bug#57728: 29.0.50; Emacs writes wrong glyph at the bottom-right corner of text terminals

[Akib Azmain Turja]

Eli Zaretskii <eliz@gnu.org> writes:

>> From: Gerd Möllmann <gerd.moellmann@gmail.com>
>> Cc: gregory@heytings.org,  57728@debbugs.gnu.org,  akib@disroot.org
>> Date: Mon, 12 Sep 2022 13:59:05 +0200
>> 
>> Eli Zaretskii <eliz@gnu.org> writes:
>> 
>> >> From: Gerd Möllmann <gerd.moellmann@gmail.com>
>> >> This is because 'write' deliberatly leaves the bottom-right corner alone
>> >> if the terminal has "auto right margin" (autowrap).
>> >
>> > But AFAIU, the bug actually shows that we somehow _do_ write there,
>> > although the display engine assumes we don't.  Right?
>> 
>> My theory is that no-one but tty_write_glyphs knows that it didn't write
>> to the bottom-right corner.
>
> You are saying that update_frame_line tells tty_write_glyphs to write
> the '\', but tty_write_glyphs doesn't in this case?
>
> But why would we need to write that character if we know it's already
> there (because all lines end with it)?  That should only happen if we
> scroll the region instead of rewriting lines one by one.  Is that what
> happens in this case?

The symptoms indicate so.

-- 
Akib Azmain Turja

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