Merge pull request #315 from christian-rauch/lang_cxx_optional

make C++ language requirements optional

.github/workflows/colcon-workspace.yml

@@ -5,14 +5,13 @@ on: [push, pull_request]
 jobs:
   # build on Ubuntu docker images
   build_linux:
-    name: "Ubuntu (${{ matrix.ros_distribution }}, shared: ${{ matrix.cmake_shared_libs }})"
+    name: "Ubuntu (${{ matrix.ros_distribution }})"
 
     runs-on: ubuntu-latest
 
     strategy:
       matrix:
         ros_distribution: [noetic, humble]
-        cmake_shared_libs: ['ON', 'OFF']
         include:
           - docker_image: ubuntu:20.04
             ros_distribution: noetic
@@ -42,27 +41,24 @@ jobs:
         with:
           package-name: apriltag
           target-ros1-distro: ${{ matrix.ros_distribution }}
-          extra-cmake-args: "-DBUILD_SHARED_LIBS=${{ matrix.cmake_shared_libs }}"
 
       - name: ROS 2 CI Action
         if: ${{ matrix.ros_version == 2 }}
         uses: ros-tooling/action-ros-ci@v0.3
         with:
           package-name: apriltag
           target-ros2-distro: ${{ matrix.ros_distribution }}
-          extra-cmake-args: "-DBUILD_SHARED_LIBS=${{ matrix.cmake_shared_libs }}"
 
 
   # build on Windows native
   build_windows:
-    name: "Windows (${{ matrix.ros_distribution }}, shared: ${{ matrix.cmake_shared_libs }})"
+    name: "Windows (${{ matrix.ros_distribution }})"
 
     runs-on: windows-2019
 
     strategy:
       matrix:
         ros_distribution: [noetic, humble]
-        cmake_shared_libs: ['ON', 'OFF']
         include:
           - ros_distribution: noetic
             ros_version: 1
@@ -84,26 +80,23 @@ jobs:
         with:
           package-name: apriltag
           target-ros1-distro: ${{ matrix.ros_distribution }}
-          extra-cmake-args: "-DBUILD_SHARED_LIBS=${{ matrix.cmake_shared_libs }}"
 
       - name: ROS 2 CI Action
         if: ${{ matrix.ros_version == 2 }}
         uses: ros-tooling/action-ros-ci@v0.3
         with:
           package-name: apriltag
           target-ros2-distro: ${{ matrix.ros_distribution }}
-          extra-cmake-args: "-DBUILD_SHARED_LIBS=${{ matrix.cmake_shared_libs }}"
 
   # build on macOS native
   build_macos:
-    name: "macOS (${{ matrix.ros_distribution }}, shared: ${{ matrix.cmake_shared_libs }})"
+    name: "macOS (${{ matrix.ros_distribution }})"
 
     runs-on: macos-latest
 
     strategy:
       matrix:
         ros_distribution: [humble]
-        cmake_shared_libs: ['ON', 'OFF']
 
     steps:
       - uses: actions/checkout@v4
@@ -122,4 +115,3 @@ jobs:
         with:
           package-name: apriltag
           target-ros2-distro: ${{ matrix.ros_distribution }}
-          extra-cmake-args: "-DBUILD_SHARED_LIBS=${{ matrix.cmake_shared_libs }}"

CMakeLists.txt

@@ -1,5 +1,5 @@
 cmake_minimum_required(VERSION 3.16)
-project(apriltag VERSION 3.3.0 LANGUAGES C CXX)
+project(apriltag VERSION 3.3.0 LANGUAGES C)
 
 if(POLICY CMP0077)
     cmake_policy(SET CMP0077 NEW)
@@ -192,6 +192,7 @@ if (BUILD_EXAMPLES)
     set(_OpenCV_REQUIRED_COMPONENTS core imgproc videoio highgui)
     find_package(OpenCV COMPONENTS ${_OpenCV_REQUIRED_COMPONENTS} QUIET CONFIG)
     if(OpenCV_FOUND)
+        enable_language(CXX)
         # NB: contrib required for TickMeter in OpenCV 2.4. This is only required for 16.04 backwards compatibility and can be removed in the future.
         #     If we add it to the find_package initially, the demo won't build for newer OpenCV versions
         if(OpenCV_VERSION VERSION_LESS "3.0.0")