Subject: 29.0.50; set-fontset-font and font clipping issues

From: Visuwesh <[email-masked]>
Date: Thu, 31 Mar 2022 09:07:30 +0530

I have the following line [1] in my init.el to make Emacs use "Kurinto
Seri" for the Tamil script,

    (set-fontset-font t 'tamil "Kurinto Seri")

and this leads to font "clipping" issues.  The text is shaped properly
in that it combines the diacritics but I see "clipping" problems
instead.  See screenshot below:

I type C-x C-+, then the clipping problem goes away until I increase the
font size again a bit and the problem gets worse:

I cannot seem to reproduce this from emacs -Q, nor do I see this issue
when I start Emacs up (I use the daemon if that makes a difference [2]).
It naturally shows up after using Emacs for a while, sometimes reopening
the frame fixes the clipping problems, sometimes I have to reevaluate
the set-fontset-font form to fix it.  And this issue isn't font-specific
as well: I had the same problem with "Noto Serif."  I would highly any
hints towards nailing the problem down; I'm really out of ideas.

If I didn't make it clear, there are no such problems if I don't modify
the default fontset.

[1] I also modify the default fontset for other scripts,

      (set-fontset-font t 'mathematical "Kurinto Mono" nil 'prepend)
      (set-fontset-font t 'mathematical "Latin Modern Math" nil 'append)
      (set-fontset-font t 'symbol "Latin Modern Math" nil 'append)
      (set-fontset-font t 'emoji "Kurinto Mono")
      (set-fontset-font t 'emoji "Kurinto Sans" nil 'append)
      (set-fontset-font t 'emoji "DejaVu Sans" nil 'append)

    and I set the language and the locale environment to Tamil and
    ta_IN.utf8 respectively, before modifying the fontset.

[2] Modifying the fontset in `server-after-make-frame-hook' does not
    make a difference.  I don't see the issue when I do not use the
    daemon but I believe I haven't run the non-daemon session long
    enough.

In GNU Emacs 29.0.50 (build 1, x86_64-pc-linux-gnu, X toolkit, cairo version 1.16.0, Xaw scroll bars)
Repository revision: ca3858563c7ba8ee3caa82fbd2b7c386ea60c0d3
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