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

[Robert Pluim]

>>>>> On Wed, 13 Oct 2021 16:12:42 +0300, Eli Zaretskii <eliz@gnu.org> said:

    >> From: Robert Pluim <rpluim@gmail.com>
    >> Cc: Jimmy Yuen Ho Wong <wyuenho@gmail.com>,  emacs-devel@gnu.org
    >> Date: Wed, 13 Oct 2021 12:22:26 +0200
    >> 
    >> 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.

    Eli> These composition-function-table entries for these characters
    Eli> come from emoji-zwj.el, so we could simply add the above sequences to
    Eli> that, by suitable change in emoji-zwj.awk, right?  And then the
    Eli> font_ranges trick should cause us select an Emoji font, right?

The triggering character would not be an emoji,so weʼd need to change
font_range. See below

    Eli> But is it worth the trouble?  IOW, do these characters have pretty
    Eli> appearance when they are followed by VS-16?

They do. The difference is quite pronounced.

    Eli> I wouldn't add the characters themselves to the 'emoji' script, as
    Eli> that would have much wider consequences, not necessarily good ones.
    Eli> For example, I don't think that these characters, when they aren't
    Eli> followed by VS-16 or something Emoji-like, should be displayed using
    Eli> the Emoji fonts.

So if I change emoji-zwj.awk to emit codepoint+U+FE0F rules for these
problematic codepoints which have Emoji_presentation = No, and change
font_range to try looking up the emoji font for them, all the
'codepoint+U+FE0F' from Jimmy's test file display as Emoji, and the
'codepoint+U+FE0E' display as text.

It would mean emitting rules in emoji-zwj.awk for, and checking in
font_range for, the following codepoints.

U+261D, U+26F9, U+270C, U+270D, U+2764, U+1F3CB, U+1F3CC, U+1F3F3,
U+1F3F4, U+1F441, U+1F574, U+1F575, U+1F590

As an added bonus, those U+1xxxx codepoints would no longer be part of the
'emoji' script.

    >> - We could fix the backwards looking issue with
    >> composition-function-table (I have no idea how complex that is)

    Eli> I don't think it's complicated, and I already asked Kenichi Hand about
    Eli> that, hopefully he will either agree with my conclusions or explain
    Eli> where I'm wrong.

OK. Let's cross that bridge when we get to it.

Robert
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