# VM2 — which detail-texturing path does retail actually run? (cdb, live)

**Date:** 2026-08-22 · **Campaign:** VM slice VM2 · **Status:** CLOSED — answered
**Method:** read-only cdb attach to the live PDB-paired retail client
(`C:\Turbine\Asheron's Call\acclient.exe`, v11.4186, PDB GUID
`9e847e2f-777c-4bd9-886c-22256bb87f32`, verified `MATCH` by
`tools/pdb-extract/check_exe_pdb.py`), in-world on the owner's AMD GPU.
Scripts: `tools/cdb/vm2-detail-caps.cdb` (+ runner) and
`tools/cdb/vm2-trysinglepass.cdb`. No breakpoints; `qd` at top level.

## The question

Campaign AR's #226 port (`mesh_detail.frag`, pipeline blend
`DSTCOLOR + INVSRCALPHA`) reproduces the path retail takes when
`ACRender::SetDetailSurfaceInternal(0)` is called — the **two-pass
framebuffer fallback**. `RenderMeshSubset` (0x0059ca10) and `landPolyDraw`
(0x006b6320) only take that path when
`trysinglepass == 0 || !m_caps.bCanDoSinglePassDetailing`. Otherwise they
call `SetDetailSurfaceInternal(1)` and the combine is the texture-stage
setup in `D3DPolyRender::SetSurface` (0x0059c4d0). The review (F3) said the
fallback was "probably" what players saw. That was a guess. This settles it.

## The readings (verbatim from the logs)

```
acclient!RenderDevice::render_device->m_caps
      +0x008 MaxSimultaneousTextures : 8
      +0x00c MaxTextureBlendStages : 8
      +0x01c bCanDoSinglePassDetailing : 1     <-- THE ANSWER
      +0x01d bTexOpDotProduct3 : 1
      +0x01e bTexOpBumpEnvMap : 1

trysinglepass (file-static, decomp 0x00820e40 / 0x00835c04 / 0x00835c10)
00820e40  00000001
00835c04  00000001
00835c10  00000001

acclient!Render::m_RenderPrefs
   +0x004 LandscapeDetailTextures : 0
   +0x005 EnvironmentDetailTextures : 1
   +0x006 MultiPassAlpha   : 1

acclient!Render::landscape_detail_surface   = 0x00000000   (OFF)
acclient!Render::building_detail_surface    = 0x0332e6a8   (ON)
acclient!Render::environment_detail_surface = 0x03416de0   (ON)
acclient!Render::object_detail_surface      = 0x00000000   (OFF)
acclient!Render::landscape_detail_tiling    = 4
acclient!Render::building_detail_tiling     = 4
acclient!Render::environment_detail_tiling  = 4
acclient!Render::object_detail_tiling       = 4
acclient!Render::curr_detail_src_blend      = 5   (static default; unused on this path)
acclient!Render::curr_detail_dst_blend      = 6
```

## What this means

**Retail on this hardware uses the single-pass texture-stage path.** The
framebuffer blend that Campaign AR ported — and that the 2026-08-21 findings
doc and the AR review both analysed as "retail's detail pass brightens" —
is the fallback for adapters that cannot advertise
`D3DTEXOPCAPS_PREMODULATE`. A modern AMD driver advertises it. The reviewer's
recollection that consumer drivers rarely did was **wrong**; recorded here so
nobody repeats it.

The single-pass combine, from `D3DPolyRender::SetSurface` with the detail
flag set (args are `(stage, op, arg1, arg2)`; `0 = DIFFUSE`, `1 = CURRENT`,
`2 = TEXTURE`):

```
stage 0  colour = MODULATE(TEXTURE, DIFFUSE)            = base.rgb * diffuse.rgb
stage 0  alpha  = PREMODULATE(DIFFUSE, DIFFUSE)         = diffuse.a * detail.a   (premodulate = multiply by the NEXT stage's texture)
stage 1  colour = BLENDCURRENTALPHA(TEXTURE, CURRENT)   = detail.rgb * f + current.rgb * (1 - f),  f = stage-0 alpha
stage 1  alpha  = MODULATE(TEXTURE, CURRENT)            = detail.a * current.a
stage 2  DISABLE
```

So the pixel retail actually draws is

```
lerp(base * diffuse,  detail.rgb,  detail.a * diffuse.a)
```

a **blend toward the detail colour by the detail alpha** — not
`dest × (detail + 1 − α)`. With the live category texture `0x06006D58`
(mean rgb 0.165, mean α 0.132) and opaque diffuse (α = 1), the average
effect is `≈ 0.868 × base + 0.022`: a mild **darkening** noise of roughly
−10 % on mid-tones. Rougher and darker — the intended look — not brighter.

Consequences:

1. The community remark "they did it backwards, looks like it reflects
   more" describes the **fallback** path. On hardware like the owner's it
   does not apply.
2. Campaign AR's #226 port reproduces the wrong path for every modern GPU.
   It must be re-ported (below). The existing `RetailDetailTextureContract`
   "brightening is expected" statement and the findings doc §2 table are
   true only of the fallback and must say so (VM4).
3. There is **no distance fade on either path** (VM1 stands): the stage-1
   sampler is LINEAR/LINEAR/LINEAR with WRAP; attenuation is the mip chain
   converging to the texture mean.
4. `LandscapeDetailTextures` is a real, separate preference, **0** here.
   Landscape detail is off by preference, not only by the `ChangeRegion`
   literal; there is no Options row for it in the 2013 client. Terrain
   detail remains out of #226's scope.
5. `bTexOpDotProduct3 = 1`, `bTexOpBumpEnvMap = 1`: the DOT3 machinery is
   available to retail on this hardware, which makes "what uses the BumpMap
   path" (findings §7 q4) a live question, still untraced.

## The re-port (folds into VM1; it is small)

Because the lerp is expressible as a framebuffer blend, the existing
separate detail replay pass stays; only its pixel contract changes:

- pipeline blend: `SRCALPHA + INVSRCALPHA`, `ADD` (the pair retail stores
  as 5/6) instead of `DSTCOLOR + INVSRCALPHA`;
- `mesh_detail.frag` outputs `vec4(detail.rgb, detail.a * diffuseAlpha)`,
  where `diffuseAlpha` is the base subset's vertex/material alpha (1 for
  opaque subsets; the translucent subsets already carry it);
- neutral point: `detail.a == 0` (no blend), not `detail.rgb == detail.a`;
- `RetailDetailTextureContract.FramebufferFactor` becomes
  `lerp(1, detail.rgb / base, detail.a)` semantics — rewrite the helper and
  its tests around `Expected(base, detail, diffuseAlpha)`;
- the 10 m / 50 m fade is deleted as planned (VM1).

A register row is **not** needed for the single-pass port — it is the
retail path. A row IS needed if the fallback is ever exposed (it should
not be).

## Closed / corrected by this note

- Review F3: answered — single-pass. The review's "probably fallback" was
  wrong.
- Findings doc `2026-08-21-terrain-and-atmospheric-rendering-findings.md` §2
  "retail's own detail pass BRIGHTENS": true for the fallback only; the
  hardware path darkens. VM4 amends the doc.
- AR plan + #226 pseudocode note: same amendment.