In early 2008, as part of writing and typesetting CJKV Information Processing, Second Edition and preparing the latest version of Adobe Tech Note #5078 (The Adobe-Japan1-6 Character Collection), I built a small—in terms of the number of glyphs—special-purpose font for displaying registration marks for glyphs, and named it Tombo. Such registration marks are incredibly useful for showing the relative position of a glyph within its em-box, and for conveying the visual horizontal advance (aka glyph width). The excerpt above shows this font’s use in the Source Han Sans ReadMe (note that the PDF file will download if clicked).
In 2008, support for Adobe-Identity-0 ROS CID-keyed OpenType/CFF fonts wasn’t very broad, so I built this as a name-keyed OpenType/CFF font. For simplicity, I mapped U+230C (BOTTOM RIGHT CROP) and U+230D (BOTTOM LEFT CROP) to its only two functional (and non-spacing) glyphs, which are actually pre-composed forms of <230C 230E> and <230D 230F>.
I spent part of yesterday and today building a new version of this font, renamed as Tombo SP (トンボ SP), with the following enhancements:
- I rebuilt the font as an Adobe-Identity-0 ROS CID-keyed OpenType/CFF font.
- The number of functional glyphs tripled. In addition to pre-composed glyphs that correspond to <230C 230E> and <230D 230F>, I also included individual glyphs for all four characters.
- The ‘ccmp‘ (Glyph Composition / Decomposition) GSUB feature is used to substitute the sequences <230C 230E>, <230E 230C>, <230D 230F>, and <230F 230D> for their pre-composed left- and right-side forms.
- For user convenience, the pre-composed glyphs are also mapped from U+005B (LEFT SQUARE BRACKET) and U+005D (RIGHT SQUARE BRACKET).
In any case, I released the font this morning on GitHub as the open-source Tombo SP project.