HUD — Heads-Up Display Layout (.HUD)¶

FA_2.LIB contains 46 .HUD files — one per aircraft type (e.g. A7.HUD, F22.HUD). Each defines the cockpit HUD layout for that aircraft. Each is a Win32 PE DLL loaded at runtime; all observed files decompress to 4608 bytes.

Tools¶

fx¶

fx hud dump <file.HUD>                                     # gauge parameter table and sprite name references
fx hud set  <file.HUD> <gauge.field=value ...> [-o out]    # edit gauge params / icon_a..icon_d labels

File Layout¶

All multi-byte integers are little-endian.

HUD files use Phar Lap PE format (signature PL\0\0). The CODE section is a pure data structure — no imports, no dispatch table, no x86 code. The engine loads HUD assets by name at runtime. All HUD files have identical CODE virtual size (0x2BB = 699 bytes), confirming a fixed-size struct regardless of aircraft.

String analysis of F22.HUD and B2.HUD reveals the asset reference pattern:

String	Role
`~f22` / `~b2`	Aircraft 3D model reference
`~f22h` / `~b2h`	HUD overlay image (heads-up display graphic)
`~f22s` / `~b2s`	HUD symbol set
`hudsym`	HUD symbol font (`HUDSYM*.FNT`)
`GEAR`, `FLAP`, `BRAKE`	Indicator label strings
`~f22_p` / `~b2_p`	Aircraft propulsion/engine panel reference
`~f22_w` / `~b2_w`	Weapons panel reference
`winfont`	Window font (`WIN*.FNT`) reference

The ~ prefix indicates LIB-resident asset references. The HUD DLL binds its aircraft-specific assets at load time using these names.

String layout (A7.HUD)¶

VA	String	Role
00001001	`~a7`	Aircraft model base name
0000100E	`~a7h`	High-AoA/hook variant
0000101B	`~a7s`	Speed-brake variant
00001038	`hud`	HUD identifier
00001051	`hudsym`	HUD symbol set
0000113C–000011A4	`~a7_l/c/r`, `~a7_lh/ch/rh`, `~a7_ls/cs/rs`	Left/centre/right sub-panel states
00001245	`GEAR`, `FLAP`, `BRAKE`, `HOOK`	Warning indicator labels
00001275	`~a7_p`, `~a7_w`	Engine/weapons panel sprites
00001297	`winfont`	Window font reference

Sub-panel sprite suffix semantics — confirmed¶

Suffix pattern	Meaning
`_l` / `_c` / `_r`	Left / centre / right panel — normal state
`_lh` / `_ch` / `_rh`	Left / centre / right panel — high-AoA state
`_ls` / `_cs` / `_rs`	Left / centre / right panel — stowed/small state

F22.HUD omits all _l/c/r sprites entirely — the F22 has no separate sub-panels. It also uses BAY (weapons bay indicator) instead of HOOK.

Gauge parameter layout — confirmed¶

All gauge positions are stored as signed s16 offsets from the HUD anchor point. Confirmed by tracing the HUD draw functions (HUDInit, ?HUDDrawHeading, ?HUDDrawSpeed, ?HUDDrawAlt, HUDDrawHVel, ?HUDDrawWeaponInfo, ?HUDDrawRangeInfo) in the game executable via Ghidra.

After loading, the struct is resident at hud. Field offsets within the copied struct:

Struct offset	Global	Gauge	Field
`0x1E1`	`DAT_00521541`	Heading tape	width (pixels)
`0x1E5`	`DAT_00521545`	Heading tape	dy from anchor
`0x1ED`	`DAT_0052154d`	Heading tape	tick spacing (dy)
`0x1F7`	`DAT_00521557`	Speed tape	dx from anchor
`0x1FB`	`DAT_0052155b`	Speed tape	dy from anchor
`0x1FF`	`DAT_0052155f`	Speed tape	height (pixels)
`0x209`	`DAT_00521569`	Speed tape	tick increment
`0x214`	`DAT_00521574`	Altitude tape	dx from anchor
`0x218`	`DAT_00521578`	Altitude tape	dy from anchor
`0x21C`	`DAT_0052157c`	Altitude tape	height (pixels)
`0x226`	`DAT_00521586`	Altitude tape	tick increment
`0x231`	`DAT_00521591`	Flight path marker	dx from anchor
`0x233`	`DAT_00521593`	Flight path marker	dy from anchor
`0x235`	`DAT_00521595`	Flight path marker	box half-width
`0x237`	`DAT_00521597`	Flight path marker	box half-height
`0x238`	`DAT_00521598`	Unknown	No cross-references found
`0x239`	`DAT_00521599`	Lock indicator flag A	3-state lock display; checked against `missile+0xa6 & 0x10`
`0x23A`	`DAT_0052159a`	Lock indicator flag B	Paired with A; selects state 5 (no lock) vs 6 (partial)
`0x23B`	`DAT_0052159b`	HUD center dot enable	Non-zero: draw center pip and radar velocity vector
`0x23C`	`DAT_0052159c`	ECM bar enable	Non-zero: enables ECM/threat bar draw (`FUN_00408c8b`)
`0x23D`	`DAT_0052159d`	Active-lock threat enable	Combined with 0x23C for active-lock threat bar
`0x23E`	`DAT_0052159e`	HVel altitude max	i16; HVel indicator (`HUDDrawHVel`) hidden above this altitude; also radar lock altitude gate
`0x240`	`DAT_005215a0`	Lead indicator enable	Non-zero: draw lead angle / velocity prediction overlay
`0x241`	`DAT_005215a1`	Score indicator dx	i8; X offset for score/fuel threshold indicator (`FUN_004078b0`)
`0x243`	`DAT_005215a3`	Score indicator dy	i8; Y offset for score/fuel threshold indicator
`0x245`	`DAT_005215a5`	Advisory icon C	8-byte icon data; drawn when `DAT_0050cfef & 0x040`
`0x24D`	`DAT_005215ad`	Advisory icon A	8-byte icon data; drawn when `DAT_0050cfef & 0x100`; `!= ' '` → advisory active
`0x255`	`DAT_005215b5`	Advisory icon B	8-byte icon data; drawn when `DAT_0050cfef & 0x080`
`0x25D`	`DAT_005215bd`	Advisory icon D	8-byte icon data; drawn when `DAT_0050cfef & 0x200` or `(& 0x400) && (DAT_0050d322 & 2)`
`0x265`	`DAT_005215c5`	Warning lights	dx from anchor (A7=65, F22=70) — `FUN_00407930`
`0x267`	`DAT_005215c7`	Warning lights	dy from anchor (A7=−38, F22=−46)
`0x269`	`DAT_005215c9`	Throttle/engine readout	dx from anchor (A7=−65, F22=−70) — `FUN_00407a00`
`0x26B`	`DAT_005215cb`	Throttle/engine readout	dy from anchor (A7=−38, F22=−46)
`0x26D`	`DAT_005215cd`	Weapon info	dx from anchor
`0x26F`	`DAT_005215cf`	Weapon info	dy from anchor
`0x271`	`DAT_005215d1`	Range info	dx from anchor
`0x273`	`DAT_005215d3`	Range info	dy from anchor

Advisory icon names (label strings embedded in the HUD file, order confirmed from A7.HUD string block at VA 0x00001245):

Icon	Bit	Struct offset	Label in A7.HUD	Label in F22.HUD	Subsystem
A	`0x100`	`+0x245`	`GEAR`	`GEAR`	`FMFlaps` — gear actuator (input 0x66)
B	`0x080`	`+0x24D`	`FLAP`	`FLAP`	`FMBrakes` — flap actuator (input 0x62)
C	`0x040`	`+0x255`	`BRAKE`	`BRAKE`	`FMGear` — speedbrake actuator (input 0x67)
D	`0x200`/`0x400`	`+0x25D`	`HOOK`	`BAY`	`FMBay` (tailhook, input 0x6f) / `FMHook` (bay door, input 0x68)

Engine Notes¶

Loading mechanism¶

HUDInit (HUD init, called at aircraft load time): 1. Loads the HUD DLL by name via RMAccess 2. Bulk-copies the entire CODE section (0xAC dwords + 2 bytes = 690 bytes) to hud 3. Scales every gauge parameter left by the display xscale/yscale factor (bVar3/bVar4)

The anchor point (DAT_00521d94/DAT_00521d96) is not read directly from the HUD file — it is computed dynamically at runtime via a smooth-follow interpolation that tracks the player aircraft's screen position.

`DAT_0050cfef` Advisory/State Flags — confirmed¶

DAT_0050cfef is the HUD state flags word. Bits are set by the game's subsystems at each simulation tick; FUN_00407930 and the tape render functions read them to gate icon and display variants.

Bit	Hex	Source function	Meaning
0	`0x00001`	`_DAMAGEDoHit@12` damage state `0x50d3ff`	Aircraft damage indicator level 1
1	`0x00002`	`_DAMAGEDoHit@12` damage state `0x50d400`	Aircraft damage indicator level 2
2	`0x00004`	`_DAMAGEDoHit@12` damage state `0x50d401`	Aircraft damage indicator level 3
3	`0x00008`	`_DAMAGEDoHit@12` damage state `0x50d3f7` (also clears bit 5)	Aircraft damage / engine-out state — cleared bit 5 indicates afterburner disabled by damage
4	`0x00010`	`_DAMAGEDoHit@12` damage state `0x50d40c`	Aircraft damage indicator level 4
5	`0x00020`	`FUN_00407a00`; cleared by `_DAMAGEDoHit@12` state `0x50d3f7`	Aircraft has afterburner AND throttle is at max (`DAT_0050d06e == 0x6400`) — shows `"THR: AFT"` instead of numeric throttle
6	`0x00040`	`HUDDrawSpeed`, `HUDDrawAlt`, `FUN_00407930`; set/cleared by `FMGear` (speedbrake actuator) via input 0x67	Advisory icon C active — speedbrake deployed; speed tape swaps live reference marker to approach-speed source (`DAT_0050d3aa`); altitude tape draws approach-altitude bracket markers (`DAT_0050d0aa`, `DAT_0050d3ae`)
7	`0x00080`	`FUN_00407930`; set/cleared by `FMBrakes` (flap actuator) via input 0x62	Advisory icon B active — flap deployed
8	`0x00100`	`FUN_00407930`; set/cleared by `FMFlaps` (gear actuator) via input 0x66	Advisory icon A active — landing gear deployed (down)
9	`0x00200`	`FUN_00407930`; set/cleared by `FMBay` (tailhook actuator) via input 0x6f	Advisory icon D active (single-player path) — tailhook deployed
10	`0x00400`	`FUN_00407930`; set/cleared by `FMHook` (bay-door actuator) via input 0x68	Advisory icon D active (multiplayer path, also requires `DAT_0050d322 & 2`) — weapon bay door / hook variant open
11	`0x00800`	`HARDSetFlags` (weapon-state scan, each tick)	Active weapon lock — at least one weapon has ammo and an acquired lock
12	`0x01000`	`FUN_00407a00`; toggled by `SetAutopilot` via input 0x61	Flight-lock / autopilot active — replaces throttle/G readout with lock sprite (`DAT_004ebf94`)
13	`0x02000`	`FlightKey` case 0x61 (autopilot key handler)	Autopilot ILS/ACLS sub-mode — set alongside bit 12 when flight mode is 6 and aircraft has ACLS capability (PT+0xe9 ≠ 0); gates carrier-approach glide-slope computation
14	`0x04000`	`?MPReceive@@YGDXZ` (0x46C980 → the 8.6 KB packet handler `FUN_0046c98f`, writes at 0x46db2b) in multiplayer. In single-player the flags word is written wholesale by the state-transition wrappers `FUN_004bc177`/`FUN_004bc190` (`DAT_0050cfef = EAX; @EnterState@4`) — the value is computed by the caller, which is why no `OR [mem], 0x4000` constant exists. Read in `ServicePlayer` during ejection states 0x11/0x12 in conjunction with `DAT_0050d0b1` (nearest entity pointer) and entity+0xFB range comparison; also gates aerodynamic integrator reset (`stickX`/`ec`, `rudder`).	Runtime-set — a network-synced or proximity-alert advisory state whose exact single-player trigger is re-gameplay (see Open Questions)
15	`0x08000`	`PLANECheckFuel` via `FMUpdatePlaneFields` (fuel monitor, runs every 5 ticks)	Bingo fuel threshold reached — `@SAYLowFuelMessage@8` checks `(0x8000 set) && (0x80000 clear)` → plays "Bingo fuel" voice line, then sets bits 19–20 as inhibit
16	`0x10000`	`PLANECheckFuel` via `FMUpdatePlaneFields`	Joker fuel threshold reached — plays "Joker fuel" voice line, sets bit 20 inhibit
17	`0x20000`	`PLANECheckFuel` via `FMUpdatePlaneFields`	Running on fumes threshold reached — plays "Running on fumes" voice line, sets bits 19–21 inhibit
18	`0x40000`	`PLANECheckFuel` via `FMUpdatePlaneFields`	Out of fuel threshold reached — plays "We're out of gas / I'm out of fuel" voice line, sets bits 19–22 inhibit
19	`0x80000`	set by `@SAYLowFuelMessage@8` when Bingo or higher voice line plays	Bingo voice line played (inhibit) — prevents replaying
20	`0x100000`	set by `@SAYLowFuelMessage@8` when any fuel warning voice line plays	Joker/any-warning voice line played (inhibit)
21	`0x200000`	set by `@SAYLowFuelMessage@8` when Fumes or Out-of-fuel line plays	Fumes voice line played (inhibit)
22	`0x400000`	set by `@SAYLowFuelMessage@8` when Out-of-fuel line plays	Out-of-fuel voice line played (inhibit)
28	`0x10000000`	`HUDDrawSpeed`, `HUDDrawAlt`; set by `_DAMAGEDoHit@12` state `0x50d40e`	Classified / redacted display — speed tape substitutes string at `0x004ebfbc`; altitude tape substitutes `s_XXXXX_004ebfd8` ("XXXXX"); tape tick-mark rendering skipped entirely; also triggered by aircraft-out-of-control damage state
29	`0x20000000`	`_DAMAGEDoHit@12` damage state `0x50d410`	Emergency state — aircraft critical / imminent crash indicator
30	`0x40000000`	`_DAMAGEDoHit@12` damage state `0x50d40f` (conditional on `Rand(3)` result); also read by carrier HGR renderer (`AnalyzeHGR.txt` lines 4143/4315): when set, suppresses normal slot-dot rendering and fixes the approach-angle indicator at position 2 (of 0–9) instead of computing the live angle from `DAT_0050ce9f`	Emergency state variant A — aircraft spinning / uncontrolled flight
31	`0x80000000`	`_DAMAGEDoHit@12` damage state `0x50d40f` (conditional on `Rand(3)` result)	Emergency state variant B — aircraft spinning / uncontrolled flight (alternate roll)

The command dispatcher is FlightKey. Each input case passes (current_bit == 0) to the actuator, which deploys the surface when TRUE (bit clear = currently retracted) and retracts it when FALSE (bit set = currently deployed). The actuator function updates the 3D model state and writes the advisory bit.

Round-Trip Notes¶

hud_repack (#99) rebuilds a HUD DLL around edited gauge parameters and advisory icon labels. The write path re-emits only what the parser models:

Gauge parameters — written back at their fixed struct offsets, with range checks for the s8/u8 fields. All known fields must be supplied exactly once; unknown names reject rather than silently no-op.
Advisory icon labels — written into their fixed 8-byte slots with a terminating NUL when shorter than the slot (mirroring the reader, which stops at a NUL or 8 bytes); slot bytes past the NUL carry over.
Everything else — PE headers, asset-string regions, and unmodelled struct bytes carry over verbatim. Asset strings are informational in HudFile and not editable through the repack.

An unedited parse→repack is therefore byte-identical; proven per-overlay over all 46 install HUDs (tests/test_hud.cpp, FX_FA_ROOT census).

Open Questions¶

1. Struct byte +0x238 and state-flag bit 14¶

Static analysis is exhausted on both; the residuals are runtime observations.

+0x238 (DAT_00521598) — a fresh cross-reference scan confirms zero static references anywhere in the game executable. No instruction reads or writes the absolute address, so its role (if any) can only be confirmed by watching the byte in the running game.
HUD flag bit 14 (0x04000) — the write mechanism is now identified: the multiplayer writer is the 8.6 KB packet handler FUN_0046c98f (entry ?MPReceive@@YGDXZ 0x46C980, store at 0x46db2b); in single-player the flags word DAT_0050cfef is rebuilt wholesale by the state-transition wrappers FUN_004bc177/FUN_004bc190 (DAT_0050cfef = EAX; @EnterState@4), so the bit is carried in a caller-computed value rather than set by a constant OR — which is why the constant search found nothing. The precise single-player state that raises bit 14 is a runtime-state question.

Status: static exhausted — re-tagged re-gameplay (#56) for the Phase 6 bench.

Formats: BRF — .PT aircraft type records the HUD pairs with; FNT — fonts used to render HUD text elements; PIC — bitmap assets used for HUD graphical elements.