Summary

This repository provided as a working example of additions to the Adobe OpenType Feature File Specification currently under review.

It contains glyph outline sources for the Roman face of Source Serif 4 Variable (in the form of 9 UFOs) together with a single set of feature files, a build script, and other related files.

This example is intended to serve multiple purposes:

• To demonstrate how a variable font can now be built using a single feature file hierarchy (rather than one hierarchy per-UFO).
• To provide a context for experimenting with the grammar by adding to or changing one or more feature files, building the altered font, and examining the result.
• To introduce a beta version of AFDKO that supports the feature file syntax additions.

Building the sources

The font can be built by following these steps:

1. Clone (or otherwise download) a copy of this repository to a directory on a computer with an installation of Python 3.9, 3.10, 3.11, or 3.12.

2. If the operating system is Windows or MacOS X, you should be able to install the needed version of AFDKO (5.0.0b15) using pip or another Python package installer. For example, you could run

   pip install afdko==5.0.0b15

   If the operating system is Linux you may be able to install from the PyPI wheel, but more likely you will need to compile AFDKO from source. Tag 5.0.0b15 corresponds to the intended release; more recent updates to this version of the code may be available in the addfeatures branch. The repository code contains advice on installation. We do not recommend attempting to build against Python 3.13 at this time.

3. Execute the buildVF.py build script. It should run without any arguments. The optional -v argument will make the script show the output of the commands it runs. The optional --hinted argument will use otfautohint to add PostScript-style hinting to the built font.

4. After a successful build output will be in the target/VAR subdirectory

About AFDKO 5.0.0b15

The AFDKO release that can build these sources is fully-featured but experimental. The current (at the time of writing) 4.0.1 release of AFDKO is built from C-language sources for separate programs packaged in a somewhat idiosyncratic way. Virtually all of the code for the 5.0.0b15 release has been ported to at least low-level C++ and much of it is fully ported to modern, object-based C++. It is intended to do all of what 4.0.1 does, and passes our automated test suite, but there may still be bugs. We do not recommend building fonts intended for publication with the new code until it is included in a "standard" release.

Help or Advice

If you have questions about this repository or are having trouble building from the sources, open the Discussions tab and look to see if there is relevant help. If not, start a new discussion and we will try to assist you or provide you with more information.

Kerning and Mark Data Processing

The files kern.fea and locations.fea in the features directory were produced by running

bin/kernFeatureWriter.py -s Roman/SourceSerif4Variable-Roman.designspace

and the files mark.fea and mkmk.fea in the same directory were produced by running

bin/markFeatureWriter.py -t -m Roman/SourceSerif4Variable-Roman.designspace

It is not necessary to re-run these scripts to build the font. If you wish to run them the Python packages fonttools and defcon must be installed.

The scripts are included to demonstrate how UFO kerning and mark data from separate UFOs can be translated into variable values in a feature file.

Note that the location names in locations.fea (which is required by the output of markFeatureWriter.py, but only produced by kernFeatureWriter.py) are taken from the com.adobe.shortInstanceName entry in each UFO's lib.plist file. If this key is not present the script will automaticaly generate a (not very clever) location name for the instance corresponding to that UFO.