git:20260713.f0e8d5c to git:20260716.2ce13bc
120 added, 1 removed. Audit C to A.
- ../../threejs-procedural-buildings-and-cities/SKILL.md
+ ---
+ name: threejs-procedural-buildings-and-cities
+ description: Compile procedural buildings, cities, and semantic site assemblies in Three.js r185 WebGPU/TSL. Use for building massing and facades, city-scale architectural batching and LOD, or deterministic placement of heterogeneous site assets around architecture.
+ ---
+
+ # Procedural Buildings and Cities
+
+ Treat architecture as a compiler: decide the runtime package, produce and
+ validate a serializable plan, then emit geometry. The plan owns massing,
+ exposed surfaces, placements, material slots, and stable identity.
+
+ ## Process
+
+ 1. **Select the runtime package from mutability and repetition.**
+
+ | Workload | Package |
+ | --- | --- |
+ | Static building or chunk | merged indexed `BufferGeometry` per material slot |
+ | Editable varied modules | `BatchedMesh` per compatible material slot |
+ | Repeated identical topology | spatially paged `InstancedMesh` |
+ | District-scale streaming | bounded chunks with projected-error LOD |
+
+ Initialize `WebGPURenderer` before gating WebGPU features. Architecture
+ planning can remain CPU-deterministic; add storage or compute only for a
+ measured city-scale visibility or update bottleneck.
+
+ **Complete when:** every architectural element has one package, and every
+ package has an explicit mutability, visibility, and identity reason.
+
+ 2. **Produce a valid building plan.** Normalize units and settings, then apply
+ the mass-operator rail: footprint pieces -> union/court subtraction ->
+ extrude/stack -> inset/split -> optional connector. Choose only
+ prevalidated alternatives; give every operator result a stable ID and
+ validate it before the next operator. Read
+ [grammar-and-mesh-compiler.md](references/grammar-and-mesh-compiler.md) when
+ implementing these operators. Serialize footprints, mass volumes, exposed
+ intervals, placements, module usage, ownership, material slots, UV scale,
+ and budgets.
+
+ **Complete when:** the same inputs reproduce the same operator choices and
+ IDs, every operator output passes its topology/dimension/ownership gate, and
+ geometry emission is unnecessary to diagnose an invalid plan.
+
+ 3. **Resolve exposed boundaries before facade placement.** Subtract shared or
+ blocked side intervals, quantize each surviving interval into legal bays,
+ and attach facade, roof, trim, and corner placements to those intervals.
+ Read [grammar-and-mesh-compiler.md](references/grammar-and-mesh-compiler.md)
+ when implementing footprint subtraction, bay quantization, placement
+ ownership, or module-local frames.
+
+ **Complete when:** no facade interval lies inside the footprint, every legal
+ interval has a declared placement or semantic blank, and corner ownership is
+ unambiguous.
+
+ 4. **Close and validate the plan.** Add visible caps, decks, soffits, and
+ closure surfaces for validated connectors; resolve every placement through
+ the module registry; then test registry completeness, ownership uniqueness,
+ general overlap, winding, bounds, material membership, and UV density.
+
+ For a heterogeneous site assembly, keep domain assets delegated to their
+ owning skills and register each ruin, dock, boat, rock, vegetation cluster,
+ or prop with a stable placement ID, owner, transform/frame/scale, support and
+ clearance volumes, anchor, and LOD policy. Place the landmark first, then
+ solve access, support, and clearance before repeated detail.
+
+ **Complete when:** every placement resolves, every surface has one owner,
+ overlaps are empty or explicitly permitted, support/clearance gates pass,
+ stable IDs replay deterministically, and all emitted geometry or delegated
+ assets trace to a plan record.
+
+ 5. **Compile by material slot and spatial boundary.** Keep semantic material
+ identities stable while choosing merge, batch, or instance emission. In
+ Three.js r185 WebGPU, `BatchedMesh` iterates visible multi-draw entries: it
+ improves object/state management but does not prove GPU draw collapse.
+ Merge compatible static geometry or instance identical topology when draw
+ collapse is required. Read
+ [grammar-and-mesh-compiler.md](references/grammar-and-mesh-compiler.md) when
+ implementing slot writers, paging, projected-error LOD, or draw accounting.
+
+ **Complete when:** slot membership is complete, indexed bounds are finite,
+ pages are independently cullable, LOD error is gated in physical pixels, and
+ actual backend draw items are reported.
+
+ 6. **Bind materials and presentation.** Use `MeshStandardNodeMaterial` or
+ `MeshPhysicalNodeMaterial` per semantic slot. Preserve physical texture
+ scale and data/color encodings. Hand final color to the scene's one
+ `RenderPipeline` output transform, then dispose replaced geometries,
+ batches, textures, and node resources.
+
+ **Complete when:** flat material, grazing light, and final output agree on
+ geometry and normals; one component owns output conversion; replacement and
+ disposal leave no stale bounds or live resources.
+
+ 7. **Verify the compiler.** Exercise simple and compound footprints, courts,
+ bridges or connectors when supported, minimum legal spans, dense placement,
+ repeated modules, and district paging across multiple seeds. Inspect
+ silhouette, untextured geometry, corners, openings, setbacks, roofs, and LOD
+ transitions.
+
+ **Complete when:** every fixture has a valid plan, no internal facade
+ intervals or placement overlaps, a complete registry, deterministic replay,
+ correct bounds and material slots, stable UV scale, and measured triangle and
+ draw counts.
+
+ ## Ownership Boundary
+
+ - Use `$threejs-procedural-geometry` for reusable profiles, sweeps, arches,
+ frames, and low-level mesh writers.
+ - Use `$threejs-procedural-materials` for masonry, glass, metal, weathering,
+ filtering, and material-field authoring.
+ - Use `$threejs-procedural-fields` for terrain and parcel fields consumed by a
+ city layout.
+ - Use `$threejs-scalable-real-time-shadows`, `$threejs-image-pipeline`, and
+ `$threejs-visual-validation` for scene-wide shadow, output, and evidence
+ ownership.
+
+ This skill owns building massing, facade semantics, architectural module and
+ site placement, plan validation, material-slot compilation, and architectural
+ spatial LOD; delegated skills still own nonarchitectural asset generation.
+