---
id: bgf-format
title: "BGF Model Format (DIV-BIZ2 geometry) + the render gotchas"
status: established
source_sections: "docs/BGF_FORMAT.md (full spec); CLAUDE.md §5, §10 render-fidelity notes"
related_topics: [asset-formats, rendering, decomp-reference]
key_terms: [BGF, DIV-BIZ2, PMESH, CONN, PCONN, LOD, material-ramp, SV_SPECIAL]
open_questions:
  - "Replacement-LOD selection for NON-additive multi-LOD models (hot-spot/reference semantics)"
---

# BGF Model Format

`.BGF` = **`DIV-BIZ2`** little-endian nested Tag-Length-Value geometry. Full byte-level parsing
spec (verified against all 1275 content `.BGF` files) lives in **`docs/BGF_FORMAT.md`** — this
topic captures the structure + the hard-won gotchas that cost real debugging. Loader of record:
`engine/MUNGA_L4/bgfload.cpp` (game-callable via `LoadBgfFile`); standalone reference reader
`DivLoader/VGCDivLoader.cpp`. Tag names: `dsys/PFBIZTAG.H`.

## Structure
`OBJECT → LOD → PATCH (geogroup) → PMESH`. Interleaved float32 verts; **QUAD faces (must
triangulate `[a b c][a c d]`)**; materials referenced by `library:material` name (resolved
against the map's `.BMF` libs). Damage/articulation are **name-driven via `SV_SPECIAL` (0x2037)
`dz_*` tokens**, not stored geometry. [T1]

## Indices — the CONN/PCONN story (two corrections)
A PMESH carries faces in `CONNECTION_LIST` (0x0047) and/or `PCONN_LIST`:
- `CONNECTION_LIST` is a **FLAT TRIANGLE LIST** (3 indices/face) — NOT "one polygon, fan-triangulate"
  (the original doc was wrong; fan-triangulating turned buttec's 115 tris into 341 fan-garbage).
  Corpus-verified: ALL 3488 CONN chunks have n%3==0. [T2]
- **CONN and PCONN COEXIST** — a pmesh can carry quads/hexes in PCONN PLUS loose triangles in
  CONN. **370 of 841 GEO models** had mixed pmeshes silently dropping their CONN triangles until
  both were processed always (the "turret base missing panels" bug). `ppf=6` hexagons exist. [T2]

## LODs — the √3 decode
Each LOD chunk carries a `0x2046` header = **[near..far) viewing band**. The board selected the
LOD whose band contains the camera distance.
- **√3 range decode:** every stored band value is the authored euclidean distance ÷ √3 (92% of
  the corpus is exactly nice-number/√3; hand-conversion typos prove it). Multiply parsed bands by
  `√3` (`kLodRangeScale=1.7320508`). [T2]
- **Metric = the instance-transformed OBJECT ORIGIN distance**, ONE shared `d` for all LODs of an
  object (a bounding-sphere-SURFACE metric desyncs sibling bands — wrong). [T2]
- **ADDITIVE_LODS** (object-level `SV_SPECIAL` token, 135 pod BGFs — all arena structures): at eye
  distance d, EVERY LOD with `d < OutDist` draws (near detail ADDS onto coarser massing). Non-additive
  keep first-LOD-only (the 2007 engine's own behavior). [T2]
- **PUNCH** (patch-level `SV_SPECIAL`): cutout geogroups — black texels = HOLES (alpha-test in the
  opaque pass). Coplanar shells inside one LOD z-fight → depth-bias by submission ordinal. [T2]

## Shading model (from libDPL DPLTYPES.H)
Shading is selected PER-GEOMETRY by vertex type:
- **No-normal geometry** (XYZ_UV / XYZ_RGBA_UV: mesas/ground/sky/buildings/mech, WHITE baked
  verts) is UNLIT, colorized by the material's 2-endpoint **RAMP** (see [[material-ramp]]).
- **Normal-bearing geometry** (XYZ_N_UV: ~150 vehicle/missile files) is LIT by the map light.
- **Applying the ramp to lit geometry = the "dusty white blobs" bug** — gate on `hasNormals`. [T2]

## Skeleton assembly
A mech is not one BGF — it's a `.SKL` skeleton (a DCS tree of joints) whose each joint's
`Object=part.bgf` is loaded + posed, then animated by `.ANI` clips. See [[asset-formats]] /
[[locomotion]] for skeleton + animation. [T1]

## Key Relationships
- Detailed spec: `docs/BGF_FORMAT.md`.
- Consumed by: [[rendering]] (the D3D9 draw path), [[locomotion]] (skeleton parts).
- Related: [[asset-formats]] (BMF/BSL/SKL/ANI), [[decomp-reference]].
