BT412/context/decomp-reference.md

id, title, status, source_sections, related_topics, key_terms, open_questions

id	title	status	source_sections	related_topics	key_terms	open_questions
decomp-reference	Decomp Reference — resource types, ClassIDs, offsets, addresses, env gates	established	CLAUDE.md §10c; game/reconstructed/CLASSMAP.md; reference/decomp/all/part_*.c	subsystems combat-damage reconstruction-gotchas build-and-run gauges-hud	ClassID resource-type subsystem-roster BTL4OPT factory	0xBCE weapon family fully mapped? (GaussRifle : Emitter, FireWeapon is a no-op in this build)

Decomp Reference

The quantitative hub for the reconstruction: resource-type enum, ClassID map, mech struct offsets, key FUN_ addresses, and env gates. Cite a section here rather than re-deriving. Everything is [T1] (decompiled + byte-verified) unless tagged otherwise. The living source-of-truth is reference/decomp/all/part_*.c; the class map is game/reconstructed/CLASSMAP.md.

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1. Resource lookup

ResourceFile::FindResourceDescription(name, type, index=-1) (FUN_00406ff8 = find-by-type-and-name; FUN_00407064 = SearchList(resourceID, type)). Lookup is by NAME or by ID. Mech::ResolveAnimationClip(prefix,suffix) builds a name and calls it.

⚠ A clip_id from ResolveAnimationClip is a DIRECT resource ID → FindResourceDescription(clip_id), NOT SearchList(clip_id, 16) (which treats the arg as a LIST → walks garbage → AV). [T1]

Resource type enum

Type	Value	Holds
SkeletonStream	—	.SKL skeletons
DamageZoneStream	0x14	damage-zone records (Mech ctor reads count + array)
ModelList	18	model/mech names (bhk1, madcat, …)
AnimationResourceType	16 (0x10)	animation clips (lowercase: blhrrl=904, blhrrr=905, blhwwli=910, blhrrli=916)
damage-zone segment list	0x14	per-zone segment list
critical-subsystem segment	0x1e	crit subsystem segments

Animation clip names in BTL4.RES are lowercase. [T1]

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2. ClassID map (subsystem factory)

Base 3000 = 0xBB8. The factory switches on the resource ClassID; the case <Name>ClassID LABELS are systematically mislabeled — trust the // FUN_004xxxxx ctor-address comment reconciled via CLASSMAP.md, not the case label. [T1]

ClassID	Real class	ctor @	Notes
0xBB9	Mech	@004a2d48 (Mech::Make)	sizeof 0x854 (binary); reconstructed 0x638
0xBBD	Condenser	@4ae568	valve; case="?"
0xBBE	AggregateHeatSink (heat-sink BANK)	@4ae8d0	GUID 0x50e590, sizeof 0x1E4; case=SensorClassID
0xBC0	Reservoir	@4af408	case=Condenser
0xBC1	Generator	@4b…	power bus
0xBC2	PoweredSubsystem	@004b0f74	sizeof 0x31C
0xBC3	Sensor	—	case=MyomersClassID
0xBC4	Gyroscope	@004b3778	DEFERRED (NaN integrator; reverted to stub)
0xBC5	Torso	@004b6b0c	sizeof 0x280; case=SinkSource
0xBC6	Myomers	@4b8fec	case=Actuator; INERT un-stub
0xBC8	Emitter	@004b1d18	sizeof 0x478; energy weapon
0xBCB	AmmoBin	—	case=JumpJet; sizeof 0x22C
0xBCD	ProjectileWeapon	@4bc3fc	sizeof 0x448 (case≠ this — see VDATA.h)
0xBCE	GaussRifle	@4bdcb4	: Emitter; FireWeapon is a no-op in this build
0xBD0	MissileLauncher	@4bcff0	sizeof 0x44C
0xBD3	SubsystemMessageManager	—	DEFERRED (WAVE 8; the valve/message control hub @mech+0x190)
0xBD4	PPC (: Emitter)	—	same FireWeapon as Emitter; factory calls it GaussRifle
0xBD6	HUD	—	alloc 0x2a4; case=MechDisplay-ish
0xBD8	Searchlight	—	case=LegSubsystem
0xBDC	MechTech	—	alloc 0x104
0xBDE	ThermalSight	—	case=MechDisplay

Identify a class at runtime with sub->GetClassID() (== sub+4). [T1]

Class hierarchy (the two branches that share only MechSubsystem)

• Heat leaf: PoweredSubsystem : HeatSink : HeatableSubsystem : MechSubsystem (Emitter/PPC/Sensor/Myomers/weapons chain here). [T1]
• Watcher branch: Torso/Gyroscope/Searchlight/ThermalSight/HUD : PowerWatcher : HeatWatcher : MechSubsystem; AmmoBin : HeatWatcher. Uses a 0xC connection + 0x54 alarm (NOT the 4/8-byte heat-leaf types). [T1]

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3. Mech struct offsets (Mech*, binary layout)

Reconstructed access MUST use named members/accessors — these raw offsets are the BINARY's, valid for reading the decomp, NOT for our compiled layout (see reconstruction-gotchas). [T1]

Offset	Field	Notes
+0x11c / +0x120	damageZoneCount / damageZones[]	inherited Entity; Mech ctor populates the array
+0x124 / +0x128	subsystemCount / subsystemArray[]	the subsystem-roster (NOT the segment table)
+0x190	messageManager	the 0xBD3 SubsystemMessageManager (damage guard / valve+message route source)
+0x260 / +0x26c	localOrigin = { Point3D linearPosition; Quaternion angularPosition }	ORIGIN.h:15; position@+0x100 in some subsystem views
+0x300	segment table	skeleton EntitySegments (muzzle sites, joints)
+0x37c	target world Point3D	aim source
+0x388	target Entity*	HasActiveTarget() gate
+0x38c	targeted sub-zone (int)	-1 = whole
+0x42c	shadowJointNode (Joint*)	ShadowJointName @model+0xB4
+0x438	torso subsystem cache	HUD/mapper read it
+0x5b4	HUD subsystem cache	(factory case 0xBD6 writes param_1[0x16d])
+0x650	deathAnimationLatched / crashed flag
+0x7cc	damageableSubsystems chain	the condenser chain (GUID 0x50e4fc) RecomputeCondenserValves iterates

mech+0x100 (a subsystem-view of localOrigin.linearPosition): .x@+0x100, .z@+0x108. [T1]

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4. Damage delivery

• Entity::TakeDamageMessage(id, size, inflictingEntityID, zone, Damage&) → target->Dispatch(&msg).
• Base Entity::TakeDamageMessageHandler IGNORES zone==-1 — send a VALID zone index (the Mech cylinder-lookup override for unaimed hits is not reconstructed). [T1]
• class Damage { damageType(enum Collision/Ballistic/Explosive/Laser/Energy), damageAmount, damageForce, surfaceNormal, impactPoint, burstCount }. [T1]
• Weapon effect id: "explode" = 13 (Explosion::Make). [T2]
• DestroyEntityMessage(id,size) removes an entity — but a killed mech STAYS (a WRECK); death = a STATE transition (SetGraphicState(DestroyedGraphicState)), NOT removal. Issuing removal-on-death is the P5 teardown bug (do not). [T2]

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5. Weapon fire-rate constants (recovered)

From the weapon .SUB records + the charge-curve .data constants (PE-parsed as x87 float10). [T1]

• DischargeTime = beam-on time. ER-medium laser (BLH) = 0.2 s.
• RechargeRate = recharge time in seconds exactly (the two ln5 factors cancel): ER-S 1.0 / ER-M 2.0 / ER-L 4.0 / PPC 5.0.
• One BLH ER-M cycle = 0.2 + 2.0 = 2.2 s; ~12 lasers staggered → aggregate ≈ 5/s.
• WeaponRange 500 (ER laser), DamageAmount 3.5, PipColor 1.0 0.0 0.0 (RED).
• Charge constants: _DAT_004bb3c4=1.0, _DAT_004bb3b8=1e-4, _DAT_004bb3b4=0.5; RatedVoltage (GENRATOR.SUB)=1e4; fire threshold seekVoltage[rec]=0.8*RatedVoltage.

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6. Env-var gates (runtime; default OFF unless noted)

The authentic stack is DEFAULT-ON (BTEnvOn, mechrecon.hpp): BT_GAIT_CUTOVER, BT_GAIT_SM, BT_COLLISION, BT_REAL_CONTROLS default ON — set =0 to fall back. ⚠ Gates check getenv(name) != NULL, so BT_X="" (empty) still ENABLES; use Remove-Item Env:\BT_X.

Var	Effect
BT_FORCE_THROTTLE	auto-walk forward (no key)
BT_SPAWN_ENEMY	spawn a target mech 120u ahead along the spawn facing
BT_FORCE_FIRE	auto-fire on cooldown
BT_ASSERT_TO_DEBUGGER	route CRT asserts to the debugger, not a modal box
BT_HEAPCHECK	whole-heap validation on every alloc/free (O(n²) at mission load — SLOW)
BT_PROBE_BGF=<name|ALL>	boot-time BGF loader probe, exits after
BT_LOG=<file>	per-instance log file (in content/)
BT_GAUGE_ATTR_LOG	[attr] <binding> OK/NULL per config binding
BT_GAUGE_SKIP_LOG	[gskip] <primitive> per unregistered gauge widget the parse skips
BT_VALVE_LOG	condenser valve flow distribution
BT_SECTOR_LOG	SectorDisplay Make/Execute
BT_NET_TRACE	[net-tx]/[net-rx]/[net-upd] MP tracing
BT_DEV_GAUGES	render the 6 pod MFD surfaces in a separate dev window

Full render/locomotion gates (BT_RAMP, BT_MATPRI, BT_CULL, BT_SHADOW_*, BT_LODSEL, BT_ADDLOD, BT_PUNCH, …) are catalogued in rendering.

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7. Tools

• tools/disas2.py <VA> [len] — capstone disassembly of BTL4OPT.EXE at a VA (recovers x87 math Ghidra drops; folds known call targets + float constants). THE tool for any FUN_ the assert-anchored exporter didn't capture (e.g. @0x4ae464 MoveValve, @0x4ca07c Execute).
• tools/disas2.py-style PE reads: scratchpad/rdva.py (4-byte VA read), rdtbyte.py (80-bit float10).
• reference/ghidra_scripts/ExportBTSource.java — the headless assert-anchored decompiler.
• reference/ghidra_scripts/DecompVSS.java — headless address-list decompiler (any skipped fn).
• tools/btconsole.py — the MP console emulator. tools/mapscan.py/resscan.py — content scanners.

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Key Relationships

• Feeds: subsystems (factory + ClassIDs), combat-damage (damage delivery), gauges-hud (attribute binding).
• Verified against: reconstruction-method (the decomp loop), reconstruction-gotchas (why raw offsets fail).