minimal RTL support for single lines

[yzn-h]

version=0.1.0-main+4ac9610b

right now this is how
بسم الله الرحمن الرحيم

will look in ghostty

and like this in konsole

there are multiple issues
first the characters shaping is wrong
in Arabic and Persian each glyph changes shape depending on the glyph behind it and after it for example:

ignore the "e)" it is there just to make the Arabic text left aligned

e) ي + ز + ن
the first letter is "ي" and the last is "ن"
should be shaped like this
e) يـ + ـز + ن
not like this
e) ( ي + ز + ن ) or (ي + ز + ـن)

the second issue is glyph order in each word
e) علي (correct)
even if the first issue was fixed the text will look like this
e) ﻲﻠﻋ (wrong)

the third issue is word ordering, I don't think there is one correct answer there are two options
the first is to not change anything
firstWord secondWord
or make it like konsole
secondWord firstWord

[mitchellh]

I'll say up front I'm not very familiar with RTL languages on computers. I have read the full RTL/Bidi terminal spec here and I don't currently plan on supporting that in the near term since it requires a very significant amount of effort that I'm not ready to put forward. One day, I'd like to support this.

If what you're suggesting can be resolved in a renderer/shaping-only way then I think we can at least get partial RTL support, so I'll keep this open for that. 😄 More research necessary.

Thank you for the example text and screenshots, this will help significantly.

[asibahi]

Hello. I meant to open an issue regarding this but found this one. I am using the 1.0 Dec26 version of Ghostty. I am on MacOS.

The shaping seems to work fine. All the letters are shaped properly. Problem is they are the wrong order. If I were to guess, they are probably passed to the shaper in the opposite order of what they should be. I don't know what shaper you're using, but HarfBuzz and rustybuzz want the text in the logical order and they give you the rendering order from left to right.

minimal example

Here is how it looks (correctly) in Terminal.app

[eifr]

same on fedora 41
kitty(right) ordering the letters correctly:

[motaz-shokry]

Until the RTL Support added in the future I encourage you to use bicon with ghostty, or use wezterm "it supports RTL very will

[mjec]

Could I suggest a slight tweak to the wording of the features page related to this? That page currently says:

Certain languages like Arabic and Hebrew are also rendered correctly (LTR only).

which is a little like saying "English text renders correctly (backwards only)." I think it would be clearer to say something like:

While only left-to-right text is supported, characters from RTL scripts including Arabic and Hebrew are correctly clustered and rendered.

[mitchellh]

@mjec Happy to make that change, would you be open to PR-ing it to the website repo?

[Flimm]

Could I suggest a slight tweak to the wording of the features page related to this? That page currently says:

Certain languages like Arabic and Hebrew are also rendered correctly (LTR only).

which is a little like saying "English text renders correctly (backwards only)." I think it would be clearer to say something like:

While only left-to-right text is supported, characters from RTL scripts including Arabic and Hebrew are correctly clustered and rendered.

Ghostty does not render characters in RTL scripts correctly, though. They are rendered backwards. Would you say olleh is a correct clustering and rendering of hello? It would be much clearer to say that Ghostty does not support RTL scripts (like Arabic and Hebrew).

[mjec]

Would you say olleh is a correct clustering and rendering of hello?

I would say that each grapheme is correctly clustered and rendered, even though the text direction is wrong. My understanding is individual grapheme clusters in RTL scripts are correctly rendered, though RTL text direction isn't.

If that's incorrect, let me know; I'm certainly not an expert. But if that's correct and you think the proposed text doesn't accurately capture that idea, I'd be very open to suggested changes.

(Ideally this conversation should probably happen on the website repo, but I'm yet to open the promised PR.)

[ShadiZade]

?hsilgnE troppus yttsohG soeD

[Majoramari]

The only good RTL terminal I’ve used so far is Konsole.

I hope to see this feature added to Ghostty soon.

I was misled by the documentation claiming it supports Arabic, but it doesn’t handle RTL properly. Instead, it reverses the text—for example, Hello World becomes dlroW olleH.

[ebraminio]

Maybe libraqm's minimal implementation can be helpful on how to integrate a bidi library with shaper https://github.com/HOST-Oman/libraqm

macOS side, ghostty vs macOS terminal vs iterm2, the second one is correct, the text is "ابراهیم"