---
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` (archive-only; in-repo reimplementation: `engine/MUNGA_L4/image.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`, `dpl_Punchize` = FUN_00490308 → VPX board cmd `0x20`, tokens
  `{0x80000003,0x80000017,0x80000004}` — a CONSTANT geogroup-modifier opcode, no color key; the
  sibling `dpl_Damagize` FUN_004902b0 uses the same cmd with a different triple). Two cases: [T1]
  - **Textured** punch (arena walls/catwalks): black texels = HOLES (alpha-test in the opaque
    pass). Coplanar shells inside one LOD z-fight → depth-bias by submission ordinal. [T2]
  - **FINAL mechanism (i860 VREND.MNG firmware, decoded 2026-07-11): a punch geogroup is a
    THREE-CHUNK STENCIL-CUT KIT** -- in file order: aperture MASK (invisible per-pixel cutout),
    visible HULL (the only colour-drawn chunk, drawn where not masked), byte-identical hull TWIN
    (the damage-reset record, never visible).  Visible result = hull-minus-apertures.  Applies
    to cockpit canopies, arena punch (AR02 etc.) and outside-torso punch (VUX_TOR) alike -- the
    port's arena "black texels = holes" alpha-test path is a visual approximation that predates
    this decode (works; revisit for exactness).  Port: bgfload punch-kit roles + the L4D3D
    stencil cut (D24S8).  See [[cockpit-view]] + [[decomp-reference]] for firmware addresses.
    [T1 mechanism / T2 render-verified all 8 cockpits]

## 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]

## The PNAME/PLACE name-plate atlas (the only TEXT-bearing BGF geometry) [T1/T2]
`PNAME1-8.BGF` + `PLACE1-8.BGF` (`content/VIDEO/GEO/`, 235/238 bytes) are the MP
scoreboard's 16 billboard plates — each ONE flat quad (4 verts, `XYZ_UV`, `PCONN` ppf=4,
**no LOD chunk = 1 implicit LOD**, no normals, no `SV_SPECIAL`). PNAME = 1.0×0.25 m,
PLACE = 0.5×0.25 m, planar Z=0. Consumers: `FUN_00454a70` (the scoreboard, resource type
0x46) and `BTReticleRenderable` @004cc40c (PNAME only). See [[open-questions]].

**They are the only geometry in the corpus whose texture is TEXT**, which makes them the
sole asset that can prove BSL row order and slice mapping — and they CONFIRM the port's
pair-swapped nibble decode (`image.cpp:122-125`): slices 0→3 come out as "PLAYER 1/2",
"3/4", "5/6", "7/8" in exact index order. [T2 — decoded + read visually]

One shared 128×64 texmap: `bmap:` → `VIDEO/MAT/BMAP.BMF` → 6 `TEXTURE` records
`bmap1_tex..bmap6_tex`, all `TEXTURE_MAP=bmap` with `BITSLICE` 0..5 → `VIDEO/TEX/BMAP.BSL`
(`DIV-BSL2`, 128×64, depth 4, texels @0x70). Cell map (UVs read straight from each BGF):

| material | slice | plates → UV sub-rect |
|---|---|---|
| `name12_mtl`→`bmap1_tex` | 0 | PNAME1 `v[.5,1]`, PNAME2 `v[0,.5]` (full U; 128×32 cells) |
| `name34_mtl`→`bmap2_tex` | 1 | PNAME3 `v[.5,1]`, PNAME4 `v[0,.5]` |
| `name56_mtl`→`bmap3_tex` | 2 | PNAME5 `v[.5,1]`, PNAME6 `v[0,.5]` |
| `name78_mtl`→`bmap4_tex` | 3 | PNAME7 `v[.5,1]`, PNAME8 `v[0,.5]` |
| `place1234_mtl`→`bmap5_tex` | 4 | PLACE1-4 = 2×2 grid of 64×32 cells (`u[0,.5]/[.5,1]` × `v[.5,1]/[0,.5]`) |
| `place5678_mtl`→`bmap6_tex` | 5 | PLACE5-8 = same 2×2 grid |

**The BSL is a RUNTIME COMPOSITING TARGET, not final art [T0 engine source].**
`DPLRenderer::MakeBitSliceStorage` (L4VIDEO.cpp:9888) allocates `uint32[128*64]`;
`LoadBitSliceTexture` merges a 1bpp egg BitMap into it; `FlushBitSliceTexture`
(L4VIDEO.cpp:5682, stubbed in 2007) did `dpl_LookupTexture("bmap:bmap1_tex")` +
`dpl_TexmapTexels2D(texmap, buf, 128, 64, 4)` — one upload rewrites ALL SIX slices. So the
1995 engine painted the **egg's callsign + ordinal bitmaps** onto these plates every mission;
the baked "PLAYER n" text is only the shipped DEFAULT. Two stacked 128×32 large-name bitmaps
per slice = exactly the PNAME v-halves; two stacked 128×32 ordinal bitmaps ("1st|2nd") = exactly
the PLACE 2×2 grid. Corollaries:
- **The shipped BMAP.BSL has only 4 distinct planes** — slice4 aliases slice0 and slice5
  aliases slice3 (nibble3==nibble7, nibble4==nibble6; nibbles 0/1 zero). The ordinal art was
  never baked, so a naive PLACE draw shows "PLAY"/"ER 1"/… fragments. [T1 measured]
- The placeholder cells are stored **scanline-reversed** vs the compositor's top-down order
  (`LoadBitSliceTexture` writes y=0..31 top-down), so a naive PNAME draw gives the RIGHT
  number upside-down. Don't chase it — implement the compositor instead. [T1 / T3 fix choice]
- These 6 materials carry **no DIFFUSE/AMBIENT/EMISSIVE/RAMP** — only `NAME`,
  `MATERIAL_TEXTURE` and tag **`0x0027`** (12 B = {0.5,0.5,0.5}), which is
  **`dpfB_MATERIAL_OPACITY_TAG`** — `[T0` `engine/MUNGA_L4/libDPL/dsys/PFBIZTAG.H]`, NOT specular
  (that earlier [T4] guess is retracted). So the material contributes **no colour at all**: the
  authentic plate is the **unmodulated callsign raster at ~50% opacity**. `bgfload` would fall
  back to the grey placeholder `0xFFB0B0B8`; the reticle plate's 2D path therefore draws it as
  `0x80FFFFFF` (white, half alpha) — see [[gauges-hud]] §Lock ring. And `decodeBSL` emits **alpha=255** for mono slices, so the plate
  draws as an OPAQUE black rectangle — a billboard needs black→alpha-0 keying (which is exactly
  what the 2D path's A4R4G4B4 `0xFFFF/0x0000` upload does).

## 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]].