Build on modern macOS (Apple Silicon) + Metal depth backend

[hbmartin]

Updates libfreenect2 so it configures, builds, and runs on a current Apple Silicon Mac (CMake 4.x, Xcode 26, Apple clang 21), while preserving Linux/CUDA compatibility. Every macOS-specific change is gated behind IF(APPLE) / #ifdef LIBFREENECT2_WITH_METAL_SUPPORT.

Combines the useful pieces of upstream PRs OpenKinect#1158, OpenKinect#1189, OpenKinect#1208, OpenKinect#1209, OpenKinect#1210.

Changes

Fix	Source	Notes
CMAKE_MINIMUM_REQUIRED 2.8.12.1 → 3.5 (3 files)	OpenKinect#1209	CMake ≥ 4.0 rejects <3.5 — the hard configure blocker
Guard CL_ICDL_VERSION redefinition	OpenKinect#1189	For OpenCL headers ≥ 3.0.16; used the cleaner #if !defined form
ENABLE_VIDEOTOOLBOX option	OpenKinect#1208	Defaults OFF on arm64 to avoid the VTRgbPacketProcessor heap-corruption crash on Apple Silicon (falls back to TurboJPEG); stays ON for Intel Macs
Metal GPU depth backend	OpenKinect#1210	New metal pipeline for Apple platforms
streamer_recorder OpenCV fix	OpenKinect#1158	cv::IMWRITE_JPEG_QUALITY + C++14 (tool remains OFF by default)

Additional glue beyond the source PRs:

• Protonect accepts metal as a pipeline argument (the factory was wired but the example parser was not).
• The compiled default.metallib is emitted into the library output dir so the runtime loader finds it beside libfreenect2.dylib in both the build tree and after make install.

Verification (Apple M2 Pro, macOS 26.5, Xcode 26, CMake 4.3.4)

• Clean configure + full build (library, Metal shader, Protonect) with zero errors.
• Metal pipeline initializes on the M2 Pro and loads its shader library.
• OpenCL, OpenGL, and CPU pipelines all initialize (OpenCL builds its program on the M2 Pro GPU).
• make install places default.metallib beside the dylib.

Not exercised: a live frame (no Kinect connected). The Metal backend (from OpenKinect#1210) compiles and initializes correctly but its depth-decode output has not been validated against real hardware.

🤖 Generated with Claude Code

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Summary by cubic

Modernized macOS build for Apple Silicon and added a Metal depth pipeline, while keeping Linux/CUDA builds intact. Installs default.metallib next to libfreenect2.dylib and defaults to TurboJPEG on arm64 for stability.

• New Features

  • Added Metal GPU depth packet processor (MetalPacketPipeline), selectable via "metal".
  • Protonect now accepts "metal"; default.metallib is built and installed beside libfreenect2.dylib.
  • New ENABLE_METAL CMake option (ON on Apple).

• Migration

  • Requires CMake ≥ 3.5.
  • On Apple Silicon, ENABLE_VIDEOTOOLBOX defaults OFF to avoid a crash; RGB decoding uses TurboJPEG unless explicitly enabled.
  • Tools: streamer_recorder builds as C++14 and uses cv::IMWRITE_JPEG_QUALITY.

^{Written for commit 5b50c2c. Summary will update on new commits.}

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Review details

⚙️ Run configuration

Configuration used: Organization UI

Review profile: ASSERTIVE

Plan: Pro

Run ID: a2ae44a1-69eb-4741-8c63-02af96e6605f

📥 Commits

Reviewing files that changed from the base of the PR and between fd64c5d and 5b50c2c.

📒 Files selected for processing (15)

• CMakeLists.txt
• examples/CMakeLists.txt
• examples/Protonect.cpp
• include/internal/libfreenect2/depth_packet_processor.h
• include/libfreenect2/config.h.in
• include/libfreenect2/packet_pipeline.h
• src/libfreenect2.cpp
• src/metal_depth_packet_processor.metal
• src/metal_depth_packet_processor.mm
• src/opencl_depth_packet_processor.cpp
• src/opencl_kde_depth_packet_processor.cpp
• src/packet_pipeline.cpp
• tools/streamer_recorder/CMakeLists.txt
• tools/streamer_recorder/recorder.cpp
• tools/streamer_recorder/streamer.cpp

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch mac-build-fixes

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