Day

App icons and interface icons

An app has two kinds of icons: the app icon shown by the operating system, and the icons used inside its interface. Day generates platform-specific app icons from a source image and makes interface SVGs available as typed Rust resources. This guide covers both, from source files to build outputs.

App icon source

The scaffold includes resource/icons/icon.svg. Replacing that file sets the app icon. day icon build can also take an explicit source path; otherwise it searches for icon.svg, day-icon.svg, then icon.png in resource/icons/.

An SVG master can mark top-level elements as semantic layers by id:

<rect id="day:background" …/>    <!-- the full-bleed backdrop -->
<g id="day:foreground">…</g>     <!-- the motif; day:foreground-2 … for more layers -->
<g id="day:monochrome">…</g>     <!-- themed/tinted appearances -->

The combined image supplies full-bleed outputs; separate layers supply adaptive and layered formats. An unlayered SVG or PNG supplies the legacy formats and becomes the adaptive foreground over a derived background color. Text must be converted to outlines; see rendering limits.

For temporary artwork, day icon new creates a layered icon. --seed <int|string> repeats a design, and --out preview.svg saves a preview without requiring a project.

Generated platform assets

day prepare writes platform assets to build/day/host/:

  • macOS — PNG icons with the required shape and margins, day-icon.icns, and the asset catalog the Xcode project compiles.
  • iOS — the asset catalog with an opaque 1024 px image, plus an Icon Composer package (AppIcon.icon/) for Xcode 26’s Liquid Glass icons.
  • Android — the launcher resource tree: adaptive ic_launcher_{foreground,background}.png, the legacy icon, mipmap-anydpi-v26/ic_launcher.xml, and, from a layered master, the Android 13 themed icon; beside it play-store-512.png for the listing.
  • HarmonyOS — startIcon.png and the layered icon (layered_image.json with foreground and background), linked into both module resource roots and referenced by app.json5/module.json5.
  • Windows — a multi-size day.ico (16/32/48/256) and day-icon-256.png.
  • Linux — PNGs at the sizes appstream tooling accepts (48/128/256/512).
  • png/ — day-icon-{16…1024}.png for favicons and general use.

The files in build/day/host/ are generated and should not be committed. Native projects reference them, and build, launch, and packaging commands regenerate them when the source icon or Day version changes. day prepare -t <target> limits generation to one platform family.

Platform-specific sources override the shared icon: resource/icons/macos.svg supplies the macOS icon, and resource/icons/ios/AppIcon.icon/ supplies an Icon Composer bundle for iOS.

Native projects and CI

day open -t ios-uikit prepares assets before opening Xcode; day open -t android-mdc does the same for Android Studio. The corresponding VS Code commands also prepare assets first.

CI can check whether generated files are current without writing them:

day prepare --check

The command exits 0 when outputs match and 5 when files are missing or stale. build/day/host/host.lock.json records the generator version and source and output digests. A version mismatch requests regeneration rather than comparing outputs from different generators.

Keep master artwork under resource/icons/ and remove obsolete generated copies and their references from customized native projects before running day prepare. Generated native projects use the current paths automatically. See native project migration.

Interface icons

Interface icons belong in resource/vectors/. Supported sources are SVG files, SF Symbols template exports, and Xcode .symbolset bundles. Template sources can include Light and Bold variants. The build generates a res::vectors:: constant for each resource:

use day::prelude::*;

vector(res::vectors::home)
    .tint(Color::rgba(0.18, 0.50, 0.94, 1.0))
    .frame(24.0, 24.0)

Vector modifiers control appearance: .tint(color) recolors a monochrome glyph where the backend can, .weight(VectorWeight::Light | Bold) selects a weight variant, and .decorative() hides the glyph from accessibility. Navigation items, tabs, toolbar_button(…).image(…), and bar_action also accept res::vectors:: constants as image names.

Rendering limits

Interface icons are supported on every backend. Android uses VectorDrawable where possible; Apple targets, HarmonyOS, and web render SVG. GTK, Qt, and XAML use a 256 px raster generated at build time.

  • SVG text must be converted to outlines. Both app icons and interface icons reject <text> elements.
  • Android VectorDrawable supports solid fills and strokes; art with gradients, clips, masks, or filters falls back to the 256 px raster, and day lint flags it as day::lint::vector-raster-fallback when android-mdc is a declared target. day lint also catches unreadable art, empty .symbolset bundles, and glyph-embedded text.
  • Tint has coverage limits. AppKit, UIKit, Android, GTK, and ArkUI recolor; Qt, XAML, and web draw the authored colors. Use authored colors when the color must match across backends.
  • Weights need template sources. A plain SVG aliases Light and Bold to the same glyph, so .weight(…) degrades to Regular rather than to a missing asset. True weight variants come from SF template exports and .symbolset bundles.

Reference

icons — master layering, the generator, the full output table, and the lock file. vectors — source forms, the per-backend staging table, weights, and tint coverage.