Text shaping and font fallback

[hecrj]

wgpu_glyph uses glyph-brush, which in turn uses rusttype. While the current implementation is able to layout text quite nicely, it does not perform any text shaping.

Text shaping with font fallback is a necessary feature for any serious GUI toolkit. It unlocks support to truly localize your application, supporting many different scripts.

The only available library that does a great job at shaping is HarfBuzz, which is implemented in C++. skribo seems to be a nice HarfBuzz wrapper for Rust.

This feature will probably imply rewriting wgpu_glyph entirely, as caching will be more complicated and the API will probably need to ask for more data.

[hecrj]

After the report in #48, I did a bit of research on script-aware font fallback in font-kit and skribo. It looks like it's an unsolved problem for the time being. Here are some interesting links that may be useful in the future:

• Script-aware fallback servo/font-kit#37
• Script matching in skribo
• Interaction with CSS font matching algorithm linebender/skribo#22

[piaoger]

After the report in #48, I did a bit of research on script-aware font fallback in font-kit and skribo. It looks like it's an unsolved problem for the time being. Here are some interesting links that may be useful in the future:

* [servo/font-kit#37](https://github.com/servo/font-kit/issues/37)

* [Script matching in `skribo`](https://github.com/linebender/skribo/blob/master/docs/script_matching.md)

* [linebender/skribo#22](https://github.com/linebender/skribo/issues/22)

Recently, it seems that a new player is comming.

allsorts@github

blog

[dabreegster]

Something else to follow: a native Rust harfbuzz port, which will unlock vector text in WASM. Both by @RazrFalcon.