0,0) | None:PowerAndData local=(-0.5,0,0) facing=(0,0,0) | None:PowerAndData local=(0.5,0,0) facing=(0,0,0)]
FDT PROBE StructureCableJunctionH4 body=(444,400,448) buildStates=1 ports=[None:PowerAndData local=(0,0,-0.5) facing=(0,0,0) | None:PowerAndData local=(0,0,0.5) facing=(0,0,0) | None:PowerAndData local=(-0.5,0,0) facing=(0,0,0) | None:PowerAndData local=(0.5,0,0) facing=(0,0,0)]
FDT PROBE StructureCableStraight body=(444,400,452) buildStates=1 ports=[None:PowerAndData local=(0,0,-0.5) facing=(0,0,0) | None:PowerAndData local=(0,0,0.5) facing=(0,0,0)]
FDT PROBE StructureCableStraightH body=(444,400,456) buildStates=1 ports=[None:PowerAndData local=(0,0,-0.5) facing=(0,0,0) | None:PowerAndData local=(0,0,0.5) facing=(0,0,0)]

Normalized (offsets from the registered body position, identity rotation):

Prefab Build states Ports (role : type @ local offset)
StructureRTG 1 None : Power @ (0, +0.5, 0)
StructureTransformerSmall 1 Input : PowerAndData @ (-0.5, 0, 0); Output : Power @ (+0.5, 0, 0)
StructureWallLight 1 None : PowerAndData @ (0, -0.5, 0)
StructureGrowLight 1 None : Power @ (0, -0.5, 0)
StructureConsole 2 None : PowerAndData @ (0, -0.5, 0)
StructureWallCooler 1 None : PowerAndData @ (0, +0.5, 0)
StructureWallHeater 1 None : PowerAndData @ (0, +0.5, 0)
StructureCableCorner 1 2x None : PowerAndData @ (-0.5, 0, 0) and (0, 0, +0.5)
StructureCableCornerH 1 2x None : PowerAndData @ (0, 0, -0.5) and (-0.5, 0, 0)
StructureCableJunction 1 3x None : PowerAndData @ (0, 0, -0.5), (0, 0, +0.5), (-0.5, 0, 0)
StructureCableJunctionH 1 3x None : PowerAndData @ (+0.5, 0, 0), (-0.5, 0, 0), (0, 0, -0.5)
StructureCableJunction4 1 4x None : PowerAndData @ all four horizontal half-cells
StructureCableJunctionH4 1 4x None : PowerAndData @ all four horizontal half-cells
StructureCableStraight 1 2x None : PowerAndData @ (0, 0, -0.5) and (0, 0, +0.5)
StructureCableStraightH 1 2x None : PowerAndData @ (0, 0, -0.5) and (0, 0, +0.5)

Notable facts

  • The small transformer's two ports differ in type: the Input port is PowerAndData, the Output port is Power only. A data-carrying read reaches the transformer only from its input side wiring.
  • The RTG's single port points up ((0, +0.5, 0) at identity rotation) and is Power only, consistent with the RTG exposing no logic surface.
  • Wall-mount devices put their port half a cell toward the mount face: WallLight / GrowLight / Console at (0, -0.5, 0), WallCooler / WallHeater at (0, +0.5, 0). GrowLight's port is Power only; the other wall devices carry PowerAndData.
  • StructureConsole is the only probed prefab with 2 build states; everything else in this set completes at state 0. A 2-state device spawned or placed at state 0 is grid-invisible until completed (the completion boundary, Structure.md).
  • All facing offsets read (0,0,0) for single-cell devices: the faced cell is the body cell, so a connecting cable end must occupy the port's half-cell and aim at the device body.
  • Cable pieces expose role None on every end; only the transformer distinguishes Input / Output roles in this set.

Verification history

  • 2026-07-17: page created from the live probe capture on the dedicated server (fresh Lunar world, game 0.2.6403.27689) plus the decompile-cited connection law; all 16 probe lines quoted verbatim.

Open questions

  • Multi-cell prefabs (cable straights ⅗/10, large devices) and non-identity mount rotations were not probed; their per-cell port lists and facing cells are uncaptured.
  • Port geometry for the APC, batteries, and the large transformer family is uncaptured (the probe set covered the fresh-device-trace chain only).