Custom fonts

[tomassedovic]

Egui currently ships with built-in fonts and (as far as I could see) there's no way for the library user to switch those out.

Font customisation is done via ctx.set_fonts which accepts a FontDefinitions. But that requires a FontFamily which is an enum containing the hardcoded fonts and a no way to change them.

Would bringing your own font be within Egui's scope? The built-in fonts are great for e.g. debugging, level editor etc. UIs, but for a user-facing one (e.g. in-game menu, windows) the fonts often need to match the look & feel of the game.

If this is welcome, I'll be happy to work on it (albeit slowly) and follow any design considerations you might have.

My initial thought is adding a third variant FontFamily::Custom(u32) and provide a way to register a new font e.g.: impl Context { pub add_custom_font(font: &[u8]) -> u8; }

Where the function and the enum variant would both use a font ID (or maybe a hashed name) to support multiple fonts at the same time.

For reference, this is a commit I'm maintaining in my Egui fork to be able to use a (single) custom font:

tomassedovic@47c7942

And it's used like this in my game:

let font_definitions = {
    use egui::paint::fonts::{FontFamily, TextStyle};
    let family = FontFamily::Mononoki;

    let mut def = egui::paint::FontDefinitions::default();
    def.fonts.insert(TextStyle::Body, (family, font_size_px));
    def.fonts.insert(TextStyle::Button, (family, font_size_px));
    def.fonts.insert(TextStyle::Heading, (family, font_size_px));
    def.fonts
        .insert(TextStyle::Monospace, (family, font_size_px));
    def
};
ctx.set_fonts(font_definitions);

[emilk]

Hello!

There are (at least) two separate issues here:

A) Being able to override the default fonts used by Egui
B) Being able to add additional user fonts

Egui should definetly support both! I think A) is probably the first priority. In this case, maybe what you really wanted to do is to change TextStyle::Monospace to use Mononoki, so A) would have indeed solved it.

There is some design work to be done here before we start coding.

Let's start with thinking about A). We could start by having FontDefinitions contain a map from FontFamily to the TTF font data (e.g. as a ttf: HashMap<FontFamily, Vec<u8>> member). FontDefinitions::default() could use the default fonts, but you could then override it as such:

let mut fonts = egui::paint::FontDefinitions::default();
fonts.ttfs[FontFamily::Monospace] = include_bytes!("mononoki.ttf").to_vec();
ctx.set_fonts(fonts);

What do you think, is something like that a good start?

[tomassedovic]

Greetings!

What you proposed looks perfect! It would cover my needs completely.

I agree there's multiple things "custom font support" could mean and focussing on being able to swap the default fonts for user-specified ones is a great start.

[emilk]

Let me know if you start working on this, otherwise I'll get to it... some time? :)

[tomassedovic]

It would probably be some time here too. I'll post here if/when I pick it up! Thanks for the great suggestion!

[tomassedovic]

This is awesome, thank you so much!

This doesn't work...

77 |         fonts.ttfs[FontFamily::Monospace] = include_bytes!("../assets/fonts/NotoEmoji-Regular.ttf").to_vec();
   |               ^^^^ unknown field
   |
   = note: available fields are: `font_data`, `families`

[emilk]

@Eskerepvp it's because you are reading a two year old issue instead of the latest documentation.