Missing glyphs (⎛, ⎞, ⎝, ⎠, and ⋅) cause apparent alignment issue in SageMath with unicode_art in Cool Retro Term

[kaimers]

Problem seen in QTerminal too, which is also based on KDE4 Konsole derived qtermwidget, but not in KDE5 Konsole or Gnome Terminal.
Other font that has this problem are Inconsolata and Ubuntu Mono, but the same problem does not appear with font Andale Mono, Courier, Fira Code or Source Code Pro.

[rbanffy]

I think those glyphs are missing. Can you paste the screen text to speed things up? I don't think I have Sage here.

Never mind. Got it.

[rbanffy]

It is a missing glyph issue, but it doesn't happen on a Mac (at least not with Terminal.app)

This may indicate an issue with the fallback font in your system.

Regardless of that, the glyphs are missing and that should be fixed.

[kaimers]

It is a missing glyph issue, but it doesn't happen on a Mac (at least not with Terminal.app)

This may indicate an issue with the fallback font in your system.

Regardless of that, the glyphs are missing and that should be fixed.

I don't think it necessarily has to do with fallback font in my system.

I just checked for various fonts that don't work, and they seem to be wrong in different ways, e.g. Fixedsys Excelsior. And as described in issue, the font works perfectly on Gnome Terminal and KDE5 Terminal.

I believe on the other side there's some thing missing in KDE4's QTermWidget which is used by both QTerminal and Cool Retro Term, but I don't know enough about this to make a guess.

[kaimers]

@rbanffy You could have been right about the fallback font. I just checked Fixedsys Excelsior and the glyphs involved are included in that font even though it has problems. Still strange how I don't have problem with other terminal emulators though.

[kaimers]

@rbanffy You could have been right about the fallback font. I just checked Fixedsys Excelsior and the glyphs involved are included in that font even though it has problems. Still strange how I don't have problem with other terminal emulators though.

Maybe the other terminals just render in grids while KDE4's QTermWidget don't do that. And when you fallback to font with different size (which is probably always the case) the problem naturally arises.

[rbanffy]

Found something interesting (we'll have to pass this, maybe, to the QTermWidget team). Note how the parentheses components mismatch below:

Now note how they mismatch after I select the '⋅' glyph on the second line:

And, if I select more:

(added capture, Mac running X server, Linux laptop running Konsole):

konsole-misalignment.mov

It doesn't happen when Konsole uses the default font. Can you check it with the other fonts you mentioned, @kaimers?

[rbanffy]

Reported it at https://bugs.kde.org/show_bug.cgi?id=433604

[kaimers]

@rbanffy I did tests on QTerminal and KDE 5's Konsole.

KDE 5's Konsole: No alignment issue with either IBM 3270 or Fira Code.
QTerminal: Problem reproduced with IBM 3270 but not with Fira Code or Source Code Pro.

The behavior in your capture is really weird but I don't think KDE is in charge of QTermWidget, it seems to be maintained by LXQt(https://github.com/lxqt/qtermwidget)

[rbanffy]

@kaimers I don't have Sage installed anywhere here right now, but the KDE folk tell me this is fixed since KDE5. Can you give it a try again?