ofl-font-baker 0.1.4

Font merge engine — combine two font files into one via cmap-based glyph replacement

Font Merge Engine

English | 日本語

The core font merge engine behind OFL Font Baker. The code in this directory is MIT-licensed and can be freely used in other projects.

Merges a base font (typically CJK) with a sub font (typically Latin or kana) into a single font file, replacing glyphs and OpenType features via cmap-based mapping.

For details on features and background, see the OFL Font Baker repository.

Installation

pip install ofl-font-baker

Requires Python 3.9+. fonttools and brotli are installed automatically.

Usage

Provide a JSON config on stdin. When outputDir is present, the engine produces a full export directory with font files and metadata.

cat config.json | python3 merge_fonts.py

Export Mode

Input:

{
  "base": {
    "path": "/path/to/base.otf",
    "scale": 1.0,
    "baselineOffset": 0,
    "axes": []
  },
  "latin": {
    "path": "/path/to/latin.ttf",
    "scale": 1.0,
    "baselineOffset": 0,
    "axes": []
  },
  "outputDir": "/exports",
  "outputFolderName": "MyFont-Regular",
  "overwrite": false,
  "outputFamilyName": "My Font",
  "outputWeight": 400,
  "outputItalic": false,
  "outputWidth": 5,
  "outputOptions": {
    "includeWoff2": true,
    "writeConfigJson": false,
    "bundleInputFonts": false
  }
}

Output (JSON manifest on stdout):

{
  "outputDir": "/exports/MyFont-Regular",
  "fontPath": "/exports/MyFont-Regular/MyFont-Regular.otf",
  "woff2Path": "/exports/MyFont-Regular/MyFont-Regular.woff2",
  "oflPath": "/exports/MyFont-Regular/OFL.txt",
  "settingsPath": "/exports/MyFont-Regular/Settings.txt",
  "configPath": null,
  "files": [...]
}

Progress is emitted as JSON lines on stderr.

outputOptions

Key	Default	Description
includeWoff2	true	Generate a WOFF2 file alongside the main font.
writeConfigJson	false	Write an ExportConfig.json that records the merge settings.
bundleInputFonts	false	Copy the input fonts into a source/ subdirectory and rewrite paths in ExportConfig.json to relative paths (e.g. ./source/Base.otf). Automatically enables writeConfigJson. Makes the export directory self-contained and reproducible.
fontDir	null	Write the font file (OTF/TTF) directly into this directory instead of the default export subfolder. The directory is created if it doesn't exist.
woff2Dir	null	Write the WOFF2 file into this directory instead of alongside the font file. The directory is created if it doesn't exist.
writeOfl	true	Write OFL.txt into the export directory. Set to false if you manage the license file yourself.
writeSettings	true	Write Settings.txt into the export directory.

Top-level options

Key	Default	Description
metricsSource	"base"	Which font's vertical metrics (OS/2, hhea) to use. "base" keeps the base font metrics and expands only when the Latin font is larger. "latin" overwrites with the Latin font's metrics.

Tests

python3 -m pytest python/tests/test_merge.py -v

Test fonts are in testdata/fonts/ (repository root).

License

The source code in this directory is licensed under the MIT License. See LICENSE for details.

Other parts of the parent repository (OFL Font Baker) are licensed under AGPL-3.0-or-later and are not covered by this MIT notice.