Building OpenCASCADE for iOS/macOS

This guide explains how to build OCCT as static libraries for use with OCCTSwift.

Prerequisites

macOS 13+ (Ventura or later)
Xcode 15+ with Command Line Tools
CMake 3.20+ (brew install cmake)
About 10GB free disk space (source + build)

Quick Start

cd /path/to/OCCTSwift
./Scripts/build-occt.sh

This will:

Download OCCT 8.0.0-rc5 source from GitHub tag V8_0_0_rc5
Build for iOS (arm64) and iOS Simulator (arm64)
Build for macOS (arm64)
Create Libraries/OCCT.xcframework (~568MB with all 3 slices)

Manual Build Steps

1. Download OCCT Source

cd /path/to/OCCTSwift/Libraries

# Clone from GitHub (recommended for RC releases)
git clone --depth 1 --branch V8_0_0_rc4 \
    https://github.com/Open-Cascade-SAS/OCCT.git occt-src

# Or for stable releases, use the official repo:
# git clone --depth 1 --branch V8_0_0 \
#     https://git.dev.opencascade.org/repos/occt.git occt-src

2. Configure CMake for iOS

Create a toolchain file ios.toolchain.cmake:

set(CMAKE_SYSTEM_NAME iOS)
set(CMAKE_OSX_ARCHITECTURES arm64)
set(CMAKE_OSX_DEPLOYMENT_TARGET 15.0)
set(CMAKE_XCODE_ATTRIBUTE_ONLY_ACTIVE_ARCH NO)

# Ensure we build static libraries
set(BUILD_SHARED_LIBS OFF CACHE BOOL "" FORCE)

# Find the iOS SDK
execute_process(
    COMMAND xcrun --sdk iphoneos --show-sdk-path
    OUTPUT_VARIABLE CMAKE_OSX_SYSROOT
    OUTPUT_STRIP_TRAILING_WHITESPACE
)

3. Build for iOS Device

mkdir -p occt-build-ios && cd occt-build-ios

cmake ../occt-src \
    -DCMAKE_TOOLCHAIN_FILE=../ios.toolchain.cmake \
    -DCMAKE_BUILD_TYPE=Release \
    -DCMAKE_INSTALL_PREFIX=../occt-install-ios \
    -DBUILD_SHARED_LIBS=OFF \
    -DBUILD_MODULE_Draw=OFF \
    -DBUILD_MODULE_Visualization=OFF \
    -DUSE_FREETYPE=OFF \
    -DUSE_FREEIMAGE=OFF \
    -DUSE_RAPIDJSON=OFF \
    -DUSE_TBB=OFF \
    -DUSE_VTK=OFF \
    -DUSE_OPENGL=OFF

cmake --build . --config Release --parallel $(sysctl -n hw.ncpu)
cmake --install .

4. Build for iOS Simulator

mkdir -p occt-build-sim && cd occt-build-sim

# Modify toolchain for simulator
cmake ../occt-src \
    -DCMAKE_SYSTEM_NAME=iOS \
    -DCMAKE_OSX_ARCHITECTURES=arm64 \
    -DCMAKE_OSX_SYSROOT=$(xcrun --sdk iphonesimulator --show-sdk-path) \
    -DCMAKE_OSX_DEPLOYMENT_TARGET=15.0 \
    -DCMAKE_BUILD_TYPE=Release \
    -DCMAKE_INSTALL_PREFIX=../occt-install-sim \
    -DBUILD_SHARED_LIBS=OFF \
    -DBUILD_MODULE_Draw=OFF \
    -DBUILD_MODULE_Visualization=OFF \
    -DUSE_FREETYPE=OFF \
    -DUSE_FREEIMAGE=OFF \
    -DUSE_RAPIDJSON=OFF \
    -DUSE_TBB=OFF \
    -DUSE_VTK=OFF \
    -DUSE_OPENGL=OFF

cmake --build . --config Release --parallel $(sysctl -n hw.ncpu)
cmake --install .

5. Build for macOS

mkdir -p occt-build-macos && cd occt-build-macos

cmake ../occt-src \
    -DCMAKE_OSX_ARCHITECTURES=arm64 \
    -DCMAKE_OSX_DEPLOYMENT_TARGET=12.0 \
    -DCMAKE_BUILD_TYPE=Release \
    -DCMAKE_INSTALL_PREFIX=../occt-install-macos \
    -DBUILD_SHARED_LIBS=OFF \
    -DBUILD_MODULE_Draw=OFF \
    -DBUILD_MODULE_Visualization=OFF \
    -DUSE_FREETYPE=OFF \
    -DUSE_FREEIMAGE=OFF \
    -DUSE_RAPIDJSON=OFF \
    -DUSE_TBB=OFF \
    -DUSE_VTK=OFF \
    -DUSE_OPENGL=OFF

cmake --build . --config Release --parallel $(sysctl -n hw.ncpu)
cmake --install .

6. Create XCFramework

# Combine all static libraries into single fat library per platform
# (OCCT produces many .a files, we need to combine them)

# For each platform, create combined library:
libtool -static -o libOCCT-ios.a \
    occt-install-ios/lib/*.a

libtool -static -o libOCCT-sim.a \
    occt-install-sim/lib/*.a

libtool -static -o libOCCT-macos.a \
    occt-install-macos/lib/*.a

# Create XCFramework
xcodebuild -create-xcframework \
    -library libOCCT-ios.a -headers occt-install-ios/include \
    -library libOCCT-sim.a -headers occt-install-sim/include \
    -library libOCCT-macos.a -headers occt-install-macos/include \
    -output OCCT.xcframework

Required OCCT Modules

For OCCTSwift, we need these modules:

Module	Purpose	Required
TKernel	Core utilities	Yes
TKMath	Math primitives	Yes
TKG2d	2D geometry	Yes
TKG3d	3D geometry	Yes
TKGeomBase	Geometric entities	Yes
TKGeomAlgo	Geometric algorithms	Yes
TKBRep	B-Rep structures	Yes
TKTopAlgo	Topological algorithms	Yes
TKPrim	Primitives	Yes
TKShHealing	Shape repair	Yes
TKBO	Boolean operations	Yes
TKFillet	Fillet/chamfer	Yes
TKOffset	Offset/shell	Yes
TKMesh	Meshing	Yes
TKSTEP	STEP export	Yes
TKSTL	STL export	Yes
TKBinXCAF	Persistent storage	Optional
TKXCAF	Assembly framework	Optional

Build Options Explained

# Disable modules we don't need
-DBUILD_MODULE_Draw=OFF          # Interactive test harness
-DBUILD_MODULE_Visualization=OFF # OpenGL visualization (using SceneKit instead)

# Disable optional dependencies
-DUSE_FREETYPE=OFF    # Font rendering (not needed)
-DUSE_FREEIMAGE=OFF   # Image loading (not needed)
-DUSE_RAPIDJSON=OFF   # JSON (not needed for core)
-DUSE_TBB=OFF         # Intel threading (iOS has GCD)
-DUSE_VTK=OFF         # VTK visualization (not needed)
-DUSE_OPENGL=OFF      # Direct OpenGL (using SceneKit)

Troubleshooting

“No CMAKE_CXX_COMPILER could be found”

Install Xcode Command Line Tools:

xcode-select --install

Undefined symbols for architecture arm64

Make sure all libraries are built for the same architecture:

lipo -info libTKernel.a  # Should show: arm64

Build fails with C++17 errors

Ensure CMake uses C++17:

set(CMAKE_CXX_STANDARD 17)
set(CMAKE_CXX_STANDARD_REQUIRED ON)

Library too large

The full OCCT build can be 500MB+. To reduce size:

Build only required modules (see table above)
Strip debug symbols: strip -S libOCCT.a
Use -Os optimization: -DCMAKE_CXX_FLAGS="-Os"

Simulator build fails

Ensure you’re using the correct SDK:

xcrun --sdk iphonesimulator --show-sdk-path

Verifying the Build

Check library contents

# List symbols
nm -g OCCT.xcframework/ios-arm64/libOCCT.a | grep BRepPrimAPI

# Check architectures
lipo -info OCCT.xcframework/ios-arm64/libOCCT.a

Test in Xcode

Create new iOS app project
Drag OCCT.xcframework into project
Add simple test code:

// In a .mm file
#include <BRepPrimAPI_MakeBox.hxx>

void testOCCT() {
    BRepPrimAPI_MakeBox box(10, 20, 30);
    TopoDS_Shape shape = box.Shape();
    // If this compiles and runs, OCCT is working
}

Automated Build Script

The actual build script is at Scripts/build-occt.sh. It handles:

Downloading OCCT source (GitHub for RCs, official repo for stable releases)
Building for all 3 platforms with proper cross-compilation flags
Combining 48 static libraries per platform into a single fat library
Creating the XCFramework with 7,005 headers

To update the OCCT version, edit the variables at the top of the script:

OCCT_VERSION="8.0.0"
OCCT_RC="rc4"       # Clear this for stable releases

Make executable:

chmod +x Scripts/build-occt.sh

Alternative: Pre-built Binaries

If you don’t want to build OCCT yourself:

Open Cascade Commercial: Contact sales@opencascade.com for pre-built iOS libraries
Community Builds: Check OCCT forum for community-provided builds
Build Service: Use GitHub Actions to build (see .github/workflows/build-occt.yml)