RadioButton unicode circle display has a line through it

[presstab]

The bug

Issue: When using RadioButton in a RadioSet, the toggle glyph (●) renders with a visible horizontal line through it, making it appear broken or misaligned.

Environment: Ubuntu 22.04.5 LTS using the default GNOME Terminal.

textual diagnose

Textual Diagnostics

Versions

Name	Value
Textual	2.1.2
Rich	13.9.4

Python

Name	Value
Version	3.10.12
Implementation	CPython
Compiler	GCC 11.4.0
Executable	/usr/bin/python3

Operating System

Name	Value
System	Linux
Release	6.8.0-52-generic
Version	#53~22.04.1-Ubuntu SMP PREEMPT_DYNAMIC Wed Jan 15 19:18:46 UTC 2

Terminal

Name	Value
Terminal Application	GNOME Terminal
TERM	xterm-256color
COLORTERM	truecolor
FORCE_COLOR	Not set
NO_COLOR	Not set

Rich Console options

Name	Value
size	width=123, height=50
legacy_windows	False
min_width	1
max_width	123
is_terminal	True
encoding	utf-8
max_height	50
justify	None
overflow	None
no_wrap	False
highlight	None
markup	None
height	None

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[TomJGooding]

The problem is that the circle glyph used for the radio button is missing in your terminal font - see #3091

Try a different terminal emulator or changing your terminal font to something with better Unicode support, such as DejaVu Sans Mono.

[presstab]

It renders the circle glyph with no issue when BUTTON_RIGHT is set to "" instead of its default of "▌" which causes the issue. This issue happens with other characters as well, for example changing BUTTON_INNER to "\u2794" shows the same issue, which is fixed by setting BUTTON_RIGHT to an empty string. See #5722

[presstab]

closing this, I suppose its a Ubuntu feature not a bug

[willmcgugan]

The issue seems to be that Gnome terminal is rendering that glyph too wide. Having one cell overlap with a subsequent cell just shouldn't happen. So I think the fault lies with GT.

But I don't like to pass the buck with such things. Even if Gnome fix it, it will be a long time before every user gets the update. So finding a workaround is desirable.

Unfortunately we can't make that change, as it would break the output on other terminals. Here are some alternative options as I see it.

Find an alternative glyph that happens to work across all terminals, and looks good.
Sniff the terminal and change only affected terminals. I generally don't like to do that, as it can be brittle. But it is an option.
I'm going to open the original issue, as it is still valid. We can move the discussion there.

[TomJGooding]

The problem is there isn't any glyph that will work across all terminals. It really depends on the terminal font and the font fallback for missing glyphs. For example, there's countless issues about how Textual looks in the old Windows conhost, because it doesn't have any font fallback. The problem with the GNOME Terminal in Ubuntu is that its default monospace font (Ubuntu Mono) has limited Unicode support and its font fallback causes glyphs to overlap. If you change the terminal font to something with better Unicode support like DejaVu Sans Mono (which I think is the default terminal font in Fedora), then Textual will render much better.