chopping-block

Chopping block

A showcase piece, not an example. Procedural chopping block (a log round with a riveted iron hoop and a felling axe buried in the sawn face) then the shipped pipeline: unique-cell UVs, Cycles high-to-low normal bake, LOD chain, convex collider, Unity glTF export.

The log is an out-of-round loft whose radius is a closed-form function of angle and height; the hoop, its rivets, the top rim and the drying checks are all generated from that same function, so they stay seated when a dimension changes. The hoop is a lapped strip with two domed rivets through the lap. The axe head is one lofted shell from poll to bit with its chamfers modelled into the section profile, and the haft is swept through the eye rather than pushed into it. The haft is oval, bows away from the bit, and hooks toward it at the knob.

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.

Axis	Declared	Measured (4.5.11 / 5.1.2 / 5.2.1)
Base triangles	1730–1870	1800 / 1800 / 1800
LOD1 ratio	0.32–0.62 of base	0.5000 / 0.5000 / 0.5000
LOD2 ratio	0.10–0.35 of base	0.2200 / 0.2200 / 0.2200
Materials	exactly 4 distinct; ≥160 bark, ≥90 grain, ≥170 metal, ≥150 haft faces	4 slots; 180 / 216 / 404 / 176
UVs	in 0..1, AABB overlap ≤ 1e-5	in range, overlap 0
Outer AABB	(0.526, 0.526, 1.006) m ± 0.012	(0.5264, 0.5264, 1.0064)
Collider tris	≤ 560	538
Export	written, size > 0	180588 / 180588 / 180572 bytes

The triangle band, the outer AABB and the collider ceiling were re-fitted in the quality pass that added the lap, the rivets and the 16-segment oval haft (1472 → 1800 triangles, collider 434 → 538). The triangle band is centred on the new measurement, ± 4 %.

Hygiene

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

Axis	Declared	Measured (all three)
Non-manifold edges	0	0
Loose verts / edges	0 / 0	0 / 0
Doubles merged at 1e-5	0	0
Zero-area faces	0	0
N-gons	0	0
Coplanar disjoint face pairs	0	0
Grounded: zmin	within 1e-4 of 0	0.0000
Log axis out of plumb	≤ 1e-5	0.0000000
Log size	0.535 × 0.360 m ± 0.030 / ± 0.010	0.5464 × 0.3600
Haft section, wide over thick at the grip	1.25–1.60	1.3500

Joint fit

Six shells that have to meet correctly: log, hoop, head, haft, and the two rivets through the hoop's lap.

Axis	Declared	Measured (all three)
Shell count	exactly 6	6
Haft clearance inside the eye	≥ 0.006 m	0.01800
Haft engagement through the eye	≥ 0.020 m	0.08225
Haft breakout margin below the head	≥ 0.006 m	0.02175
Bit bury below the sawn top	≥ 0.030 m	0.07871
Bit inset from the rim	≥ 0.030 m	0.14647
Hoop bite into the log, every segment	0.002–0.007 m	0.00371–0.00422
Haft clearance above the log	≥ 0.015 m, 0 verts inside	0.07531, 0
Rivet seat into the hoop, each rivet	0.0008–0.0025 m	0.00150, 0.00154
Rivet dome proud of the hoop, each rivet	≥ 0.0025 m	0.00419, 0.00432

The hoop bite is binned by angular segment against the log's own radius function. A single global midpoint radius misclassifies outer chamfer vertices as inner ones on an out-of-round log, which is how a hoop that visibly floated on one side still passed.

The rivet seat is measured radially at each rivet vertex's own angle, against the hoop's outer face read off the mesh by a ray cast from the axis. Each rivet is aimed down the hoop's surface normal, not the radial: the log is out of round, so across one 12 mm head its surface falls by up to 1.4 mm, and radially aimed heads seated 1.87 and 2.82 mm against a 1.5 mm design bite, one edge sunk and the other lifted.

DECIMATE COLLAPSE triangle counts happen to agree across all three series here; the gate is still a ratio band, not an exact count. Bake pixels are stochastic; the gate is has_data plus operator FINISHED, not byte-identity. Construction uses no RNG: two runs on each binary print identical measurements, and the three binaries agree on every gated axis. Export byte counts differ by 16 B on 5.2.1 (glTF serializer), not a gated axis.

Shading and materials

Only the axe head is flat-shaded: it is a chamfered forging, and its facets are its form. The log and the hoop are smooth-shaded. Flat-shaded, the log's 36 equal facets read as coopered staves and the block as a tub, and the hoop threw one highlight per facet. The log's wobble still reads in the silhouette, and its surface is carried by the materials: vertical bark furrows with a bump, growth rings about an off-centre pith on the sawn face, and dark radial checks drawn at the same angles the geometry notches. Every material boundary is a hard edge, so the sawn rim stays crisp against the bark.

The haft has its own material slot. It used to share the bark's, which made the hickory handle the darkest wood on the piece.

Falsifiers

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

Flag	Budget violated	Exit
--skip-decimate	LOD1 ratio band	9
--stray-vert	loose vertex count is 0	15
--lift-z	bounding box zmin is 0	16
--fat-haft	haft clearance inside the eye	17
--round-band	hoop bite into the log	18
--float-rivets	rivet seat into the hoop	18
--round-haft	haft section wide over thick	19

--fat-haft thickens the haft across the cheeks only, which is the dimension the eye clearance measures. Scaling the whole oval section grew the knob 16 mm past the bounding box, so it exited 8 instead.

Run

blender --background --python chopping_block.py --
blender --background --python chopping_block.py -- --skip-decimate
blender --background --python chopping_block.py -- --stray-vert
blender --background --python chopping_block.py -- --lift-z
blender --background --python chopping_block.py -- --fat-haft
blender --background --python chopping_block.py -- --round-band
blender --background --python chopping_block.py -- --float-rivets
blender --background --python chopping_block.py -- --round-haft
blender --background --python chopping_block.py -- --output chopping-block.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.

Code	Meaning
0	Success
1	Uncaught exception (FATAL wrapper)
2	argparse / usage
3	Mesh did not build / no UV layer
4	Base triangle count outside range
5	Material count ≠ 4 distinct slots, or a face-count floor missed
6	UVs outside 0..1
7	UV AABB overlap above tolerance
8	World AABB off declared outer size
9	LOD ratio band (--skip-decimate lands here)
10	Framing gate (render path only)
11	Collider triangle count above ceiling
12	Bake did not finish or image has no data
13	Export file missing or empty
14	--output produced no file
15	Mesh hygiene: loose, non-manifold, zero-area, doubles, n-gons, z-fight
16	Not grounded: bounding box zmin off 0
17	Joint fit: shell count, eye clearance, engagement, breakout, bury, inset
18	Contact fit: hoop bite band, haft fouling the log, or a rivet off its seat band
19	Log out of plumb, off its stated real-world size, or a round haft section