arcattackandClaude Opus 4.8
1cd57ade85
Adapt the spark-lesson / expert-seed.md progressive-context pattern to the bt411 port:
a thin router + context/*.md knowledge graph so the 2236-line CLAUDE.md's deep knowledge
loads on-demand instead of every session.
NON-DESTRUCTIVE foundation pass (live CLAUDE.md unchanged; proposed router is a draft):
- reference/glossary.yaml -- ~45 terms (engine/formats/scene/reconstruction)
- context/decomp-reference.md -- the quantitative hub: resource types, ClassID map,
mech offsets, damage delivery, weapon constants, env gates, tools
- context/reconstruction-gotchas.md -- the 12 systemic bug classes (conventions/DO-NOT hub)
- context/bgf-format.md -- geometry format + CONN/PCONN + LOD-sqrt3 + ramp shading
- context/gauges-hud.md -- the gauge/MFD system (the just-completed wave)
- context/open-questions.md -- deferred systems + get-from-Nick
- context/_ROUTER-DRAFT.md -- the proposed slim CLAUDE.md (identity, protocols,
quick-lookup, evidence tiers T0-T4, conventions, structure)
- phases/phase-01-context-restructure.md -- design + migration plan + status
docs/*.md ledgers stay as the DETAILED logs; context/*.md are the curated digests that
route into them. Remaining: ~10 topic files (project-overview, subsystems, combat-damage,
rendering, locomotion, wintesla-port, build-and-run, ...) then the CLAUDE.md swap.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
65 lines
3.8 KiB
Markdown
65 lines
3.8 KiB
Markdown
---
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id: bgf-format
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title: "BGF Model Format (DIV-BIZ2 geometry) + the render gotchas"
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status: established
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source_sections: "docs/BGF_FORMAT.md (full spec); CLAUDE.md §5, §10 render-fidelity notes"
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related_topics: [asset-formats, rendering, decomp-reference]
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key_terms: [BGF, DIV-BIZ2, PMESH, CONN, PCONN, LOD, material-ramp, SV_SPECIAL]
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open_questions:
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- "Replacement-LOD selection for NON-additive multi-LOD models (hot-spot/reference semantics)"
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---
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# BGF Model Format
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`.BGF` = **`DIV-BIZ2`** little-endian nested Tag-Length-Value geometry. Full byte-level parsing
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spec (verified against all 1275 content `.BGF` files) lives in **`docs/BGF_FORMAT.md`** — this
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topic captures the structure + the hard-won gotchas that cost real debugging. Loader of record:
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`engine/MUNGA_L4/bgfload.cpp` (game-callable via `LoadBgfFile`); standalone reference reader
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`DivLoader/VGCDivLoader.cpp`. Tag names: `dsys/PFBIZTAG.H`.
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## Structure
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`OBJECT → LOD → PATCH (geogroup) → PMESH`. Interleaved float32 verts; **QUAD faces (must
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triangulate `[a b c][a c d]`)**; materials referenced by `library:material` name (resolved
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against the map's `.BMF` libs). Damage/articulation are **name-driven via `SV_SPECIAL` (0x2037)
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`dz_*` tokens**, not stored geometry. [T1]
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## Indices — the CONN/PCONN story (two corrections)
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A PMESH carries faces in `CONNECTION_LIST` (0x0047) and/or `PCONN_LIST`:
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- `CONNECTION_LIST` is a **FLAT TRIANGLE LIST** (3 indices/face) — NOT "one polygon, fan-triangulate"
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(the original doc was wrong; fan-triangulating turned buttec's 115 tris into 341 fan-garbage).
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Corpus-verified: ALL 3488 CONN chunks have n%3==0. [T2]
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- **CONN and PCONN COEXIST** — a pmesh can carry quads/hexes in PCONN PLUS loose triangles in
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CONN. **370 of 841 GEO models** had mixed pmeshes silently dropping their CONN triangles until
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both were processed always (the "turret base missing panels" bug). `ppf=6` hexagons exist. [T2]
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## LODs — the √3 decode
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Each LOD chunk carries a `0x2046` header = **[near..far) viewing band**. The board selected the
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LOD whose band contains the camera distance.
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- **√3 range decode:** every stored band value is the authored euclidean distance ÷ √3 (92% of
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the corpus is exactly nice-number/√3; hand-conversion typos prove it). Multiply parsed bands by
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`√3` (`kLodRangeScale=1.7320508`). [T2]
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- **Metric = the instance-transformed OBJECT ORIGIN distance**, ONE shared `d` for all LODs of an
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object (a bounding-sphere-SURFACE metric desyncs sibling bands — wrong). [T2]
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- **ADDITIVE_LODS** (object-level `SV_SPECIAL` token, 135 pod BGFs — all arena structures): at eye
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distance d, EVERY LOD with `d < OutDist` draws (near detail ADDS onto coarser massing). Non-additive
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keep first-LOD-only (the 2007 engine's own behavior). [T2]
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- **PUNCH** (patch-level `SV_SPECIAL`): cutout geogroups — black texels = HOLES (alpha-test in the
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opaque pass). Coplanar shells inside one LOD z-fight → depth-bias by submission ordinal. [T2]
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## Shading model (from libDPL DPLTYPES.H)
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Shading is selected PER-GEOMETRY by vertex type:
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- **No-normal geometry** (XYZ_UV / XYZ_RGBA_UV: mesas/ground/sky/buildings/mech, WHITE baked
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verts) is UNLIT, colorized by the material's 2-endpoint **RAMP** (see [[material-ramp]]).
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- **Normal-bearing geometry** (XYZ_N_UV: ~150 vehicle/missile files) is LIT by the map light.
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- **Applying the ramp to lit geometry = the "dusty white blobs" bug** — gate on `hasNormals`. [T2]
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## Skeleton assembly
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A mech is not one BGF — it's a `.SKL` skeleton (a DCS tree of joints) whose each joint's
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`Object=part.bgf` is loaded + posed, then animated by `.ANI` clips. See [[asset-formats]] /
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[[locomotion]] for skeleton + animation. [T1]
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## Key Relationships
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- Detailed spec: `docs/BGF_FORMAT.md`.
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- Consumed by: [[rendering]] (the D3D9 draw path), [[locomotion]] (skeleton parts).
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- Related: [[asset-formats]] (BMF/BSL/SKL/ANI), [[decomp-reference]].
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