replace EGL with Mesa for CPU off-screen rendering

[m-reuter]

Refactor headless rendering: EGL → OSMesa, clean up GL subpackage

• Replace EGL with OSMesa for headless rendering on Linux. OSMesa requires no GPU, no /dev/dri/ devices, and no display server. Installed via libosmesa6 (system package, no new Python dependency).
• Delete gl/egl_context.py, add gl/osmesa_context.py as a cross-platform drop-in with the same public API (make_current, read_pixels, destroy). Raises a clear RuntimeError with a platform-specific install hint if libOSMesa is not found.
• Delete gl/_platform.py — the PYOPENGL_PLATFORM=egl env-var setter is no longer needed; OSMesa sets the context implicitly via OSMesaMakeCurrent.
• Delete gl/views.py — redistributed its contents to their natural homes:
  • get_view_matrices / get_view_matrix → utils/types.py (pure numpy, no GL, lives alongside ViewType which it maps over)
  • ViewState, arcball_*, compute_view_matrix → cli/whippersnap.py (only consumer; no reason to be in a shared module)
  • Rename _egl_context → _offscreen_context in gl/utils.py — the old name was a historical artefact.
• CI (pytest.yml): Ubuntu installs libosmesa6 for headless rendering. macOS and Windows runners use a GLFW invisible window backed by their GPU drivers — no OSMesa needed, rendering tests expected to run on all three platforms (not skip).
• Docs: Remove all EGL mentions from README.md, DOCKER.md, and Dockerfile; replace with accurate OSMesa descriptions.

[codecov]

Codecov Report

❌ Patch coverage is 50.96774% with 76 lines in your changes missing coverage. Please review.
✅ Project coverage is 37.93%. Comparing base (34d1514) to head (3111537).

Files with missing lines	Patch %	Lines
whippersnappy/cli/whippersnap.py	0.00%	39 Missing ⚠️
whippersnappy/gl/utils.py	43.58%	16 Missing and 6 partials ⚠️
whippersnappy/gl/osmesa_context.py	80.28%	9 Missing and 5 partials ⚠️
whippersnappy/utils/types.py	80.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #61      +/-   ##
==========================================
- Coverage   40.02%   37.93%   -2.09%     
==========================================
  Files          23       21       -2     
  Lines        2131     2019     -112     
  Branches      327      311      -16     
==========================================
- Hits          853      766      -87     
+ Misses       1177     1163      -14     
+ Partials      101       90      -11     

Flag	Coverage Δ
unittests	37.93% <50.96%> (-2.09%)	⬇️

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[Copilot]

Pull request overview

Refactors WhipperSnapPy’s headless OpenGL rendering path to use Mesa OSMesa (CPU software rendering) instead of EGL, and reorganizes view-matrix utilities out of the gl subpackage while updating CI/Docker/docs accordingly.

Changes:

• Replace EGL headless context with a new OSMesa-based offscreen context and update GL context creation/teardown paths.
• Move canonical view-matrix helpers into utils.types and relocate GUI-only view state/arcball utilities into the CLI module.
• Update CI workflows, Docker image dependencies, and documentation to reflect OSMesa-based headless rendering.

Reviewed changes

Copilot reviewed 19 out of 19 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
whippersnappy/utils/types.py	Adds canonical per-view 4×4 numpy view matrices + accessors alongside ViewType.
whippersnappy/snap.py	Updates imports to use get_view_matrices from utils.types.
whippersnappy/gl/views.py	Removes view matrices + interactive view state helpers from gl package.
whippersnappy/gl/utils.py	Switches fallback headless rendering path from EGL to OSMesa; adds platform selection env var logic; updates context handling.
whippersnappy/gl/osmesa_context.py	Introduces new OSMesa offscreen context implementation via ctypes.
whippersnappy/gl/egl_context.py	Removes EGL headless context implementation.
whippersnappy/gl/_platform.py	Removes EGL-specific PyOpenGL platform bootstrapper.
whippersnappy/gl/__init__.py	Updates package exports/docs now that views/EGL are removed and view matrices live in utils.
whippersnappy/cli/whippersnap.py	Moves GUI-only ViewState + arcball helpers into CLI (only consumer) and updates view-matrix usage.
whippersnappy/__init__.py	Removes previous EGL platform selection / display probing logic.
tests/test_array_and_rendering.py	Adjusts rendering test behavior and introduces macOS CI skip for rendering tests.
doc/conf.py	Tweaks numpydoc configuration for dataclass attribute documentation and ignore patterns.
README.md	Updates user-facing docs from EGL to OSMesa headless rendering description.
Dockerfile	Swaps EGL system dependency for libosmesa6 to support headless CPU rendering.
DOCKER.md	Updates Docker guide to describe OSMesa-based headless rendering.
.github/workflows/pytest.yml	Installs libosmesa6 on Ubuntu; adds Windows Mesa software OpenGL setup; documents platform strategy.
.github/workflows/publish.yml	Updates Ubuntu system deps from EGL to OSMesa.
.github/workflows/doc.yml	Updates Ubuntu system deps from EGL to OSMesa.
.github/workflows/build.yml	Updates Ubuntu system deps from EGL to OSMesa.

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