Grindstone

A showcase piece, not an example. A procedural grindstone: a sandstone wheel, a timber A-frame trestle, iron shoes, axle, hubs and crank, and an open trough. The piece then runs the shipped pipeline: unique-cell UVs, a Cycles high-to-low normal bake, an LOD chain, a convex collider, and a Unity glTF export.

Each A-frame is a king post with two diagonals tenoned 12 mm into its faces and into a fatter sill. It is not two sticks meeting at a point. The sills stand in iron shoes, cups one 6 mm reveal proud of the sill on every side. The trough is one manifold basin seated into the sills and carried on two end stretchers, which it bites by 4 mm. Every timber and iron edge is chamfered. The stone is 48 smooth segments with hard chamfer rings, in a mottled sandstone material. Stated size is a 0.50 m × 0.095 m stone in a 0.72 × 0.42 × 0.61 m frame.

The hero turns the crank toward the camera, since the crank is the part that says the wheel is turned by hand, and fills the trough. The water is render-only dressing parented to the piece, set 12 mm under the rim, so the stone (28 mm under the rim) runs 16 mm under water; the stone darkens and glosses in a band that fades out 45 mm above the water line. Neither the water nor the wet band is part of the asset: no budget reads them, the export does not carry them, and the asset sheet renders the grindstone dry.

It asserts budget conformance of the generated result. It does not witness an API contract. "It rendered without error" is not a check.

Composes skills mesh-editing-and-bmesh, bake-high-to-low, depsgraph-and-evaluated-data, engine-export-presets, and snippets bake_normal_high_to_low.py, setup_bake_target_image.py, lod_chain.py / decimate_to_budget.py, convex_hull_collider.py, export_preset_unity.py (helpers copied, not imported as a package).

Budgets#

Declared as named constants; every gate recomputes from the mesh, materials, UVs, evaluated LOD, collider, or export file.

The collider ceiling moved from 240 to 320 with the stone. 48 segments put more of its rim on the hull (198 → 304 triangles).

Hygiene#

Recomputed from the generated mesh, not asserted about the script.

The coplanar budget counts pairs from different shells within 0.05 m, using hay-bale's constants. The first build matched only faces whose centres fell within 0.1 mm of each other, and no real overlap ever does. It reported 0 while the shoes shared three planes with every sill end, seen as a lit slit in each foot close-up.

Joint fit and seat#

DECIMATE COLLAPSE triangle counts can differ across series, so the gate is a ratio band, not an exact count. Bake pixels are stochastic. The gate is has_data plus operator FINISHED plus the texel floor, not byte-identity. Per-member wood tone comes from random.Random(TONE_SEED), so it is identical run to run. Export byte counts differ by 12 B on 5.2.1 (glTF serializer), which is not a gated axis.

Falsifiers#

Each violates one named budget. All thirteen were run on 4.5.11, 5.1.2 and 5.2.1 and returned the same code on each.

--flush-shoes moves the shoe envelope 12 mm inside BBOX_TOL (15 mm), so the AABB gate cannot steal it. --sharp-handle leaves the triangle count inside its band, so only the edge budget sees it.

Run#

blender --background --python grindstone.py --
blender --background --python grindstone.py -- --skip-decimate
blender --background --python grindstone.py -- --stray-vert
blender --background --python grindstone.py -- --flush-shoes
blender --background --python grindstone.py -- --lift-z
blender --background --python grindstone.py -- --short-legs
blender --background --python grindstone.py -- --float-crank
blender --background --python grindstone.py -- --float-legs
blender --background --python grindstone.py -- --narrow-trough
blender --background --python grindstone.py -- --no-dip
blender --background --python grindstone.py -- --low-stretchers
blender --background --python grindstone.py -- --sharp-handle
blender --background --python grindstone.py -- --low-bake
blender --background --python grindstone.py -- --output grindstone.png

Smoke passes no flags.

Exit codes#

File-local. 9 is a valid check code. 10 is reserved for gallery_framing.check_framing on the --output path. 15–19 are the hygiene and joint-fit family.