Add CI support for building Windows on ARM wheels

.github/workflows/build_wheels_windows.yml

@@ -1,4 +1,4 @@
-name: Windows x86_64
+name: Windows
 
 on:
   pull_request:
@@ -17,12 +17,11 @@ on:
 
 jobs:
   Build:
-    runs-on: windows-2025
+    runs-on: ${{ matrix.platform == 'arm64' && 'windows-11-arm' || 'windows-2025' }}
     strategy:
       fail-fast: false
       matrix:
-        python-version: ['3.9']
-        platform: [x86, x64]
+        platform: [x86, x64, arm64]
         with_contrib: [0, 1]
         without_gui: [0, 1]
         build_sdist: [0]
@@ -32,6 +31,8 @@ jobs:
       ENABLE_HEADLESS: ${{ matrix.without_gui }}
       ENABLE_CONTRIB: ${{ matrix.with_contrib }}
       OPENCV_TEST_DATA_PATH: ${{ github.workspace }}\opencv_extra\testdata
+      PYTHON_VERSION: ${{ matrix.platform == 'arm64' && '3.11' || '3.9' }}
+      CMAKE_VERSION: ${{ matrix.platform == 'arm64' && '4.1.0' || '3.24.2' }}
     steps:
     - name: Cleanup
       shell: bash
@@ -50,22 +51,25 @@ jobs:
       with:
         submodules: false
         fetch-depth: 0
-    - name: Set up Python ${{ matrix.python-version }}
+    - name: Set up Python ${{ env.PYTHON_VERSION }}
       uses: actions/setup-python@v4
       with:
-        python-version: ${{ matrix.python-version }}
+        python-version: ${{ env.PYTHON_VERSION }}
         architecture: ${{ matrix.platform }}
     - name: Setup MSBuild.exe
       uses: microsoft/setup-msbuild@v1.1
+      with:
+        msbuild-architecture: ${{ matrix.platform }}
     - name: Setup NASM
+      if: matrix.platform != 'arm64'
       uses: ilammy/setup-nasm@v1
     - name: Build a package
-      # CMake 3.25 regression fix. See https://stackoverflow.com/questions/74162633/problem-compiling-from-source-opencv-with-mvsc2019-in-64-bit-version
+      # CMake 3.25 regression fix for x86/x64. See https://stackoverflow.com/questions/74162633/problem-compiling-from-source-opencv-with-mvsc2019-in-64-bit-version
       run: |
         python --version
         python -m pip install --upgrade pip
         python -m pip install --upgrade setuptools
-        python -m pip install cmake==3.24.2
+        python -m pip install cmake==${{ env.CMAKE_VERSION }}
         python -m pip install toml && python -c "import toml; c = toml.load('pyproject.toml'); print('\n'.join(c['build-system']['requires']))" >> requirements.txt | python -m pip install -r requirements.txt
         set "CI_BUILD=1" && python setup.py bdist_wheel --py-limited-api=cp37 --dist-dir=%cd%\wheelhouse -v
       shell: cmd
@@ -74,21 +78,31 @@ jobs:
       with:
         name: wheel-${{ matrix.with_contrib }}-${{ matrix.without_gui }}-${{ matrix.build_sdist }}-${{ matrix.platform }}
         path: wheelhouse/opencv*
-
+  
   Test:
     needs: [Build]
-    runs-on: windows-2025
+    runs-on: ${{ matrix.platform == 'arm64' && 'windows-11-arm' || 'windows-2025' }}
     defaults:
       run:
         shell: cmd
     strategy:
       fail-fast: false
       matrix:
+        platform: [x86, x64, arm64]
         python-version: ['3.7', '3.8', '3.9', '3.10', '3.11', '3.12', '3.13']
-        platform: [x86, x64]
         with_contrib: [0, 1]
         without_gui: [0, 1]
         build_sdist: [0]
+        exclude:
+          # actions/setup-python does not provide prebuilt arm64 Python before 3.11
+          - platform: arm64
+            python-version: '3.7'
+          - platform: arm64
+            python-version: '3.8'
+          - platform: arm64
+            python-version: '3.9'
+          - platform: arm64
+            python-version: '3.10'
     env:
       ACTIONS_ALLOW_UNSECURE_COMMANDS: true
       OPENCV_TEST_DATA_PATH: ${{ github.workspace }}\opencv_extra\testdata

pyproject.toml

@@ -1,9 +1,9 @@
 [build-system]
 requires = [
   "numpy<2.0; python_version<'3.9'",
-  "numpy==2.0.2; python_version>='3.9' and python_version<'3.13'",
-  "numpy==2.1.3; python_version=='3.13'",
-  "numpy==2.3.2; python_version=='3.14'",
+  "numpy==2.0.2; python_version >= '3.9' and python_version < '3.13' and (sys_platform != 'win32' or platform_machine != 'ARM64')",
+  "numpy==2.1.3; python_version == '3.13' and (sys_platform != 'win32' or platform_machine != 'ARM64')",
+  "numpy==2.3.1;sys_platform == 'win32' and platform_machine == 'ARM64'",
   "packaging",
   "pip",
   "scikit-build>=0.14.0",

setup.py

@@ -102,11 +102,12 @@ def main():
 
     # Files from CMake output to copy to package.
     # Path regexes with forward slashes relative to CMake install dir.
+    # Note: FFMPEG dlls are not yet provided for Windows ARM64
     rearrange_cmake_output_data = {
         "cv2": (
-            [r"bin/opencv_videoio_ffmpeg\d{4}%s\.dll" % ("_64" if is64 else "")]
-            if os.name == "nt"
-            else []
+            ([r"bin/opencv_videoio_ffmpeg\d{4}%s\.dll" % ("_64" if is64 else "")]
+             if not (platform.machine() == "ARM64" and sys.platform == "win32")
+             else [])
         )
         +
         # In Windows, in python/X.Y/<arch>/; in Linux, in just python/X.Y/.
@@ -260,6 +261,11 @@ def main():
             cmake_args.append("-DWITH_LAPACK=ON")
             cmake_args.append("-DENABLE_PRECOMPILED_HEADERS=OFF")
 
+        if sys.platform.startswith('win') and platform.machine().lower() in ("arm64", "aarch64"):
+            # MSVC does not support OpenCV dispatch features such as NEON_FP16, NEON_BF16 and NEON_DOTPROD. So use NEON as both baseline and dispatch units
+            cmake_args.append("-DCPU_BASELINE=NEON")
+            cmake_args.append("-DCPU_DISPATCH=NEON")
+
     # works via side effect
     RearrangeCMakeOutput(
         rearrange_cmake_output_data, files_outside_package_dir, package_data.keys()