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

[Kai Ma]

On May 9, 2022, at 10:38, Eli Zaretskii <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).

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

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

BTW,

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

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

       (v "[\uEDA0-\uEDA9]”) ; vowel

       (cv (concat v c)))

  (set-char-table-range

   composition-function-table '(#xeda0 . #xeda9)

   (list 

    (vector cv 1 #'zbalermorna-shape-gstring)

    [nil 0 font-shape-gstring])))

(defun zbalermorna-shape-gstring (gstring direction)

  (message "shape %s" gstring) ; debugging

  gstring)

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

Have you any pointers? Thanks!