Monospaced East Asian fonts

[Ken Lunde]

Does anyone have experience developing monospaced OpenType/CFF East Asian fonts, which are different from Western monospaced fonts in that there are two different monospaced widths? One width applies to the glyphs for non-CJK characters, such as Latin. The other width applies to the glyphs for CJK characters, such as Ideographs, kana, hangul, and full-width symbols and punctuation.

The important table fields appear to be the following:

  CFF.isFixedPitch
  OS/2.xAvgCharWidth
  OS/2.panose (4th byte, Proportion)
  hhea.advanceWidthMax
  hhea.xMaxExtent
  post.isFixedPitch

Mainstream authoring apps can handle such fonts, because they simply respect the per-glyph metrics. However, terminal or terminal-like apps exhibit different behavior.

While there appear to be TrueType (non-CFF) East Asian fonts that behave as expected in terminal or terminal-like apps, we have yet to be able to build OpenType/CFF fonts that behave as expected. Here's an example of a TrueType font that apparently behaves correctly:

  https://github.com/edihbrandon/RictyDiminished/blob/master/RictyDiminished-Regular.ttf

My conclusions are 1) that it may not be possible to build such OpenType/CFF fonts due to yet-to-be-understood assumptions on the part of either the app or OS; or 2) that heuristics may be at work here, and the widths for two particular characters are used to establish the two different monospaced widths for such fonts. Those are just wild guesses, especially the second conclusion.

Regards...

-- Ken