Adobe ventures into open fonts

Adobe surprised many in open source circles with its August 2 release of Source Sans Pro, an open font made available under the standard SIL Open Font License (OFL). Adobe has not historically been an open source player (beyond its involvement with standard file formats like PDF or SVG), so Source Sans Pro is not only its first foray into open fonts, but may also herald an interest in adopting open source development methods.

Designer Paul Hunt announced the font in a post on the Adobe typography blog. The font is available in six weights, with regular and italic versions for each. The first release covers an extended Latin character set, but according to the comments other writing systems are reportedly still to come. Downloads are hosted at SourceForge.net.

Hunt said Adobe created the new font to provide a user interface (UI) font for the company's open source software projects, including its Strobe media playback framework and Brackets code editor, both of which are web applications. An open font allows Adobe to control the UI by delivering the font to the user's browser via CSS's @font-face rule.

The design of the font is inspired by early-20th-Century gothics from American Type Founders, such as News Gothic and Franklin Gothic, but it is the original work of Hunt and not a derivative of those originals. This distinction is a subtle one, but comparing Source Sans Pro to News Cycle (which is my own open font designed as a faithful revival of News Gothic), there are clear differences. In addition to miscellaneous differences between specific glyphs, Source Sans Pro is set wider, is a bit rounder, includes a bit more contrast, and incorporates a different approach to accents. Hunt said in the blog post that he intentionally paid attention to distinguishing between l (lower-case L), I (upper-case i), and 1 (the numeral), which was a less common concern a century ago.

Although the font covers "only" Latin characters, the implementation supports a wide array of languages that use the variations of the basic Latin alphabet (such as additional base characters and diacritic marks). Some of the languages supported, such as Vietnamese, Romanized Chinese, Navajo, and various Eastern European languages, are often under-served by even the commercial font industry. The font also includes some typographic features often omitted from open fonts, such as old-style or "text figure" numerals and alternate styles of various letters (such as variations of I (upper-case i) with and without horizontal top- and bottom-caps, which can further distinguish it from l and 1).

There are also Multiple Master (MM) versions of the fonts included in the release, which is unusual. MM fonts are a rarely-employed format developed at Adobe, in which a set of parameters (usually weight and width) can be adjusted at will to change the appearance of the font. For example, an MM font might ship with an Extra Light and an Extra Black version, representing the lightest and darkest ends of the weight spectrum. The user can then use MM to interpolate smoothly between these extremes to find the right look for the project at hand. It is a clever idea, and spares the designer the overhead of producing separate versions for Extra Light, Light, Demi Bold, Bold, Extra Bold, and so on, ad nauseum.

Similarly, the differences between Condensed and Extra Wide versions can be interpolated to produce various widths in between. Software could naively interpolate between two widths of a non-MM font, too, but the naive approach produces undesirable results (such as fattening or squeezing the line widths in addition to the open spaces of the characters). The MM format is designed to produce eye-pleasing output. In practice, though, most people rarely use more than one or two weight or width variations, so MM has not taken the world by storm.

Building

The release itself is in the form of Zip archives, one of which contains the fonts themselves in both TrueType and OpenType CFF format, and one of which contains the fonts plus the source files used to generate them. The contents of the source package will not be easy to take advantage of for Linux users, however. It consists of spline font sources (in Postscript .SFA format), sources for the proprietary Fontlab editor (in .VFB format), and a set of auxiliary text files used by Adobe's build tools. These text files contain information such as hinting, kerning pairs, and tables of characters composed out of other components (primarily accented letters). The auxiliary files are built for use with Adobe Font Development Kit for OpenType (AFDKO), Adobe's "font SDK."

AFDKO implements the font-building portion of Adobe's font development workflow. The glyph outlines are developed in a separate application (such as Fontlab) in PostScript Type 1 format. AFDKO includes proofing and validation tools, plus scripts that add OpenType features (such as substitution rules or stylistic alternates) based on text configuration files like those included with the Source Sans Pro package. It also includes scripts to build installable font files. Although the documentation says several of the individual scripts in AFDKO are open source, the download as a whole is not; the license agreement forbids reverse-engineering. The auxiliary files themselves are not in a standard, documented format that other tools can utilize.

However, that does not mean the auxiliary files are of no value. Some of their information could be extracted with minimal fuss and the judicious application of scripting. Many of the same features can also be extracted from the font files themselves in an open source editor like FontForge. Vernon Adams, developer of KDE's Oxygen font, commented on the blog post that he was interested in extracting the horizontal spacing information from Source Sans Pro and adapting it to Oxygen.

In the purely-open-source font development workflow, adding OpenType features to a font is typically done in FontForge — although it is far from pleasant. FontForge hides the necessary options and tools remarkably well, and effectively dictates that building the final font files be done manually. Better command-line tools like those in AFDKO could help automate the procedure. Intriguingly enough, several commenters in the blog post discussion raised questions about AFDKO, and Hunt replied with interest asking what would be necessary to make the release buildable on Linux.

In reply, Hunt got advice not just on the build process, but on how to set up Source Sans Pro as a "real" project and not just a Zip-dump — including issue tracking, revision control, and a development mailing list. He gave a hopeful-sounding response:

Bug reports and fixes are already beginning to queue up, too. Several on the Open Font Library list noticed problems with the weight values of the fonts (numeric metadata used to sort the various "light" to "heavy" versions of the font). As John Haltiwanger put it, "And (finally) we are legally allowed to fix a broken element in an Adobe font!"

Fonts and project management

Adobe is not alone among open font projects that come up short on bug tracking, revision control, and other development tools. Only a few large font projects tackle these challenges, and they do so in decidedly different ways. DejaVu, Liberation, SIL, and Ubuntu all employ different methods for tracking issues and feature requests, managing source code, merging patches, and making releases. Individuals working on a handful of personal font projects are even less likely to deploy such support utilities.

The lack of formal source code repositories and issue trackers generally means that distributions undertake the work of packaging and testing open fonts. Because Source Sans Pro relies on the non-free Fontlab and AFDKO, one might think it has scant chances of working its way into distribution packages, but Fedora's Ian Weller observed that Fedora's guidelines do not require that a font be buildable with open source software alone — they merely recommend it. A Fedora review request was opened on August 4. There is also a package request for the font in Debian, although Debian's guidelines dictate that a font with a non-free build path will be packaged for contrib.

There are a few inconsistencies in the Zip files, such as which feature files are present in which directories, and which include .SFA versus .VFB source files. Those are problems that source code management would help quash. Hunt also teased the future release of a monospace version of the font, which would be of particular interest to developers. Seeing such ongoing work in the open would also be a nice touch, and would allow the community to contribute to the process. However, one should not lose sight of Source Sans Pro's importance even in Zip format: Adobe has released its first open font, its team seems well aware of the issues involved (licensing and tool support included), and is expressing interest in fitting the project into the expected conventions and procedures of open source.