Add Windows ARM64 support for 5.x

.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-2022
+    runs-on: ${{ matrix.platform == 'arm64' && 'windows-11-arm' || 'windows-2022' }}
     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 +31,7 @@ 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' }}
     steps:
     - name: Cleanup
       shell: bash
@@ -50,17 +50,20 @@ 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
@@ -77,18 +80,26 @@ jobs:
 
   Test:
     needs: [Build]
-    runs-on: windows-2022
+    runs-on: ${{ matrix.platform == 'arm64' && 'windows-11-arm' || 'windows-2022' }}
     defaults:
       run:
         shell: cmd
     strategy:
       fail-fast: false
       matrix:
         python-version: ['3.8', '3.9', '3.10', '3.11', '3.12', '3.13', '3.14']
-        platform: [x86, x64]
+        platform: [x86, x64, arm64]
         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: '3.8'
+          - 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

setup.py

@@ -101,10 +101,11 @@ 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{3}%s\.dll" % ("_64" if is64 else "")]
-            if os.name == "nt"
+            if os.name == "nt" and not (platform.machine() == "ARM64" and sys.platform == "win32")
             else []
         )
         +
@@ -157,9 +158,13 @@ def main():
 
     # HACK: Disabled generic assembler for now.
     # Windows 2025 CI environment does not provide suitable assembler or build is broken in OpenCV MLAS.
+    # On ARM64, NOTFOUND also avoids a MinGW toolchain on PATH being misdetected by CMake's ASM probe.
     ci_cmake_generator = (
-        ["-G", "Visual Studio 17 2022",
-         "-DCMAKE_ASM_COMPILER="]
+        ["-G", "Visual Studio 18 2026",
+         "-DCMAKE_ASM_COMPILER=CMAKE_ASM_COMPILER-NOTFOUND"]
+        if os.name == "nt" and platform.machine() == "ARM64"
+        else ["-G", "Visual Studio 17 2022",
+              "-DCMAKE_ASM_COMPILER="]
         if os.name == "nt"
         else ["-G", "Unix Makefiles"]
     )
@@ -198,7 +203,8 @@ def main():
              # Emulated cmake requires following flags to correctly detect
              # target architecture for windows/arm64 build
              "-DOPENCV_WORKAROUND_CMAKE_20989=ON",
-             "-DCMAKE_SYSTEM_PROCESSOR=ARM64"]
+             "-DCMAKE_SYSTEM_PROCESSOR=ARM64",
+             "-DWITH_OPENCL=OFF"]
             if platform.machine() == "ARM64" and sys.platform == "win32"
             # If it is not defined 'linker flags: /machine:X86' on Windows x64
             else ["-DCMAKE_GENERATOR_PLATFORM=x64"] if is64 and sys.platform == "win32"
@@ -264,6 +270,11 @@ 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()