Compatibility of glfw with the Apple software render in github CI

[HinTak]

Github CI has a mac os runner which is headless AFAIK, but it has a software renderer. However, glfw can't get to it - this can be illustrated by this pull (do not merge) which runs glfwinfo after build:
#2569

Both OSX OpenGL (the GLUT part) and SDL2 can get at the apple software renderer within github CI, so this is a glfw specific problem. It would be useful to nake this work, to allow glfw to be used within github's own CI workflow for testing.

I came to be here after going down the rabbit hole of trying to look at a mac os specific problem in skia-python (which has CI testing for all three platforms, and been using glut for testing on mac os x for the above reasons, instead of glfw as in the case of linux with Xvfb):
kyamagu/skia-python#214
and downstream FlorianRhiem/pyGLFW#80

[HinTak]

That sdl2 and opengl on osx works happily headless can been seen in the CI in FlorianRhiem/pyGLFW#80 (comment)

[dougbinks]

Copying the output of the MacOS run of glfwinfo here for more information:

Error: NSGL: Failed to find a suitable pixel format
GLFW header version: 3.5.0
GLFW library version: 3.5.0
GLFW library version string: "3.5.0 Cocoa NSGL Null EGL OSMesa monotonic"
GLFW platform: Cocoa
GLFW supported platforms:
 Cocoa
 Null
Vulkan loader: missing

[dougbinks]

#2080 is related

[HinTak]

For a successful run (with either SDL2 or GLUT) within github CI's macos 14 runner, the GL context reports its vendor/renderer, version, shader version as:

b'Apple Inc.'
b'Apple Software Renderer'
b'4.1 APPLE-21.0.19'
b'4.10'

[HinTak]

Glfw itself has an offscreen rendering example : https://github.com/glfw/glfw/blob/master/examples/offscreen.c . It probably should be run post-build to check that it can run!

[HinTak]

In my fork's ci branch I have added the two lines from #2080, as well as running both glfwinfo and the offscreen example. Here is the result from github action:

Run ./build-cocoa-static/examples/offscreen
  ./build-cocoa-static/examples/offscreen
  shell: /bin/bash -e {0}
  env:
    CFLAGS: -Werror
    MACOSX_DEPLOYMENT_TARGET: 10.11
    CMAKE_OSX_ARCHITECTURES: x86_64;arm64
0s
Run ./build-cocoa-static/tests/glfwinfo
GLFW header version: 3.5.0
GLFW library version: 3.5.0
GLFW library version string: "3.5.0 Cocoa NSGL Null EGL OSMesa monotonic"
GLFW platform: Cocoa
GLFW supported platforms:
 Cocoa
 Null
OpenGL context version string: "2.1 APPLE-21.0.19"
OpenGL context version parsed by GLFW: 2.1.0
OpenGL context renderer string: "Apple Software Renderer"
OpenGL context vendor string: "Apple Inc."
OpenGL context shading language version: "1.20"
OpenGL framebuffer:
 red: 8 green: 8 blue: 8 alpha: 8 depth: 32 stencil: 8
 samples: 0 sample buffers: 0
 accum red: 0 accum green: 0 accum blue: 0 accum alpha: 0 aux buffers: 0
Vulkan loader: missing

[HinTak]

In stock, running the offscreen example post-build gives:

Run ./build-cocoa-static/examples/offscreen
Error: NSGL: Failed to find a suitable pixel format
Error: NSGL: Failed to create OpenGL context
Error: OpenGL version string retrieval is broken
Error: Process completed with exit code 1.

[HinTak]

Linked from #589 is
d79056f on the software-context branch, which contains most of the knowledge. However, my goal is that glfw (and its dependent, pyglfw) should be usable within github's own CI system, preferably without client-side code change or addition. Adding a Xvfb line is not too painful, but no-client-side special hint is preferred.