0031 Colour emoji from teleprinter
GitHub

0031. Colour emoji are Patina's: the Teleprinter code, with the font a git crate

Date: 2026-11-07

Status

Accepted. The user saw, in the other Patina apps, the emoji problems Teleprinter had already solved, and asked for Patina to bundle that emoji set. The patina-desktop emoji picker is the second user (its ADR-0120).

Context

egui (epaint 0.35) draws each glyph from its outline into a coverage-only atlas tinted with the text colour, and never reads COLR, CBDT or sbix, so emoji in any egui label are monochrome shapes from egui's own emoji fonts, or boxes. Teleprinter solved it (its ADR-0013) by bundling Noto Color Emoji's CBDT font and painting emoji as images, found through the font's cmap and GSUB ligatures. The picker copied that code, and every other app would have had to.

Decision

  • patina::emoji, behind the emoji cargo feature: glyph(text) for a sequence's glyph, texture and paint for its image, runs(text) to split text into plain and emoji runs, and label(ui, text) to show it.
  • The font is the app's to bring, not part of patina-ui and not looked for by it. It is 10 MB, which put the package over crates.io's 10 MiB limit (a cargo feature doesn't help: the limit is on the uploaded package, features or not), and where a system font lives, or whether there is one, differs on every platform Patina runs on (Linux, macOS), so Patina doesn't guess. emoji::install(bytes) takes the bytes of any Noto Color Emoji in its CBDT build (PNG images, the format Face::glyph_raster_image reads; a font without them is refused), and emoji::install_file(path) reads a file. The app decides where the font comes from: it ships one, finds one, or lets the user choose.
  • Sector F's desktop bundles ours: patina-emoji-font (emoji-font/ in this repository, a workspace member with publish = false) is the font as FONT: &[u8], and the apps that show emoji call install(patina_emoji_font::FONT). It is a git dependency, which crates.io refuses, so patina-ui can't depend on it (only its tests do, as a dev-dependency), and an app published there brings its own font instead.
  • Without a font, nothing breaks: install and the others say false, runs finds no emoji, label is a plain label, and emoji look as they did before.
  • Optional, as markdown is, because it adds about 11 MB to a binary.
  • It is the Teleprinter code, not a rewrite, so an emoji looks the same in every Patina app. Teleprinter can drop its copy for this when it next changes.

Consequences

  • An app gets colour emoji by enabling the feature, installing a font and using emoji::label where its text may have emoji. egui's own labels, text edits and widgets still draw monochrome ones; that needs egui to draw colour glyphs, or a widget of our own for each. The markdown Editor is one such: with both features on, it lays emoji out in transparent text and paints the image over them.
  • The packaged crate is about 1 MiB, and publishes to crates.io. An app published there can't depend on the git-only patina-emoji-font, so it ships or finds a font itself. Only the CBDT build of Noto Color Emoji is read: not macOS's Apple Color Emoji (sbix), nor Noto's newer COLR build.
  • label lays plain text and emoji out as separate widgets in a wrapped row, so it wraps between runs and the line height can differ slightly from a plain label's.