Step 2 Blend

A Blender addon that imports STEP and STP CAD files using OpenCASCADE.

Blender doesn't ship with a STEP importer. Step 2 Blend brings production-quality CAD import to the platform: analytic NURBS normals, real materials, mesh-instance dedup for assemblies, and non-destructive re-import that lets you refresh a CAD model without losing materials, modifiers, or transforms.

Install

1. Download the zip for your platform from the latest release:
   • Step2Blend-vX.Y.Z-mac-arm64.zip for macOS (Apple Silicon)
   • Step2Blend-vX.Y.Z-windows-x64.zip for Windows (x86_64)
2. In Blender: Edit > Preferences > Add-ons > Install, then pick the zip.
3. Tick the Step 2 Blend checkbox to enable it.
4. Use File > Import > STEP (.step, .stp).

The bundled OpenCASCADE 7.9 runtime ships inside the zip, so you don't need to install OCCT separately.

First-launch warnings

Both zips are currently unsigned. On macOS, Gatekeeper might say "Apple cannot check it for malicious software" the first time the binary runs. Right-click the addon zip and choose Open if needed. On Windows, SmartScreen might show "Microsoft Defender prevented an unrecognised app". Click More info then Run anyway. Codesigning is on the roadmap.

Requirements

• Blender 3.0 or later
• macOS 12+ on Apple Silicon, or Windows 10/11 x86_64

Linux isn't supported in the official builds yet. The CMake project should compile against a Homebrew-style Linux OCCT, but you'd need to write your own bundle script. PRs welcome.

Quick start

1. Enable the addon in Preferences.
2. File > Import > STEP (.step, .stp) and pick a CAD file.
3. The status bar shows progress while the converter runs in the background. Esc cancels.
4. When the import lands, materials carry friendly names like S2B Silver or S2B Dark Blue. Surfaces shade smoothly even at coarse triangle counts.
5. When a CAD revision arrives, re-import the same file. The addon detects the existing objects and refreshes their geometry without touching your materials, modifiers, animation, or parenting.

Features

• Analytic NURBS normals. Curved surfaces shade smoothly even at coarse triangle counts. No Weighted Normals modifier, no manual smoothing groups.
• Friendly material naming. STEP file colours import as S2B Silver, S2B Dark Blue, etc., not Material_3. The curated colour table covers around 80 named tones; everything else falls back to clean hex.
• Per-project material database. Author your materials once, save them to a .blend, and apply them automatically to every STEP import in the project.
• Non-destructive re-import. When CAD revisions land, one click refreshes the geometry on existing objects while preserving your materials, modifiers, animation, and parenting.
• Mesh-instance dedup. Assemblies with dozens of identical hardware parts collapse to a single shared mesh datablock automatically.
• Assembly hierarchy preservation. Proper STEP assemblies preserve their structure as parent-child relationships in the outliner.
• Auto-detect file units. Reads the unit declaration from the STEP header. There's an override for the rare mis-tagged file.
• Async import with status feedback. Blender stays responsive while the converter does its work. Status bar shows progress, Esc cancels.

Repository layout

step2blend/
├── step_importer/          # Blender addon (Python). Ships verbatim into
│   ├── __init__.py         # the user's addon zip.
│   ├── material_db.py
│   └── icons/S2B_Logo.png
├── step2glb/               # The C++ converter. CMake plus OCCT 7.9.x.
│   ├── step2glb.cpp        # ~400 lines: STEP read, tessellate with
│   │                       # BRepMesh, analytic NURBS normals, GLB write.
│   ├── CMakeLists.txt
│   ├── vcpkg.json          # Windows: declares opencascade dependency.
│   ├── bundle_macos.sh     # macOS: gathers dylibs, rewrites rpaths,
│   │                       # ad-hoc codesigns.
│   ├── bundle_windows.ps1  # Windows: walks dumpbin /dependents and
│   │                       # copies DLLs alongside the EXE.
│   ├── test.stp            # Generic test fixture
│   └── test2.stp           # Five named colors
├── scripts/
│   └── ship-mac.sh         # macOS one-shot: cmake build, bundle,
│                           # install, zip.
└── .github/workflows/
    ├── build-mac.yml       # CI: builds Mac zip on every push to main
    │                       # and every v* tag.
    └── build-windows.yml   # CI: builds Windows zip on every push to
                            # main and every v* tag.

step_importer/bin/ and step_importer/lib/ are git-ignored. They get regenerated by scripts/ship-mac.sh on every build.

Building from source

macOS

Prereqs: Xcode CLT, CMake, OCCT 7.9.x via Homebrew.

brew install cmake opencascade
git clone https://github.com/BlueLazyFish/step2blend.git
cd step2blend
./scripts/ship-mac.sh

That single script rebuilds step2glb, runs the bundle script, copies bin and lib into step_importer/, and refreshes the release zip at the repo root. Pass --install to also drop the addon into your live Blender addons folder.

Windows

The Windows binary is built by GitHub Actions, so no local Windows machine is required to ship a release. Tag a v* ref and the workflow at .github/workflows/build-windows.yml produces a release zip and attaches it to the matching GitHub Release.

If you want to iterate locally on Windows, install Visual Studio 2022 Build Tools and vcpkg, then:

cd step2glb
vcpkg install --triplet x64-windows
cmake -S . -B build `
  -DCMAKE_TOOLCHAIN_FILE=$env:VCPKG_INSTALLATION_ROOT/scripts/buildsystems/vcpkg.cmake `
  -DVCPKG_TARGET_TRIPLET=x64-windows
cmake --build build --config Release --parallel
pwsh ./bundle_windows.ps1

The first CI Windows build takes around 45 minutes while vcpkg compiles OCCT from source. Subsequent builds hit the GitHub Actions cache and finish in around 5 minutes.

Roadmap

• Codesigning for both platforms (clears the Gatekeeper / SmartScreen warning)
• Linux build script + CI
• Material database UI improvements

If any of those land high on your list, open an issue.

Contributing

Issues and pull requests welcome. A few conventions and past gotchas worth knowing if you're touching the C++ converter:

• Don't reverse normals manually in compute_analytic_normals(). OCCT's RWMesh_FaceIterator::NormalTransformed() already calls aNorm.Reverse() for TopAbs_REVERSED faces. Reversing here too produces a double-flip and mirrored bodies render half-dark.
• Build a fresh outDoc for monolithic compounds. Never mutate the source XCAF doc. XCAFDoc_ShapeTool::RemoveShape is unreliable; the GLB writer can still see "removed" labels.
• Copy length unit explicitly to any new XCAF doc with XCAFDoc_DocumentTool::SetLengthUnit(outDoc, srcUnit). Forgetting this lets the writer treat coords as metres, which produces 1000x too-large imports.
• _force_smooth_shading() in the addon must run after the gltf import. Blender flags around 3% of polygons flat-shaded based on coincidental normal alignment, which discards the analytic split normals.

License

Step 2 Blend is licensed under the GNU General Public License v3.0 or later (GPL-3.0-or-later). See LICENSE for the full text.

Bundled third-party components (notably Open CASCADE Technology, which is LGPL-2.1) retain their original licences. See LICENSES-third-party.txt for the full attribution.

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Built by Louis Rist. www.mrrist.com