Use JSON UFOs for intermediate output

[madig]

Glyphs files are converted to normal UFOs currently, which is slow. Writing out JSON blobs is faster, especially for bigger projects.

[eliheuer]

Thanks! This can all be done just with ufoLib2 right? The stuff from this PR?

[madig]

Yep. Instead of Font.open(...) and ufo.save(...) you do Font.json_loads(...) ufo.json_dumps(...) or whatsitcalled.

[anthrotype]

if you're calling fontmake as a subprocess (as you should) you just need to pass --ufo-structure=json option, optionally with --indent-json if you want it human readable (probably not if you care about speed).
If you're messing with fontmake internal API, there's a ufo_structure and indent_json parameters to various methods on FontProject that accomplish the same (grep for it).

[anthrotype]

also, you want to depend on fontmake[json] extra which activates ufoLib2[json] extra which in turns pulls in cattrs and orjson

[simoncozens]

After much trial and error I discovered that I need to write a function like this:

def open_ufo(path):
    if os.path.isdir(path):
        return ufoLib2.Font.open(path)
    else:
        return ufoLib2.Font.json_loads(open(path, "rb").read())

[anthrotype]

yes, like fontmake itself does: https://github.com/googlefonts/fontmake/blob/6a8b2907891537ce559dd3d6fcfe68d8b55d6bc9/Lib/fontmake/font_project.py#L160-L169

we didn't want Font.open to handle json because this is not an official UFO format but only a private ufoLib2-only serialization format

[anthrotype]

@simoncozens your open_ufo snippet above would not correctly handle .ufoz (zipped UFOs, which are also not a directory), it's better you check if the suffix is .json, treat it as such otherwise let ufoLib2 Font.open handle the others

[simoncozens]

I sort of see that for UFO libraries in general, this is ufoLib2 and we're talking about ufoLib2-specific format. It should be able to open its own files.

[simoncozens]

Using standard UFOs in the new builder, on Noto Sans Mono (158 build steps, 120 targets)

1238.11s user 90.81s system 654% cpu 3:23.10 total
1274.70s user 91.34s system 667% cpu 3:24.56 total

Using JSON UFOs:

998.50s user 31.00s system 665% cpu 2:34.74 total
1047.40s user 33.79s system 626% cpu 2:52.69 total

20% speed-up. Nice.

[simoncozens]

Closing this because builder2 (which is the future) does it.