---
id: rendering
title: "Rendering — the D3D9 pipeline, materials, sky, beams, performance"
status: established
source_sections: "PROGRESS_LOG.md §10 (render-fidelity notes); docs/BGF_FORMAT.md"
related_topics: [bgf-format, asset-formats, wintesla-port, locomotion, pod-hardware]
key_terms: [L4D3D, material-ramp, BSL, LOD, DPL, beam]
open_questions:
  - "Replacement-LOD for NON-additive multi-LOD models; day/night material path priority (BT_MATPRI)"
---

# Rendering

The port renders via the WinTesla `L4D3D`/`L4VIDEO` Direct3D9 path ([[wintesla-port]]), carrying our
BT loader (`bgfload.cpp`) + fidelity work. The goal: match the authentic pod footage. Geometry/LOD
mechanics are in [[bgf-format]]; this topic covers the D3D9 draw path + the fidelity fixes. Full
detail: `docs/PROGRESS_LOG.md §10`.

## The IG-board shading model (from libDPL DPLTYPES.H)
Shading is selected PER-GEOMETRY by vertex type: **no-normal geometry** (terrain/mesas/sky/buildings/
mech — WHITE baked verts) is UNLIT, colorized by the material's 2-endpoint **[[material-ramp]]**
(`dpl_SetMaterialRamp` — texture luminance indexes a low→high gradient); **normal-bearing geometry**
(~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]

## The big render-fidelity fixes (dbase/desert matched to pod footage)
- **Geometry:** CONN is a flat trilist (not fan); CONN+PCONN coexist — see [[bgf-format]]. Malformed
  fan-garbage was the "faceted mountains" bug. [T2]
- **RAMP colorize** (default-on `BT_RAMP`) + **day/night material priority** (default-on `BT_MATPRI` for
  the ramps): the `mat\day` libs carry the warm ramps; the generic GEO libs are gray. Terrain/mesas
  render warm tan; the sky's `dsky_mtl` ramp (0→0.99) gives bright clouds. `hasNormals` gate keeps
  vehicles LIT (colored trucks). Ramp tint rule: explicit diffuse + NEUTRAL ramp ⇒ tint; coloured ramp
  ⇒ white. [T2]
- **Sky:** a `*sky.bgf` dome/plane drawn in a dedicated fullbright **PASS_SKY** (LIGHTING off, extended
  far=9000 + world fog); tagged `drawAsSky` at load (the `.x` sidecar path doesn't exist). [T2]
- **The env pipeline** (`DPLReadEnvironment`→`DPLReadINIPage`, reads **`content/BTDPL.INI`** via
  `L4DPLCFG`): resolves map+time → clip/fog/ambient + a directional sun. Bring-up stubs
  (EnsureValidProjection / per-frame ambient / uninit cloud colours) had clobbered it — now they
  RE-ASSERT the env values. Debug: copy BTDPL.INI → *DBG.INI with `debug=True`. [T2]

## Backface culling (default CW, `BT_CULL`)
The bring-up `D3DCULL_NONE` drew interior/back faces (the "dark wedge" shapes = mesh insides). CW is
correct for the BGF quad triangulation `[a b c][a c d]`. [T2]

## LODs (default: shipping-engine first-LOD + ADDITIVE_LODS; `BT_ADDLOD`/`BT_LOD_SCALE`/`BT_PUNCH`)
See [[bgf-format]] for the √3 range decode, the ADDITIVE_LODS cumulative rule, PUNCH cutouts, and the
coplanar-shell submission-order depth bias. Replacement LOD selection for NON-additive multi-LOD
models is deferred (needs the board's hot-spot semantics). [T2]

## Mech skins (BSL bit-slice — the rainbow-mech fix)
`.BSL` is a bit-sliced container (6 grayscale sub-images per file); the BMF `0x18 BITSLICE` tag picks
the slice. Reading it as RGB overlaid 2-3 gray sheets = the "rainbow/graffiti" bug. Fixed:
`image.cpp decodeBSL` slice-decodes; `bgfload` threads the 0x18 channel; a cross-library RAMP registry
resolves the mech-skin `softer` ramp (defined in OTHER libs). Every mech renders authentic gray-metal
paint now. See [[asset-formats]]. [T2]

## Weapon beams (the unported dpl_* layer)
The `dpl_*` beam renderable was never ported → beams are drawn by `BTPushBeam`/`BTDrawBeams`
(L4VIDEO). The real look is the `ermlaser.bgf` TUBE (native Z 0..−2000, UVs tiled) with the scrolling
`bexp` grit texture (from the `.VMF` `SCROLL`). ER lasers red, PPC blue, standard yellow. The beam
origin re-anchors to the live muzzle every frame (can't run out from under your own beam). See
[[combat-damage]] for fire-rate/muzzle. [T2]

## Performance — the 10fps→60fps fix (~50-80× render speedup)
The 10fps baseline had THREE stacked causes, all fixed (engine tree): (1) **`D3DCREATE_SOFTWARE_
VERTEXPROCESSING`** — every vertex transformed+lit on the CPU → HARDWARE first; (2) D3DX `DrawSubset`
attribute-table scan (our double-sided tris broke OptimizeInplace) → explicit `SetAttributeTable` +
direct `DrawIndexedPrimitive`; (3) no frustum culling → bounding-sphere culling per frame. ⚠ LESSON:
the user plays the DEBUG build, but the 10fps was NOT the debug build (RelWithDebInfo identical) —
split draw-vs-present + check the DEVICE flags before blaming the compiler. Diagnostics kept:
`[spike]/[loadobj]/[rstat]`. [T2]

## Key Relationships
- Geometry/LOD: [[bgf-format]]. Base: [[wintesla-port]] (L4D3D). Shadow/visual-conform: [[locomotion]].
- Renders on: [[pod-hardware]] (main 3D view).
