CI: build macOS x86_64 by cross-compiling on the arm64 runner

Intel (macos-13) runners queue indefinitely on GitHub capacity, so build the
x86_64 macOS binary on the reliable Apple-Silicon runner instead: compile a
static x86_64 SDL2 from source (release-2.30.x) and build the app with
CMAKE_OSX_ARCHITECTURES=x86_64 (deployment target 10.13), producing a
self-contained Intel binary. CMake now also accepts the SDL2::SDL2-static
target. arm64 stays native (brew SDL2).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: Appolonnius

.github/workflows/build.yml

@@ -15,8 +15,11 @@ jobs:
       matrix:
         include:
           - { os: ubuntu-latest,  name: linux }
-          - { os: macos-13,       name: macos-x86_64 }   # Intel runner
-          - { os: macos-14,       name: macos-arm64 }    # Apple Silicon runner
+          # Both macOS builds run on the reliable Apple-Silicon runner: one native
+          # arm64, one cross-compiled to x86_64 (static SDL2 from source), so the
+          # Intel build no longer depends on scarce Intel-runner capacity.
+          - { os: macos-14,       name: macos-arm64,  mac_arch: arm64 }
+          - { os: macos-14,       name: macos-x86_64, mac_arch: x86_64 }
           - { os: windows-latest, name: windows }
     steps:
       - uses: actions/checkout@v4
@@ -25,20 +28,39 @@ jobs:
         if: runner.os == 'Linux'
         run: sudo apt-get update && sudo apt-get install -y cmake build-essential libsdl2-dev libgl1-mesa-dev
 
-      - name: Install deps (macOS)
-        if: runner.os == 'macOS'
+      - name: Install deps (macOS arm64, native)
+        if: matrix.mac_arch == 'arm64'
         run: brew install sdl2
 
+      - name: Build x86_64 SDL2 from source (macOS cross)
+        if: matrix.mac_arch == 'x86_64'
+        run: |
+          git clone --depth 1 -b release-2.30.x https://github.com/libsdl-org/SDL SDLsrc
+          cmake -S SDLsrc -B sdlbuild -DCMAKE_BUILD_TYPE=Release \
+            -DCMAKE_OSX_ARCHITECTURES=x86_64 -DCMAKE_OSX_DEPLOYMENT_TARGET=10.13 \
+            -DSDL_SHARED=OFF -DSDL_STATIC=ON -DSDL_TEST=OFF \
+            -DCMAKE_INSTALL_PREFIX="$PWD/sdlx86"
+          cmake --build sdlbuild -j3 --target install
+
       - name: Configure
-        run: cmake -B build -DCMAKE_BUILD_TYPE=Release
+        shell: bash
+        run: |
+          if [ "${{ matrix.mac_arch }}" = "x86_64" ]; then
+            cmake -B build -DCMAKE_BUILD_TYPE=Release \
+              -DCMAKE_OSX_ARCHITECTURES=x86_64 -DCMAKE_OSX_DEPLOYMENT_TARGET=10.13 \
+              -DCMAKE_PREFIX_PATH="$PWD/sdlx86"
+          else
+            cmake -B build -DCMAKE_BUILD_TYPE=Release
+          fi
 
       - name: Build
-        run: cmake --build build --config Release -j 2
+        shell: bash
+        run: cmake --build build --config Release -j 3
 
       - name: Verify arch (macOS)
         if: runner.os == 'macOS'
         run: |
-          echo "runner arch: $(uname -m)"
+          echo "runner arch: $(uname -m)  target: ${{ matrix.name }}"
           file build/msxforge-gui
           lipo -archs build/msxforge-gui || true
 

CMakeLists.txt

@@ -48,7 +48,9 @@ else()
   # Linux / macOS: use the system SDL2 (apt install libsdl2-dev / brew install sdl2).
   find_package(SDL2 REQUIRED)
   if(TARGET SDL2::SDL2)
-    target_link_libraries(msxforge-gui PRIVATE SDL2::SDL2)
+    target_link_libraries(msxforge-gui PRIVATE SDL2::SDL2)         # shared (brew/apt)
+  elseif(TARGET SDL2::SDL2-static)
+    target_link_libraries(msxforge-gui PRIVATE SDL2::SDL2-static)  # static (cross build)
   else()
     target_include_directories(msxforge-gui PRIVATE ${SDL2_INCLUDE_DIRS})
     target_link_libraries(msxforge-gui PRIVATE ${SDL2_LIBRARIES})