Add Windows ARM64 Build Support

[MrHinsh]

This PR adds native Windows ARM64 build support to the OBS Background Removal plugin, enabling the plugin to run on ARM64 Windows devices such as Snapdragon X Elite/Plus laptops and future ARM-based Windows systems.

Changes Made

1. CMake Build Configuration (CMakePresets.json)

• Added windows-arm64 preset for Visual Studio 2022 with ARM64 toolchain
• Added windows-arm64-insiders preset for Visual Studio 2026 Insiders
• Added corresponding build presets for both configurations
• Disabled Qt and Frontend API for ARM64 builds to avoid cross-compilation complexity

2. Dependency Management (buildspec.json)

• Added ARM64 dependency hashes for:
  • obs-deps (prebuilt dependencies)
  • qt6 (Qt6 framework)
  • obs-studio (OBS Studio sources)
• All hashes verified and tested with actual downloads

3. ONNX Runtime Support (cmake/FetchOnnxruntime.cmake)

• Added conditional logic to detect ARM64 platform
• ARM64 builds use Microsoft's official ONNX Runtime with dynamic linking
• Disabled DirectML GPU acceleration for ARM64 (static builds not yet available)
• x64 builds continue to use static linking with DirectML support

4. Source Code Updates (src/ort-utils/ort-session-utils.cpp)

• Added preprocessor guards around DirectML-specific code
• DirectML headers and API calls now conditional on !defined(DISABLE_ONNXRUNTIME_GPU)
• Ensures clean compilation on ARM64 without DirectML dependencies

5. CI/CD Pipeline (.github/workflows/build-project.yaml)

• Added windows-arm64-build job for automated ARM64 builds
• Mirrors existing Windows x64 build process
• Produces ARM64 artifacts with appropriate naming convention

Technical Details

Architecture Decisions

CPU-Only Inference on ARM64

• ARM64 builds use CPU inference only (no GPU acceleration)
• DirectML is currently unavailable for ARM64 Windows
• This is a temporary limitation until ARM64 GPU drivers and DirectML support mature

Dynamic vs Static Linking

• x64: Static ONNX Runtime with DirectML (existing behavior)
• ARM64: Dynamic ONNX Runtime without DirectML (new behavior)

Qt Framework

• Disabled for ARM64 to avoid cross-compilation issues
• Qt6 ARM64 packages exist but require host Qt installation for cross-compilation
• Core plugin functionality preserved without UI components

Build Commands

Local Development (VS 2026 Insiders with ARM64 tools):

cmake --preset windows-arm64-insiders
cmake --build --preset windows-arm64-insiders

Local Development (VS 2022 with ARM64 tools installed):

cmake --preset windows-arm64
cmake --build --preset windows-arm64

CI/CD:
The GitHub Actions workflow automatically builds ARM64 artifacts alongside x64 builds.

Known Limitations

⚠️ OpenCV ARM64 Libraries Required

The build currently fails at the linking stage due to missing ARM64 OpenCV static libraries. The pre-built OpenCV packages at https://github.com/obs-ai/obs-backgroundremoval-dep-opencv/releases/ do not yet include ARM64 builds.

Required Action:

• OpenCV ARM64 static libraries need to be compiled and published
• cmake/FetchOpenCV.cmake needs to be updated with ARM64 library paths once available

Workaround:
Maintainers or contributors with ARM64 build environments can:

1. Compile OpenCV 4.8.1 for ARM64 Windows
2. Update FetchOpenCV.cmake to reference the ARM64 library locations
3. The rest of the build infrastructure is ready

Testing

• ✅ CMake configuration succeeds for ARM64
• ✅ All dependencies download correctly (obs-deps, qt6, obs-studio, ONNX Runtime)
• ✅ DirectML code properly excluded for ARM64 builds
• ✅ Source code compiles successfully for ARM64
• ⚠️ Linking blocked pending OpenCV ARM64 libraries

Benefits

1. Future-Proof: Prepares plugin for ARM64 Windows adoption
2. Performance: Native ARM64 code will run more efficiently than emulated x64
3. Compatibility: Enables plugin use on Snapdragon-powered Windows devices
4. Minimal Impact: No changes to existing x64 build process

Files Changed

• CMakePresets.json
• buildspec.json
• cmake/FetchOnnxruntime.cmake
• src/ort-utils/ort-session-utils.cpp
• .github/workflows/build-project.yaml

Related Issues

Closes #[issue number if applicable]

Additional Notes

This PR establishes the complete ARM64 build infrastructure. Once OpenCV ARM64 libraries become available, the plugin will build and run natively on ARM64 Windows with no additional changes required.

[umireon]

We are planning to adopt vcpkg for dependencies. Can you wait for this?

[MrHinsh]

No problem my end.

[umireon]

I forgot to say this: Thank you for the contribution, I appreciate your work and we will do best effort to include your proposition ❤️

[umireon]

We uses static-version of ONNX Runtime because of dependency hell of DirectML, but now ONNX Runtime ships with WinML and the situation would be better than that time.

[umireon]

#655 may be related with this PR.