Add experimental Windows wheel build support

[zym1998year]

Depends on GalSim PR GalSim-developers/GalSim#1359.

Draft PR against releases/0.8 (baseline 367a861, v0.8.0).
Branch on file: windows-port.

Status

• Verified locally: pip install . -v (Ninja+MSVC), pip wheel,
  delvewheel repair, fresh-venv install with separately-built GalSim
  Windows wheel (no conda PATH), import batoid, LSST yaml load,
  raytrace, SellmeierMedium, ObscPolygon, Bicubic, and 176 / 204
  pytest cases passing.
• Test failures (28) are all in tests/test_notebooks.py, all
  ModuleNotFoundError: No module named 'nbformat' — jupyter test
  infra not installed. Not Windows-specific.
• Linux / macOS code paths are textually unchanged outside the
  member rename and the or->|| swap (which GCC/Clang accept
  identically). Existing CI should pass without changes; not re-run
  from this branch.

Dependency

batoid depends on GalSim. GalSim does not currently ship Windows
wheels; a companion PR adds Windows support to GalSim
(releases/2.8 branch, windows-msvc-port). Once that PR or a
subsequent GalSim release exposes a win_amd64 wheel on PyPI, this
PR's wheel becomes installable purely with pip install. Until then,
end users on Windows would need to install GalSim from the companion
branch.

This PR does not change install_requires=['galsim', ...]; it only
enables batoid itself to build.

Summary

Three small commits make batoid build, install, and pass its
non-notebook test suite on native Windows x64 with the MSVC
toolchain. The patches address one Windows-SDK macro collision, three
independent MSVC source-level issues, and two CMake / pybind11 build
quirks. Diff totals +40 / -11 across six files.

What this PR changes

#	Commit	Files	Diff
1	Avoid Windows SDK macro collision in SellmeierMedium	include/medium.h, src/medium.cpp	+7 / -4
2	Make batoid C++ sources MSVC compatible	src/batoid.cpp, src/obscuration.cpp, src/table.cpp	+12 / -6
3	Make batoid CMake extension build portable on Windows	setup.py	+21 / -1

Branch tip: d28bc8a.

Per-commit detail (click to expand)

1. SellmeierMedium macro collision

The Windows SDK header ctype.h defines preprocessor macros named
_C1, _C2, _C3 (control-character classification masks).
Including Windows.h — which any Windows MSVC translation unit
eventually does — expands those macros over the matching
SellmeierMedium private members and the file no longer parses.

Rename to _sellC1 / _sellC2 / _sellC3 with a one-line comment
in the header explaining why. Updates the constructor's
member-initializer list, getN(), and the BATOID_GPU device-pointer
constructor. Public API and Sellmeier coefficient ordering unchanged.

2. C++ sources for MSVC

Three independent fixes:

• src/batoid.cpp: convert the two #pragma omp parallel for loops
  in applyForwardTransformArrays / applyReverseTransformArrays
  from size_t i to ptrdiff_t i (with a ptrdiff_t nloop = static_cast<ptrdiff_t>(n) mirror so the upper bound width is
  preserved). MSVC OpenMP requires a signed integral loop counter.
  Other parallel loops in this file already used int i and did not
  need touching. Adds <cstddef> for ptrdiff_t.
• src/obscuration.cpp: replace or with || in the polygon
  point-in-polygon test and the y-grid bounds early-exit. MSVC parses
  or as an identifier without /Za plus <ciso646>.
• src/table.cpp: replace or with || in the two bounds-check
  expressions in Table::eval and the gradient variant.

3. CMake extension build for Windows

setup.py only:

• Drop build_args += ["--", "-j8"] and replace with
  build_args += ["--parallel", str(jobs)] driven by
  CMAKE_BUILD_PARALLEL_LEVEL, falling back to a bare --parallel.
  MSBuild rejects -j8 outright (it expects /m / -maxCpuCount);
  --parallel is generator-agnostic.
• Add -Dpybind11_DIR= from pybind11.get_cmake_dir() to
  cmake_args, guarded by a try/except around import pybind11.
  PEP 517 isolated builds install pybind11 in a temporary directory
  that CMake's find_package(pybind11) cannot otherwise discover.

Verification

Built and tested on Windows 11 x64, Python 3.11.15 (conda-forge), VS
2026 Community (MSVC 14.50.35717), CMake 3.30, Ninja 1.13, pybind11
3.0.3.

Build / wheel

pip install . -v --no-build-isolation                 # 0 errors
pip wheel . -w dist -v --no-build-isolation --no-deps # 0 errors
delvewheel show dist\batoid-*-win_amd64.whl           # see table
delvewheel repair --add-path %CONDA_PREFIX%\Library\bin \
                  -w wheelhouse dist\batoid-*-win_amd64.whl

Bundled into wheel	Assumed present on host
msvcp140.dll	vcruntime140.dll, vcruntime140_1.dll
vcomp140.dll	python311.dll, kernel32.dll, api-ms-win-crt-*

batoid does not link FFTW directly (the FFT dependency goes through
GalSim), so the batoid wheel does not bundle fftw3.dll.

Smoke (touches each patch)

Test	Result	Patch covered
import batoid	0.1.dev1069+gd28bc8a36	build / setup.py
SellmeierMedium(BK7).getN(550 nm)	1.5185223876207927	SellmeierMedium rename
Optic.fromYaml('LSST_r.yaml')	4 sub-items	end-to-end
LSST_r raytrace, polar, theta=(0.5deg, 0)	132 rays in, 114 not vignetted/failed, ~2 um focal-plane spread	OpenMP parallel-for
ObscPolygon([0,1,1,0],[0,0,1,1]).contains(0.5,0.5) / (2,2)	True / False	obscuration.cpp or
Bicubic of 0.01*(x*x+y*y), sag at (0.2, 0.3) and off-grid (5,5)	0.0013... / nan	table.cpp or

Full pytest

:: Run from outside the source tree so pytest resolves the installed
:: package, not the source-layout `batoid/` subdir.
python -m pytest batoid/tests/ -o "addopts=--durations=10 -ra" --timeout=180 --rootdir=batoid

176 passed, 28 failed in 62 s. The 28 failures are all in
tests/test_notebooks.py, all ModuleNotFoundError: No module named 'nbformat' (jupyter test infra not installed; not Windows-specific).

The 176 passing tests cover Asphere, Bicubic, Coating, CoordSys,
CoordTransform, Lattice, Medium, OPDScreen, Obscuration, Optic,
Paraboloid, Plane, Quadric, RayVector, Sphere, Sum, Tilted, Zernike,
analysis, plot, zemax. The OpenMP parallel paths and both alt-token
sites are exercised.

Slowest test cases (top 3)

Test	Time
tests/test_zemax.py::test_HSC_huygensPSF	11.55 s
tests/test_analysis.py::test_doubleZernike	2.64 s
tests/test_Asphere.py::test_sag	1.47 s

Fresh-venv install (no conda PATH)

python -m venv .venv-clean
:: PATH set to .venv-clean\Scripts;System32;... (no conda Library\bin)
.venv-clean\Scripts\pip install <galsim-2.8.4-cp311-...whl> LSSTDESC.Coord astropy
.venv-clean\Scripts\pip install <batoid-...-cp311-...whl> pyyaml scipy matplotlib
.venv-clean\Scripts\python batoid_smoke.py

The cleaned PATH does not include %CONDA_PREFIX%\Library\bin. The
six smoke tests above pass with byte-identical numeric output to the
conda-env run, demonstrating the wheel is self-contained modulo the
GalSim wheel's bundled FFTW.

Wheel notes

• Bundled DLLs: msvcp140.dll, vcomp140.dll. No FFTW (uses
  GalSim's).
• vcomp140.dll is the Microsoft OpenMP runtime, used by the loops
  in batoid.cpp / obscuration.cpp. Choosing /openmp:llvm would
  switch this to libomp.dll. This PR keeps the simpler /openmp
  (set via CMake's find_package(OpenMP)).
• Wheel size: ~8.5 MB; ~6 MB of that is the bundled
  LSST/Rubin/HSC/DECam YAML data files, not C++ code.

Follow-ups

None blocking; each is a separate PR candidate.

• GitHub Actions CI: a windows-latest job + cibuildwheel
  matrix (cp39 .. cp313 -win_amd64). Better aligned after the
  GalSim Windows wheel is upstream so batoid CI can pip install galsim directly.
• Notebook tests: install nbformat, nbclient, ipyvolume in
  CI Windows so the 28 test_notebooks.py cases run.
• Python_EXECUTABLE -> Python3_EXECUTABLE migration:
  setup.py still passes the older form. Works today; can be
  modernized in a separate PR.

Risk and compatibility

• Linux / macOS: every change is either Windows-only logic
  guarded by _WIN32 / generator-aware (setup.py) or a textual
  swap that GCC/Clang accept identically (or -> ||,
  size_t -> ptrdiff_t, member rename).
• OpenMP loop counter signed-vs-unsigned change: switching
  size_t i to ptrdiff_t i on a 64-bit platform preserves range
  for any practical batoid input.
• Sellmeier rename: members are private; not part of the
  documented API.
• MSVC toolset vs bundled runtime: delvewheel warns when the
  bundled msvcp140.dll is older than the toolset that built the
  .pyd. Locally I built with VS 2026 (14.50) and bundled
  conda-forge's 14.44 redistributable. Smoke and pytest both ran
  cleanly. CI on windows-latest (VS 2022, 14.4x) would not see
  the mismatch.

Reviewer questions

1. GalSim Windows wheel timeline: should I plan around it, or is
   it acceptable to land this batoid PR ahead of the GalSim PR (with
   a note that pip install is gated until GalSim ships a Windows
   wheel)?
2. /openmp vs /openmp:llvm for the eventual CI/wheel build.
3. PYTHON_EXECUTABLE -> Python3_EXECUTABLE migration: fold
   into this PR, or separate?
4. CI: a windows-latest + cibuildwheel workflow can follow
   once questions 1-2 are settled. Draft strategy available locally
   if helpful.

Happy to split, rebase, or extend as the project prefers.

[jmeyers314]

Hi! Thanks for this.

Same basic comments as the GalSim PR:

• Please rebase onto / target main
• Please add a Windows CI build since I have no direct access to a Windows machine.

I'll take a closer look when that's ready.