OCP Addons

Usage of ocp_addons

• Serializer

  from ocp_addons.serializer import *

  Available functions:

  • serialize_shape()
  • deserialize_shape()
  • serialize_location()
  • deserialize_location()

• Optimized Tessellator

  Will be auto-detected by ocp_vscode

  • Disable optimized teasellator: disable_native_tessellator()
  • Ensable optimized teasellator: enable_native_tessellator()

  Else use from ocp_addons.tessellator import tessellate

Building ocp-addons

Clone the repository

git clone https://github.com/jdegenstein/ocp-addons.git
cd ocp-addons

Create the development environment

micromamba env create -f environment.yml
micromamba activate build-ocp-addons

On Linux for OCP 7.8.1 also install g++ 9.x

sudo add-apt-repository ppa:ubuntu-toolchain-r/ppa -y
sudo apt update
sudo apt install gcc-9 g++-9

Build ocp-addons

Edit pyproject.toml and change dependencies = ["cadquery_ocp==7.8.1.1.post1"] under [project] to the version you want to build ocp-addons for

Then

• Linux (x86_64): make wheel-linux
• MacOS (Apple Silicon): make wheel-macos
• Windows (Intel): make wheel-windows

Test the library

mkdir test
cd test
uv venv -p 3.12
source .venv/bin/activate
uv pip install ../wheelhouse/ocp_addons-1.0.0.rc1-cp312-cp312-macosx_11_0_arm64.whl

This should be installed for cadquery_ocps 7.8.1.1.post1:

Resolved 14 packages in 5ms
Installed 14 packages in 33ms
 + cadquery-ocp==7.8.1.1.post1
 + contourpy==1.3.3
 + cycler==0.12.1
 + fonttools==4.60.1
 + kiwisolver==1.4.9
 + matplotlib==3.10.7
 + numpy==2.3.3
 + ocp-addons==1.0.0.rc1 (from file:///Users/bernhard/Development/CAD/ocp-addons/wheelhouse/ocp_addons-1.0.0.rc1-cp312-cp312-macosx_11_0_arm64.whl)
 + packaging==25.0
 + pillow==11.3.0
 + pyparsing==3.2.5
 + python-dateutil==2.9.0.post0
 + six==1.17.0
 + vtk==9.3.1

Now install build123d and ocp_vscode and run the test:

uv pip install build123d ocp_vscode

cp  -R ../examples ../test.py .  # or similar under Windows
python test.py

Contribution

Windows pybind11 Type Sharing

On Windows, pybind11 uses pointer comparison for std::type_info (unlike Linux/macOS which use string comparison). This causes type mismatch errors when passing OCP types to ocp_addons functions:

RuntimeError: Unable to cast Python instance of type <class 'OCP.OCP.TopoDS.TopoDS_Shape'> to C++ type '?'

Solution: Instead of relying on pybind11's automatic type casting, we directly access the C++ object pointer from the pybind11 instance's internal simple_value_holder[0] field. The utilities are in src/ocp_utils.h:

• ocp_utils::extract_shape(py::handle) - Extract TopoDS_Shape* from OCP Python object
• ocp_utils::extract_location(py::handle) - Extract TopLoc_Location* from OCP Python object
• ocp_utils::create_shape(const TopoDS_Shape&) - Create OCP Python object from C++ shape
• ocp_utils::create_location(const TopLoc_Location&) - Create OCP Python object from C++ location

Usage example

#include "ocp_utils.h"
using namespace ocp_utils;

// Accepting OCP types: use py::object parameter and extract pointer
py::bytes serialize_shape(py::object obj, bool triangles, bool normals) {
    TopoDS_Shape *shape_ptr = extract_shape(obj);
    // ... use *shape_ptr
}

// Returning OCP types: create OCP Python object
py::object deserialize_shape(const py::bytes &buf) {
    TopoDS_Shape shape;
    // ... deserialize into shape
    return create_shape(shape);
}

This approach works because pybind11's instance struct layout places the C++ object pointer at simple_value_holder[0] after PyObject_HEAD, allowing us to bypass the type registry entirely