Not enough space for U+07FD NKO DANTAYALAN in some contexts

[dscorbett]

Font

NotoSansNKo-Regular.otf

Where the font came from, and when

Site: https://github.com/googlefonts/noto-fonts/blob/154977565b8fbc74859fdb1b2208dac419a7888b/unhinted/otf/NotoSansNKo/NotoSansNKo-Regular.otf
Date: 2021-04-01

Font version

Version 2.001

Issue

After three letters, U+07FD NKO DANTAYALAN doesn’t get enough space: it overlaps or almost overlaps adjacent glyphs.

Character data

߸ߌ߽߸ߨ߽߸ߩ߽
U+07F8 NKO COMMA
U+07CC NKO LETTER I
U+07FD NKO DANTAYALAN
U+07F8 NKO COMMA
U+07E8 NKO LETTER JONA JA
U+07FD NKO DANTAYALAN
U+07F8 NKO COMMA
U+07E9 NKO LETTER JONA CHA
U+07FD NKO DANTAYALAN

Screenshots

[moyogo]

1. A resolution would be to add contextual positioning when 07FD NKO DANTAYALAN is next to a U+07F8 NKO COMMA, U+2010 HYPHEN, U+2011 NON-BREAKING HYPHEN. Note: U+2010 HYPHEN and U+2011 NON-BREAKING HYPHEN sit on the baseline in NKo, they need to be added to Noto Sans NKo.
   @dscorbett Do you think there are other contexts?

For reference, here is the description of NKO DANTAYALAN in L2-15/338 https://www.unicode.org/L2/L2015/15338-n4706-nko-additions.pdf:

The DANTAYALAN is used with individual letters to abbreviate units of measure. This character is a combining mark which fuses with the base-line of the letter in question. It does not interfere with shaping behaviour; one appropriate font mechanism for handling this might be to use four precomposed shaping glyphs for each letter with the DANTAYALAN fused to it. Andrij Rovenchak proposed this character in L2/14-126 “Proposal to encode an additional Nko character”. The use of this character is productive, and can appear with many (and in principle all) N’Ko letters. For instace, it is used with ߞ ka as ߞ߽ to abbreviate ߞߎߘߍ kúdɛ ‘kilometre’, with ߝ fa as ߝ߽ to abbreviate ߝߟߋ fele ‘megametre’, with ߜ gba as ߜ߽ to abbreviate ߜߟߊߜߟߊ gbàlàgbala ‘metre’, with ߛ sa as ߛ߽ to abbreviate ߛߌߘߐ sidɔ ‘gram’, and with ߕ ta as ߕ߽ to abbreviate ߕߏ߲ߜߊ tóngba ‘litre’. Examples of letters with DANTAYALAN connected to another letter are ߜߥ߽ gbaw. ‘mm.’ and ߜߗ߽ gbach. ‘cm.’. (See Figures 1, 2, 3.)

2. L2-15/338 also has a chart showing the NKo reportoire with shaping forms combined with DANTALAYAN. Noto Sans NKo does not seem to have the correct shaping form for:
   ߍ߽
   U+07CD NKO LETTER E
   U+07FD NKO DANTALAYAN:

ߍ߽ in Noto Sans NKo	ߍ߽ in L2-15/338

[dscorbett]

Item 1 is a good start. I recommend handling it beside all supported characters with ink near the baseline. Maybe U+07FD should always get advance width on the side(s) of its base that are not cursively connected.

Item 2 should be opened as a new issue.

[moyogo]

It looks like U+07F8 NKO COMMA is mostly used with a space before and after. What context did you spot this issue in?

[dscorbett]

I noticed it while inspecting the font. I wasn’t looking at any N’Ko documents.

[simoncozens]

I've added contextual kerning around the dantayalan and comma. It was a nice fun scripting exercise to get it even for all glyphs. I have not added baseline hyphen and non-breaking hyphen, because in the arflreq thread above, there is some discussion as to whether the hyphen should be baseline or not; non-baseline hyphen seems to be used with numerals. So I'm not doing anything about that until we have a good solution.

I also reshaped the "wide open" dantayalan for letter E.