park-bench

Park bench

A showcase piece, not an example. A procedural wrought-iron park bench (round-bar legs bent in one piece from scroll toe to post, with the rear pair bending again into a reclined back; a slatted seat and back; armrests on quarter-round brackets), then the shipped pipeline: unique-cell UVs, a Cycles high-to-low normal bake, an LOD chain, a convex collider and a Unity glTF export.

Every leg is one bar swept along one path: a quarter-circle toe about (hy ± R, R), tangent to the post where it meets it, then the post, and at the back a 12° bend into the upright that carries the back slats. The seat slats bear on the side rails, the back slats on the uprights, and each armrest on its arm bar and the front leg's tenon, each by a named bite. The H-stretcher meets the legs at the shared stations (HX, HY, SEAT_Z, ARM_Z, SCROLL_R, BACK_TOP).

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). Hygiene combinatorics match examples/mesh-hygiene-audit (copied, not imported).

Intended size: 1.40 m sitting width, 0.50 m seat depth, 0.43 m seat height, 0.64 m arm height, back reclined 12°. Outer AABB 1.295 × 0.632 × 0.887 m.

Budgets

Declared as named constants. Every gate recomputes its value 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	2900–3700	3272 / 3272 / 3272
LOD1 ratio	0.32–0.62 of base	0.5000 / 0.5000 / 0.5000
LOD2 ratio	0.10–0.35 of base	0.2194 / 0.2194 / 0.2194
Materials	exactly 2 distinct, ≥48 metal, ≥24 wood	2 slots, 1008 metal / 756 wood
UVs	in 0..1, AABB overlap ≤ 1e-5	in range, overlap 0
Outer AABB	(1.295, 0.632, 0.887) m ± 0.015	(1.2945, 0.6316, 0.8870), zmin 0
Collider tris	≤ 180	64
Export	written, size > 0	245620 / 245620 / 245604 bytes

Base triangles rose from 2520 to 3272 in the second quality pass. The square posts and 6-gon scroll tubes became 8-gon round bar swept along each leg, the back gained its bend, and armrest brackets were added. The band was re-fitted around the measurement and narrowed from 2200–4200.

DECIMATE COLLAPSE triangle counts are not guaranteed identical across series — the gate is a ratio band, not an exact count. This mesh matched on 4.5.11 / 5.1.2 / 5.2.1. Bake pixels are stochastic; the gate is has_data plus operator FINISHED, not byte-identity. Slat widths are closed-form and plank tones are seeded, so repeated runs on one binary print identical measurements. Export byte counts differ by 16 B on 5.2.1 (glTF serializer), not a gated axis.

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
Named toes	4, each zmin ≤ 0.002	4, 0.00000

Joint fit, bearing and form

Axis	Declared	Measured (all three)
Stretcher-to-leg BVH gap	≤ 0.008 m	0.00111
Slat-to-leg BVH gap	≤ 0.008 m	0.00016
Seat span vs 2·hx	± 0.08 m	1.2720 vs 1.260
Bearing bite (exit 20): 7 seat slats × 2 side rails, 5 back slats × 2 uprights, 2 armrests × (front leg + arm bar), overlap depth either way round	28 bites, each ≥ 0.0015 m	28, min 0.00201
Legs in one piece (exit 21): the shell under each toe station is a leg reaching the seat	4	4
Back recline (exit 19): each upright, from a low and a high slab centroid	9°–16°	12.00° / 12.00°

The bearing bite takes the overlap either way round. A round rail has vertices only at its end rings, so under a mid-span slat it is the slat's corner that sits in the rail, not a rail vertex in the slat.

Falsifiers

Each violates one named budget. All 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
--short-feet	named toes plant at z=0	16
--float-stretcher	stretcher-to-leg BVH gap	17
--gap-slats	slat-to-leg BVH gap	18
--narrow-seat	seat span vs 2·hx	19
--upright-back	back recline band (measured 0.00°)	19
--float-slats	bearing bite (seat slats 6 mm up; measured −0.00354)	20
--split-feet	legs in one piece (measured 0 of 4)	21

--short-feet lifts only the outward toe verts. After recentring, the bottom of the scroll is the AABB zmin, so the AABB gate would still pass. The named-toe stations fail. --split-feet restores the first build: each foot is an arc stopped short of its post, and each post starts at the arc's top. The toes still ground and every gap budget still passes. Only the one-piece budget sees the 14 mm of daylight. --upright-back keeps the back top where it was, so the envelope does not move.

Run

blender --background --python park_bench.py --
blender --background --python park_bench.py -- --skip-decimate
blender --background --python park_bench.py -- --stray-vert
blender --background --python park_bench.py -- --lift-z
blender --background --python park_bench.py -- --short-feet
blender --background --python park_bench.py -- --float-stretcher
blender --background --python park_bench.py -- --gap-slats
blender --background --python park_bench.py -- --narrow-seat
blender --background --python park_bench.py -- --upright-back
blender --background --python park_bench.py -- --float-slats
blender --background --python park_bench.py -- --split-feet
blender --background --python park_bench.py -- --output bench.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. 20 and 21 are this piece's own.

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 ≠ 2 distinct slots, or wood/metal faces missing
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	Hygiene (--stray-vert lands here)
16	Grounded zmin / named toes (--lift-z, --short-feet)
17	Stretcher-to-leg gap (--float-stretcher)
18	Slat-to-leg gap (--gap-slats)
19	Seat span (--narrow-seat) or back recline (--upright-back)
20	Bearing bite on slats and armrests (--float-slats)
21	Legs not bent in one piece from toe to seat (--split-feet)