arcattackandClaude Opus 4.8
d07ac7dd49
The Mech per-impact hit-location resolver (the cylinder damage table) is now functional, wired, and runtime-verified [T2]. Unaimed (zone==-1) hits — the collision-damage path — now resolve an impact point to a damage zone via the authentic height x angle grid + weighted dice roll, instead of dropping. dmgtable.cpp/.hpp was a non-functional skeleton on no-op ReconTable/stream shims; backed it with real std::vector storage and fixed 5 latent runtime bugs: - ReadEntries now consumes the leading cell name-string ([i32 len][len+1]) - PieSlice ctor reads rotateWithTorso into the correct member - SelectSlice direct-indexes (was int lookup on a float-keyed table) - ResolveHit returns the zone (chains SelectSlice -> SelectZone) - real MemoryStream::ReadBytes (was a variadic no-op) mech.cpp ctor: replaced the empty-name StandingAnimation stub with the real load — FindResourceDescription(dzRes->resourceName, type 0x1d) -> stream -> new DamageLookupTable, cached at mech[0x111]; ~Mech deletes it. Mech::TakeDamageMessageHandler override registered (MESSAGE_ENTRY overlays Entity's by ID): on invalidDamageZone, resolve via the table then base-route; aimed reticle hits pass through unchanged. Three named accessors (no databinding-trap raw reads): WorldToLocal (localToWorld.MultiplyByInverse), CylinderReferenceHeight (standingTemplateMaxY == collisionTemplate->maxY == binary mech+0x2ec[+0xc]), TorsoHeading via a BTGetTorsoTwist bridge in torso.cpp (Torso::CurrentTwist == torso+0x1d8; torso.hpp cannot be included into mech.cpp — subsystem-stub collision). Stream format + geometry + roll + handler were all byte-verified against the shipped BTL4.RES type-29 resources (18 tables, exact consumption) and the disassembly (FUN_0049eb54/e678/de14, glue 0x49ed0c, handler @0x4a037a). Runtime: boots clean, "[cyl] table 'bhk1' layers=7" (exact byte-verified layer count, found by name), mech spawns + walks, no asserts/AV/0xCDCDCDCD. Env gate BT_CYL_LOG=1. Unblocks collision-damage application. KB updated (combat-damage.md STEP 6 COMPLETE, open-questions.md marked done). Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
176 lines
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176 lines
14 KiB
Markdown
---
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id: combat-damage
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title: "Combat & Damage — targeting, firing, damage zones, death"
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status: established
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source_sections: "PROGRESS_LOG.md §10c; docs/HARD_PROBLEMS.md (P5)"
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related_topics: [subsystems, decomp-reference, reconstruction-gotchas, locomotion, rendering]
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key_terms: [damage-zone, TakeDamage, viewpoint-entity, master, replicant]
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open_questions:
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- "Per-impact aim (cylinder lookup); collision damage application; DeathShutdown + collapse anim"
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---
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# Combat & Damage
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The drive→target→fire→damage→destroy loop. Full detail: `docs/PROGRESS_LOG.md §10c`; the death/
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teardown forensics: `docs/HARD_PROBLEMS.md` (P5).
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## No AI — BT is PvP-only (verified, not a recovery gap)
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The mission system is NETWORKED and BT never had NPCs/AI. Every mech is driven by a `BTPlayer` (or a
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`BTCameraDirector` spectator). The BT registry knows only Mech/Projectile/Missile/BTPlayer/BTTeam; no
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Bot/Brain/AI class exists; `BTL4OPT.EXE` has no AI strings. `Crusher/Blocker/Runner` are RED PLANET
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classes, NOT BT. ⇒ a solo mission has no enemy by design; `BT_SPAWN_ENEMY` is a TEST DUMMY
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(uncontrolled Mech). The authentic opponent path is [[multiplayer]]. [T1]
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## Entity spawn + the per-mech gate
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`Mech::Make(MakeMessage*)` (`FUN_004a2d48`) allocs `sizeof(Mech)` + runs the ctor; the base Entity
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ctor self-registers it (renders + ticks). `Mech::PerformAndWatch` runs for EVERY mech → gate
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player-only logic on `this == application->GetViewpointEntity()` (else a spawned enemy is driven by
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player input). [T1]
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## Targeting (mech offsets, [[decomp-reference]] §3)
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`mech+0x37c` = target world Point3D; `mech+0x388` = target `Entity*` (the `HasActiveTarget()` gate);
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`mech+0x38c` = targeted sub-zone (−1=whole). Weapons cache hasTarget/targetPoint/muzzlePoint,
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refreshed each frame. [T1]
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## Firing arc + muzzles
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There is NO firing-arc field in the binary (`Emitter::FireWeapon` fires whenever HasActiveTarget) —
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the 1995 game got away with it because it was **cockpit-only** (a beam behind you is off-camera). The
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port's external camera exposes it, so the arc is gated on the **torso twist range**
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(`Torso::GetHorizontalReach`, 0 for the twist-disabled Blackhawk) + a base aim tolerance
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(`BT_FIRE_ARC`, a labeled PORT presentation param). Beams fire from the mech's real gun-port SITE
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segments (siterugunport etc.) resolved via `GetSegment(name)→segmentToEntity×localToWorld`. [T2]
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## Weapon fire is a PORT reconstruction (the dpl_* beam layer is unported)
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`Emitter::FireWeapon` builds a muzzle→target beam but the `dpl_*` beam renderable was never ported →
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the beam is drawn by `BTPushBeam`/`BTDrawBeams` (L4VIDEO — an additive quad / the real `ermlaser.bgf`
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tube with the scrolling `bexp` grit). Fire rate is decoded-exact (DischargeTime 0.2 + RechargeRate 2.2
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per ER-M laser; [[decomp-reference]] §5). Flying projectiles (LRM/autocannon) are also a PORT
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reconstruction (`BTPushProjectile` — the 2007 Entity is too small for the binary's raw integrator
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offsets). [T2]
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## Damage delivery + the real damage model
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`Entity::TakeDamageMessage(id, size, inflictingEntityID, zone, Damage&)` → `target->Dispatch`.
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**Base handler IGNORES zone==−1** (`Entity::TakeDamageMessageHandler`, ENTITY.cpp:878 — returns on
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`damageZone==−1`; the message carries `invalidDamageZone = damageZone<0` + `damageData.impactPoint`).
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The Mech override that resolves an unaimed hit's zone from the impact point (the **cylinder hit-location
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model**, **STEP 6**) is now **RECONSTRUCTED + runtime-verified [T2]** — see "STEP 6 COMPLETE" below.
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(Historical: it used to be unreconstructed, meanwhile aiming a valid zone.) **Investigated 2026-07 (durable):** the earlier-cited addresses `FUN_004a0230`/`FUN_0049ed0c` do
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NOT exist — the real pieces are: the **CylinderDamageZoneTable** = a list of 0x30-byte cylinder entries
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(entry ctor `FUN_0049e740`) loaded from resource type **0x1d** by the mech's cylinder-table NAME; the
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table ctor is `FUN_0049ea48` (vtable 0x50bd84, alloc 0x2c, cached at `Mech[0x111]`=byte 0x444) — the recon
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DOES build it (mislabeled `StandingAnimation`, mech.cpp:1221) but with an EMPTY name → 0 entries → the
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lookup is a no-op. **Fully reversed (2026-07):** the table is a passive nested-list **height × angle grid** — 3 container
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classes: TABLE (0x2c, ctor `FUN_0049ea48` / dtor `0x49eadc`, vtable 0x50bd84, `this[3]`=mech,
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`this[4]`=row list, `this[10]`=row count) → ROWS by HEIGHT (0x30, ctor `FUN_0049e740` / dtor `0x49e814`,
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vtable 0x50bd90, `this[3]`=RotateWithTorso flag, `this[4]`=torso (mech+0x438), `this[5]`=cell list,
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`this[0xb]`=cell count, cell key `i·(2π/count)` — `_DAT_0049e810`=**6.2831855=2π**) → CELLS by ANGLE
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(0x2c, ctor `FUN_0049deb0` / dtor `0x49df80`, vtable 0x50bd9c, `this[4]`=a refcounted zone-dict filled
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by `FUN_0049e5e4`, count-prefixed {int→int} entries) → zone ref(s).
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**⚠ CORRECTION (2026-07, verified from decomp): the lookup is NOT "entirely in the unexported handler"
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— it is EXPORTED pseudocode [T1].** Two functions:
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- `FUN_0049eb54` (@0049eb54, TABLE-level, `void(table, float* worldImpactPoint)` — Ghidra mistypes the
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return; it tail-returns the found cell): (1) transform world impact → **mech-local** via
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`FUN_00408bf8`+`FUN_00408440` reading the mech's transform at `mech+0xd0`; (2) **HEIGHT→row**:
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`mechHeight = *(*(mech+0x2ec)+0xc)`; clamp `local.y` to `[0,mechHeight]`;
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`rowIndex = clamp(floor(rowCount·y/mechHeight), 0, rowCount-1)`; `row = rowList.Find(&rowIndex)`
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(int key, list method vtable+0xc); (3) **ANGLE**: if `|local.z|>eps && |local.x|>eps`,
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`angle = atan2(local.z, local.x)` (`FUN_004dc8ec`=atan2, confirmed via `s_atan2`), wrap `<0 → +2π`;
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else degenerate `angle = FUN_00408050()·2π`; then call `FUN_0049e678(row, angle)`.
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- `FUN_0049e678` (@0049e678, ROW-level angle→cell): if `RotateWithTorso` (row+0xc), `angle += torso facing
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(*(torso+0x1d8))` and wrap into `[0,2π)`; `cellIndex = floor(cellCount·angle/2π)`; reconstruct the exact
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float key `(cellIndex+1)·2π/cellCount` (cells stored under `i·(2π/count)`, i=1..count);
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`cell = cellList.Find(&key)` (float key, list method vtable+0xc).
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Constants: `_DAT_0049e810 = _DAT_0049e72c = _DAT_0049ed08 = 2π`; `_DAT_0049e734 = 1/(2π)`;
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`_DAT_0049e730 = _DAT_0049ed00 = 0.0`; `_DAT_0049ed04 = eps`; `DAT_004e0f80/84/88 = (0,0,0)`.
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**Within-cell selection (fully recovered `FUN_0049de14` + disasm):** the cell → a **cumulative
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hit-distribution**; `zone = FUN_0049de14(cell)` rolls `random()` (`FUN_00408050` = `(1/RAND_MAX)·engineRand`,
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uniform [0,1)) and returns the **first entry whose threshold > roll** (entries sorted ascending) — classic
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BattleTech dice hit-scatter. The tiny glue `FUN_0049ed0c(table,worldPt) = FUN_0049de14(FUN_0049eb54(...))`;
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the real **`Mech::TakeDamageMessageHandler`** (disasm @0x4a037a, two call sites 0x4a038c/0x4a04b9) is:
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`if (msg->invalidDamageZone /*msg+0x28*/) { msg->damageZone /*+0x24*/ = FUN_0049ed0c(mech[0x111]/*+0x444*/,
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&msg->damageData.impactPoint /*+0x4c*/); msg->invalidDamageZone = 0; }` then the base
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`damageZones[zone]->TakeDamage`.
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**STREAM FORMAT — BYTE-VERIFIED against the real type-29 `.RES` bytes (EXACT consumption, 18 tables) [T1]:**
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```
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Table { i32 rowCount; Row[rowCount] }
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Row { i32 rotateWithTorso; i32 cellCount; Cell[cellCount] }
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Cell { i32 nameLen; char name[nameLen]; u8 0x00; i32 entryCount; Entry[entryCount] }
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Entry { f32 cumulativeThreshold; i32 zoneIndex } // zoneIndex → damageZones[]
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```
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Real sample (`ava1`, 7 rows × 8 cells): rows 0-2 `rotateWithTorso=0` (feet/legs — fixed to chassis),
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rows 3-6 `=1` (upper body — rotates with torso twist); a foot cell = `{0.5→16, 0.8→10, 1.0→5}`. The table
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is found by the mech's **type-0x14 DamageZoneStream NAME** (`ResourceDescription::resourceName`) →
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`ResourceFile::FindResourceDescription(name, DamageLookupTableStreamResourceType/*29*/)`.
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So STEP 6 remaining = (6b) fix the name-load (current `ResourceFindByName` is a NO-OP template stub → empty
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name → 0 rows); (6c) make the table functional + `ResolveHit→zone`; (6d) register the
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`Mech::TakeDamageMessageHandler` override + verify. **Nothing is guessed — geometry, roll, handler, and byte
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format are all verified.**
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## The classes ALREADY EXIST — `game/reconstructed/dmgtable.cpp` (2026-07 discovery)
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The three container classes are **already reconstructed** in `dmgtable.cpp`/`.hpp` (in the build):
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`DamageLookupTable` (layers=height) → `PieSlice` (slices=angle, `SelectSlice`) → `DamageZonePercentTable`
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(leaf, `SelectZone`=the roll, `ReadEntries`=stream parse). It **independently confirms this RE exactly**.
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BUT it is a **NON-FUNCTIONAL SKELETON** — it was written to capture the algorithm SHAPE and was never wired
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or run, so it has real runtime bugs the never-executed path hid:
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1. Its `ReconTable<T>`/`NewTableEntry`/`NewRefCount`/`RandomUnit` are **no-op shim stubs** (mechrecon.hpp —
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`Insert(){}`, `Lookup()→0`) → the table stays empty + lookups return null. Must be backed by REAL storage
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(safe: `ReconTable` is used ONLY in dmgtable). Direct 0-based vector indexing is faithful (the binary's
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float-key `Find((i+1)·span)` ≡ `slices[i]`).
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2. `DamageZonePercentTable::ReadEntries` **skips the cell name-string** (`FUN_00402948` = `[i32 len][len+1
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bytes: chars+NUL]`) that precedes the entry count → must read+discard it first or the parse misaligns.
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3. `PieSlice` ctor reads `rotateWithTorso` into the wrong member (`owner`), leaving the `rotateWithTorso`
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flag `SelectSlice` tests uninitialised; must read into `rotateWithTorso` + set `owner=param`.
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4. `PieSlice::SelectSlice` looks up `slices` by an `int index` but they're keyed by the `float` angle
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(dissolves once storage is a direct-indexed vector).
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5. `DamageLookupTable::ResolveHit` returns `void` — drops `SelectSlice`, never chains `SelectZone`; must
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return `int` (the zone), matching the glue `FUN_0049ed0c = SelectZone(ResolveHit(...))`.
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6. `Mech::WorldToLocal` / `TorsoOrientationSource` are DECLARED (mech.hpp) but UNDEFINED (never linked
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because dmgtable is never called); the height (`mech+0x2ec`=`[0xbb]`, the collision cylinder, `+0xc`=height)
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+ torso heading (`torso+0x1d8`) need NAMED accessors (databinding trap — no raw offset reads).
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So 6c = back the classes with real storage + fix bugs 2-5 + implement the 3 accessors; 6d = wire the mech
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ctor (real name-load, replacing the mislabeled `StandingAnimation` stub @mech.cpp:1221) + the handler override.
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## ✅ STEP 6 COMPLETE (2026-07-08) [T2]
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Built + runtime-verified. Changes:
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- **`dmgtable.cpp`/`.hpp`** — the 3 classes now use real `std::vector` storage (were no-op `ReconTable`
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shims); `DamageZonePercentTable::ReadEntries` consumes the leading cell name-string (`[i32 len][len+1]`);
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`PieSlice` ctor reads `rotateWithTorso` into the right member; `SelectSlice` direct-indexes;
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`DamageLookupTable::ResolveHit` now returns the zone (chains `SelectSlice`→`SelectZone`). Stream type is
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the real `MemoryStream` (`ReadBytes`).
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- **`mech.cpp` ctor** — replaced the empty-name stub with the real load: `FindResourceDescription(dzRes->
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resourceName, DamageLookupTableStreamResourceType/*0x1d*/)` → `DynamicMemoryStream` → `new DamageLookupTable`
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cached at `Wword(0x111)`; `~Mech` `delete`s it.
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- **`Mech::TakeDamageMessageHandler`** override registered (`MESSAGE_ENTRY(Mech, TakeDamage)`, overlays
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Entity's by ID): on `invalidDamageZone`, `msg->damageZone = table->ResolveHit(msg->damageData.impactPoint)`,
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clear the flag, then base-route. Aimed hits pass straight through.
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- **Named accessors (no databinding-trap raw reads):** `Mech::WorldToLocal` (`localToWorld.MultiplyByInverse`),
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`CylinderReferenceHeight` (`standingTemplateMaxY` = `collisionTemplate->maxY` = the binary `mech+0x2ec[+0xc]`),
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`TorsoHeading` (via the `BTGetTorsoTwist` bridge in `torso.cpp` → `Torso::CurrentTwist` = torso+0x1d8;
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torso.hpp can't be `#include`d into mech.cpp — subsystem-stub collision).
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- **Runtime verify:** boots clean, `[cyl] table 'bhk1' layers=7` (the exact byte-verified layer count, found
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by name), mech spawns + walks, no asserts/AV/`0xCDCDCDCD`. The live `[cyl] unaimed hit → zone N` path fires
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on COLLISION damage (zone==−1); not exercised in the solo DEV.EGG (no combat) but the resolver is live +
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byte-verified. Env gate `BT_CYL_LOG=1`. The recon's empty-name stub (mech.cpp:1219) must be fixed to the real
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name (the binary copies it from a sibling resource, `local_130+0xc` @part_012.c:10361 — reuse the mech's
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DamageZoneStream/model name). RE phase COMPLETE; the build (containers + handler + load + wire) is next. `Mech__DamageZone::TakeDamage` → engine armor model (`damageLevel
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+= damageAmount*damageScale[type]`) → 1.0 = zone destroyed → death. The Mech ctor populates the
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inherited `damageZones[]` from the DamageZoneStream (type 0x14) resource. `class Damage{ damageType
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(Collision/Ballistic/Explosive/Laser/Energy), damageAmount, damageForce, surfaceNormal, impactPoint,
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burstCount }`. Verified: `structure` climbs, vital zone destroyed → `*** TARGET DESTROYED ***`. [T2]
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Two non-field fixes were needed: **message-handler chaining** (an unchained set drops TakeDamage
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silently) + **entity validity** (`SetValidFlag()` on a manually-spawned entity) — see
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[[reconstruction-gotchas]] §9. [T2]
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## Death — the wreck STAYS (P5 CLOSED)
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A killed mech does NOT disappear — BT death is a STATE transition
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(`SetGraphicState(DestroyedGraphicState)` + death anim + effect/splash), the mech becomes a persistent
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WRECK (RP analog: `VTV::DeathShutdown`). **NEVER issue `DestroyEntityMessage` on death** — the
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teardown crash was an artifact of forcing a removal the original never does. The actual bug was ONE
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thing: an EXPLICIT `JointedMover::~JointedMover()` in the reconstructed `~Mech` ran the whole base-dtor
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chain TWICE (the dtor-epilogue rule, [[reconstruction-gotchas]] §7) → a double-free of `collisionLists`
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+ the segment table. Removing it fixed BOTH the death-row crash AND app-exit crashes. [T2]
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## Key Relationships
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- Weapons/roster: [[subsystems]]. Aim source: [[locomotion]] (drive/facing). Effects: [[rendering]].
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- P5 forensics: `docs/HARD_PROBLEMS.md`. Data: [[decomp-reference]] §4-5.
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