compas-occt 0.1.17

Nanobind wrapper for OCCT

compas_occt

Direct, lean nanobind bindings to the OpenCASCADE Technology (OCCT) 8 geometry kernel, packaged as a drop-in replacement for compas_occ.

compas_occt exposes the exact same public API as compas_occ — NURBS curves and surfaces (OCCNurbsCurve, OCCNurbsSurface), Boundary Representations (OCCBrep and its vertex/edge/loop/face components), booleans, fillet/offset/slice, STEP/IGES/STL/BREP I/O, and the COMPAS plugin factories so compas.geometry.Brep.from_box(...) returns an OCCBrep. The difference is the backend: instead of pythonocc-core, it links OCCT directly through a single compiled extension module, with no pythonocc-core dependency.

Design

• One extension module. All OCCT-backed functions live in a single compas_occt._occt module that links OCCT exactly once. This keeps RTTI/memory consistent across the whole API (required for STEP/IGES) and is far leaner than one OCCT copy per submodule.
• Functional backend + opaque handles. Thin C++ free functions operate on four opaque handle wrappers (Shape, GeomCurve, Geom2dCurve, GeomSurface); the Python classes hold one of these in self._native and delegate.
• Zero-copy data transfer. Bulk coordinate data (mesh tessellation, NURBS control points, curve discretisation) crosses the C++↔Python boundary as numpy arrays that view the C++ buffer directly (no copy). numpy — not jax — is the right tool here: it is the zero-copy buffer-protocol partner for nanobind's ndarray, lightweight, and already a dependency.

Installation

pip install compas_occt

Development install (builds OCCT 8 from source on first build; cached afterwards):

git clone https://github.com/petrasvestartas/compas_occt.git
cd compas_occt
pip install --no-build-isolation -ve ".[dev]"

A C++17 compiler, CMake ≥ 3.15 and Ninja are required for the source build. On Windows, run the command from a Visual Studio "x64 Native Tools" prompt (or after calling vcvars64.bat).

Development with uv

uv gives a fast, reproducible environment. The first build downloads and compiles OCCT 8 (~30–60 min); it is then cached in external/occt, so later builds take a few minutes.

# 1. create the environment (Python >= 3.9; 3.14 is used here)
uv venv --python 3.14

# 2. install the build backend + the runtime and dev/docs dependencies
uv pip install scikit-build-core nanobind cmake ninja
uv pip install -e ".[dev,docs]" --no-build-isolation

# 3. (only to run the viewer examples) install compas_viewer and patch it for Python 3.14
uv pip install compas_viewer
python tools/patch_compas_viewer.py

# 4. run the tests, examples, or docs
uv run pytest tests/ -v
uv run mkdocs serve
uv run python docs/examples/breps/brep_booleans.py

On Windows, run the commands from a Visual Studio "x64 Native Tools" prompt (or after calling vcvars64.bat) so the MSVC toolchain and the .venv are both on PATH.

Python 3.14 note. compas_viewer 2.0.2 crashes on Python 3.14 (it reads self.__annotations__ in a dataclass, which PEP 749 no longer resolves to the class). tools/patch_compas_viewer.py applies the one-line upstream fix; it is idempotent and only needed to run the visualisation examples (the core compas_occt API does not need it).

Usage

from compas.geometry import Box, Point
from compas.geometry import Brep, NurbsCurve

# COMPAS plugin dispatch -> OCC implementation
brep = Brep.from_box(Box(1))
brep.to_step("box.step")

curve = NurbsCurve.from_points([Point(0, 0, 0), Point(3, 6, 0), Point(6, -3, 3), Point(10, 0, 0)])
print(curve.length())

Tests

pip install --no-build-isolation -ve ".[dev]"
python -m pytest tests/ -v

Documentation

Built with mkdocs (pip install -e ".[docs]", then mkdocs serve). Mirrors the compas_occ tutorial, examples, and API reference.

Issue Tracker

Please report bugs on the issue tracker.