[MPEG-OTSPEC] Is it valid to use a GSUB sequence with a leading ZWJ character please?

[William_J_G Overington]

An interesting discussion about glasses emoji is taking place in the 
Unicode public mailing list.

https://corp.unicode.org/pipermail/unicode/2022-October/date.html

Thinking about this, earlier this morning here in England I adapted one 
of my own fonts to add some additional glyphs to run a test, and it 
worked. I used the High-Logic FontCreator program to make the font and 
Serif Affinity Publisher to run the test.

The font that I adapted is the Mariposa.otf font that is available from 
the following web page, though in fact I started with a copy of the 
unpublished High-Logic project file for the font.

http://www.users.globalnet.co.uk/~ngo/mariposa_novel.htm

To the font I added glyphs for three Unicode characters and for one 
unmapped glyph.

U+200D ZERO WIDTH JOINER though I used a wide visible glyph design

U+1F453 EYEGLASSES

U+1F469 WOMAN

unmapped ceyeglasses, a copy of the glyph used for eyeglasses, moved 
2048 font units to the left and the glyph having zero advance width.

Within the liga table I added the following line.

   sub uni200D u1F453 -> ceyeglasses;

that is, for "combining eyeglasses".

Please note that the substitution starts with a ZERO WIDTH JOINER

In the test in Affinity Publisher I used the Glyph Browser to enter the 
three characters

U+1F469 U+200D U+1F4F3

and the result displayed was of a woman wearing the eyeglasses as the 
display was of the glyph for WOMAN with the glyph for ceyeglasses 
superimposed upon it.

So if it is valid to use a glyph substitution with a leading ZWJ in this 
way then the issue appears to be solved.

Is it valid to use a glyph substitution with a leading ZWJ in this way 
please?

One could go further with a sequence also involving a pink square and a 
large circle to produce stylish large round pink rimmed glasses for the 
lady to be wearing.

Indeed the technique could be adapted so that the lady is also wearing a 
U+1F452 WOMANS HAT in a stylish purple colour.

William Overington

Friday 14 October 2022


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