arcattackandClaude Fable 5
96b8892e7c
The user caught the inversion (blocked viewports, see-through frames); the
answer came from the rasterizer board itself: an i860 disassembly of the
VREND.MNG firmware decoded the damageize handler (@0xf040f6f8) -- cmd 0x20
(vr_damage_action) writes the dpl_Punchize token triple onto the punch
geogroup's first three geometry chunks IN FILE ORDER:
chunk1 = the detailed window-aperture shapes -> an invisible per-pixel MASK
chunk2 = the coarse hull -> the ONLY colour-drawn geometry (where not masked)
chunk3 = byte-identical hull twin -> the damage-reset record, never visible
Visible canopy = hull-minus-apertures. Both earlier readings were wrong ways
around the same three chunks: dropping all punch left floating fragments (no
hull); hiding the duplicate pair hid the HULL and drew the MASK -- the exact
inversion observed.
Port: bgfload tags per punch patch {non-paired pmesh = mask (role 1),
first twin = hull (role 2), second twin = skip}; L4D3D DrawMesh runs
mask->stencil-1 (no colour/z-write, z-tested), hull->stencil-NOTEQUAL,
mask->stencil-0; device D24X8 -> D24S8 + stencil clear. The cut never
touches z, so later-drawn entities show through the apertures.
BT_COP_PLATES=1 disables (diag).
In-game, all 8 mechs on pure defaults: connected dark frames with clear
viewports -- thor (the footage mech) shows the central viewport + surrounding
frame exactly as filmed. Combat regression clean (kill + no NaN).
Arena textured punch uses the same firmware kit; the black-texel alpha path
there is a working approximation, flagged in the KB.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
77 lines
4.9 KiB
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77 lines
4.9 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`, `dpl_Punchize` = FUN_00490308 → VPX board cmd `0x20`, tokens
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`{0x80000003,0x80000017,0x80000004}` — a CONSTANT geogroup-modifier opcode, no color key; the
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sibling `dpl_Damagize` FUN_004902b0 uses the same cmd with a different triple). Two cases: [T1]
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- **Textured** punch (arena walls/catwalks): black texels = HOLES (alpha-test in the opaque
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pass). Coplanar shells inside one LOD z-fight → depth-bias by submission ordinal. [T2]
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- **FINAL mechanism (i860 VREND.MNG firmware, decoded 2026-07-11): a punch geogroup is a
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THREE-CHUNK STENCIL-CUT KIT** -- in file order: aperture MASK (invisible per-pixel cutout),
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visible HULL (the only colour-drawn chunk, drawn where not masked), byte-identical hull TWIN
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(the damage-reset record, never visible). Visible result = hull-minus-apertures. Applies
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to cockpit canopies, arena punch (AR02 etc.) and outside-torso punch (VUX_TOR) alike -- the
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port's arena "black texels = holes" alpha-test path is a visual approximation that predates
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this decode (works; revisit for exactness). Port: bgfload punch-kit roles + the L4D3D
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stencil cut (D24S8). See [[cockpit-view]] + [[decomp-reference]] for firmware addresses.
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[T1 mechanism / T2 render-verified all 8 cockpits]
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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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