implement glyph_by_name method

[srijs]

This change implements looking up glyphs by their name, which is useful when dealing with fonts that may not have a cmap (in my case certain CFF files).

Implementing this outside fontkit, although possible, is quite cumbersome as I basically need to mirror all the platform-specific dependencies and compilation flags.

There's two rough edges at the moment that I'm happy to try and fix up if you're generally interested in this change. One being the FFI binding for CTFontGetGlyphWithName that should probably move into the core-text crate, and the other that there appears to be no simple way to do name-based lookup using the DirectWrite APIs.

Let me know what you think!

[srijs]

I've opened a PR against core-text over here: servo/core-foundation-rs#293

[rvolgers]

Some notes for DirectWrite. Indeed it looks like there's no other way than parsing cff yourself...

https://docs.microsoft.com/en-us/windows/desktop/api/dwrite/nf-dwrite-idwritefontface-trygetfonttable

CFF:
https://docs.microsoft.com/en-us/typography/opentype/spec/cff

CFF2 (but these probably also have a cmap, so not relevant to the stated use case):
https://docs.microsoft.com/en-us/typography/opentype/spec/post
https://github.com/harfbuzz/harfbuzz/blob/70a52d6bd8c45630ca90e945fc4d716fe9114010/src/hb-ot-post-table.hh#L140

(Note: this is just a driveby comment since I happened to come across this issue.)

[pcwalton]

Looks like upstream has this method now; can we switch to using it?

[srijs]

@pcwalton it's been merged, but it looks like core-text hasn't cut a new release yet. Is that something you could help out with?

[jdm]

I'll publish a new version when servo/core-foundation-rs#294 is merged.

[srijs]

@pcwalton updated the PR to use new functionality in core-text. Should be good to merge from my perspective.

[srijs]

Just got a report of a problem with the freetype loader over in srijs/rpdf#2, I‘ll have a go at fixing it later today!

[srijs]

Should be all fixed now!