Asked what was next for the rebuild, went to measure it, and found I had told
the operator the wrong thing one turn earlier.
THE CORRECTION. I said mech2.cpp (the gait state machine) was the next
package. It sits on top of SequenceController's playback methods, and all
three of those -- SelectSequence, Advance, Reset -- were Fail() stubs. Advance
is the function that actually walks a clip's keyframes and writes each
animated joint. mech2 without it would have called straight into a Fail. So
the dependency runs:
Mech::AdvanceLegAnimation mech2.cpp -- the STATE MACHINE, still absent
-> SequenceController::Advance THIS -- keyframes -> joint writes
-> Joint::SetHinge / SetRotation / SetTranslation
-> the joint DCS flush fixed in 5.3.88
5.3.88 fixed the bottom link, this fixes the middle, the top is still missing.
WHAT THIS DOES NOT DO: make the legs move. Nothing calls any of it yet -- no
gait state is ever selected because mech2 is unreconstructed -- so a run looks
identical to yesterday's. This removes a blocker. Saying otherwise would be
easy and wrong.
RECONSTRUCTED (compile-verified, BT 50/50, links clean):
SelectSequence @004277a8 -- find + lock the clip, parse its layout. The
fetch is FindResourceDescription and NOT SearchList: the ID arriving here is
already resolved, and SearchList would treat it as a resource LIST and walk
the clip bytes as IDs.
Advance @0042790c -- snap through every keyframe the new time has passed
(writing authored poses), then interpolate the partial frame. Returns the
forward distance covered, which is what the gait feeds into mech motion.
Reset @004283b8 -- return every animated joint to neutral, so an abandoned
gait doesn't leave the skeleton frozen on a stale frame.
THE PART THAT CANNOT BE SEEKED. The pose block is packed BY JOINT TYPE -- 8
bytes hinge, 12 ball, 24 ball+translation -- so the root-translation table
behind it is not reachable by arithmetic on any stored count. SelectSequence
must walk the entire skeleton summing per-joint sizes to find it. Which also
means the parse depends on the mech's own skeleton agreeing with the clip: an
unresolvable slot returns NULL and contributes 0, keeping the walk honest
rather than drifting keyframeData onto garbage.
TWO CONTRACTS worth recording before mech2 is written against them:
move_joints == 0 is NOT "do nothing" -- it advances the clock and
accumulates distance while leaving the skeleton alone. That is how the body
channel measures a stride without fighting the leg channel over the same
joints.
The finished callback is RE-ENTRANT BY DESIGN. At end of clip it picks the
next state, re-arms this controller through SelectSequence (rewinding it to
frame 0), and advances the carryover itself -- so its return value is the
distance that carryover covered, folded straight into Advance's own return.
mech2's BodyClipFinished has to honour that or the gait double-counts.
NOT CARRIED OVER from the donor: its BT_HIP_LOG diagnostic and audio
footstep-broadcast path, neither of which is 1995 code. footStepThreshold IS
parsed -- the field is real and authored -- but nothing reads it yet.
AND A CAVEAT ON THE 91% I QUOTED: seqctl.cpp is not in the 50-TU BT census at
all (its code sits below the BT address range the census was built from), and
that figure counts a TU as done if the FILE EXISTS -- 18 files still carry 26
Fail() stubs between them. The census understates what "playable" needs.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
CydandClaude Fable 5
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