Tombo SP is a special-purpose OpenType/CFF font that is intended to be used to display registration marks for glyphs, which is useful for illustrating glyph widths or the position of glyphs within the em-box. The positioning of the glyphs assumes that the em-box is set 12% below the Latin baseline and is one-em tall, meaning that it is tailored for CJK use.
The glyphs are mapped from U+230C through U+230F, and the 'ccmp' GSUB feature is used to access pre-composed forms of the left- and right-side pairs, meaning that <230D 230F> or <230F 230D> can be used to form the left-side registration marks, and that <230C 230E> or <230E 230C> can be used to form the right-side ones. For user convenience, the pre-composed left- and right-side pairs are also mapped from U+005B and U+005D, respectively.
To build the binary font file from source, you need to have installed the Adobe Font Development Kit for OpenType (AFDKO). The AFDKO tools are widely used for font development today, and are part of most font editor applications.
In this repository, all necessary files are in place for building the OpenType/CFF font, and the COMMANDS.txt file provides the command lines that are used.
For any suggestions for changes, please create a new issue for consideration.