No knock on people who spend their time working on Free Software, but I genuinely don't understand why discussion threads turn sour so quickly when it comes to terminal emulators and ligatures. Both in the linked thread and in the case of libvte [1] (a terminal emulator widget used in tons of popular emulators) the maintainers seem to be aggressively against ligatures. It's a shame because I can't find a single terminal emulator on Linux that is as usable as iTerm2, and not having ligatures is the biggest knock against most of them IMO.

1: https://bugzilla.gnome.org/show_bug.cgi?id=584160

Most terminal emulators date back to a time when one byte of input occupied one character-cell on-screen. Since Unicode arrived with combining characters, terminals have adapted to N bytes of input occupying one character-cell, or under special circumstances (Chinese characters, emoji) two character-cells.

Proper ligature support requires terminals to support N bytes of input mapping to M character cells... and unlike the N:1 or N:2 cases, the N:M case doesn't allow a hard-coded list of how many cells an input string covers, it varies from font to font. And that risks software designed for one font breaking in a terminal that uses a different font, if it has a different set of ligatures, or the ligatures are different sizes.

Yeah, this stuff is hard. The approach used in wezterm is to use unicode graphemes for cells, and use the unicode width of the grapheme to decide whether a given cell is double-width.

Ligatures are handled at rendering time, partly because the terminal emulation and model layer doesn't know about fonts (it can run "headless" in a multiplexer where there are no fonts), and partly because the shaper library doesn't output information about cells but rather about which glyphs to render in which positions--that information doesn't easily map to the terminal cell model.

For extra pain, some font designers have ligatured sequences that map to a single glyph that may be several cells wide, while others use alternative glyph fragments for each component of the ligature, and others may emit two blank glyphs, followed by a triple wide glyph with a negative x offset of almost two blank glyphs in width. It's difficult to map this information to cells.

The problem actually existed before Unicode appeared. Terminals which supported Chinese, Japanese, or Korean characters have had to deal with 2 cell wide glyphs, even for text encodings which use 1 byte per glyph.

If you see the term "full width" character in old terminal related specs and documents, they are talking about 2 cell CJK glyphs/characters.

If "usable as iTerm2" means the terminal actually aims to have features, then you can try my project Extraterm ( https://extraterm.org/ ). It supports ligatures and more.

Thanks for the plug! I'll try it out over the weekend. I've held off on using an Electron-based terminal emulator so far because of memory concerns - I usually have tons of terminal windows open, leaving the job of tiling them to i3. But working on a mac with iTerm for work makes me really miss it on my own time, so I guess I'll try extraterm out.

Thanks in advance for trying it out. If you stay using it or not, do create issues on GitHub for missing features or things which could be improved, otherwise I just won't know what people need/want.

I can understand your concerns around resource usage. Extraterm doesn't follow a minimalist philosophy, more of a swiss army chainsaw one. But as an application it still needs to make you think "what I'm getting out of this is worth the resources". Features and new features you can't find else where, plus becoming a platform for plugins and deeper integration with other software is the broad idea here.

Does it support wayland? I don't see this mentioned via a github search.

The underlying stack is Electron. So if Chrome runs on on Wayland, then Extraterm will too.

It wasn't clear it was Electron, which does not work on Wayland.

Umlauts? How come one needs ligatures for umlauts as they are independent characters with own Unicode or even old ASCII set codes[0].

[0] https://resources.german.lsa.umich.edu/schreiben/unicode/

I believe that Unicode has multiple representations for Latin characters with diacritics: ä can be represented as a single character, but it can also be represented as two characters, “a”, plus “add two dots to the previous character”.

You can convert between these forms.

You do not need ligatures for umlauts, but that does not stop the odd software (or maybe user?) here and there refusing to do it the “sensible way”.