Recommendations for rendering a mixed language string, like "Hi, 你好"

[rnikander]

I'm drawing text fields in my app UI with rustybuzz, but now as I start trying other languages, I get into trouble. My app had one font (Roboto, which I downloaded from Google's font site), so when I tried drawing Chinese characters ("你好") there were no glyphs. I downloaded a new font that has the glyphs (NotoSansSC), but ... what's the recommended approach here?

Do I use the unicode-script crate to split my string into pieces by "script" property, and then call rustybuzz::shape(...) on each string piece separately? I could have a map from Script values to different fonts.

[behdad]

Do I use the unicode-script crate to split my string into pieces by "script" property, and then call rustybuzz::shape(...) on each string piece separately? I could have a map from Script values to different fonts.

That's roughly where you start, yes.

[behdad]

https://raphlinus.github.io/text/2020/10/26/text-layout.html

[asibahi]

This probably goes against the design decisions of Harfbuzz and Rustfybuzz, but I can't help but feel many apps would just magically support BiDi (the example I have in mind rn is Ghostty) if harfbuzz implemented the UnicodeBidi Algorithm itself, at least on a line by line basis.

[RazrFalcon]

@asibahi Can't say for @behdad, but from my point of view the problem with this approach is that there always more.

• Why do you not have BIDI built-in
• Why do you not have paragraphs built-in
• Why do you not have styling built-in
• Why do you not have hypenation built-in
• Why do you not have font fallback built-in
• Why do you not have rendering built-in
• ...

Harfbuzz/rustybuzz does shaping. That's it. It's intentionally a low-level library that shouldn't be used directly.

[asibahi]

most of these are things that people actually do bother to implement , tho 😄

[behdad]

HarfBuzz can't implement bidi automagically, because the bidi algorithm needs to see the full paragraph text to do its job. By the time HarfBuzz gets the text, it's too small a chunk typically.

If you mean HarfBuzz implementing it as new API, that has certainly crossed our mind. But the bidi algorithm in its current version is very gnarly to implement, and free implementations exist.

Libraqm is a good place to start if one needs bidi, line breaking, font fallback, shaping, all working together.

[RazrFalcon]

My recommendation is to ask harfbuzz authors. rustybuzz is just a port. It works the same.
If you want more concrete examples, you can check how resvg works.