prop-origin-transform

Prop Origin Transform

A runnable example that builds a street utility pedestal with a bolted conduit accessory and proves the origin / scale-apply / MPI contract a prop pipeline relies on before engine ingest — following operators and the data-API parenting idiom from parent-inverse-orrery.

Pipeline arc neighbors: MPI + stale matrix_world in parent-inverse-orrery, export origin sensitivity in gltf-export-roundtrip, collision bounds in collision-hull-proxy, and mesh hygiene in mesh-hygiene-audit. Origin at the base center with applied scale is what placement and physics ingest assume.

Scope: this witnesses the bpy-level contract a prop pipeline relies on (post-bake scale exactly (1,1,1), local bbox min.z == 0, world bbox unchanged, MPI so a parented accessory does not teleport). It is not an engine exporter — it proves the transform properties such an asset must have.

What it witnesses:

• Stale matrix_world. After a location edit, matrix_world is unchanged until view_layer.update() (same half of the orrery contract).
• Scale apply via data API. Non-uniform scale baked into verts; obj.scale == (1,1,1) exactly afterward.
• Origin at base center. Local bbox min.z == 0, XY centered; world AABB delta across the bake is 0 (gate 1e-5).
• Bare-parent trap. Parenting the accessory without MPI jumps it (~0.43 m measured); setting matrix_parent_inverse restores world location (err ~3e-8).

What each check catches on failure: skipping scale apply leaves non-identity scale; skipping origin bake leaves min.z ≈ -0.756; skipping MPI leaves the accessory teleported.

Version witness: byte-identical numbers on Blender 4.5.11 LTS and 5.1.2.

The render is a dual panel: left TRAP (bare parent — flanged conduit teleports off a deep shadowed mount socket) vs right MPI KEEP (same metal fitting seated in the socket), with emissive origin markers at each pedestal's base. Accessory and pedestal stay in one material family so displacement — not color — carries the proof. Check closed forms are unchanged.

Run

blender --background --python prop_origin_transform.py --
blender --background --python prop_origin_transform.py -- --output origin.png
blender --background --python prop_origin_transform.py -- --output origin.png --engine cycles

Exits non-zero on failure. The blender-smoke workflow runs the check on Blender 4.5 LTS and 5.1. The --output render path additionally measures framing against the Layer 1 band via examples/gallery_framing.py (exit 10 on violation) before writing the still.