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From: Ihor Radchenko <yantar92@gmail.com>
To: Eli Zaretskii <eliz@gnu.org>
Cc: 57693@debbugs.gnu.org
Subject: bug#57693: 29.0.50; Is there a more reliable version of `char-displayable-p'?
Date: Sun, 11 Sep 2022 17:31:06 +0800	[thread overview]
Message-ID: <87v8puw945.fsf@localhost> (raw)
In-Reply-To: <831qsjboy0.fsf@gnu.org>

Eli Zaretskii <eliz@gnu.org> writes:

>> Yup. And I am asking if there is such test exposed to Elisp. Display
>> code certainly knows when some character cannot be displayed and must be
>> replaced by its hex code.
>
> The display engine only knows it retroactively, when it tried and
> failed to display a character.

The situation is similar to `string-pixel-width'.
Trying to display and checking retroactively should be a valid option,
unless I miss something.

>> This is not great. I am really hoping that we can make nicer defaults
>> when possible and only fallback to something robust when fancy version
>> cannot be used.
>
> I'm not sure I understand how this could be done even in principle.
> The conditions and restrictions you put forward can only be tested by
> trying to display the character at its specific place in a specific
> buffer and a specific window (because all of those can potentially
> affect the face and thus the font).  We can code a function that
> emulates the display, but such a function can only work if the
> offending character was already inserted into its place and is part of
> buffer text.  Is this something you'd consider good enough, to have to
> do something like
>
>   insert the character
>   call the new magic
>   if the new magic says NO-CAN-DO
>      replace the character with something else
>
> If the above is acceptable, I think it can be done, although it would
> not be very useful in other situations.  But if you want to know the
> answer before you insert the character, I don't think we know how to
> satisfy your requirements with 100% accuracy.  At least I cannot see
> how it could be done; maybe someone else will.

The described approach should be acceptable.
What I have in mind is a function like

  (insert-displayable '("fancy version" "backup"))

The function will try to insert "fancy version" first; check if all the
characters are displayable, and replace the inserted text with "backup"
if not.

-- 
Ihor Radchenko,
Org mode contributor,
Learn more about Org mode at https://orgmode.org/.
Support Org development at https://liberapay.com/org-mode,
or support my work at https://liberapay.com/yantar92





  reply	other threads:[~2022-09-11  9:31 UTC|newest]

Thread overview: 44+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-09-09 13:25 bug#57693: 29.0.50; Is there a more reliable version of `char-displayable-p'? Ihor Radchenko
2022-09-09 13:38 ` Eli Zaretskii
2022-09-09 22:25   ` Stefan Kangas
2022-09-10  6:01     ` Eli Zaretskii
2022-09-10  6:06       ` Ihor Radchenko
2022-09-10  6:35         ` Eli Zaretskii
2022-09-10  6:44           ` Ihor Radchenko
2022-09-10  4:48   ` Ihor Radchenko
2022-09-10  6:24     ` Eli Zaretskii
2022-09-10  6:37       ` Ihor Radchenko
2022-09-10  7:56         ` Eli Zaretskii
2022-09-10  8:17           ` Ihor Radchenko
2022-09-10  8:42             ` Eli Zaretskii
2022-09-11  9:31               ` Ihor Radchenko [this message]
2022-09-11  9:43                 ` Eli Zaretskii
2022-09-11 10:07                   ` Eli Zaretskii
2022-09-12  5:46                     ` Ihor Radchenko
2022-09-12 11:15                       ` Eli Zaretskii
2022-09-13  1:44                         ` Ihor Radchenko
2022-09-13 11:19                           ` Eli Zaretskii
2022-09-14  1:52                             ` Ihor Radchenko
2022-09-14  2:43                               ` Eli Zaretskii
2023-02-17 19:18                       ` Stefan Kangas
2023-02-17 19:29                         ` Eli Zaretskii
2023-02-17 22:31                           ` Stefan Kangas
2023-02-18  6:56                             ` Eli Zaretskii
2023-02-18  9:00                               ` Stefan Kangas
2023-02-18  9:18                                 ` Eli Zaretskii
2023-02-18 11:32                                   ` Ihor Radchenko
2023-02-18 11:56                                     ` Eli Zaretskii
2023-02-19 11:31                                       ` Ihor Radchenko
2023-02-19 11:55                                         ` Eli Zaretskii
2023-02-19 12:08                                           ` Ihor Radchenko
2023-02-19 12:23                                             ` Eli Zaretskii
2023-02-19 14:19                                               ` Ihor Radchenko
2023-02-19 15:02                                                 ` Eli Zaretskii
2023-02-18 11:35                               ` Ihor Radchenko
2023-02-18 12:00                                 ` Eli Zaretskii
2022-09-12  5:24                   ` Ihor Radchenko
2022-09-09 13:46 ` Robert Pluim
2022-09-09 22:25   ` Stefan Kangas
2022-09-10  4:56     ` Ihor Radchenko
2022-09-10  6:02     ` Eli Zaretskii
2022-09-10  4:53   ` Ihor Radchenko

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