Re: Entering emojis

[Gregory Heytings <gregory@heytings.org>]

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>
> Yes, I know.  But ligatures are not the only way of handling this. When 
> a font produces a ligature, i.e. a precomposed glyph that should be 
> displayed instead of several characters, it produces a single font 
> glyph.  The other way is to produce several font glyphs, each one with 
> offsets relative to the base-line.  Emacs supports both ways. However, 
> for any of the two to work, both the shaping engine and the font should 
> recognize the sequence, and the font should produce one or more glyphs 
> with the offsets for that sequence.
>

In this case, ISTM that the problem is not the font, but the shaping 
engine.  If Harfbuzz does not know how handle the joiners and segment 
delimiters, it should behave as they did not exist, and use the font 
ligatures (if the font does have ligatures), instead of displaying the 
fictitious glyph at that codepoint (at the codepoint of the joiner or 
delimiter).  If it knows how to handle joiners and delimiters, it should 
ignore the font ligatures and create the final glyph with the individual 
glyphs in the font.  IIUC, that way a single font can be used with and 
without ligatures and with and without joiners and segment delimiters.

>
> I mean what the Unicode Standard says: it says that two hieroglyphs 
> should be displayed "normally", i.e. as separate characters at the same 
> vertical position, unless there's the vertical joiner between them, in 
> which case one should be above the other.
>

I understand.  But what the standard says doesn't make sense I think, 
because it means that it requires one to ignore font ligatures and instead 
requires one to use joiners and segment delimiters.  Again I know next to 
nothing about hieroglyphs (although I did learn a few things about them 
today), but I'd guess that if the Aegyptus font uses ligatures, it's 
because the number of combinations between hieroglyphs to produce a 
quadrat is, in practice, limited.  Just like in ancient greek you cannot 
put a rough breathing above an arbitrary letter for example.

>
> Which then means that you cannot write anything where these 4 characters 
> are displayed in an arrangement different from that particular one 
> that's encoded in the font, unless you use non-joiners.
>

That's not entirely correct.  Aegyptus provides an alternative arrangement 
for most quadrats, sometimes it even provides two alternative 
arrangements.  But indeed you have to use non-joiners if you want to 
ignore the automatic arrangement provided by the font.  Which is I guess 
much easier to use in practice than joiners and segment delimiters.  It 
would be a pain to type, in a language with diacritics, the letter itself, 
a joiner to indicate where the diacritic should be placed, and the 
diacritic itself, if in the vast majority of cases the diacritic is always 
placed in the same way.

>
> However, the composition rules I defined went with Unicode, and need to 
> be fixed to support what the Aegyptus font does.  Does the patch below 
> help?
>

It does!  Thanks.

Here's a combined patch, with the comment you asked.

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From c16dd1bb2b45eb4c41d6efc0ca825e3e6da4fb78 Mon Sep 17 00:00:00 2001
From: Gregory Heytings <gregory@heytings.org>
Date: Thu, 28 Oct 2021 20:58:02 +0000
Subject: [PATCH] Make hieroglyphs display correctly in Emacs for the moment.

* etc/HELLO: Remove hieroglyph format controls.

* lisp/language/misc-lang.el: Use font-shape-gstring instead of
egyptian-shape-grouping until hieroglyph format controls are supported
by fonts and shaping engines.
---
 etc/HELLO                  |  2 +-
 lisp/language/misc-lang.el | 15 ++++++++++++++-
 2 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/etc/HELLO b/etc/HELLO
index 577c2828de..8bd489fb40 100644
--- a/etc/HELLO
+++ b/etc/HELLO
@@ -38,7 +38,7 @@ Czech (čeština)	Dobrý den
 Danish (dansk)	Hej / Goddag / Halløj
 Dutch (Nederlands)	Hallo / Dag
 Efik  /ˈɛfɪk/	Mɔkɔm
-Egyptian Hieroglyphs (𓂋𓐰𓏤𓈖𓆎𓅓𓏏𓐰𓊖)	𓅓𓊵𓐰𓐷𓏏𓊪𓐸, 𓇍𓇋𓂻𓍘𓇋
+Egyptian Hieroglyphs (𓂋𓏤𓈖𓆎𓅓‌𓏏𓊖)	𓅓𓊵𓏏𓊪, 𓇍𓇋𓂻𓍘𓇋
 Emacs	emacs --no-splash -f view-hello-file
 Emoji	👋
 English /ˈɪŋɡlɪʃ/	Hello
diff --git a/lisp/language/misc-lang.el b/lisp/language/misc-lang.el
index a2ca678b2b..de4f092dc1 100644
--- a/lisp/language/misc-lang.el
+++ b/lisp/language/misc-lang.el
@@ -192,7 +192,20 @@ egyptian-shape-grouping
    composition-function-table
    #x13437
    (list (vector "\U00013437[\U00013000-\U0001343F]+"
-                 0 #'egyptian-shape-grouping))))
+                 0 #'egyptian-shape-grouping)))
+  ;; As of late 2021, Egyptian Hieroglyph Format Controls are not yet
+  ;; supported in existing fonts and shaping engines, but some fonts
+  ;; do provide ligatures with which texts in Egyptian Hieroglyphs are
+  ;; correctly displayed.  If and when these format controls are
+  ;; supported, the five lines below (which cancel the effect of the
+  ;; above lines) can be removed, and the entry in etc/HELLO can be
+  ;; restored to:
+  ;; Egyptian Hieroglyphs (𓂋𓐰𓏤𓈖𓆎𓅓𓏏𓐰𓊖)	𓅓𓊵𓐰𓐷𓏏𓊪𓐸, 𓇍𓇋𓂻𓍘𓇋
+  (set-char-table-range
+   composition-function-table
+   '(#x13000 . #x1342E)
+   (list (vector "[\U00013000-\U0001342E]+"
+                 0 #'font-shape-gstring))))
 
 (provide 'misc-lang)
 
-- 
2.33.0