Python 3 library/tool to compare two TTF fonts against each other. It's capable of producing diff images using Harfbuzz, Cairo and FreeType. It can also produce Markdown reports for Github.

Currenly only supports TrueType flavoured fonts - CFF/OTF flavour fonts are not supported!

Glyph matching

Most differs will only compare glyphs if they have matching names. Diffenator matches glyphs by creating a key consisting of the unicodes and OT features used to produce the glyph. This allows us to make comparisons where font A uses AGl names whilst font B uses uniXXXX names.

Mark positioning

Marks coordinates are relative to the glyph's outlines, not the glyph metrics.

Kerning

Pair and class to class kerning are supported. The class kerns get flattened into pairs. Unfortunately this approach is very slow and needs improving.

Upm aware

Values by default are scaled in relation to the font's upm. This means we can easily compare fonts with differing upms. e.g

font_before @1000upm

• kern = pos A V -100;

font_after @2000upm

• kern = pos A V -200

This example won't produce a match, visually they will appear the same.

• gsub_diff: Cannot parse gsub rules LookupTypes 5, 6, 8

The developers of fontTools are working on otlLib which will make working with GPOS and GSUB tables much easier.

pip install fontdiffenator

To generate images, you will need to install Cairo, FreeType and Harfbuzz. Easiest way to do this is by using a package manager. For OS X we can use brew.

brew install cairo
brew install freetype
brew install harfbuzz

$ git clone https://github.com/googlefonts/fontdiffenator
$ cd fontdiffenator
$ virtualenv venv
$ source venv/bin/activate
$ pip install . # -e . for dev installation

$ diffenator ./path/to/font_before.ttf ./path/to/font_after.ttf

# Generate before and after gifs

$ diffenator ./path/to/font_before.ttf ./path/to/font_after.ttf -r ./path/to/out_gifs

>>> from diffenator import DiffFonts
>>> from diffenator.font import DFont
>>> font_before = DFont('./path/to/font_before.ttf')
>>> font_after = DFont('./path/to/font_after.ttf')
>>> diff = DiffFonts(font_before, font_after)
...

Tests are located in the /tests dir. Tests are based on the standard unittest framework.

sh ./tests/run.sh