mongfontbuilder

The Python library that helps font designers and developers produce a standard-compatible Mongolian script font, as clarified by the documentation of the working draft of UTN #57, Encoding and Shaping of the Mongolian Script (the Mongolian UTN). It also acts as the reference implementation of that document.

The library is maintained in this project and published to PyPI. To install it in terminal:

pip install mongfontbuilder

The library includes various utilities, including:

• Python API for the data files.
• Dynamic generation of OpenType Layout rules.
• Construction of a complete font from a minimal glyph set.

A CLI is also available — it reads a source UFO font and writes a complete font with the generated OTL rules. Run from the repository root:

uv run python -m mongfontbuilder input.ufo output.otf --locales MNG

Both .ufo and .otf output formats are supported. See --help for available locales.

The documentation, the specification data, and the Glyphs templates are maintained in the repository this project belongs to, Kushim-Jiang/mongolian.

Development

The project is developed with uv. It is a member of the uv workspace the repository root declares, so the environment and the lockfile it is developed with are the ones of the repository root, and the commands below are run from there. Set up the environment and install the development tools (pytest, ruff, pyright, uharfbuzz, glyphsLib) with:

uv sync

Tests

The test suite is run with:

uv run pytest

The harness builds each test font on the fly using the package API, shapes the test strings with HarfBuzz, and compares the resulting glyph sequence with the expected output. The tests are organized per writing system, each with its own UFO test font and test cases under tests/data/:

• Hudum (MNG), from tests/fonts/hudum.ufo, is validated against the EAC and core suites (eac-hud, core-hud);
• Manchu (MCH), from tests/fonts/manchu.ufo and tests/fonts/manchu-ag.ufo, is validated against the core suite (core-man);
• Sibe (SIB), from tests/fonts/sibe.ufo, is validated against the core suite (core-sib).

A font that writes with every writing system at once, from tests/fonts/unified.ufo, is validated against the same cases by tests/test_unified.py; the font it composes and the cases it runs are in tests/unified.py.

Cases the EAC expects differently

The EAC suite is settled by the Hudum standard alone. Where the UTN model disagrees with it, the case is marked as an expected failure — it is kept in the suite, and the reason is kept in tests/fixtures.py — so that the run stays green and the disagreement stays visible.

A font that writes with every writing system at once (test_unified.py) is the one that has to be marked for the cases below: the meeting held that the effect of an FVS does not depend on the locale, so the FVS stays valid and selects its variant wherever the character is shared. A font that writes with one writing system answers them as the EAC expects.

• MND11-2, MNM10-2, MNM11-2, MNS11-26, MNZ11-3, MNZ21-5, XIM11-11, XIM11-675, XIM11-678, XIM11-681, XIM11-684, XIM11-687, XIM11-690, XIM11-694

XIM11-46 (e n fvs3 mvs e) is answered differently by every font as well, but for a reason of its own: the FVS3 follows the n, and the UTN model draws the form it selects rather than the one the EAC expects.

The cases below are marked for every font, because the UTN model answers them differently from the EAC in a way that does not depend on which writing systems a font carries.

• XIM11-39, XIM11-40, XIM11-41 — the UTN model keeps the old functionality of NNBSP, so the features of NNBSP stay on.
• XIM11-1012 — a letter before an MVS is in the final position, so the FVS after it selects the final variant.

Glyphs templates

The Glyphs templates in the repository's templates/ directory are generated from the test UFO fonts and the output of the OTL composer, and are updated from the repository root with:

uv run python templates/update.py

This rewrites hudum.glyphs/hudum.fea and manchu.glyphs/manchu.fea. Template generation is macOS-only (it requires the Glyphs app via glyphsLib), and the corresponding tests in tests/test_templates.py are skipped on other platforms.