fastframe-fonts

The apps’ interface font, and installed fonts for every other script, for egui.

  • Inter, bundled: Inter 4.001 as a variable font with its tabular figures frozen into the character map, so a timer or a counter keeps its width as it changes (see fonts/README.md for how it was made). The same file ZapFast, Spotifast and Solco ship.
  • Weights: 400 is egui’s proportional family; 500, 600 and 700 are named families (inter-medium, inter-semibold, inter-bold), each falling back like the regular one.
  • System fallbacks: one installed face per script Inter lacks (CJK, Arabic, Hebrew, Indic scripts, Thai, Yi, symbols and more), chosen the way the desktop would, aligned to Inter’s baseline, and Arabic enlarged to read as large as Latin text.

Usage

use fastframe_fonts::{FontSetup, Weight};

// The default: Inter at 400/500/600/700, egui's monospace, system fallbacks.
let mut fonts = FontSetup::default().definitions();
// Follow the desktop's hinting (fastframe-text), then hand them to egui:
fastframe_text::detect().apply_to(&mut fonts);
ctx.set_fonts(fonts);

let title = Weight::SemiBold.font_id(16.0);
let body = Weight::Regular.font_id(14.0); // FontFamily::Proportional

Apps choose:

FontSetup::default()
    .weights(&[Weight::SemiBold])                  // regular is always there
    .monospace(Monospace::Inter)                   // or EguiDefault, or Font { name, data }
    .companion("noto_emoji", Arc::new(emoji))      // right after Inter, in every family
    .system_fallbacks(!demo)                       // off for reproducible screenshots
    .install(ctx);                                 // or .definitions() to adjust first

definitions() starts from FontDefinitions::default(), so egui’s own fonts (with its default_fonts feature) stay behind Inter and any companions, and the system fallbacks come last.

System fallbacks

fastframe_fonts::system::fallbacks() finds the faces once per process and reuses them for every window.

Platform How the face is chosen
macOS CoreText names the face it draws each script with, in the language the user reads, and its cascade behind it. Faces epaint cannot draw (Apple’s hvgl outlines in PingFangUI.ttc) are skipped for the next in the cascade.
Linux Every font under fontconfig’s configured directories (NixOS lists its store paths only there), the XDG data directories, Flatpak’s /run/host/fonts, ~/.fonts and $XDG_DATA_HOME/fonts is probed through a memory map. The best regular sans face per script wins: a face named for the script beats incidental coverage, sans beats serif, mono and display cuts, weight near 400 beats far, and for Han the locale’s regional cut (and a face declaring that region’s code page) wins.
Windows The same probe over %SystemRoot%\Fonts and the per-user font directory; the display language picks the Han cut.

Each chosen face gets y_offset_factor so its baseline sits on Inter’s (epaint centres a fallback’s line box on the primary’s, which shifts faces with other vertical metrics), and an Arabic face drawn small beside Inter is scaled up by at most 25%.

Why a crate of its own

fastframe-text follows the desktop’s rendering settings and works with any font; this crate decides which fonts. Keeping them apart keeps the 880 KB font, the font parser and the platform font code out of an app that only wants the rendering settings, and keeps fastframe-text free of unsafe code (memory-mapping fonts and asking CoreText and Win32 need it here).

What stays in the app

Font sizes and text styles, the colour emoji rendering ZapFast draws over text, Spotifast’s skin bitmap font and its Winamp playlist face, and any face an app bundles besides Inter (TonePush’s IBM Plex Mono goes in through Monospace::Font).

Licences

The code is MIT. Inter is under the SIL Open Font License 1.1; apps ship fonts/Inter-LICENSE.txt with their other licences, as they already do.