step2glb

Convert STEP CAD files to GLB for the web. The output is deterministic.

Features

• Reads STEP assemblies and writes Draco-compressed GLB files.
• Gives every occurrence a stable ID. A name change does not change the ID.
• Records the semantic role and the material field for each part.
• Enforces limits on depth, occurrences, triangles, vertices, and bytes.
• Reads native GLB assemblies and re-exports them with the same metadata.
• Runs as a CLI or as a stdin worker.

Install

npm install step2glb

Node.js 22 or later is required.

Usage

Inspect an assembly:

step2glb inspect model.step

The command prints a manifest as JSON. The manifest lists the root, the assemblies, and the parts. The field units is m.

Build a GLB file:

step2glb build model.step --out model.glb

Apply mappings from a file:

step2glb build model.step --out model.glb --mapping mapping.json

A mapping file is a JSON array:

[
  {
    "occurrence_id": "occ_...",
    "display_name": "Body",
    "semantic_role": "body",
    "material_field_key": "body_color",
    "surface_finish": "smooth"
  }
]

Run the worker:

echo '{"version":1,"operation":"inspect","source_path":"model.step","source_sha256":"..."}' | step2glb worker

The worker reads one request on stdin and writes one response on stdout. Use it to convert files in a sandbox.

Units

step2glb requests meters from the STEP reader. The manifest states the unit as m. The GLB file also uses meters.

Limits

Item	Limit
Assembly depth	32
Occurrences	512
Triangles	2000000
Vertices	2000000
Output file	16 MiB
Manifest	2 MiB

GLB metadata

Every node carries extras with these fields:

Field	Meaning
step2glb_occurrence_id	The stable occurrence ID.
step2glb_definition_id	The stable definition ID. Parts that share a mesh share this ID.
step2glb_display_name	The display name.
step2glb_semantic_role	The role of the part.
step2glb_material_field_key	The material field for the part.
step2glb_surface_finish	The surface finish.
source_name	The name in the source file.

An occurrence with the role ignore is not exported.

Roles

unassigned, body, lid, insert, hardware, decoration, other, ignore.

Surface finishes

inherit, fuzzy, smooth.

Determinism

The same source and the same mappings produce the same bytes. Occurrence IDs depend on the hierarchy path, not on names. Draco compression uses 24-bit positions and 12-bit normals.

Development

npm ci
npm test

License

MIT. See LICENSE. The third-party licenses are in THIRD_PARTY.md.