Rendering complex scripts in terminal and OSC 66
thottingal.in
thottingal.in
Yeah, and ideally you want the backward compatibility, so we don't have to recompile the world or patch things like e.g. cat.
But yeah, the root of the problem is that a) the TUI-like application that manually drives the terminal, with cursor movement/line folding/redrawing etc. needs to know, at every single moment, the precise location of the cursor and the coordinates of every single character it outputted (to e.g. properly handle backspacing, including over the line folds: \b explicitly doesn't move to the previous line by default and very wide and old convention), and b) getting that coordination info from the terminal in quick, reliable, and side-effect free manner is impossible, so you have to guess.
It could just be the path to a Unix domain socket in an environment variable, where that socket speaks some kind of RPC protocol
If getting the current cursor position in the terminal were as easy (and as fast) as calling GetConsoleScreenBufferInfo, instead of sending "\e[6n" to the terminal and then reading input from it and looking for "\e[(\d+);(\d+)R" inside and then somehow unreading the input before that device report, yeah, that'd be nice and would allow solving a lot of problems with mere brute force. Sadly, it is not, and so most reimplementations of e.g. readline/linenoise functionality in shells and prompts (Erlang's shell went through 2 internal reimplementations just in my time using it, for example) are flying blind, hoping that their implementation of wcwidth(3) matches the terminal's one.
[0] https://learn.microsoft.com/en-us/windows/console/console-fu...
What I personally have in mind is something very different-a terminal ioctl which gives you an fd which speaks a completely different protocol, such as JSON-RPC - or whatever else you prefer - to avoid endless disputes over which alternative protocol to use, it could be you pass the ioctl a string saying what alternative protocol you want, and it gives you an fd if the pty master has registered support for that protocol, an error otherwise. The “other fd” could actually be a Unix domain socket. This also means the kernel code change required would be minimal - it doesn’t have to actually understand the alternative protocol, just let the pty master register a mapping of protocol name strings to listening sockets.
> This API has just recently finally lost to UNIX's in-line signaling, because the in-band controls can be proxied through almost anything, including literal serial line with two RX-TX wires and a common ground; the downside, of course, is that you have to build "out-of-line" signalling on your own.
SSH/etc is totally capable of carrying “secondary channels” - that’s how it implements X11 forwarding, port forwarding, etc - admittedly would require some code change in SSH clients/servers but the change would be modest rather than massive.
The Windows approach can’t be so easily forwarded over the network because it is defined in terms of a C language API not a wire protocol. My idea doesn’t have that issue
print 'This is a line of text which is being line-edited in an imaginary editor.'
if no line-wrap happened:
# move left a manually calculated amount of 17 (wcswidth?), delete
# everything to the right, reprint the rest of the line
print '\e[17D\e[Keditor.'
else:
# You need to know how much fit on the previous line, and the
# terminal's width. Let's assume 80, and that wrap happened
# after 'imagi', so 'nary' was on the next line. Move up 1, move
# right 63 (or do \r and move right 75), clear the rest of the
# screen, reprint
print '\e[A\e[63C\e[Jeditor.'
EDIT: Without saying that I think this is worthy and cool. I am just curious about the costs and benefits of such a tool.
If you speak the languages that use those scripts? Then all the time, I imagine. The support for double-char width cells in the terminals started to appear all the way back in the late seventies because Japan, you know, existed and kinda mattered.
All the languages I am literate in use an alphabet and I have never encountered a script in anything other alphabetic scripts in the terminal, and never anything not in English for serious work.
I would think we would probably have far fewer characters with hard to determine widths being printed in terminal (before LLMs) as most of it would be rendered in the GUI, which state of the art terminal emulators somewhat rely on anyway.
My guess is that LLMs made translation for these sorts of tools much easier (just needing someone fluent in both languages to verify rather than translate from scratch) but that's why I am asking. Is it more common now than ever before?
Beyond that the examples given were of scripts that are widely used in India which is a country with the world's largest English speaking population and one of the world's most spoken English dialects and also a huge IT sector.
I get that CJK has an existing double width carve out, that is being proposed to be kept by the objection linked in the article.
As for the scripts, Unicode is slowly rounding up with the actually used scripts, but it's still not quite there yet.
And then there are emojis, of course, which we get new sets every couple of years, which makes the life of the terminal emulators simply terrible. There is simply no good way to support emoji sequences in the terminal, I believe. Consider e.g. HEART ON FIRE (READ HEART, ZWJ, FIRE) and PHOENIX (BIRD, ZWJ, FIRE) emojis: the terminal emulator may or may not be aware of the existences of those emoji sequences depending on which version of ICU it is build against, and even if it is aware of them, then the currently selected font may not have the required glyphs so it has to fall back to the fallback display (4 cells of two basic emojis vs. 2 cells of the combined glyph). And of course, the font itself may have completely bonkers dimensions for its glyphs: as I understand it, Google's Noto Emoji font has glyphs for playing cards that are 1.5 cells wide even though they're supposed to be narrow (only 1 cells wide); there is nothing much the terminal emulator can do with that.
- Everybody just uses english text, right?
- Ok, sometimes there might some weird accents or something
- Every character is about the same width
- Well, they're all integer numbers of characters wide
- No character is taller than an english I
- Everybody writes left to right
- Everyone writes horizontally
Also https://jeremyhussell.blogspot.com/2017/11/falsehoods-progra...
EDIT: How the hell do you format lists in HN comments
It can't handle terminal window resize and the layout gets messed up
I was surprised to see node based cli work much better with resize?
Anyone knows why?
Most products in terminal these days use widget tree or virtual dom.
Things like aider use prompt toolkit and loses the layout when you resize window. Because the screen is printed on each change with diffing, upon resize there is no issue when you use stuff like ink or textual library in python.