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Gait: turn-then-walk stutter ROOT-CAUSED + FIXED -- one skeleton writer (task #64)

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User repro (100%): turn in place, push forward before the turn stops -> the gait
skips/stutters + visibly reduced bob; standstill starts always clean.  Three-layer
fix, user-verified:

1) THE DISPLAY BUG (the actual visible artifact): v5's "body advances first with
mj=1, leg overwrites last, so body drift can't show" was FALSE.  Whenever the two
gait channels phase-split, the BODY channel's out-of-phase joint writes leaked
into the rendered skeleton (rhythmic leg skips, averaged-down bob) while every
leg-channel trace read clean -- the leg DATA was fine, the RENDERED pose wasn't
the leg's.  v6: AdvanceBodyAnimation(dt, mj=0) -- the body still advances +
projects for replication (records/cycle speeds unchanged) but no longer touches
the skeleton.  One writer, structurally; matches the binary's own observable
("body phase drift is locally INVISIBLE in the binary").  BT_BODY_MJ=1 = old A/B.

2) THE SPLIT SEED: the bring-up trn trigger armed only the LEG channel, so a
turn-in-place entry guaranteed the channels re-entered walk frames apart and the
walk cycles ran permanently out of phase.  Lockstep: the Standing trn entry arms
BOTH channels the same frame (body case-4 twin added, same rate/keying), gated on
both Standing.  The authentic dispatcher (un-decompiled master-perf gap 0x4a9b5c-
0x4ab188, the sole reader of turnDemand/turnCapable) armed both -- the body's
case-4 machinery is dead code otherwise [T1].

3) THE POSE-MATCH INVARIANT: the engine has NO pose blending; transitions avoid
pops purely by authored pose-matched boundaries.  The old trn exits cut the pivot
clip MID-STEP (legFrm 7->1 teleport).  Now: entry gated on near-zero speed
(turn-IN-place); on forward command the pivot FAST-FORWARDS to completion (x4)
and the authentic finish callback lands Standing at the stand pose -> the normal
pose-matched stand->walk runs.  Decompiled reverse abort kept; the standSpeed
mid-clip abort subsumed (it WAS the pose cut).  [T3: 0.25*standSpeed threshold +
4x rate stand in for the gap's constants.]

Harness: BT_FORCE_TURN now reaches gBTDrive.turn (was silently inert for the
gait), BT_WALK_DELAY=<s> holds forced throttle then ramps (the turn-first repro),
BT_GAIT_TRACE=1 per-frame gait trace.  Regressions: standstill start, turn-entry,
pure pivot loops, run cycle -- all clean, bob full amplitude (1.33/1.32).
KB: locomotion.md v6 section + trn reconstruction + symptom-family closure.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
This commit is contained in:
arcattack
2026-07-13 23:52:35 -05:00
co-authored by Claude Opus 4.8
parent c0a0ec5e69
commit bfdd41bb9d
3 changed files with 218 additions and 40 deletions
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game/reconstructed/mech2.cpp
+98 -24
View File
@@ -595,18 +595,39 @@ Scalar
else
{
distance = 0.0f;
// TURN-IN-PLACE entry (bring-up TRIGGER, real machinery): the trn
// clip/state-4 advance/exit are binary-verified, but the authentic
// entry DISPATCHER isn't yet located in the decomp -- enter from
// Standing on a live turn demand with no speed demand. The clip's
// finished-callback drops back to stand; while the demand persists
// this trigger re-arms it (a looping pivot step).
// TURN-IN-PLACE entry. The authentic entry DISPATCHER lives in the
// un-decompiled master-perf gap (0x4a9b5c-0x4ab188), the sole reader of
// turnDemand(+0x12c) + turnCapable(+0x588); the decompiled lifecycle is
// case-4 advance/exit (below) + the clip-finish drop-to-stand. The
// authentic gate is turn-IN-PLACE == NEAR-ZERO commanded speed. The old
// stand-in gated on `ZeroSpeed <= commandedSpeed` -- i.e. it re-armed trn
// for ANY forward speed in [0, standSpeed~6.83], so pushing forward mid-
// turn SWALLOWED the throttle (the mech kept pivoting) until spd crossed
// standSpeed, then lurched to walk (task #64 user-reported stutter). Gate
// on near-zero speed instead: the instant real throttle is applied the trn
// re-arm stops, the in-flight pivot finishes to Standing, and case 0 hands
// off to walk normally. turnEntrySpeed = 0.25*standSpeed is a STAND-IN for
// the gap's threshold constant [T3]; the deadband mirrors the replicant's.
const Scalar turnEntrySpeed = standSpeed * 0.25f;
if (hasCrashSet != 0 && mppr != 0
&& ZeroSpeed <= commandedSpeed
&& commandedSpeed >= ZeroSpeed && commandedSpeed < turnEntrySpeed
&& (mppr->turnDemand > 0.05f
|| mppr->turnDemand < -0.05f))
|| mppr->turnDemand < -0.05f)
&& bodyAnimationState == StandingAnimation) // weld: enter only when BOTH can
{
SetLegAnimation(4); // turn-in-place (trn)
// LOCKSTEP (task #64): arm BOTH channels on the same frame. Arming
// only the leg let the body enter walk on its own schedule ~7-20
// frames apart -> the two walk cycles ran permanently out of phase
// and the body's pose flashed through on leg clip-boundary frames
// (the rhythmic gait skip + reduced bob). Both SequenceControllers
// bind the same trn clip at the same frame + advance at the same
// rate (case 4 twins), so they complete + re-enter walk together --
// the same phase-weld a standstill start gets for free. This is the
// workflow plan's "master perf arms both channels" reconstruction
// (the authentic dispatcher in the un-decompiled 0x4a9b5c gap arms
// both -- the body's case-4/finish machinery is dead code otherwise).
SetLegAnimation(4); // turn-in-place (trn), channel A
SetBodyAnimation(4); // channel B, same frame [lockstep]
goto advance_normally;
}
if (ZeroSpeed <= commandedSpeed)
@@ -642,26 +663,48 @@ Scalar
break;
case 4: // TURN-IN-PLACE (trn clip)
// BINARY-VERIFIED (raw FUN_004a5028 case 4, part_012.c:12013): state 4 is
// the turn-in-place animation (animationClips[4] = the "trn" clip, loaded
// under turnCapable@0x588). It EXITS to stand when a real speed is
// commanded (standSpeed < demand -- the earlier draft had this comparison
// INVERTED, the same bug class as the Standing case) or when reverse is
// commanded; otherwise it ADVANCES the turn clip while the mech pivots.
if (standSpeed < commandedSpeed)
{
legStateAlarm.SetLevel(0);
ForceUpdate(8); // FUN_004a4c54(this,8): type-3 record
break;
}
distance = 0.0f;
// state 4 is the turn-in-place animation (animationClips[4] = the "trn" clip,
// loaded under turnCapable@0x588). THE POSE-SNAP RULE (task #64, root-caused
// from the user's BT_GAIT_TRACE): this engine has NO pose blending -- every
// authored transition is pose-MATCHED at its boundary (swr starts from the
// stand pose; the walk clips alternate at matched extremes). Any exit that
// abandons the pivot MID-CLIP (SetLevel(0) or SetLegAnimation(5)) hard-resets
// the next clip to frame 0 while the legs are mid-step -> the legs TELEPORT
// (legFrm 7->1 in the trace) = the 100%-repro turn-then-walk stutter. Three
// prior fixes all failed because each still cut the clip mid-step, just at a
// different speed threshold.
//
// The reconstruction: when forward is commanded past the turn-in-place band,
// FAST-FORWARD the pivot to completion (accelerated advance) -- the feet
// hurry down to the plant, the clip's own finished-callback (case 4 ->
// SetLevel(0), the DECOMPILED one-shot tail) drops to Standing AT THE STAND
// POSE, and the normal pose-matched stand->walk path takes over. No mid-clip
// cut anywhere. trn has zero root translation, so the fast-forward moves no
// distance. [T3: the release threshold (0.25*standSpeed) + hurry rate (4x)
// stand in for the un-decompiled master-perf dispatcher constants (gap
// 0x4a9b5c); the completion->Standing tail itself is T1 decompiled.]
//
// The decompiled REVERSE abort is kept verbatim; the decompiled standSpeed
// abort is deliberately SUBSUMED by the hurry (it was the mid-clip pose cut
// itself -- any spd above the band fast-forwards to the plant instead, and
// Standing picks up the walk one frame after the callback). [T3 deviation
// from the literal case-4 exit, in service of the pose-match invariant.]
if (commandedSpeed < ZeroSpeed)
{
legStateAlarm.SetLevel(0);
ForceUpdate(8); // type-3 record
distance = 0.0f;
break;
}
goto advance_normally;
{
Scalar trnRate = 1.0f;
if (standSpeed * 0.25f < commandedSpeed)
trnRate = 4.0f; // forward commanded: hurry the plant [T3]
distance = legAnimation.Advance( // same advance advance_normally does,
time_slice * globalTimeScale * idleStrideScale * trnRate, 1); // rate-scaled
legCycleSpeed = distance / time_slice; // trn z=0 -> stays 0 (no travel)
}
break;
case 6: case 7: // WalkToRun
//
@@ -869,7 +912,38 @@ Scalar
}
// FALLTHROUGH
case 2: case 3: case 4: case 5: case 8: case 9: case 10: case 0x0b:
case 4: // TURN-IN-PLACE, LOCKSTEP twin (task #64)
// The body channel runs trn in LOCKSTEP with the leg: armed together at
// entry (leg Standing cross-arms both), advanced at the SAME rate keyed on
// the SAME live speedDemand, so both clips complete on the same frame and
// both channels re-enter walk on the same frame. Without this the body
// entered walk ~7-20 frames apart from the leg and the two walk cycles ran
// permanently out of phase -- the body's pose flashes through on the leg's
// clip-boundary frames (body advances mj=1 FIRST, leg overwrites LAST;
// boundary frames the leg doesn't write) = the rhythmic gait skip + halved
// bob the user reproduced 100% from turn-then-walk (standstill starts weld
// the phases, which is why they never stuttered). [T3 rates/threshold; the
// per-channel case-4 machinery itself is T1 decompiled.]
{
MechControlsMapper *bm = MappingMapper();
const Scalar bspd = (bm != 0) ? bm->speedDemand : 0.0f;
if (bspd < ZeroSpeed) // reverse abort (leg-symmetric)
{
bodyStateAlarm.SetLevel(0);
ForceUpdate(8);
distance = 0.0f;
break;
}
Scalar trnRate = 1.0f;
if (standSpeed * 0.25f < bspd)
trnRate = 4.0f; // hurry the plant (leg-symmetric)
distance = bodyAnimation.Advance(
time_slice * globalTimeScale * idleStrideScale * trnRate, loop);
bodyCycleSpeed = distance / time_slice;
}
break;
case 2: case 3: case 5: case 8: case 9: case 10: case 0x0b:
case 0x0e: case 0x0f: case 0x10: case 0x11: case 0x14: case 0x15:
case 0x1c: case 0x1d: case 0x1e: case 0x1f: case 0x20:
distance = bodyAnimation.Advance( // FUN_0042790c(this+0x6bc, ...)