bug#57607: Feature request: Use the character cell on bottom-right corner of a terminal

[Akib Azmain Turja via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

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Eli Zaretskii <eliz@gnu.org> writes:

>> From: Akib Azmain Turja <akib@disroot.org>
>> Cc: 57607@debbugs.gnu.org,  gerd.moellmann@gmail.com
>> Date: Tue, 04 Oct 2022 18:00:57 +0600
>> 
>> > Please try with some 2-column CJK characters, I'm not sure the example
>> > with ^L is relevant here.  You can find the list of wide characters in
>> > characters.el (search for "width"); for example, characters in the
>> > U+FF00 block can be useful.
>> 
>> Thanks, "CJK STROKE D" doesn't work as expected, and the result depends
>> on terminal in use.  How can I determine the width of a glyph?
>
> Like this:
>
>   (char-width CHAR)
>
> where CHAR is the character you are interested in.  For example:
>
>   (char-width #x31D4)
>    => 2
>
> From C, you can call char_width, like Fchar_width (which see) does.
>
> One other subtle point: the argument STRING to tty_write_glyphs is a
> string of 'struct glyph' objects, not a string of characters.  Each
> struct glyph has the code of the character to display in its u.ch
> member, if the glyph is a simple character glyph; for the full story
> see encode_terminal_code.

Thanks.

I just discovered new type of glyph: padding glyph.  What's this?  Is
this a nop glyph?  I guess it's used to make string of width N use N
numbers of glyph.  But how?  Is this like [CJK PAD] or [PAD CJK]?

>
>> > (And the existing code could have bugs,
>> > no need to assume it is always correct.)
>> 
>> Yes, it can, but in most cases, my brain has more bugs.
>
> Indeed, that the existing code has bugs should not be our first
> hypothesis.  But it shouldn't be axiomatic that there are no bugs
> there ;-)
>
>> > face_id is an integer, and zero is a valid value (it means the default
>> > face), so NULL won't do.  But you can use -1 to mean "no face ID".
>> > Just make sure you never pass it to FACE_FROM_ID etc.
>> >
>> > Thanks.
>> 
>> OK, I'll try that.  Thanks.
>
> TIA

-- 
Akib Azmain Turja

Find me on Mastodon at @akib@hostux.social.

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