watchtower

Watchtower

A showcase piece, not an example. Procedural timber lookout (corner posts through a plank platform, lower-bay X-braces, hatch and ladder whose stiles plant at Z=0, coursed shake roof over a solid cone, mitered iron collars and shoes) then the shipped pipeline: unique-cell UVs, Cycles high-to-low normal bake, LOD chain, convex collider, Unity glTF export.

The first quality pass left the platform floating: there were no bearers at deck level, the two joists stopped 0.19 m short of the front edge and at the back edge in the air, the plank ends hung past nothing at the sides, and the side guardrails stopped 0.30 m short of the front posts for a "hatch clearance" the hatch never needed (it sits at the centre of the front edge). Four deck girts now tenon into the posts under the planks, the joists run girt to girt, the hatch trims end on the front girt, and the side rails span post to post like the back rail. Two budgets assert it. Wood carries grain and a tone per piece, the shakes are weathered, and the iron is rusted rather than chrome.

The old roof was a wood U with incomplete shake coverage; rails showed through the eave. The cone plus non-overlapping courses close the pyramid. Shoes are added after the zmin snap so a bevel undershoot cannot lift them.

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	6200–8200	6840 / 6840 / 6840
LOD1 ratio	0.32–0.62 of base	0.5000 / 0.5000 / 0.5000
LOD2 ratio	0.10–0.35 of base	0.2199 / 0.2199 / 0.2187
Materials	exactly 3 distinct; ≥80 metal, ≥40 roof faces	3 slots; 300 metal, 126 roof
UVs	in 0..1, AABB overlap ≤ 1e-5	in range, overlap 0
Outer AABB	(1.594, 1.594, 2.973) m ± 0.01	(1.5940, 1.5940, 2.9731), zmin 0
Collider tris	≤ 180	150
Export	written, size > 0, removed after measuring	494508 / 494508 / 494492 bytes

Base triangles rose from 5220 to 6408 in the first quality pass (a taller eave-true roof and coursed shakes) and to 6840 in the second (four deck girts), not hidden interior faces.

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 supports: 4 iron shoes	each zmin ≤ 1e-3	4, shoe_z 0.00000
Plan	1.56 m eave × 2.97 m height ± 0.08 / ± 0.28	1.5940 × 2.9731

Joint fit and seat

Axis	Declared	Measured (all three)
Rail-to-post engage (back rails)	≥ 0.012 m	0.0180
Side-rail engage: 4 side rails, each tenoned into the front and the back post	≥ 0.012 m at both ends	0.0180
Deck bearing: 4 deck girts; each of 2 joists inside the front and the back girt	≥ 0.012 m at both ends	0.0315
Girt-collar standoff	≤ 0.010 m	0.00200
Post plumb (XY drift)	≤ 0.010 m	0.00000

DECIMATE COLLAPSE triangle counts are not identical across series — 5.2.1 is leaner on LOD2. The gate is 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; the per-piece wood tone is drawn from a seeded random.Random(TONE_SEED), the same every run. Export byte counts differ by 16 B on 5.2.1 (glTF serializer), not a gated axis.

Falsifiers

Each violates one named budget. Every falsifier was 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-shoes	named shoe supports at Z=0	16
--short-rails	rail-to-post joint fit	17
--open-sides	side-rail engage (front ends stop 0.30 m short again: −0.2460 m)	17
--short-joists	deck bearing (joists back to the old span, girts kept: −0.1625 m)	17
--float-band	iron-collar seat	18
--rake-posts	post plumb	19

Run

blender --background --python watchtower.py --
blender --background --python watchtower.py -- --skip-decimate
blender --background --python watchtower.py -- --stray-vert
blender --background --python watchtower.py -- --lift-z
blender --background --python watchtower.py -- --short-shoes
blender --background --python watchtower.py -- --short-rails
blender --background --python watchtower.py -- --open-sides
blender --background --python watchtower.py -- --short-joists
blender --background --python watchtower.py -- --float-band
blender --background --python watchtower.py -- --rake-posts
blender --background --python watchtower.py -- --output tower.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 ≠ 3 distinct slots, or metal/roof 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	Mesh hygiene: loose, non-manifold, zero-area, doubles, n-gons, z-fight
16	Not grounded: bounding box zmin off 0, or a named shoe floats
17	Joint fit: rail-to-post engage, side-rail engage, or deck bearing
18	Seat: girt-collar standoff
19	Post plumb or plan off the stated real-world size