research(vm2): retail runs SINGLE-PASS detail texturing - the #226 port targets the fallback

Live cdb read on the PDB-paired retail client (owner's AMD GPU):
  m_caps.bCanDoSinglePassDetailing = 1, trysinglepass = 1,
  MaxSimultaneousTextures = 8, bTexOpDotProduct3 = 1,
  LandscapeDetailTextures = 0, EnvironmentDetailTextures = 1,
  landscape/object detail surfaces null, building/environment non-null,
  tiling 4 everywhere.

So retail's detail combine on modern hardware is the texture-stage path in
D3DPolyRender::SetSurface (stage0 alpha PREMODULATE, stage1 colour
BLENDCURRENTALPHA): lerp(base*diffuse, detail.rgb, detail.a*diffuse.a) -
a mild DARKENING (~-10% mid-tones with 0x06006D58), not the
DSTCOLOR+INVSRCALPHA brightening that Campaign AR ported and that the
2026-08-21 findings doc + AR review both analysed. Those described the
fallback for adapters without D3DTEXOPCAPS_PREMODULATE; the reviewer's
guess that consumer drivers rarely advertised it was wrong.

VM1 now carries the re-port (SRCALPHA+INVSRCALPHA, detail.rgb /
detail.a*diffuseAlpha, neutral at a==0) together with the fade removal.
No distance fade exists on either path. Scripts are read-only attaches
with no breakpoints.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

docs/plans/2026-08-22-visualmaster-campaign.md

@@ -52,15 +52,14 @@ moves a pack-off pixel outside its declared mask is a bug, not a tuning.
 |---|---|---|
 | VM0 | F1 — default-path invariance | automated + Fable report |
 | VM1 | F2 — invented detail fade | automated |
-| VM2 | F3 — which retail detail path ran | **owner action** (launch retail) |
+| VM2 | F3 — which retail detail path ran | **CLOSED 2026-08-22** — single-pass; see [cdb note](../research/2026-08-22-vm2-retail-detail-path-cdb.md) |
 | VM3 | F4 — linear-light post stack | automated + **owner visual** |
 | VM4 | F5 — overclaiming docs, incl. the reviewer's own | docs |
 | VM5 | F8 — volumetric banding; F7 filed | automated |
 | VM6 | Foliage wind | automated + **owner visual** |
 | VM7 | Closeout: full gates, register, roadmap, merge | **owner** |
 
-Order is VM0 → VM1 → VM4 → VM5 → VM3 → VM6 → VM2 (whenever the owner has
+Order is VM2 (done) → VM0 → VM1 → VM4 → VM5 → VM3 → VM6 → VM7. VM0 goes first because everything after it is measured
-retail up) → VM7. VM0 goes first because everything after it is measured
 against the baseline it establishes.
 
 ---
@@ -114,7 +113,7 @@ explains it.
 `DrawBuilding`/`DrawEnvCell`/`RenderMeshSubset`/`SetDetailSurfaceInternal`
 carry no distance term; attenuation is the LINEAR mip chain.
 
-**Decision (Fable, retail-faithful rule):** remove the ramp. Mip averaging
+**Decision (Fable, retail-faithful rule):** remove the ramp. **Amended by VM2:** VM1 also re-ports the blend to the single-pass math (see the VM2 outcome) — the fade removal and the blend correction land together, with the `RetailDetailTextureContract` helper and tests rewritten around `Expected(base, detail, diffuseAlpha)`. Mip averaging
 already converges the live category texture to its 1.033 mean factor.
 
 **Implementation**
@@ -155,6 +154,8 @@ review doc.
 
 **Acceptance:** the value is recorded with the binary GUID and the date.
 
+**OUTCOME (2026-08-22): `bCanDoSinglePassDetailing = 1`, `trysinglepass = 1`.** Retail on the owner's GPU runs the single-pass stage path: `lerp(base·diffuse, detail.rgb, detail.a·diffuse.a)` — a mild darkening, not the fallback's brightening. The #226 port targets the wrong path and is re-ported inside VM1 (blend `SRCALPHA+INVSRCALPHA`, output `detail.rgb, detail.a·diffuseAlpha`, neutral at `detail.a == 0`). Also read: `LandscapeDetailTextures = 0` is a real separate preference. Evidence and the exact stage math: [2026-08-22-vm2-retail-detail-path-cdb.md](../research/2026-08-22-vm2-retail-detail-path-cdb.md).
+
 ## VM3 — Linear-light post stack (F4)
 
 **Why:** bloom threshold, ACES, Rec.709 luma, saturation and the 0.5

docs/research/2026-08-22-vm2-retail-detail-path-cdb.md

@@ -0,0 +1,136 @@
+# 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.

docs/research/evidence/2026-08-22-vm2-cdb-readings.txt

@@ -0,0 +1,26 @@
+00866354          acclient!Render::landscape_detail_surface = 0x00000000
+0081eca4          acclient!Render::curr_detail_dst_blend = 6
+0081eca0          acclient!Render::curr_detail_src_blend = 5
+0081ecb8          acclient!Render::curr_detail_tiling = 4
+00866364          acclient!Render::curr_detail_surface = 0x00000000
+0081eca8          acclient!Render::landscape_detail_tiling = 4
+0081ecb0          acclient!Render::building_detail_tiling = 4
+00866360          acclient!Render::object_detail_surface = 0x00000000
+0081ecb4          acclient!Render::object_detail_tiling = 4
+0081ecac          acclient!Render::environment_detail_tiling = 4
+00866358          acclient!Render::building_detail_surface = 0x0332e6a8
+0086635c          acclient!Render::environment_detail_surface = 0x03416de0
+Type does not have given member error at 'm_D3DCaps.MaxSimultaneousTextures'
+Type does not have given member error at 'm_D3DCaps.MaxTextureBlendStages'
+      +0x008 MaxSimultaneousTextures : 8
+      +0x00c MaxTextureBlendStages : 8
+      +0x010 MaxSimultaneousRenderTargets : 4
+      +0x01c bCanDoSinglePassDetailing : 1
+      +0x01d bTexOpDotProduct3 : 1
+      +0x01e bTexOpBumpEnvMap : 1
+00820e40  00000001
+00835c04  00000001
+00835c10  00000001
+   +0x004 LandscapeDetailTextures : 0
+   +0x005 EnvironmentDetailTextures : 1
+   +0x006 MultiPassAlpha   : 1

tools/cdb/vm2-detail-caps-runner.ps1

@@ -0,0 +1,7 @@
+# Campaign VM slice VM2 runner. Retail acclient.exe (2013 PDB-paired build) must be running and in-world.
+$cdb = "C:\Program Files (x86)\Windows Kits\10\Debuggers\x86\cdb.exe"
+$script = "$PSScriptRoot\vm2-detail-caps.cdb"
+$p = Get-Process -Name acclient -ErrorAction SilentlyContinue
+if (-not $p) { Write-Error "acclient.exe is not running"; exit 1 }
+Write-Host "attaching to acclient pid $($p.Id) ..."
+& $cdb -pn acclient.exe -cf $script *>&1 | Tee-Object -FilePath "$PSScriptRoot\..\..\artifacts\vm2\vm2-detail-caps.console.log"

tools/cdb/vm2-detail-caps.cdb

@@ -0,0 +1,43 @@
+* Campaign VM slice VM2 - which detail-texturing path does retail run on this GPU?
+* Read-only: attach, dump the capability + detail state, detach. No breakpoints.
+.logopen C:\Users\erikn\source\repos\acdream\.claude\worktrees\peaceful-blackburn-5333f0\artifacts\vm2\vm2-detail-caps.log
+.sympath C:\Users\erikn\source\repos\acdream\refs
+.symopt+ 0x40
+.reload /f acclient.exe
+.echo === module / pdb identity ===
+lmv m acclient
+.echo === symbol resolution ===
+x acclient!RenderDevice::render_device
+x acclient!Render::*detail*
+x acclient!Render::m_RenderPrefs
+x acclient!trysinglepass
+.echo === THE ANSWER: single-pass detailing capability ===
+?? acclient!RenderDevice::render_device->m_caps.bCanDoSinglePassDetailing
+?? acclient!RenderDevice::render_device->m_caps.bTexOpDotProduct3
+?? acclient!RenderDevice::render_device->m_caps.bTexOpBumpEnvMap
+?? acclient!RenderDevice::render_device->m_caps.MaxSimultaneousTextures
+?? acclient!RenderDevice::render_device->m_caps.MaxTextureBlendStages
+.echo === raw D3D caps (TextureOpCaps: 0x8000 = BLENDCURRENTALPHA, 0x10000 = PREMODULATE, 0x4000 = DOTPRODUCT3) ===
+?? acclient!RenderDevice::render_device->m_D3DCaps.TextureOpCaps
+?? acclient!RenderDevice::render_device->m_D3DCaps.MaxSimultaneousTextures
+?? acclient!RenderDevice::render_device->m_D3DCaps.MaxTextureBlendStages
+?? acclient!RenderDevice::render_device->m_D3DCaps.PixelShaderVersion
+.echo === full m_caps dump ===
+dt acclient!RenderDevice poi(acclient!RenderDevice::render_device) m_caps.
+.echo === trysinglepass global ===
+dd acclient!trysinglepass L1
+.echo === detail category state (null = category off) ===
+?? acclient!Render::landscape_detail_surface
+?? acclient!Render::building_detail_surface
+?? acclient!Render::environment_detail_surface
+?? acclient!Render::object_detail_surface
+?? acclient!Render::landscape_detail_tiling
+?? acclient!Render::building_detail_tiling
+?? acclient!Render::environment_detail_tiling
+?? acclient!Render::object_detail_tiling
+?? acclient!Render::curr_detail_src_blend
+?? acclient!Render::curr_detail_dst_blend
+?? acclient!Render::m_RenderPrefs.EnvironmentDetailTextures
+.echo === done, detaching ===
+.logclose
+qd

tools/cdb/vm2-trysinglepass.cdb

@@ -0,0 +1,11 @@
+.logopen C:\Users\erikn\source\repos\acdream\.claude\worktrees\peaceful-blackburn-5333f0\artifacts\vm2\vm2-trysinglepass.log
+.sympath C:\Users\erikn\source\repos\acdream\refs
+.reload /f acclient.exe
+.echo === trysinglepass candidates (decomp: 00820e40 / 00835c04 / 00835c10, all init 1) ===
+dd 00820e40 L1
+dd 00835c04 L1
+dd 00835c10 L1
+.echo === RenderPrefs ===
+dt acclient!Render::m_RenderPrefs
+.logclose
+qd