Allow specifying font index when loading a font file

[7sDream]

I try to let my egui app to use system font.

I can use some font query/loading library to find the font location and read it as binary data, however, it's a ttc file(for example, Microsoft YaHei), so egui report the data a invalid when parsing.

It seems ab_glyph do support collection, by using FontRef::try_from_slice_and_index, so any idea how can I use ttc/otc ffont file as custom font in egui?

update

Maybe there is some bug in the font loading library I used.

I changed from font-loader to fontdb, and now it's working, no invalid font report.

But, IIRC, font loading library gives whole file content, and because I can't pass the font face index to egui, current it will always using the font face at index 0, which means when using ttc/otf, the render result may not be as expected.

For example, Helvetica Neue(Normal style) is in index 10

[emilk]

If you could specify the face index in epaint::FontDefinitions (together with the FontData), would that solve the problem for you?

[7sDream]

Yes, I think add a font_face_index: HashMap<String, usize> field in FontDefinitions (with the same key in font_data, values is the index) is a feasible solution.

Considering compatibility, a default value of 0 can be used when the index cannot be found in this field.

[emilk]

It seems ab_glyph::FontArc lacks the convenience of try_from_vec_and_index and try_from_slice_and_index. If you make a PR to ab_glyph to add those I can hook them up in egui later!

[parasyte]

FontArc does implement From<FontRef> though. That should be enough?

[emilk]

Good point @parasyte - I made a PR; please try it out @7sDream !

[7sDream]

Thank you! I can try this pr tonight, after work