Nico Verbruggen 6cd3e2b20b Refactor CLI flags into modal options and add presets ...

This is a big commit that fixes a variety of issues and prevents fonts
from growing far too large without any benefits. Previously, converted
fonts would use multiple subtables for the `kern` table, but sadly those
are usually not read by renderers, so we now don't save al kern pairs,
but we prioritize.

The full list of changes can be found below.

---

Replace individual boolean flags with modal --kern and --hint options:

- --hint {skip,additive,overwrite,strip}: controls hinting behavior,
  including new ttfautohint support (additive/overwrite modes)
- --kern {add-legacy-kern,legacy-kern-only,skip}: replaces the old
  --skip-kobo-kern and --remove-gpos flags
- --preset {nv,kf}: bundled configurations for common workflows

Add upfront dependency checking (`ttfautohint`, `font-line`) so missing
tools are caught before any processing begins.

Fix GPOS Extension lookup (type 9) support: kern pairs were silently
missed in fonts that wrap PairPos subtables in Extension lookups.

Rework legacy kern table writing to respect format 0 size constraints.
The subtable length field is uint16, limiting a single subtable to
10,920 pairs. Since most renderers (including Kobo) only read the first
subtable, we write exactly one and prioritize pairs by Unicode range.

=> Basic Latin > Latin-1 Supplement > Latin Extended > rest

This way, the most commonly encountered kerning pairs are preserved
when truncation is needed (and it usually is, for quality fonts).

2026-03-14 16:28:25 +01:00

..

kerndiff.py

Max 10k pairs per kern subtable (Fixes #1)

2025-08-22 11:16:03 +02:00