The technology behind variable fonts is officially called OpenType Font Variations. It has been jointly developed by
Microsoft,
Google,
Apple, and Adobe, in an unprecedented collaborative effort also involving technical experts from font foundries and font tool developers. In addition to specifying the font format additions and revisions, the working group has also committed to the goal of interoperable implementation, defining expected behaviours and test suites for software displaying variable fonts. This should be welcome news to font developers and users, who have often struggled with incompatible implementations of earlier aspects of OpenType that were left to the interpretation of individual software companies.
OpenType Font Variations builds on the model established in Apple’s TrueType GX variations in the mid-1990s, but has fully integrated that model into all aspects of the OpenType format, including OpenType Layout, and is available to both TrueType and Compact Font Format (CFF) flavours of OpenType. This has meant not only the addition of numerous tables to the format, but also revision of many existing tables; these changes are summarised in an appendix to this article, which is intended as an introduction and technological summary, primarily for font makers and font tool developers. The full technical specification for OpenType Font Variations is incorporated into the OpenType specification version 1.8.
