List writing systems supported by a font

[RazrFalcon]

So we can check which languages/scripts can be handled by this font.

This is very useful for the font fallback resolution, when we need to find a font that can be used to write a specified text.

[raphlinus]

I've started digging into this question. It's very complicated, and not easy to get direct access. I've written up some investigations as linebender/skribo#1 and would welcome more input from experts.

[RazrFalcon]

This is how Qt works. And similar implementations for other backends.

I've tried to implement this by myself first, but I think that there are too many edge cases of which I'm not aware of.

[raphlinus]

@RazrFalcon Thanks, I'm mostly using Skia as a reference because I know it meets the needs of the web, but Qt also looks like a good source and I will dig into it. Do you have any information about whether it correctly deals with Han unification on Linux, Windows, and macOS? ETA: this is starting to become fairly clear reading through the source.

[RazrFalcon]

Do you have any information about whether it correctly deals with Han unification on Linux, Windows, and macOS?

Sadly, no.