WoW 4.0 Terrain Blend Recovery

Prompt file imported from akspa0/parp-tools (.codex/prompts/wow-400-terrain-blend-recovery.md). Copyright stays with the author.

Recover 4.0.0.11927 terrain texturing in gillijimproject_refactor.

Read First

1. gillijimproject_refactor/memory-bank/activeContext.md
2. gillijimproject_refactor/memory-bank/progress.md
3. gillijimproject_refactor/memory-bank/data-paths.md
4. gillijimproject_refactor/src/MdxViewer/memory-bank/activeContext.md
5. gillijimproject_refactor/src/MdxViewer/memory-bank/terrain_editing_plan_2026-02-14.md
6. gillijimproject_refactor/docs/archive/WoW_400_ADT_Analysis.md
7. gillijimproject_refactor/documentation/wow-400-terrain-blend-wow-exe-guide.md
8. gillijimproject_refactor/docs/ADT_WDT_Format_Specification.md

Goal

Make concrete progress on the active viewer's 4.0.0 terrain blending so it matches the wow.exe behavior more closely on the fixed development dataset.

Current Reverse-Engineered Model

• 4.0.0 is still pre-split on disk, but runtime terrain texturing is not just local MCAL decoding.
• CMapChunk_UnpackAlphaBits handles local 4-bit / 8-bit / compressed decode.
• In 8-bit mode, layers without direct alpha payload can be synthesized as residual coverage from sibling layers.
• CMapChunk_UnpackChunkAlphaSet stitches the current chunk with three linked neighbors and matches neighbor layers by texture id.
• CMapChunk_RefreshBlendTextures then creates a TerrainBlend resource from those decoded results.

Non-Negotiable Constraints

• Do not revert back to broad relaxed alpha heuristics.
• Do not claim 4.0 terrain is fixed from build-only validation.
• Do not treat old archive notes that say "4.0 is identical to 3.3.5" as authoritative.
• Keep the active implementation minimal and viewer-compatible before attempting a full TerrainBlend resource port.

Required Implementation Order

1. Confirm whether the current bug is missing local decode, missing residual synthesis, or missing edge stitching.
2. Prefer the smallest active-viewer change that maps directly to the wow.exe findings.
3. Implement residual-alpha synthesis for 8-bit 4.0 layers before broader renderer surgery.
4. Implement texture-id-based neighbor edge stitching as the next step.
5. Update documentation and memory-bank files in the same change set so future sessions do not lose the model.

Required Deliverables

Return all items:

1. exact behavior implemented
2. files changed and why
3. documentation and memory-bank files updated
4. build status
5. automated-test status
6. real-data runtime-validation status
7. remaining gaps versus the wow.exe model

First Output

Start with:

1. the current 4.0 terrain texturing gap in the active viewer
2. the minimal next implementation slice worth landing
3. what docs and memory-bank files will be updated along with the code