ex_cadmpeg

An Elixir wrapper of cadmpeg to bring native CAD files onto the BEAM: SolidWorks .sldprt, CATIA .CATPart, Inventor .ipt/.iam, Creo, NX, Fusion .f3d, FreeCAD .FCStd, Rhino .3dm, IGES, STEP, Creo View .pvz and OpenUSD read into one format-neutral CAD document, and that document written back out. Wrapped via rustler; the engine underneath is pure Rust, so there is no vendor SDK, no OpenCascade and no CAD system installed anywhere.

This build compiles in the STEP codec, so it reads and writes STEP — "Formats are compiled in" below says how a build carries another one.

{:ok, document} = Cadmpeg.open("bracket.step")

{:ok, report} = Cadmpeg.Document.write(document, "step", "bracket-strict.step")

report is the export report: what the encoder wrote, and what it could not carry. A conversion that loses something says so.

Everything is in the file's own units, in its own coordinates, and the same file always gives the same document.

What it answers

A document is parsed once: open/1 answers a handle and every later call takes it, so asking three questions about one part reads it once. The handle is a Rust resource — it serves every process on its node and cannot be sent to another node, because the document is local.

Formats are compiled in

cadmpeg's codecs are Rust features. This package compiles in the STEP codec, so formats/0 lists STEP as an input and as an output and does not pretend to read a .sldprt. Turning on another codec is a line in native/cadmpeg_nif/Cargo.toml:

cadmpeg-registry = { version = "=0.6.11", default-features = false, features = ["step", "sldprt"] }

Each codec is its own crate, so a build carries only the formats it needs. Which formats a build has is a fact about the binary in the VM, not a promise.

As an MCP server

mix cadmpeg.mcp speaks the Model Context Protocol over stdio, so an assistant can ask about a file directly:

{"mcpServers": {"cadmpeg": {"command": "mix", "args": ["cadmpeg.mcp"]}}}

Three tools: cadmpeg_formats — what this build reads and writes — cadmpeg_inspect, which answers the decode report rather than just "it opened", and cadmpeg_convert, which writes the file you name and reports what the target could not carry.

Install

def deps do
  [{:ex_cadmpeg, "~> 0.1"}]
end

The Rust engine is compiled when the dependency is: building wants a Rust toolchain (1.88 or later, which is what cadmpeg itself requires), and running wants none.

Limits, said out loud

• The document is read-only here. cadmpeg's IR can be edited; this binding does not expose editing yet, and to_json/1 is the way to a document a caller can change.
• "It opened" is not "it opened faithfully". cadmpeg scores each format on a ladder, and the decode report carries the losses; a caller that ignores the report has a document of unknown fidelity rather than an error.
• Assemblies are documents too — parts, occurrences and placements are in the IR — but walking them is not exposed yet.
• A refusal is not retried at a laxer policy. A stricter or looser policy changes the answer, so Cadmpeg.Error says what was refused and the caller decides.

Licence

MPL-2.0 (LICENSE). The engine it binds is Apache-2.0 and stays a dependency; NOTICE says what came from where.