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>
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docs/research/2026-08-22-vm2-retail-detail-path-cdb.md
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docs/research/2026-08-22-vm2-retail-detail-path-cdb.md
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# VM2 — which detail-texturing path does retail actually run? (cdb, live)
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**Date:** 2026-08-22 · **Campaign:** VM slice VM2 · **Status:** CLOSED — answered
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**Method:** read-only cdb attach to the live PDB-paired retail client
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(`C:\Turbine\Asheron's Call\acclient.exe`, v11.4186, PDB GUID
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`9e847e2f-777c-4bd9-886c-22256bb87f32`, verified `MATCH` by
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`tools/pdb-extract/check_exe_pdb.py`), in-world on the owner's AMD GPU.
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Scripts: `tools/cdb/vm2-detail-caps.cdb` (+ runner) and
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`tools/cdb/vm2-trysinglepass.cdb`. No breakpoints; `qd` at top level.
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## The question
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Campaign AR's #226 port (`mesh_detail.frag`, pipeline blend
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`DSTCOLOR + INVSRCALPHA`) reproduces the path retail takes when
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`ACRender::SetDetailSurfaceInternal(0)` is called — the **two-pass
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framebuffer fallback**. `RenderMeshSubset` (0x0059ca10) and `landPolyDraw`
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(0x006b6320) only take that path when
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`trysinglepass == 0 || !m_caps.bCanDoSinglePassDetailing`. Otherwise they
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call `SetDetailSurfaceInternal(1)` and the combine is the texture-stage
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setup in `D3DPolyRender::SetSurface` (0x0059c4d0). The review (F3) said the
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fallback was "probably" what players saw. That was a guess. This settles it.
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## The readings (verbatim from the logs)
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```
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acclient!RenderDevice::render_device->m_caps
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+0x008 MaxSimultaneousTextures : 8
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+0x00c MaxTextureBlendStages : 8
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+0x01c bCanDoSinglePassDetailing : 1 <-- THE ANSWER
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+0x01d bTexOpDotProduct3 : 1
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+0x01e bTexOpBumpEnvMap : 1
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trysinglepass (file-static, decomp 0x00820e40 / 0x00835c04 / 0x00835c10)
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00820e40 00000001
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00835c04 00000001
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00835c10 00000001
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acclient!Render::m_RenderPrefs
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+0x004 LandscapeDetailTextures : 0
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+0x005 EnvironmentDetailTextures : 1
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+0x006 MultiPassAlpha : 1
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acclient!Render::landscape_detail_surface = 0x00000000 (OFF)
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acclient!Render::building_detail_surface = 0x0332e6a8 (ON)
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acclient!Render::environment_detail_surface = 0x03416de0 (ON)
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acclient!Render::object_detail_surface = 0x00000000 (OFF)
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acclient!Render::landscape_detail_tiling = 4
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acclient!Render::building_detail_tiling = 4
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acclient!Render::environment_detail_tiling = 4
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acclient!Render::object_detail_tiling = 4
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acclient!Render::curr_detail_src_blend = 5 (static default; unused on this path)
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acclient!Render::curr_detail_dst_blend = 6
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```
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## What this means
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**Retail on this hardware uses the single-pass texture-stage path.** The
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framebuffer blend that Campaign AR ported — and that the 2026-08-21 findings
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doc and the AR review both analysed as "retail's detail pass brightens" —
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is the fallback for adapters that cannot advertise
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`D3DTEXOPCAPS_PREMODULATE`. A modern AMD driver advertises it. The reviewer's
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recollection that consumer drivers rarely did was **wrong**; recorded here so
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nobody repeats it.
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The single-pass combine, from `D3DPolyRender::SetSurface` with the detail
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flag set (args are `(stage, op, arg1, arg2)`; `0 = DIFFUSE`, `1 = CURRENT`,
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`2 = TEXTURE`):
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```
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stage 0 colour = MODULATE(TEXTURE, DIFFUSE) = base.rgb * diffuse.rgb
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stage 0 alpha = PREMODULATE(DIFFUSE, DIFFUSE) = diffuse.a * detail.a (premodulate = multiply by the NEXT stage's texture)
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stage 1 colour = BLENDCURRENTALPHA(TEXTURE, CURRENT) = detail.rgb * f + current.rgb * (1 - f), f = stage-0 alpha
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stage 1 alpha = MODULATE(TEXTURE, CURRENT) = detail.a * current.a
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stage 2 DISABLE
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```
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So the pixel retail actually draws is
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```
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lerp(base * diffuse, detail.rgb, detail.a * diffuse.a)
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```
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a **blend toward the detail colour by the detail alpha** — not
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`dest × (detail + 1 − α)`. With the live category texture `0x06006D58`
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(mean rgb 0.165, mean α 0.132) and opaque diffuse (α = 1), the average
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effect is `≈ 0.868 × base + 0.022`: a mild **darkening** noise of roughly
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−10 % on mid-tones. Rougher and darker — the intended look — not brighter.
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Consequences:
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1. The community remark "they did it backwards, looks like it reflects
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more" describes the **fallback** path. On hardware like the owner's it
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does not apply.
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2. Campaign AR's #226 port reproduces the wrong path for every modern GPU.
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It must be re-ported (below). The existing `RetailDetailTextureContract`
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"brightening is expected" statement and the findings doc §2 table are
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true only of the fallback and must say so (VM4).
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3. There is **no distance fade on either path** (VM1 stands): the stage-1
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sampler is LINEAR/LINEAR/LINEAR with WRAP; attenuation is the mip chain
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converging to the texture mean.
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4. `LandscapeDetailTextures` is a real, separate preference, **0** here.
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Landscape detail is off by preference, not only by the `ChangeRegion`
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literal; there is no Options row for it in the 2013 client. Terrain
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detail remains out of #226's scope.
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5. `bTexOpDotProduct3 = 1`, `bTexOpBumpEnvMap = 1`: the DOT3 machinery is
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available to retail on this hardware, which makes "what uses the BumpMap
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path" (findings §7 q4) a live question, still untraced.
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## The re-port (folds into VM1; it is small)
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Because the lerp is expressible as a framebuffer blend, the existing
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separate detail replay pass stays; only its pixel contract changes:
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- pipeline blend: `SRCALPHA + INVSRCALPHA`, `ADD` (the pair retail stores
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as 5/6) instead of `DSTCOLOR + INVSRCALPHA`;
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- `mesh_detail.frag` outputs `vec4(detail.rgb, detail.a * diffuseAlpha)`,
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where `diffuseAlpha` is the base subset's vertex/material alpha (1 for
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opaque subsets; the translucent subsets already carry it);
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- neutral point: `detail.a == 0` (no blend), not `detail.rgb == detail.a`;
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- `RetailDetailTextureContract.FramebufferFactor` becomes
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`lerp(1, detail.rgb / base, detail.a)` semantics — rewrite the helper and
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its tests around `Expected(base, detail, diffuseAlpha)`;
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- the 10 m / 50 m fade is deleted as planned (VM1).
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A register row is **not** needed for the single-pass port — it is the
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retail path. A row IS needed if the fallback is ever exposed (it should
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not be).
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## Closed / corrected by this note
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- Review F3: answered — single-pass. The review's "probably fallback" was
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wrong.
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- Findings doc `2026-08-21-terrain-and-atmospheric-rendering-findings.md` §2
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"retail's own detail pass BRIGHTENS": true for the fallback only; the
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hardware path darkens. VM4 amends the doc.
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- AR plan + #226 pseudocode note: same amendment.
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26
docs/research/evidence/2026-08-22-vm2-cdb-readings.txt
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docs/research/evidence/2026-08-22-vm2-cdb-readings.txt
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00866354 acclient!Render::landscape_detail_surface = 0x00000000
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0081eca4 acclient!Render::curr_detail_dst_blend = 6
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0081eca0 acclient!Render::curr_detail_src_blend = 5
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0081ecb8 acclient!Render::curr_detail_tiling = 4
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00866364 acclient!Render::curr_detail_surface = 0x00000000
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0081eca8 acclient!Render::landscape_detail_tiling = 4
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0081ecb0 acclient!Render::building_detail_tiling = 4
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00866360 acclient!Render::object_detail_surface = 0x00000000
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0081ecb4 acclient!Render::object_detail_tiling = 4
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0081ecac acclient!Render::environment_detail_tiling = 4
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00866358 acclient!Render::building_detail_surface = 0x0332e6a8
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0086635c acclient!Render::environment_detail_surface = 0x03416de0
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Type does not have given member error at 'm_D3DCaps.MaxSimultaneousTextures'
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Type does not have given member error at 'm_D3DCaps.MaxTextureBlendStages'
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+0x008 MaxSimultaneousTextures : 8
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+0x00c MaxTextureBlendStages : 8
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+0x010 MaxSimultaneousRenderTargets : 4
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+0x01c bCanDoSinglePassDetailing : 1
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+0x01d bTexOpDotProduct3 : 1
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+0x01e bTexOpBumpEnvMap : 1
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00820e40 00000001
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00835c04 00000001
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00835c10 00000001
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+0x004 LandscapeDetailTextures : 0
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+0x005 EnvironmentDetailTextures : 1
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+0x006 MultiPassAlpha : 1
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