Re: Unicode 13 Emoji ranges composed with wrong font on NS port

[Robert Pluim]

>>>>> On Tue, 12 Oct 2021 21:53:22 +0300, Eli Zaretskii <eliz@gnu.org> said:

    >> Date: Tue, 12 Oct 2021 18:40:07 +0100
    >> Cc: rpluim@gmail.com, emacs-devel@gnu.org
    >> From: Jimmy Yuen Ho Wong <wyuenho@gmail.com>
    >> 
    >> What I'm talking about specifically is when these characters are used as 
    >> a modifier base, the skin color or sex symbol that comes after them 
    >> should take effect and turn them into emoji presentation, but they are 
    >> currently not. See the attached screenshots.

    Eli> Is this about the sequences that end with VS-16?  Or are there others?
    Eli> (You again show a very large image without any indication what parts
    Eli> of it are problematic, and what sequence of codepoints was there in
    Eli> the file.)

Based on what I see here, itʼs the usual suspects: eg U+261D. Itʼs not
part of the emoji script in Emacs. The font_range change should cause

    U+261D U+FE0F

to switch to emoji presentation, but it doesnʼt since thereʼs a
composition-function-table entry for U+261D, so the backwards looking
entry for U+FE0F never comes into play.

Iʼm not sure how to fix this.

- We canʼt add U+261D to the emoji script.
- We could add a hack in font_range for U+261D, U+26F9,
U+270C..U+270D, and U+2764 to use the emoji font to check for
composition the same way as we do now when the composition trigger is
an emoji
- We could fix the backwards looking issue with
composition-function-table (I have no idea how complex that is)

Robert
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