bug#55319: 28.1.50; Abugida not rendered correctly (MacOS)

[Robert Pluim <rpluim@gmail.com>]

>>>>> On Wed, 11 May 2022 23:43:36 +0800, Kai Ma <justksqsf@gmail.com> said:

    >> On May 9, 2022, at 10:38, Eli Zaretskii <eliz@gnu.org <mailto:eliz@gnu.org>> wrote:
    >> 
    >> Emacs doesn't discover composition rules. The composition rules are
    >> part of the Emacs code, see the various *.el files in lisp/language/
    >> directory. Some of these composition rules are derived automatically
    >> from character properties, see composite.el and characters.el (which
    >> cannot happen without Emacs knowing up-front about the properties).

    Kai> Thanks for this. I didn’t know Emacs needed to manually compose characters.

    Kai> Feel free to close this report, since it is due to my misunderstanding, not a real problem nor a real “wishlist”.

    Kai> BTW,

    Kai> I did try to follow language/*.el, and come with up the following code:

    Kai> (let* ((c "[\uED80-\uED9F]\\|\uEDAA\\|\uEDAB”) ; constant

ie: "[\uED80-\uED9F\uEDAA\uEDAB]”

    Kai>        (v "[\uEDA0-\uEDA9]”) ; vowel
    Kai>        (cv (concat v c)))

You've called this 'cv', but itʼs actually 'vc'.

    Kai>   (set-char-table-range
    Kai>    composition-function-table '(#xeda0 . #xeda9)
    Kai>    (list 
    Kai>     (vector cv 1 #'zbalermorna-shape-gstring)
    Kai>     [nil 0 font-shape-gstring])))

Youʼre looking back from vowels, it might be easier to add entries for
the consonants and look forward.

    Kai> (defun zbalermorna-shape-gstring (gstring direction)
    Kai>   (message "shape %s" gstring) ; debugging
    Kai>   gstring)

    Kai> But it doesn’t work as expected. For example, “ka” should be
    Kai> composed, but the behavior here is “a” itself is composed,
    Kai> and when the first rule is matched, only the consonant “k” is
    Kai> sent to font-shape-gstring: only “k” is in the header.

    Kai> Have you any pointers? Thanks!

I think if you fix 'cv' this will work.

Robert
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