[konsole] [Bug 474009] Konsole v23.08.0+ breaks console rendering when displaying certain emojis

[Adam Fontenot]

https://bugs.kde.org/show_bug.cgi?id=474009

--- Comment #9 from Adam Fontenot <adam.m.fontenot+kde at gmail.com> ---
I've been thinking about this some more. As I understand it, the issue isn't
specific to Byobu.

Recently, we changed how Konsole renders text. Now, glyphs that take up more
than one column width are rendered correctly, even if they are rendered in
fonts other than the chosen monospace fonts. So most emojis are two column
width characters. This is expected, as otherwise you have to scale down the
font or clip the boundaries. The Foot terminal (among others) takes the same
approach.

The problem is that some old programs make simplistic assumptions about line
length and aligning characters, e.g. if you have 70 characters, they will fit
into a row 70 columns wide. This doesn't work when terminals use multiple
columns for glyphs. The problem seen in Byobu is caused (if I'm not mistaken)
by a custom script that adds emojis to the status line (none of the built in
statuses seem to do that?). Byobu sends 70 character lines to Konsole, but
these lines overflow the 70 column window width because of the emojis, so they
gets wrapped.

The solution is most likely to report this issue to Byobu and ask them to
calculate the width of "wide" characters correctly. I'm inclined to say this is
NOTABUG. In fact my issue (Bug 474310) was about the fact that Konsole is
inconsistent and *doesn't* use double width for unqualified emojis that don't
contain the presentation selector (even though the displayed glyph is the
same)!

Actually, someone reported the Byobu bug back in 2018:
https://bugs.launchpad.net/byobu/+bug/1641819

As for other issues with emojis, it's possible that some editors may have
trouble rendering them. If Konsole in particular is causing issues, having a
reproducible test case for that would be good. For what it's worth most text
editors have *never* worked for the full range of emoji for me (modern ones
like Helix and Kakoune do!), so I don't really know what broken rendering would
look like. But basic emoji (like in my attachment above) work fine for me in
every editor I've tested.

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