31 lines
1.8 KiB
Markdown
31 lines
1.8 KiB
Markdown
# Terrain Material Layers And Weight Painting (#24)
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> **Historical plan — not current implementation guidance.** Use the [documentation index](../../docs/README.md) for current behavior and architecture.
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## Scope
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- Persist up to four shared Material/Material Instance references on each `TerrainDesc`.
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- Store normalized RGBA8 layer weights per height sample with an implicit channel-zero default.
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- Blend layer albedo, normal, metallic, and roughness in the project-owned raster material path.
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- Assign, clear, reorder, and tile layers from the Terrain inspector.
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- Paint or erase one selected layer from the existing horizontal viewport toolbar.
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- Preserve one reflected history transaction per completed pointer stroke and exact cancel restore.
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## Implementation
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1. Extend the backward-compatible terrain schema with four layer descriptors and compact weights.
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2. Emit normalized weights as terrain chunk vertex colors and attach a runtime-only material binding.
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3. Build a terrain-specific `ExtendedMaterial` in `blacksite_surface`; keep invalid references on the visible fallback path with diagnostics.
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4. Add inspector layer controls and a mutually exclusive modal paint operator beside Sculpt.
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5. Cover serialization, validation, blend transport, paint normalization, cancel, undo, and redo.
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6. Update ADR 0040, terrain workflow docs, the implementation checklist, and live evidence.
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## Acceptance
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- Two or more project materials visibly blend on one terrain.
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- Layer weights remain exactly normalized and survive scene save/load.
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- Live paint preview follows the sampled terrain surface.
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- Escape/right-click restores exact pre-stroke weights; release creates one undo entry.
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- Missing or invalid material references remain visible as fallback and produce clear diagnostics.
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- Formatting, workspace check/clippy/tests, level validation, and live native-Wayland QA pass.
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