BT412/scratchpad/gyro_synthesis.md

All verification complete. The spring values live in the mech .MDL config streamed from archives (compressed — the "PosSpringX" tokens exist only in the EXE parser string pool), so the numeric equilibrium must be captured at runtime via the ctor log. Here is the synthesized plan.

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GYRO RECONSTRUCTION — DEFINITIVE IMPLEMENTATION PLAN

All contested claims re-verified against reference/decomp/all/part_013.c and raw bytes in reference/decomp/section_dump.txt. Resolved disagreement: Report 3's "WriteEyeJoint/WriteMechJoint have no caller / engine vtable pass" is WRONG. Byte-verified at section_dump.txt line 4aaf70: e8 33 7f 00 00 @0x4aaf74 = call 0x4B2EAC (WriteEyeJoint thunk, args push [ebp+0xC] dt + gyro) and e8 64 85 00 00 @0x4aaf83 = call 0x4B34EC (WriteMechJoint, gyro only). Both live in the Mech master per-frame performance FUN_004a9b5c (a decomp-export gap, 0x4a9b5c–0x4ab188), with byte-readable gates: [ebx+0x528] gyro≠0, [ebx+0x650](deathLatch)==0; WriteEyeJoint additionally [ebx+0x3B0](legAnimState)≠0 && [ebx+0x57C]==0; preceded by gyro+0x3A8 = mech+0x3F0 (swayBias feed, bytes at 0x4aaf18–0x4aaf3c); followed by call 0x4B66B4(torso=[ebx+0x438], &mech+0x360) @0x4aafab — the per-frame EyepointRotation.pitch = torso pitch writer. Everything else in the four reports is mutually consistent and I re-confirmed the ctor (part_013.c:2780–2953), both integrators (:2362–2437, :2443–2549), and both writers (:2558–2624) line-by-line. UpdateAnimationNoise @004b357c: no caller found anywhere — dead code, do not wire [T1].

1. CORRECTED MEMBER MAP (ctor @004b3778; param_1[N] = byte 4N; every byte 0x1D8–0x3CF is ctor-initialized — the binary leaves NO fill)

Offset	Name (corrected)	Init (ctor line)
0x01C/20/24	Performance triple → GyroscopeSimulation @004b275c (PTR@0050fe08)	only if (owner+0x28 & 0xC)==0 && (owner+0x29 & 1) i.e. master && flags&0x100 (:2807-2811)
0x1D8	exageration	res+0xF8 (:2812)
0x1DC	eyePosition (eye TRANSLATION integrator state)	ZERO (:2935) — NOT springConstant
0x1E8	springConstant vec3	res+0x118 (:2821)
0x1F4	dampingConstant vec3	res+0x124 (:2823)
0x200	eyeClampUpper (min-clamped against)	= posSpring via identity 3×4 transform = copy (:2876-2879)
0x20C	eyeClampLower (max-clamped against)	= negSpring, same (:2880-2883)
0x218 / 0x224	posSpring / negSpring	res+0x130 / +0x13C (:2825/:2827)
0x230	eyeForce accumulator (NOT cleared per frame; damage-impulse target @004b2d8c)	ZERO (:2936)
0x23C	eyeVelocity	ZERO (:2937)
0x248	eyeWork scratch	ZERO (:2938)
0x254	Scalar = 0 (:2931)
0x258	Scalar* externalPitchPtr = &this+0x254 (:2933); Mech post-stream re-points to &torso+0x1D8 (bt_mech.cpp.c:508-510); read by damage-response FUN_004b2980
0x25C–0x28B	3×4 work matrix: identity (:2793), rebuilt from placement (:2934)
0x28C / 0x298 / 0x2A8	placePos=0 (:2929) / identity quat {0,0,0,1} (:2928) / zero rot (:2930)
0x2B4	bodyOrientation (body ROTATION state)	ZERO (:2939)
0x2C0 / 0x2CC	rotationSpringConstant / rotationDampingConstant (Roll,Yaw,Pitch order)	res+0x148 / +0x154 (:2830/:2833)
0x2D8 / 0x2E4	bodyClampUpper = 2.0×rotationPosSpring / bodyClampLower = 2.0×rotationNegSpring	(:2884/:2885, FUN_004092fc)
0x2F0 / 0x2FC	rotationPosSpring / rotationNegSpring (Pitch,Yaw,Roll, radians)	res+0x160 / +0x16C (:2834/:2835)
0x308 / 0x314 / 0x320	bodyForce (impulse target) / bodyVelocity / bodyWork	ZERO (:2940-2942)
0x32C–0x33C	5 damage multipliers	res+0x1B8..0x1C8 (:2836-2840)
0x340–0x38F	5× DamageResponse{trans,pitchRoll,yaw,vibration}	res+0x1CC/1DC/1EC/1FC/20C (:2841-2875)
0x390/0x394/0x398	animOffset=0 / animScale=1.0f / animPhase=0 (:2921-2923)
0x39C / 0x3A0	maxAnimationNoise ← res+0xFC / minAnimationNoise ← res+0x100 (:2814/:2813 — MAX at 0x39C confirmed)
0x3A4	rotationPerSecond ← res+0x104 (:2815)
0x3A8	swayBias = 0 (:2927); overwritten every frame = mech+0x3F0 (bytes 0x4aaf18-3c)
0x3AC–0x3B8	percentageOnNormal/Destruction/Degradation/Failure ← res+0x108..0x114
0x3BC / 0x3C0 / 0x3C4	swayAngle=0 / noiseTimer=0 / noiseActive=0 (:2924-2926)
0x3C8	eyeJointNode ← resolve(res+0x178 "EyeJoint" = jointlocal) — name→segment (FUN_00424b60)→seg+0xC0 joint id→skeleton vfunc+0x34 (:2904-2915)
0x3CC	mechJointNode ← resolve(res+0x198 "MechJoint" = jointeye) (:2916-2920). NOT crossed.

Node object: node+0xC = value block ptr, +0x10 = type, +0x14 = dirty, +0x18 = owner (+0xFC stamped on write). Type 5 value block = {vec3 translation @+0, vec3 rotation euler @+0xC}. Helpers: FUN_0041cfa0=GetRotationPtr (type5→value+0xC), FUN_0041d020=SetRotation, FUN_0041d0a8=SetScalar, FUN_0041d11c=SetTranslation. FUN_004086d0 = component-wise multiply, NOT cross (part_000.c:8294). FUN_00408744 = 3×4 row-matrix × vec (identity → pass-through), NOT a clamp.

2. FAITHFUL INTEGRATORS

IntegrateEyeJoint (FUN_004b2ec0, byte-exact; CompMul = per-component multiply):

d1 = eyePosition - negSpring                 // STATE minus target (:2376)
d2 = eyePosition - posSpring                 // (:2377)
eyeForce += CompMul(springConstant, d1)      // do NOT clear eyeForce — it carries last
eyeForce += CompMul(springConstant, d2)      //   frame's damping term + hit impulses
eyeWork = eyeForce;  eyeVelocity += eyeWork * dt
eyeForce = CompMul(dampingConstant, eyeVelocity)   // OVERWRITE (:2387, +0x1F4)
eyeWork = eyeForce;  eyeVelocity += eyeWork * dt
eyePosition += eyeVelocity                   // NO dt — identity-matrix pass-through (:2391-2393)
per-axis: eyePosition = min(eyePosition, eyeClampUpper)   // 0x200 block
          eyePosition = max(eyePosition, eyeClampLower)   // 0x20C block

IntegrateBody (FUN_004b30ec, with the two x/z crossings, verified :2479-2484 and :2504-2506):

dN = bodyOrientation - rotationNegSpring;  dP = bodyOrientation - rotationPosSpring
k = rotationSpringConstant                       // BOTH terms use k, never damping
bodyForce.x += k.x*dN.z;  bodyForce.y += k.y*dN.y;  bodyForce.z += k.z*dN.x
bodyForce.x += k.x*dP.z;  bodyForce.y += k.y*dP.y;  bodyForce.z += k.z*dP.x
bodyWork = bodyForce;  bodyVelocity += bodyWork * dt
bodyForce = CompMul(rotationDampingConstant, bodyVelocity)   // uncrossed (:2498)
bodyWork = bodyForce;  bodyVelocity += bodyWork * dt
bodyOrientation.x += bodyVelocity.z;  .y += bodyVelocity.y;  .z += bodyVelocity.x
clamps in y,x,z order: min vs bodyClampUpper(0x2DC/0x2D8/0x2E0), max vs bodyClampLower(0x2E8/0x2E4/0x2EC)

Equilibrium: at rest, per-axis force ∝ 2k·(x − (pos+neg)/2), so with restoring (negative) spring constants eyePosition settles at (posSpring+negSpring)/2 per axis — a steady TRANSLATION written into jointeye (which parents siteeyepoint, rest offset tran=(-0.0039, 3.153, -1.503) per AVA.SKL:715-734). This is the authentic steady eye offset the port lacks (our stubbed gyro leaves the joint at raw baseOffset). The offset axis/magnitude depends on the .MDL PosSpring/NegSpring values, which live in the archived model configs (only the parser token strings are in BTL4OPT.EXE — not statically extractable here); capture them at runtime by logging posSpring/negSpring in the ctor under BT_GYRO_LOG. If pos = −neg the midpoint is 0 and the steady offset comes only from transient dynamics; expect a nonzero Y (down-forward settle) if asymmetric.

3. THE WRITERS

• WriteMechJoint (FUN_004b34ec) → mechJointNode (= jointeye), gated type==5 only: SetTranslation(node, eyePosition@0x1DC) via FUN_0041d11c if it differs >1e-4 from value+0; then SetRotation(node, bodyOrientation@0x2B4) via FUN_0041d020 if it differs >1e-4 from value+0xC. One node, both channels. No null check in the binary (keep the port's guard).
• WriteEyeJoint (FUN_004b33e0) → eyeJointNode (= jointlocal, the ROOT balltranslate joint): multiplicative sway attenuation of the joint's CURRENT animation value — type<3: scalar *= swayAngle(0x3BC); type 4/5: rotation euler *= swayAngle (all 3 components). It does NOT write the spring output. Because it multiplies the current value, it must run AFTER the animation pass re-writes the joint each frame, else the rotation decays geometrically to zero.
• Dispatch (byte-verified, the resolved disagreement): both are called from the Mech master performance tail each frame — NOT from GyroscopeSimulation — with gates: if (gyro) gyro->swayBias = mech->swayAccum /*mech+0x3F0*/; if (gyro && !deathLatched) { if (legAnimState != 0 && mech+0x57C == 0) WriteEyeJoint(gyro, dt); WriteMechJoint(gyro); }, then EyepointRotation.x = torso->pitch /*torso+0x1E4*/ via the FUN_004b66b4 analog (gate: torso && !deathLatched). The gyro never touches the EyepointRotation attribute; glance-look writes to it come separately from the mapper state machine FUN_004afd10 (yaw from mech+0x564/0x568, yaw=π+pitch mech+0x570 look-back, pitch mech+0x56C look-down).

4. PATCH LIST (ordered)

A. game/reconstructed/gyro.hpp:266-308 — replace the own-field block with the binary-exact layout of §1: insert the missing 0x254–0x2B3 block (Scalar spare0; Scalar* externalPitchPtr; Scalar workMatrix[12]; Vector3D placePos; Scalar placeQuat[4]; Vector3D placeRot;), reorder/rename: eyePosition@0x1DC, springConstant@0x1E8, dampingConstant@0x1F4, eyeClampUpper@0x200, eyeClampLower@0x20C, posSpring@0x218, negSpring@0x224, eyeForce@0x230, eyeVelocity@0x23C, eyeWork@0x248, [0x254 block], bodyOrientation@0x2B4, rotationSpringConstant@0x2C0, rotationDampingConstant@0x2CC, bodyClampUpper@0x2D8, bodyClampLower@0x2E4, rotationPosSpring@0x2F0, rotationNegSpring@0x2FC, bodyForce@0x308, bodyVelocity@0x314, bodyWork@0x320, Scalar damageMultiplier[5]@0x32C, Gyroscope__DamageResponse damageResponse[5]@0x340, then the existing 0x390+ scalars (correct as-is). Delete old eyeVelocity@0x1E8 / eyeLimitLow / eyeLimitHigh / eyeSpringConstant / eyeAccel / bodyPosSpring / bodyNegSpring / bodyAccel names.

B. gyro.cpp:151-155 (GyroLayoutCheck) — add static_asserts: offsetof of eyePosition==0x1DC, springConstant==0x1E8, dampingConstant==0x1F4, eyeClampUpper==0x200, eyeClampLower==0x20C, posSpring==0x218, negSpring==0x224, eyeForce==0x230, bodyOrientation==0x2B4, bodyClampUpper==0x2D8, rotationPosSpring==0x2F0, bodyForce==0x308, damageMultiplier==0x32C, damageResponse==0x340, swayAngle==0x3BC, eyeJointNode==0x3C8, mechJointNode==0x3CC, and sizeof(Gyroscope)==0x3D0 (tighten from <=).

C. gyro.cpp:235-247 (ctor) — delete eyeOrientation = r->springConstant (the confirmed poison line); add, mirroring :2812-2942:

springConstant = r->springConstant;  dampingConstant = r->dampingConstant;
posSpring = r->posSpring;  negSpring = r->negSpring;
eyeClampUpper = posSpring;  eyeClampLower = negSpring;                 // :2876-2883
rotationSpringConstant = r->rotationSpringConstant;  rotationDampingConstant = r->rotationDampingConstant;
rotationPosSpring = r->rotationPosSpring;  rotationNegSpring = r->rotationNegSpring;
bodyClampUpper = rotationPosSpring * 2.0f;  bodyClampLower = rotationNegSpring * 2.0f;  // :2884-2885
damageMultiplier[0..4] = r->collision..energyDamageMultiplier;         // :2836-2840
damageResponse[0..4]   = r->collision..energyDamageResponse;           // :2841-2875
eyePosition = eyeForce = eyeVelocity = eyeWork = Vector3D(0,0,0);      // :2935-2938
bodyOrientation = bodyForce = bodyVelocity = bodyWork = Vector3D(0,0,0); // :2939-2942
spare0 = 0;  externalPitchPtr = &spare0;                               // :2931-2933
workMatrix = identity; placePos = 0; placeQuat = {0,0,0,1}; placeRot = 0; // :2793,:2928-2934

Also add to the BT_GYRO_LOG block: print posSpring/negSpring/springConstant/dampingConstant (captures the equilibrium data + confirms constants are negative/restoring).

D. gyro.cpp:425-459 (IntegrateEyeJoint) — replace body with §2 exactly. Kills: flipped subtract (428-429), wrong constant + Cross (431-432, 441), uninitialized clamps (453-458 now use eyeClampUpper/Lower).

E. gyro.cpp:467-496 (IntegrateBody) — replace body with §2 exactly. Kills: rotationDampingConstant on the second spring term (474), missing x/z crossings (both places), Cross at 482.

F. gyro.cpp:404-414 (GyroscopeSimulation) — delete the WriteEyeJoint(); WriteMechJoint(); calls + the wrong "no direct caller" comment. The binary Performance ends after the two integrators (:2291-2293).

G. gyro.cpp:311-331 (ResetToInitialState) — replace line 324 bodyPosSpring = zero with bodyOrientation = zero (@004b2678:2194 targets 0x2B4); add eyeWork = zero; bodyWork = zero (:2193/:2197). Rename eyeAccel/eyeForce per the new names.

H. gyro.cpp (new public bridges) — void SetSwayBias(Scalar v) { swayBias = v; }, void BindExternalPitch(Scalar *p) { externalPitchPtr = p; }, and expose WriteEyeJoint/WriteMechJoint (or a WriteJoints(dt, legAnimState) bridge) for the mech-side dispatch.

I. game/reconstructed/mech4.cpp (master performance tail, near the dormant crunch hook at :3277) — add the binary dispatch (bytes 0x4aaf18-0x4aafab):

if (gyroSubsystem) {
    GyroSetSwayBias(gyroSubsystem, 0.0f /* mech+0x3F0 overspeed sway model — 0 until reconstructed */);
    if (!deathAnimationLatched) {
        if (legAnimationState != 0 /* && mech+0x57C==0 (always 0 in normal play) */)
            GyroWriteEyeJoint(gyroSubsystem);
        GyroWriteMechJoint(gyroSubsystem);
    }
}
// then (separate fidelity item): if (torso && !deathAnimationLatched) eyepointRotation.x = torso pitch (FUN_004b66b4)

Ordering: this must run AFTER the animation pass writes the joints (WriteEyeJoint is multiplicative).

J. game/reconstructed/mech.cpp:1029-1030 (enable) — swap the stub: subsystemArray[id] = CreateGyroSubsystem(this, id, seg); (extern per mech.cpp:216-218); keep line 1031. Update the stale WAVE-5 comment. Remove/park RECON_SUBSYS(Gyro) at mech.cpp:178 if now unreferenced.

K. mech.cpp:~1150 (post-stream tail) — enable the commented gyro↔torso link as GyroBindExternalPitch(gyroSubsystem, TorsoPitchAddr(sinkSourceSubsystem)) (binary: *(gyro+0x258) = torso+0x1D8, bt_mech.cpp.c:508-510). Needed by the damage-response path.

L. Deferred (flag, don't fake): the damage hub → gyro fan-out FUN_004b2980 (0x4b2980–0x4b2d8b, called @0x4a02fb) is unreconstructed — without it there's no weapon-hit bounce even with perfect integrators (the ApplyDamageImpulse/Torque/Vertical bodies at gyro.cpp:609-647 are faithful targets for it). The mech+0x3F0 overspeed sway model (bytes 0x4aade8-0x4aaf14) is also unreconstructed; feed 0 meanwhile. UpdateAnimationNoise: dead code — leave unwired. Keep the ctor Performance gate as-is but LOG owner->simulationFlags: if live masters lack flag 0x100 the gyro silently never simulates.

5. VERIFICATION (one run, BT_GYRO_LOG=1)

1. Build: all new static_asserts pass; grep the link log for unresolved externals (/FORCE trap).
2. Ctor log: eye 'jointlocal' -> <ptr> type=5 ; mech 'jointeye' -> <ptr> type=5; both non-null, mech node type MUST be 5; posSpring/negSpring/springConstant/dampingConstant printed finite, spring/damping constants negative (restoring). Confirm "Performance installed" (simulationFlags gate) fires for the player mech.
3. No-NaN: the periodic WriteMechJoint log must show finite values from frame 0 (previously −4.31e8/NaN). Add a one-shot isfinite check on eyePosition/bodyOrientation in the log block; assert-log if violated.
4. Steady offset: eye=(x,y,z) in the log converges within ~1-2 s to (posSpring+negSpring)/2 per axis (compute from the ctor-logged values) and stays; body=(≈0,≈0,≈0) at rest. Visually: cockpit eyepoint shifts from the raw jointeye baseOffset by that midpoint — screenshot before/after vs the reference footage (the "eye too far back" delta should close if the midpoint is forward/up).
5. Bounce (interim, until FUN_004b2980 lands): trigger ApplyDamageImpulse(dir, mag) from a test hook on a weapon hit — eye log shows a spike decaying back to the midpoint over ~1 s (damped oscillation), cockpit frame visibly jolts relative to the world. No residual drift after repeated hits (eyeForce carry-over is by-design, not a leak — verify it re-converges).
6. Sway sanity: with legAnimState!=0, WriteEyeJoint scales jointlocal rotation by swayAngle each frame post-anim; confirm walk-cycle sway is attenuated (healthy gyro: swayAngle→percentageOnNormal) and no geometric decay to zero pose (would indicate dispatch running before the animation pass).
7. Regression: full combat loop un-regressed (death collapse, respawn warp, -net drive); btl4.log clean of gyro asserts after a sustained session.

Key files: C:\git\bt411\game\reconstructed\gyro.hpp, C:\git\bt411\game\reconstructed\gyro.cpp, C:\git\bt411\game\reconstructed\mech.cpp (:178, :1019-1032, :~1150), C:\git\bt411\game\reconstructed\mech4.cpp (:3277 region); ground truth C:\git\bt411\reference\decomp\all\part_013.c (:2362-2437 eye, :2443-2549 body, :2558-2624 writers, :2717-2953 ctor), C:\git\bt411\reference\decomp\section_dump.txt (bytes 4aaf10-4aafb0 = dispatch + gates + EyepointRotation writer).