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refactor: #100 — remove hiddenTerrainCells / BuildingTerrainCells plumbing

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Retired in favour of Task 1's retail-faithful terrain shader Z nudge.
Pure removal — ~50 LOC of dead surface area across:

  - src/AcDream.Core/Terrain/LandblockMesh.cs (drop parameter +
    cell-collapse block)
  - src/AcDream.Core/World/LoadedLandblock.cs (drop field)
  - src/AcDream.Core/World/LandblockLoader.cs (drop method + call)
  - src/AcDream.App/Rendering/GameWindow.cs (3 sites)
  - src/AcDream.App/Streaming/GpuWorldState.cs (6 ctor sites)
  - src/AcDream.App/Streaming/LandblockStreamer.cs (1 ctor site)
  - tests/AcDream.Core.Tests/World/LandblockLoaderTests.cs (drop test)
  - tests/AcDream.Core.Tests/Terrain/LandblockMeshTests.cs (drop test)

No retail anchor — the deleted mechanism never had one; this commit
rolls our code back to the actual retail behaviour established in
the prior commit's shader nudge.

ISSUES.md #100 moved to Recently closed.

Cross-ref:
  docs/research/2026-05-25-issue-100-terrain-cutout-handoff.md
  docs/superpowers/plans/2026-05-25-issue-100-terrain-cutout.md

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
This commit is contained in:
Erik 2026-05-25 21:34:06 +02:00
parent f48c74aa8b
commit a64e6f20da
9 changed files with 52 additions and 165 deletions
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88
docs/ISSUES.md
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@ -761,56 +761,6 @@ family (sling-out — also likely).
---
## #100 — Transparent rectangular patches around every house (terrain rendering)
**Status:** OPEN
**Severity:** MEDIUM (visual regression; affects every Holtburg house)
**Filed:** 2026-05-24
**Component:** rendering, terrain
**Description:** Standing outside any Holtburg house, the ground in a
rectangular footprint around the building appears as a flat dark patch
instead of cobblestone / grass terrain. Visible as a sharp-edged
rectangle the size of the house's outdoor footprint. Same shape on
every house observed.
User report 2026-05-24 (with screenshot): "around every house now I
missing the ground texture, it is transparent. I can see through the
ground."
**Root cause / status:** **Bisect 2026-05-24 — commit `35b37df`** is the introducer (the only commit on this worktree branch that touches `src/AcDream.Core/Terrain/`). It added a `hiddenTerrainCells` parameter to `LandblockMesh.Build` that collapses terrain triangles owned by buildings to zero-area degenerates, intended so the building's own ground-level mesh visually fills the gap (avoids Z-fighting between terrain and building floor).
The hide mechanism works at **outdoor-cell granularity** — 24 m × 24 m cells indexed by `cy * 8 + cx` from `LandBlockInfo.Buildings`. A cottage building only fills ~half of one outdoor cell (cottage footprint ~12 m × 12 m vs cell 24 m × 24 m), so the entire 24 × 24 cell terrain gets hidden but the cottage geometry only covers a smaller area inside it. The visible result: a dark rectangle (sky / framebuffer clear bleeding through) around every house where terrain was hidden but no building mesh fills the gap.
Confirmed in [`src/AcDream.Core/Terrain/LandblockMesh.cs:178`](src/AcDream.Core/Terrain/LandblockMesh.cs:178):
```csharp
if (hiddenTerrainCells is not null && hiddenTerrainCells.Contains(cellIdx))
{
indices[i] = (uint)(cellIdx * VerticesPerCell); // collapse to vertex 0 → degenerate
continue;
}
```
The cells flagged hidden come from `LandblockLoader.BuildBuildingTerrainCells` (also kept by 35b37df), which reads `LandBlockInfo.Buildings` and emits one cellIdx per listed building's `cy*8+cx`.
The b3ce505 issue-#98 fix did NOT cause or interact with this — it only touched physics collision code.
**Fix paths** (need design decision):
1. **Polygon-level terrain occlusion** instead of cell-level. Build per-poly cutouts from each building's ground-footprint convex hull / bounding box, modify the terrain mesh to actually have a hole the building exactly fits. Retail-faithful for this case but a real engineering change to `LandblockMesh.Build`.
2. **Drop the hiddenTerrainCells mechanism entirely** and accept Z-fighting on the building floor vs terrain seam (or solve Z-fighting via a tiny render-only Z lift on the building floor mesh, the same trick we already use for env cell floors at line 5363 `+ new Vector3(0f, 0f, 0.02f)`).
3. **Render the building's "yard" mesh** if buildings have such a thing in retail. (Need to check — Holtburg cottages may have stone foundation polys around them that retail renders.)
Option 2 is the smallest change; option 1 is the most faithful. Option 3 needs retail visual research.
**Files:**
- `src/AcDream.Core/Terrain/LandblockMesh.cs:178` — the collapse code
- `src/AcDream.Core/World/LandblockLoader.cs` — `BuildBuildingTerrainCells`
- `src/AcDream.App/Rendering/GameWindow.cs:1808, 5366, 8761` — sites calling `LandblockMesh.Build` with `hiddenTerrainCells`
**Acceptance:** Standing outside a Holtburg house, the ground around it
renders with the same cobblestone / grass texture as the surrounding
terrain — no dark rectangular patches.
---
## #98-old-context-preserved-for-reference
@ -3474,6 +3424,44 @@ Unverified. The likely culprits, ranked by suspected probability:
# Recently closed
## #100 — [DONE 2026-05-25 · f48c74aa + 64518d59] Transparent rectangular patches around every house (terrain rendering)
**Status:** DONE
**Closed:** 2026-05-25
**Commits:** `f48c74aa`, `64518d59`
**Component:** rendering, terrain
**Resolution (2026-05-25 · #100):** Replaced the cell-level
`hiddenTerrainCells` mechanism with retail's per-vertex Z nudge
(`zFightTerrainAdjust = 0.00999999978`) applied inside the modern
terrain vertex shader. Render terrain everywhere; coplanar building
floors win the depth test by being 1 cm higher than the rendered
terrain. Physics path untouched. ~50 LOC of `BuildingTerrainCells`
plumbing removed across LandblockMesh / LoadedLandblock /
LandblockLoader / GameWindow / GpuWorldState / LandblockStreamer
plus the corresponding unit test. Retail anchors:
acclient_2013_pseudo_c.txt:1120769 + :702254.
**Description:** Standing outside any Holtburg house, the ground in a
rectangular footprint around the building appears as a flat dark patch
instead of cobblestone / grass terrain. Visible as a sharp-edged
rectangle the size of the house's outdoor footprint. Same shape on
every house observed.
User report 2026-05-24 (with screenshot): "around every house now I
missing the ground texture, it is transparent. I can see through the
ground."
**Root cause:** Bisect 2026-05-24 — commit `35b37df` is the introducer. It
added a `hiddenTerrainCells` parameter to `LandblockMesh.Build` that collapses
terrain triangles owned by buildings to zero-area degenerates. The hide
mechanism works at outdoor-cell granularity (24 m × 24 m cells), so the entire
cell terrain was hidden but the cottage geometry only covers a smaller area inside
it — leaving a dark transparent rectangle. The fix renders terrain everywhere and
uses retail's Z nudge to ensure building floors win the depth test.
---
## #101 — [DONE 2026-05-25 · 5240d65 + 6ca872f] Stair-step cylinder phantom blocks player on multi-part EnvCell entity
**Closed:** 2026-05-25