Scene Setup & Hygiene

The execution model and verification steps are in blender-core.

Procedure

1. Run scripts/scene_audit.py (add --fix purge scale paths only on files you own). It reports units, unapplied/negative scale, default names, objects in the scene root, missing images, orphans and far-off origins.
2. Set units: Metric, Unit Scale 1.0, Length meters. Keep 1.0 even for Unreal/Roblox, because exporters handle the conversion (see blender-export-pipelines).
3. Build the collection layout (below). Every object must be in a named collection, never the scene root.
4. Name everything with the conventions below. Rename after every duplicate or join so no .001 suffixes remain.
5. Set origins: props at the bottom-center (they sit on the ground at Z=0), characters at world origin between the feet, doors/hinges at the pivot.
6. Apply rotation and scale on meshes (Ctrl+A). Keep location unless the asset should export at the origin.
7. Re-run the audit. It's done when issues is empty or every remaining issue is intentional and explained.

Collection layout (one asset per .blend, or one collection per asset)

ASSET_Crate
├── Crate_high      # sculpt / subdiv source (exclude from export)
├── Crate_low       # game mesh(es) SM_Crate, SM_Crate_LOD1..
├── Crate_bake      # cages, bake helpers
├── Crate_collision # UCX_SM_Crate_00 (UE) / Crate-col (Godot)
└── Crate_ref       # reference images/blockout (hide_render)

Use Collection Exporters (4.2+) to define the export once per collection, then re-export with one call:

with bpy.context.temp_override(collection=col):
    bpy.ops.collection.exporter_add(name="IO_FH_gltf2")
ex = col.exporters[-1]; ex.export_properties.filepath = "//export/SM_Crate.glb"
with bpy.context.temp_override(collection=col):
    bpy.ops.collection.exporter_export(index=len(col.exporters) - 1)

bpy.ops.wm.collection_export_all() re-runs every collection exporter.

Naming conventions (Unreal-style, accepted by all engines)

Real-world scale reference (meters)

Door 2.0–2.1 × 0.9 · ceiling 2.4–2.7 · table 0.75 · chair seat 0.45 · counter 0.9 · stair rise 0.18 / tread 0.28 · adult human 1.7–1.8 (eyes 1.6) · car 4.5 × 1.8 × 1.5. Roblox: 1 stud ≈ 0.28 m; default character ≈ 5 studs tall. Wrong scale breaks physics, lighting falloff, DOF and texel density, so check ob.dimensions first.

Linking, appending, overrides

• Append (libraries.load(link=False)) makes a local copy. Use it for one-off reuse.
• Link (link=True) is read-only, updates from the source and is what pipelines use. To edit a linked collection, add a library override: ob.override_hierarchy_create(scene, view_layer, do_fully_editable=False). Only overridable properties (transforms, pose, and anything marked overridable) can change.
• Keep library paths relative (//). Check bpy.data.libraries for broken paths.

Asset libraries

• Mark: ob.asset_mark(); ob.asset_generate_preview(). Metadata goes in ob.asset_data (author, description, license, tags.new("wood"), catalog_id).
• Catalogs live in blender_assets.cats.txt at the library root, one line per catalog: UUID:Path/Sub:Simple Name.
• Register a library with prefs.filepaths.asset_libraries.new(name=..., directory=...). 5.2+: remote libraries via use_remote_url + remote_url. In 5.2 active_asset_library indices are offset by 2 ("All", "Essentials").
• Import method per library: LINK, APPEND, APPEND_REUSE (default; reuses already-appended data).

Hygiene rules

• Purge orphans before shipping (bpy.data.orphans_purge(do_recursive=True)). Use fake users only on purpose.
• Image paths: relative (file.make_paths_relative), or pack for single-file delivery (file.pack_all).
• Never ship multi-user mesh data that has an unapplied per-object scale. Instances are fine, but bake scale before export.
• Hide helpers with hide_render=True and exclude them from export collections; viewport hiding alone isn't enough.
• One active scene per file for delivery. Extra scenes confuse exporters (use_active_scene).