Oracle, night 7: "Unable to damage the foot panels on Loki via direct fire from
front or side. Was able to damage on Thor."
FIRST, THE MECHANISM -- it is not what the issue assumed (missing collision
geometry). A direct-fire hit gets its zone one of two ways, decided at
Mech::TakeDamageMessageHandler by `invalidDamageZone`:
AIMED (invalidDamageZone=0): the zone rides in on the message from the
per-part aim pick, MechSegmentPick (#73, btl4vid.cpp).
UNAIMED (invalidDamageZone=1): DamageLookupTable::ResolveHit runs the authored
cylinder lottery -- impact HEIGHT picks a layer, ANGLE picks a pie
slice, and a weighted random roll picks the zone from that slice.
Measured live, both paths are in use: the Thor logged 16 unaimed hits
(invalidZone=1 zone=-1 -> ResolveHit) alongside aimed ones carrying real zones.
THE FINDING. MechSegmentPick is a BOUNDING-SPHERE test whose primary key is
SMALLEST RADIUS WINS -- a larger sphere can never beat a smaller one the ray also
grazes. The leg spheres, dumped in world space and IDENTICAL on both chassis:
knee centre y=1.868 r=1.505 spans y 0.364 .. 3.373
toe centre y=0.302 r=1.689 spans y -1.387 .. 1.991
The toe sphere is BIGGER than the knee's and they overlap heavily, so the toe can
only win where the ray misses the knee sphere outright -- i.e. below y=0.364.
Against a reference height of 11.16 that is a 0.36-unit window, **3.3% of the
mech's height**, and it sits right on the ground. Everywhere else a shot at the
foot is credited to the LEG. That is the reported symptom.
This is a PORT ARTIFACT, not authentic: btl4vid.cpp's own comment concedes the
sphere test approximates "the per-part semantic the 1995 mesh intersection
produced". Real mesh intersection has no such interference -- aiming at the foot
mesh hits the foot.
NOT EXPLAINED, and stated plainly: the per-CHASSIS asymmetry. Loki and Thor have
identical leg spheres, identical foot geometry (LOK_LFOT.BGF and THR_LFOT.BGF are
both 3082 bytes with the same token layout), and identical foot layers in their
damage tables (only the upper/cockpit layers differ). So nothing found here says
the Loki should behave differently from the Thor. The bench could not settle it
because BT_AIM moves the drawn RETICLE, not the pick ray -- there is currently no
harness to aim the pick at a chosen height. That harness is the next step.
Diagnostics added:
[pickgeom] one-shot dump of every pick sphere in WORLD space (zone, r, centre)
[pickcand] which spheres a ray actually threaded, their perpendicular d, and
which won -- the probe that makes "smallest wins" visible
[dmgtable] the whole authored DamageLookupTable: layers, slices, zone weights
[dmgresolve] per hit: localY, heightRef, layer, theta, resolved zone
[cylgate] invalidDamageZone / table pointer / incoming zone at the gate
(the last three under BT_DMGTABLE_LOG, the first two under BT_PICK_LOG)
plus scratchpad/night8/footpick.sh.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
