Fonts OpenType math illuminated ∗

In recent years, we have seen the development of new TEX engines, X E TEX and LuaTEX, adopting OpenType font technology for providing Unicode typesetting support. While there are already plenty of OpenType text fonts available, both from the TEX community and from commercial font suppliers, there is little support for OpenType math fonts so far. Ironically, it was left to Microsoft to develop a de facto standard for OpenType math font information and to provide the first reference implementation of a full-featured OpenType math font. In order to develop the much-needed math support for Latin Modern and TEX Gyre fonts, it will be crucially important to develop a good understanding of the internals of OpenType math tables, much as it is necessary to develop a good understanding of Appendix G and TEX’s \fontdimen parameters to develop math support for traditional TEX fonts. In this paper, we try to help improve the understanding of OpenType math internals, summarizing the parameters of OpenType math fonts as well as illustrating similarities and differences between traditional TEX math fonts and OpenType math fonts. 1 Background on OpenType math In recent years, the TEX community has been going through a phase of very significant developments. Among the most important achievements, we have seen the development of new TEX engines, X E TEX and LuaTEX, providing support for Unicode and OpenType font technology. At about the same time we have also seen the development of new font distributions, Latin Modern and TEX Gyre, provided simultaneously in Type 1 format as a set of 8-bit font encodings as well as in OpenType format. Together these developments have enabled TEX users to keep up with current trends in the publishing industry, providing users of the new TEX engines with a comprehensive set of free OpenType fonts and enabling them to take advantage of the many offerings by commercial font suppliers. As far as text typesetting is concerned, support for OpenType font technology in the new TEX en∗ First published in Biuletyn GUST 25 (2009), pp. 7–16, proceedings of the BachoTEX XVII conference. Reprinted with permission. gines is already very advanced, supporting not only traditional typographic features of Latin alphabets, but also addressing the very complex and challenging requirements of Arabic typography. However, when it comes to math typesetting, one of the traditional strongholds of TEX, support for Unicode and OpenType math is only just beginning to take shape. Ironically, it was left to Microsoft to develop the first system to offer support for Unicode math. When Microsoft introduced support for math typesetting in Office 2007 [1, 2], they extended the OpenType font format and commissioned the design of Cambria Math [3] as a reference implementation of a fullfeatured OpenType math font. Fortunately for us, Microsoft was smart enough to borrow from the best examples of math typesetting technology, thus many concepts of OpenType math are not only derived from the model of TEX, but also go beyond TEX and introduce extensions or generalizations of familiar concepts. While OpenType math is officially still considered experimental, it is quickly becoming a de facto standard, as it has already been widely deployed to millions of installations of Microsoft Office 2007 and it is also being been adopted by other projects such as the FontForge [4] font editor and independent font designs such as Asana Math [5]. Most importantly, support for OpenType math has already been implemented or is currently being implemented in the new TEX engines, thus adopting OpenType math for the development of the muchneeded Unicode math support for Latin Modern and TEX Gyre obviously seems to be a most promising choice of technology. 2 Design and quality of math fonts When it comes to developing math fonts, designing the glyph shapes is only part of the job. Another part, which is equally important, is to adjust the glyph metrics of individual glyphs and to set up the global parameters affecting various aspects of glyph positioning in math typesetting. As we have discussed at previous conferences, the quality of math typesetting crucially depends on the fine-tuning of these parameters. Developing a good understanding of these parameters will therefore become an important prerequisite to support the development of new math fonts. In the case of traditional TEX math fonts, we have to deal with the many \fontdimen parameters which have been analyzed in Bogusław Jackowski’s paper Appendix G Illuminated and a follow-up paper by the present author [6, 7].