# n3xd-ocp

Hand-written [nanobind](https://github.com/wjakob/nanobind) bindings for the
OpenCASCADE (OCCT) geometry kernel, covering exactly the surface the N3XD CAD
backend uses — roughly 140 symbols across 48 `OCP.*` modules, not all of OCCT.

The package installs as a top-level `OCP`, so it is a drop-in replacement for
`cadquery-ocp-novtk` and the app's 437 import sites stay untouched.

Status: **not started.** The plan lives in the app repo at
`docs-private/reference/roadmap.md` (Phase 10), with the binding-layer
background in `docs-private/architecture/geometry-kernel.md`.

## Why

`cadquery-ocp` lags OCCT (it wraps 7.9.3; OCCT 8.0 shipped 2026-05), builds
Windows and macOS wheels we never use, and until recently forced a 638 MB VTK
dependency into the image. Binding *call* overhead is not a bottleneck — the
CAD hotspots live inside the C++ kernel — so this exists for version velocity,
footprint, and two defects that a binding we control prevents by construction:

- OCCT sub-shapes are returned **by value**, so a wrapper can never alias a
  `TShape` whose owner has died (this segfaulted a process-global face memo).
- Executing constructors (the two-argument `BRepAlgoAPI_*` forms) are **not
  bound**, so the double-execution footgun is unrepresentable.

It also releases the GIL around kernel calls and ships type stubs, neither of
which upstream does.

## Build

OCCT is compiled once into a builder image and reused; it is never built on the
production host (4 cores, and a kernel build is multi-hour). Wheels are built
here on a dev box and published to the Gitea package registry:

```bash
uv publish --publish-url https://git.stroblme.de/api/packages/N3XD/pypi dist/*.whl
```

Credentials go in `.secrets` (gitignored) as `UV_PUBLISH_USERNAME` /
`UV_PUBLISH_PASSWORD`. Consumers read anonymously — the package is public — via
`https://git.stroblme.de/api/packages/N3XD/pypi/simple/`.

Versions are `<occt-version>.N`, so the kernel a wheel wraps is readable from
its version alone. The registry refuses to republish a version; iteration
builds therefore carry a `.devN` suffix and are the only ones the registry's
cleanup rule collects.