Cart

A showcase piece, not an example. A procedural two-wheel handcart built on two rails that run on past the bed as shafts, with a pull bar through their tips and two prop legs under them. It has a planked floor, board walls with iron corner straps, and spoked wheels on long naves with iron bands, tyres and washers. 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.

The chassis is stacked from the axle up, and every member bites the one below it by a named depth: axle, bolster, rails, floor planks, walls. The cart stands level on four named supports: two tyres and two legs. Stated size is 1.58 m long, 0.84 m across the axle ends and 0.64 m tall. The wheels are 0.64 m in diameter and the bed is 0.92 × 0.50 m.

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.

Hygiene, supports and joints#

Recomputed from the generated mesh on all three binaries, identical on each.

DECIMATE COLLAPSE triangle counts are not identical across series. 5.2.1 is more aggressive on LOD2, 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-board tone comes from random.Random(TONE_SEED), so it is identical run to run. Export byte counts differ by a few bytes across series (glTF serializer). The gate is "written and non-empty", not a byte count, and the file is removed once measured.

The bake cage is 0.01 m: it only has to cover the chamfer difference between the 3-segment high and the 1-segment low. At 0.08 m it reached past the 74 mm between a side wall and its wheel, so rays from the wall hit the high-poly felloe. The wheel's rim baked onto the board as a black staircase.

Falsifiers#

Each flag breaks one stage so a named budget fails and the piece exits that code. Magnitudes are sized so no earlier gate can steal the failure. The wheel, leg and bed moves stay inside BBOX_TOL, so the AABB gate (exit 8) still passes, and no flag changes the triangle count by more than the band allows.

--lift-z, --float-wheel and --short-props share exit 16 and fail different budgets. --lift-z fails the AABB gate, which fires first. The other two leave the AABB grounded, so only the per-support check can catch them. --sharp-bar replaced a flag that skipped the whole iron chamfer pass. That flag dropped 1200 triangles and tripped the triangle floor (exit 4) instead of the edge budget.

Run#

blender --background --python cart.py --
blender --background --python cart.py -- --skip-decimate
blender --background --python cart.py -- --flush-tyre
blender --background --python cart.py -- --lift-z
blender --background --python cart.py -- --float-wheel
blender --background --python cart.py -- --short-props
blender --background --python cart.py -- --wide-seams
blender --background --python cart.py -- --sink-tyre
blender --background --python cart.py -- --lift-bed
blender --background --python cart.py -- --skew-wheel
blender --background --python cart.py -- --sharp-bar
blender --background --python cart.py -- --low-bake
blender --background --python cart.py -- --output cart.png

Smoke passes none of the falsifier flags and no --output.

Exit codes#

File-local. 9 is a valid check code. 10 is reserved for gallery_framing.check_framing on the --output path.