Modified U+1D9FF SIGNWRITING HEAD glyphs lack anchors

[dscorbett]

Font

NotoSansSignWriting-Regular.otf

Where the font came from, and when

Site: https://github.com/googlefonts/noto-fonts/blob/12ea769bd0bf283691d3da92089d2e9018c9d700/unhinted/otf/NotoSansSignWriting/NotoSansSignWriting-Regular.otf
Date: 2022-03-21

Font version

Version 2.003

Issue

Modified forms of U+1D9FF SIGNWRITING HEAD lack anchors, so subsequent marks fail to combine with them. As in other Noto fonts, unanchored marks overlap the following glyph for some strange reason, which means that instead of looking merely suboptimal it is completely wrong.

Character data

𝧿𝪡𝨀
U+1D9FF SIGNWRITING HEAD
U+1DAA1 SIGNWRITING ROTATION MODIFIER-2
U+1DA00 SIGNWRITING HEAD RIM

Screenshot

[marekjez86]

@dscorbett : is this a fontmake issue?

[dscorbett]

NotoSansSignwriting.glyphs includes anchor points for u1D9FF_F2 which are not present in the final font file, so I suppose it could be a fontmake issue.

[simoncozens]

Yes, it is. Because of the naming convention <something>_<something>, glyphsLib assumes that u1D9FF_F2 is a GDEF class 2 (ligature) glyph and so it looks for mark-to-ligature anchors _<anchorname>_1, _<anchorname>_2 instead of _<anchorname>. I've complained about this assumption before (googlefonts/glyphsLib#756) but the only suggested fixes make the problem worse.

We can work around it by manually assigning all these <something>_<something> to be Category=Letter, Subcategory=Other in the Glyphs sources.