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Diag: render-rate rotation-evenness probe + angular-drift instrumentation (task #50 spin residual)

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Autonomous headless spin harness (BT_AUTODRIVE+BT_FORCE_TURN) + probes that
finally measure what the eye sees, not the sim heading:
 - BT_RENDHDG (L4VIDEO render loop): per-RENDERED-frame peer heading step
   evenness -- avgStep/maxStep/max-avg ratio.  Confirmed the residual spin
   'hesitation' is UNEVEN rendered rotation (max/avg ~2.8x), correlated with the
   byAngle resync-flood bursts (maxAng ~= pi), NOT a render-vs-sim rate stall
   (render redraws a fresh heading every frame).
 - BT_SPIN / BT_ANGSIGN: resync trigger breakdown (byAngle/byVel/byRest) + the
   frame-level local/update/projected angular-Y that exposed the Abs() macro bug.
 - gBTReplRenderYaw: peer heading published from the sim to the render probe.
 - Normalize projectedOrigin.angularPosition after the peer-mirror advance
   (adding a scaled ang-vel VECTOR to a quaternion denormalizes it) -- correct,
   but NOT sufficient: the pi divergence is REAL, from the crude large-angle
   quaternion projection over the sparse angular-record interval during a PURE
   spin (linear dense-send doesn't fire when not translating; type-4 is the only
   orientation carrier and resets the horizon, so dense type-4 -> half-rate).

Residual ROOT (scoped, not yet fixed): the reckoner (MOVER.cpp:457-466) projects
rotation by ADDING vector*t to the heading quaternion -- a small-angle approx the
original kept valid via dense records; our pure-spin case has 1.6s record gaps so
it diverges to ~180deg -> uneven render.  Fix path = proper quaternion integration
in the reckoner, or refresh the angular origin without the type-4 horizon reset.
Both touch the shared engine dead-reckon -> aligning before the change.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
This commit is contained in:
arcattack
2026-07-14 16:27:04 -05:00
co-authored by Claude Opus 4.8
parent 7615ecd316
commit 9eff043973
2 changed files with 51 additions and 0 deletions
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game/reconstructed/mech4.cpp
+20
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@@ -1863,6 +1863,9 @@ void
}
}
// Peer heading published each sim update, sampled by the render loop (BT_RENDHDG).
volatile float gBTReplRenderYaw = -999.0f;
void
Mech::PerformAndWatch(const Time& till, MemoryStream *update_stream)
{
@@ -1930,6 +1933,18 @@ void
DeadReckon(dt); // engine: reckoner + lerp
localToWorld = localOrigin;
// RENDER-vs-SIM decoupling probe: publish the heading the RENDER will
// actually draw (localToWorld == localOrigin here). The render loop
// (L4VIDEO.cpp) logs this PER RENDERED FRAME; if it repeats the same
// value across render frames, the peer sim updates slower than the
// render draws -> the rotation stutters even though each sim update is
// smooth (which the per-update [replhdg] metric could not see).
{
extern volatile float gBTReplRenderYaw;
YawPitchRoll _rry; _rry = localOrigin.angularPosition;
gBTReplRenderYaw = (float)_rry.yaw;
}
// Lightweight dead-reckon smoothness probe (one flush/sec, cheap).
// PATH length (sum of |per-frame step|) vs NET displacement reveals
// jitter: a smooth walk has path==net; oscillation inflates path while
@@ -3587,6 +3602,11 @@ void
angStepM.Multiply(updateVelocity.angularMotion, dt);
projectedOrigin.angularPosition.Add(
projectedOrigin.angularPosition, angStepM);
// Adding a scaled angular-velocity VECTOR to a quaternion denormalizes
// it (the reckoner MOVER.cpp:463 does the same); a non-unit quaternion's
// extracted yaw is garbage (~pi), which spiked angDrift and FLOODED angle
// resyncs in bursts -> peer horizon reset -> uneven (max/avg ~2.8x) render.
projectedOrigin.angularPosition.Normalize();
}
Scalar angDb = (updateTurnAngleDeadband > 0.0f) ? updateTurnAngleDeadband : -1.0f;
Scalar velDb = (updateTurnVelocityDeadband > 0.0f) ? updateTurnVelocityDeadband : -1.0f;