ROS2 on iOS

Build ROS2 stack for iOS software development.

This valuable experience allows us to build and run ROS2 on Mac including graphical tools such as RVIZ as well. Even better, you can simply download our release, add some environment variables and run.

For the impatient: Instead of building ROS2 from source (see below), you can download our prebuilt libs and extract it. Then make a symlink ros2 pointing to the extracted ros2_$PLATFORM where we can find the ROS2 lib and include headers

ln -s PATH_TO_EXTRACTED_ros2_$PLATFORM ros2

You should of course change the symlink target when switching between building for real iPhone, simulator and Mac Catalyst. Now we can run the demo application which ports the official example: Run the app on two simulator instances, click on Start publishing on one and Start listening on the other.

Note: To run Mac Catalyst app on your macOS machine, you need to sign the app with your development signing certificate.

Main guides:

• Build ROS2 from source on macOS
• Cross compiling ROS2
• ROS2 Architecture

Tools preparation

We are going to need

• CMake 3.23 until this issue is sorted out
• Python 3.10
• Xcode + Command Line tools

installed. All subsequent shell commands are to be done at $REPO_ROOT.

Also, create a Python virtual environment for ease of package installation

python3 -m venv ros2PythonEnv
source ros2PythonEnv/bin/activate
python3 -m pip install -r requirements.txt

If you have other environment management such as Anaconda, remember to DEACTIVATE them.

Source and workspace preparation

1. We are going to disable most packages and add back only those that are necessary. To do that, I deviate from the guide to get the sources into unused_src instead

   mkdir unused_src
   vcs import unused_src < ros2.repos
   touch unused_src/AMENT_IGNORE       # So that colcon will not find packages in unused_src

   Note: The better method is to use colcon's --packages-up-to.

2. Move the minimal packages ros2/rcl, ros2/rmw, ros2/rosidl to src to start

   mkdir -p src/ros2
   mv unused_src/ament src/
   mv unused_src/eProsima src/
   mv unused_src/ros2/rcl src/ros2/
   mv unused_src/ros2/rmw src/ros2/
   mv unused_src/ros2/rosidl src/ros2/
   mv unused_src/ros2/common_interfaces src/ros2/

   It is good to have ros2/common_interfaces as it provides the commonly used packages such as std_msgs.

   Certain heavy graphic-based packages such as rviz are obviously not easy to port. We will run colcon commands (below) and add back more dependent packages.

   Tip: Do find unused_src -name PKG_NAME in unused_src to find the repository containing the needed package.

3. The minimal list of repositories is available in the file ros2_min.repos. So of course, one can simply import this instead. Here, I choose to use a single RMW implementation (via Fast-DDS).

4. Create a new workspace and link the src in

   mkdir -p ros2_ws
   cd ros2_ws
   ln -s $REPO_ROOT/src src

5. During development, it is good to have multiple workspaces such as

   • ament_ws: move ament here, build and source it before moving on to
   • base_ws: add rcl and its dependencies and once successful
   • rclcpp_ws: add other desired packages such as rclcpp.

   This way, one can minimize the amount of packages to rebuild.

Build ROS2 core packages for iOS

Before building, we need to change the line #include <net/if_arp.h> in src/eProsima/Fast-DDS/src/cpp/utils/IPFinder.cpp into #include <net/ethernet.h> according to this as the original header is only available in the macOS SDK.

We also disable the package rcl_logging_spdlog by

touch src/ros2/rcl_logging/rcl_logging_spdlog/AMENT_IGNORE

To build for iOS simulator on Intel Macs, do

cd ros2_ws

#Prepend with VERBOSE=1 and add --executor sequential --event-handlers console_direct+ while debugging
colcon build --merge-install \
    --cmake-force-configure \
    --cmake-args \
        -DCMAKE_TOOLCHAIN_FILE=$REPO_ROOT/cmake/iOS_Simulator.cmake \
        -DBUILD_TESTING=NO \
        -DTHIRDPARTY=FORCE \
        -DCOMPILE_TOOLS=NO \
        -DFORCE_BUILD_VENDOR_PKG=ON \
        -DBUILD_MEMORY_TOOLS=OFF \
        -DRCL_LOGGING_IMPLEMENTATION=rcl_logging_noop

For M1 Mac or for real iPhones, you would need to change iOS_Simulator.cmake appropriately.

After my tons of failures, here is what went going on behind the above command:

1. The classical method to CMake for iOS simulator in my other projects such as LibGit2 is to set the appropriate CMAKE_OSX_SYSROOT and CMAKE_OSX_ARCHITECTURES.

   Note: The right way to get clang to compile for iOS simulator is to set to CMAKE_C_FLAGS and CMAKE_CXX_FLAGS, namely -target x86_64-apple-ios-simulator -mios-version-min=14.0 together with -isysroot to find the standard headers.

   However, that is not going to work here. The reason is because of the ***_vendor packages which are proxy packages for 3rd party libraries such as libyaml: their CMake files fetch the library and passing to their CMake with the "right" options. Checking for example libyaml_vendor/CMakeLists.txt reveals that it does NOT pass along all our CMAKE_*** options except for CMAKE_C_FLAGS and even force BUILD_SHARED_LIBS=ON. We need to pass along all desired options in -DCMAKE_TOOLCHAIN_FILE and in that file, we set up all the desired CMake variables.

   Note: Even this is not going to be enough for some package such as mimick_vendor as it sets its internal variable _ARCH BEFORE considering the toolchain file!

2. BUILD_TESTING=NO to disable all test packages, without this, we are going to need a ton of third party packages such as ament/google_benchmark_vendor, ament/uncrustify_vendor, ament/googletest, osrf/osrf_testing_tools_cpp, ros2/performance_test_fixture and ros2/mimick_vendor and account for a ton of CMake issues

3. THIRDPARTY=FORCE is to ask eProsima Fast-DDS to build and use its own dependencies (asio, ...) so that we do not have to install it to the system with Homebrew

4. COMPILE_TOOLS=NO for Fast-DDS to NOT compile the fast discovery server executable.

5. FORCE_BUILD_VENDOR_PKG=ON is to build and use the *_vendor packages such as libyaml_vendor, again so that we do not have to install it to the system with Homebrew

6. BUILD_MEMORY_TOOLS=OFF is for foonathan_memory to disable building nodesize_db program

7. RCL_LOGGING_IMPLEMENTATION=rcl_logging_noop is to select the logging backend for rcl_logging. Here, I am using noop one to avoid one more dependency spdlog_vendor.

8. ROS2 depends significantly on dynamic linking. Do NOT add BUILD_SHARED_LIBS=NO, contrary to my other project LLVM where building static libs is needed!