Variation Sequence Characters in a font?

Andreas Stötzner
Andreas Stötzner Posts: 829
in Font Technology
This detail is new to me and I didn’t find very much about it: The task is to create some Standard Variation Sequence characters in a font, e.g. for mathematical relation characters or alphanumeric characters. How exactly do I have to name the variant glyph? Any special requirements for the Opentype code?

Answers

  • John Hudson
    John Hudson Posts: 3,588
    Variation selector sequences are not handled in OTL. Technically, they could have been, via the ccmp feature for example, but Microsoft wanted a solution for Unicode variation selectors that wasn’t dependent on glyph processing and shaping engines. So variation selectors are handled via a format 14 cmap subtable. This is like other cmap formats in that it maps from Unicode characters to glyph IDs, but in a format 14 format a sequence of two Unicode characters map to a single GID; the first character is the input character and the second is the variation selector character.

    This is what the format 14 subtable in STIX Two Math looks like in DTL OTMaster. Because common font tools don’t provide direct support for format 14 cmap, I hand build them in OTMaster, and then my build configuration file copies the cmap into each build of the font.


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