Fonts & Encodings

14.5. Managing AAT Tables in FontForge

Up to now we have seen how the two main software packages (FontLab and FontForge), as well as another piece of software that specializes in this task (VOLT), manage Open-Type tables. But OpenType is not the only way to enrich a TrueType font. Recall that in parallel with the work by Microsoft and Adobe on TrueType Open and OpenType, Apple developed the TrueType GX format, which was latter rechristened AAT. Currently AAT fonts can be used only under Mac OS X, but they are no less interesting for that. The magnificent font Zapfinoitself is reason enough for us to examine the possibilities of AAT fonts. The contextual character of the Arabic and Indian fonts of the Mac OS X operating system is also managed entirely by AAT.

One detail that is not insignificant: while OpenType fonts can be based on TrueType or PostScript CFF outlines, AAT fonts can be based only on TrueType outlines.

In §D.11.5.1 of this book, we provide a rather exhaustive technical description of AAT tables. In this section, we shall discuss only the insertion of these tables into TrueType fonts.

For the moment, only FontForge has seriously confronted the problem.^[14-10] The problem is in no way trivial, as AAT tables use finite automata to perform substitutions or contextual positionings. A finite automaton is a method that can be illustrated more easily with diagrams, by ...