Open3D (Agent Skills)

Open3D is a cross-platform (Windows, Linux, macOS and x86_64, arm64, CUDA and
oneAPI platforms) C++17 and Python library for 3D data processing,
visualization, reconstruction, registration, and ML-related workflows. Other
functionality is out of scope.

## Coding and PR review directions

- For any change, first research existing code and prepare a plan with definite goal, requirements, implementation steps, test method, risks and mitigations. **Lock the goal, requirements and test method, and keep the implementation steps with a log of status and decisions made.** Add plan summary to the PR description. 
- Store intermediate live research and progress reports with important findings in .md files and refer to them as needed.
- Use subagents for major steps. 
- Create new git branches when you explore implementation options - go back to previous code as required. 
- Prioritize human readability and maintainability.
- **AVOID REDUNDANT IMPLEMENTATION** when similar functionality already exists - refactor and reuse instead.
- Keep changes focused and small. Avoid broad refactors unless requested.
- Read the relevant C++ / Python / docs files together and identify whether bindings, docs, and tests must change with the source change.
- **Debugging:** Test root cause hypothesis with logging before trying fixes. Validate with logging afterwards. Undo failed fixes.
- Developer docs: Document the code with brief (2-3 lines) comments (Why and What is the code doing?), typically for each function and file. Ensure code and docs are consistent.
- User docs: Update `docs`, Doxygen docs in C++ headers and Google Sphinx RST docs in Python bindings for new / changed code behavior.  Add / update an example function use snippet in the docs.
- For new functionality, docs and examples, prefer Tensor implementations that work on CPU+CUDA+SYCL. 
- Use the Eigen library for Math operations and oneAPI TBB for multithreading. Avoid: OpenMP, stdgpu.
- Add unit tests for new behavior and bug fixes (if needed).  Add or update both C++ and Python tests when the feature is exposed in both layers.
- Keep dependencies minimal. Reuse functionality from existing dependencies if needed. Do not update 3rdparty code with patches.
- Preserve existing public APIs unless the task explicitly requires API changes.
- Avoid unnecessary compiler warnings, build breakages, and unrelated cleanup.
- Ensure smallest set of relevant tests run correctly locally. The full CI must pass for all supported SW and HW platforms in Github.

## Repository map

- Core algorithms/data structures: `cpp/open3d/` 
- New CPU+CUDA+SYCL (Tensor based) implementations: `cpp/open3d/{core,t}`
- Legacy CPU only (Eigen based) data structures and algorithms: `cpp/open3d/{camera,geometry,io,pipelines}`
- GUI visualization (based on GLFW + Dear ImGUI + Filament renderer): `cpp/open3d/visualization/{app,gui,rendering,visualizer}`
- Legacy OpenGL + GLFW visualization: `cpp/open3d/visualization/visualizer`
- C++ tests: `cpp/tests/`
- Python bindings: `cpp/pybind/`
- Python tests: `python/test/`
- Examples: `examples/`
- Build logic: `CMakeLists.txt`, `3rdparty/find_dependencies.txt`
- Tooling/style/CI helpers: `util/`
- Docs: `docs/` and inline docs in C++ headers (Doxygen) and Python bindings.

## Build

- `mkdir -p build && cd build`
- Configure: `cmake -S .. -B . -D OPTION=VALUE...`
- Build: `cmake --build . --parallel $NPROC --target TARGET` (NPROC = numn CPUs) 
- Install: `cmake --build . --target install`

If Python bindings are required, use an activated virtual environment or set
`-DPython3_ROOT=/path/to/python`.  

### Useful CMake options (specify `=ON` or `=OFF`):

- `BUILD_UNIT_TESTS`
- `BUILD_PYTHON_MODULE`
- `BUILD_[CUDA|SYCL|ISPC]_MODULE`
- `BUILD_EXAMPLES`
- `BUILD_SHARED_LIBS`

### Useful targets:
- Python package targets: `python-package|pip-package|install-pip-package`
- C++ tests: `tests`
- C++ Binary library package: `package`
- Viewer: `Open3DViewer`
- Examples: By example name.

## Test

### C++

- `./bin/tests --gtest_list_tests`
- `./bin/tests --gtest_filter=*TEST_NAME*`

### Python

- `pip install -r python/requirements_test.txt`
- `cmake --build build --target install-pip-package`
- `pytest ../python/test/SPECIFIC/TEST_FILE.PY`

## Style and formatting

- C++ follows Google-style conventions with Open3D-specific rules.
- Use 4 spaces, no tabs.
- Use `#pragma once` for header guards.
- Prefer smart pointers over naked pointers.
- Use C++17, not C++20+.
- Python follows Google Python style.

Use the repository's own formatting tools and pinned versions.

- `pip install -r python/requirements_style.txt`
- `python util/check_style.py --apply` or `cmake --build build --target apply-style --parallel`