---
id: gauges-hud
title: "Cockpit Gauges / MFD HUD system"
status: established
source_sections: "docs/GAUGE_COMPOSITE.md (full map); CLAUDE.md §8"
related_topics: [reconstruction-gotchas, decomp-reference, subsystems, pod-hardware]
key_terms: [gauge, methodDescription, attribute-pointer, GaugeRenderer, MFD, PCC]
open_questions:
  - "Condenser valve control gates on the owning BTPlayer game-mode flag (mech+0x190), likely off in basic missions"
  - "Status-message queue (StatusMessagePool) is a NULL stub -> MessageBoard is empty"
---

# Cockpit Gauges / MFD HUD

The pod's cockpit instruments: the secondary MFD (radar/heat/comm), the 5 mono MFDs, and the
engineering screens. Full map + per-widget history in **`docs/GAUGE_COMPOSITE.md`**. **The gauge
system is COMPLETE** at the registration+binding level: all 50 config attribute bindings resolve
(0 NULL) and every config gauge primitive is registered + built (0 parse-skips). [T2]

## Architecture (three layers)
1. **The config** `content/GAUGE/l4gauge.cfg` — a text file the engine `GaugeInterpreter` parses
   (`BuildConfigurationFile → Initialize → GetProcedureBody → ParsePrimitive`). Each mech's gauge
   tree is built from the label `GetGameModel()+"Init"` (e.g. `bhk1Init`), which invokes shared
   blocks (`MechInit`, `Secondary1`) that `configure` the ports and call gauge primitives. [T1]
2. **Widgets** — each `keyword(...)` in the config resolves to a `MethodDescription` in
   `BTL4MethodDescription[]` (btl4grnd.cpp). An UNREGISTERED keyword is **parse-skipped** (never
   built). Base primitives (`numeric`/`digitalClock`/`rankAndScore`/`vertBar`-base/`segmentArc`)
   are ENGINE (L4GAUGE.cpp); BT-specific ones (`vertBar`/`map`/`pilotList`/`GeneratorCluster`/
   `sectorDisplay`/`prepEngr`/`messageBoard`/`vehicleSubSystems`/the ColorMapper family) are
   reconstructed + registered. [T2]
3. **Data binding** — gauges bind to game state by NAME via the engine [[attribute-pointer]]
   system: the config's `Subsystem/Attribute` (e.g. `HeatSink/CurrentTemperature`) resolves
   through `ParseAttribute → FindSubsystem (stricmp GetName()) → GetAttributePointer`. A class
   PUBLISHES an attribute via a `<Name>AttributeID` enum + `static AttributePointers[]`
   (`ATTRIBUTE_ENTRY`) + `GetAttributeIndex()` chained to its parent. ⚠ DENSE-TABLE HAZARD (see
   [[reconstruction-gotchas]] §11). [T2]

## Reconstructing a widget — the recipe
`MethodDescription Class::methodDescription = { "keyword", Class::Make, { ParameterDescription
rows } };` + a line in `BTL4MethodDescription[]` before `&BTL4ChainToPrevious`. The static
`Make(int port, Vector2DOf<int> pos, Entity*, GaugeRenderer*)` reads `methodDescription.parameterList[]`,
allocs (`operator new(binSize)` or plain `new`), placement-news the ctor. Then ctor/dtor/
TestInstance/BecameActive/Execute. **Gotchas that bite EVERY widget:**
- Container-Execute must override (§10 gotchas) — else `Gauge::Execute` aborts.
- `/FORCE` trap — a prose-only slot AVs on first call.
- Databinding trap — never raw-read owner offsets; use a bridge (`BTGetSubsystemAuxScreen`, …).
- ReconStream no-op — use `DEBUG_STREAM` for logs, not `DebugStream`.
- Lazy build — wait for the gauge window before concluding "not built" (`BT_GAUGE_SKIP_LOG`). [T2]

## The completed widgets (this project's gauge wave)
- **Attributes published:** HeatSink table (Degradation/Failure/NormalizedPressure/CoolantMassLeakRate/
  ValveSetting/…), PoweredSubsystem (InputVoltage), MechWeapon (OutputVoltage), Mech (LinearSpeed,
  radar Position/Quaternion), Sensor (RadarPercent), **AggregateHeatSink (AmbientTemperature=300 —
  the LAST NULL)**. [T2]
- **Widgets reconstructed + registered:** ColorMapper family (cmHeat/cmCrit/cmArmor/multiArmor),
  headingPointer, vertBar (VertTwoPartBar), segmentArcRatio, oneOfSeveralPixInt, map (radar),
  PlayerStatus, vehicleSubSystems (the engineering cluster panels), LeakGauge, vertNormalSlider,
  **pilotList** (Comm KILLS/DEATHS), **GeneratorCluster**, **SectorDisplay** (radar SECTOR X/Z
  read-out — live), **PrepEngrScreen** (12 engineering-screen label overlays), **MessageBoard**
  (comm ticker — deferred-empty). [T2]
- **Condenser valve gauge:** ValveSetting→coolantFlowScale reads the authentic **1/N**
  (`RecomputeCondenserValves`, FUN_0049f788, was a no-op stub). [T2]

## Dev composite (off-pod)
`BT_DEV_GAUGES` renders the 6 pod [[MFD]] surfaces in a separate 960×384 window (bit-plane masks
over one shared `SVGA16` pixelBuffer; `SVGA16::DrawDevSurface`). On the POD they come from
`SETENV.BAT`/`L4GAUGE` on the real multi-adapter hardware (`FindBestAdapterIndices`/`BuildWindows`,
intact). The `overlay` port (SectorDisplay lives there) shares the `sec` physical surface via a
different bit-plane (0x00C0). [T2]

## Authentically-static (do NOT "fix")
`currentTemperature ~77` (huge thermalMass ~1.39e6 → a 3.5-heat shot rounds to zero);
Degradation/Failure temps are fixed markers; AmbientTemperature 300; CoolantMassLeakRate 0 on a
pristine mech (damage-gated); cmArmor/cmCrit all-green (undamaged solo player — BT is PvP-only);
RANK 1 solo; MessageBoard empty (no status messages exist in bring-up). The Heat MFD is
authentically NEAR-STATIC, not a live heat-accumulation display. [T2]

## Remaining = DATA FEEDS, not widgets (deferred systems)
The **condenser valve CONTROL** gates on the owning **BTPlayer**'s game-mode flag (`mech+0x190`,
`GetPlayerLink()`, via `MechSubsystem::IsDamaged`/`FUN_004ac9c8` reading `player+0x274`) — NOT the
0xBD3 messmgr (a common earlier misconception; 0xBD3 is a damage/explosion hub at `Mech[0x10d]`=0x434).
In a basic mission the valve/mode flags are likely off, so the dormant valve is plausibly AUTHENTIC —
see [[open-questions]] `mech+0x190`. The **MessageBoard** feed needs **StatusMessagePool** (a NULL
stub) + the per-player status queue. `SeekVoltageGraph`'s 4 Seek* attrs are a cluster-child (not
config-called). [T2]

## Cockpit HUD reticle (main screen, inside view) — LIVE
`BTReticleRenderable` (0x358 bytes, ctor @004cc40c) draws over the finished 3D frame in cockpit
view only, via the recovered **dpl2d** 2D display-list API (recorders @0x487f34-0x488630; opcode
map + coordinate model in `phases/phase-02-dpl2d-reticle.md`; port: `game/reconstructed/dpl2d.cpp`).
Geometry is the ctor's hardcoded calibration (originX 0.35, originY 0.25, scaleY 0.5, right range
ladder 0..1200 m, bottom heading tape, center cross + dot; tick ladders via FUN_004cd938). The
range caret binds to the live target range (`BTSetHudTargetRange`, fed by mech4's targeting step).
**Weapon pips:** the build loop (part_014.c:5386) registers EVERY subsystem
`IsDerivedFrom(0x511830 = MechWeapon)` — lasers, PPCs AND missile launchers (BLH = 7 pips) — via
`AddWeapon` @004cdac0 (verified store map in btl4vid.hpp).

**The per-frame `Execute` @004cdcf0 is RECOVERED (task #37, capstone disasm via
`tools/disas2.py` — the full annotated read: the task-37 commit + btl4vid.cpp comments) [T1],
and every instrument is now live [T2]:**
- **Right ladder** = range 0–1200 m: a BAR from ladder-top to the caret + the yellow caret
  translate (`-scaleY·frac`); pegs at 1200 with no target; the DISPLAYED range slides at
  **500 m/s** toward the true pick range (HudSimulation :5652 [T1]). **The weapon pips sit on
  this same ladder at each weapon's authored max-range mark** — caret below a pip = that weapon
  reaches the target. BLH authored data (live dump): 3× ER-M laser red @**500 m** (two stacked
  at one column; PipExtendedRange=1), 2× missile amber (0.6,0.4,0) @**800 m**, 2× PPC blue
  @**900 m** — so the 7 pips read as 3 weapon-SYSTEM groups. (The engineering-panel "RANGE 500M"
  labels are panel text; the authoritative reach is the streamed WeaponRange.)
- **Bottom 21-tick tape = the TORSO-TWIST indicator** (NOT a heading tape): deflection line +
  carets at `∓(span/2)·(RotationOfTorsoHorizontal / HorizontalTorsoLimit)` (HUD attrs 4/5/6).
  Fixed-torso BLH: centred (authentic static).
- **Circle-with-stem = the COMPASS** (HUD attr 0xD CompassHeading, rad→deg rotation) at
  `(botX, botY−3·tickMajor−0.03)`; the **THREAT trail** (attr 0xC ThreatVector) draws inside its
  rotated frame: 0.05-unit attack-direction marks, fresh <2 s red, expiring at 6 s, 1 s blink tick.
  Port feed: the player's TakeDamage handler pushes the impact direction.
- **Pips** (composed into subB6, master-called): hidden when the weapon's DAMAGE state == 1
  (destroyed, attr 1); LIT (A) when the FIRE-CYCLE state == 2 (loaded, attr 0x1c; port source
  rechargeLevel ≥ 1) else dark ring (B, charging); filtered by `weaponMode & elementMask&0xF`
  (the weapon-GROUP bits Front/Rear/Left/Right). **Range plays NO part** — Execute never reads
  the stored TargetWithinRange slots.
- **Lock ring** = subB9 (ring+cross) at frame centre, **SPINNING 4°/frame** while the Lock attr
  (0xA) is up. The Lock PRODUCER is the authentic HudSimulation rule (part_013.c:5619-5634 [T1],
  wired task #38): lock requires a target AND your own HUD's host zone damage < **0.75** (a
  shot-up targeting computer loses lock) AND the targeted zone's damage < **1.0** (whole-mech
  target checks zone 0 — so a wreck's dead zone can't re-lock). The hotbox stays visible without
  lock (box = HotBoxVector, ring = Lock — separate signals). The binary also hangs the PNAMEx.bgf
  player-name mesh on the 3D marker here (3D chain still deferred).
- **Simple-X mode** (PrimaryHudOn off, mask 0x20): the minimal reticle — a small green cross
  (±0.02..0.08 arms) riding the aim translate (ctor @4689-4705 [T1]) — swapped for the full HUD
  by Draw's state switch.
- **Target HOTBOX** (attr 0xB HotBoxVector) = a rectangle hugging the projected extents — x±4
  around the hotbox point, +1/−11.5 vertical (K=2.8145 baked projection; the port uses the live
  per-axis projection) — switching to the left/right edge ARROW past ±1.6 or behind.
- Reticle state Off/On + `PrimaryHudOn` (mask 0x20) picks full HUD vs the "simple X" list;
  the aim group translates by `reticlePosition` = the TORSO BORESIGHT (SetMatrix; NOT a free
  cursor — see [[combat-damage]] Targeting: the stick twists the torso, no mouse-aim exists).
This recovery also CONFIRMS the HUD attr-table ids 4/5/6/8/0xA/0xB/0xC/0xD name↔use pairings
(hud.hpp had flagged them uncertain). Deferred: PNAME1-8.bgf 3D marker chain; the `blx_cop`
canopy shell renders black and is hidden by name filter (`BT_INSIDE_COCKPIT=1` shows it) — see
[[open-questions]].

## Key Relationships
- Full history: `docs/GAUGE_COMPOSITE.md`; reticle recovery: `phases/phase-02-dpl2d-reticle.md`.
- Uses: [[attribute-pointer]] + [[reconstruction-gotchas]]; reads [[subsystems]] state.
- Renders on: [[pod-hardware]] MFD surfaces.
