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 -p <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 -p ios-uikit prepares assets before opening Xcode; day open -p 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.

Older projects that commit generated icons can migrate to this layout:

day prepare --migrate

Migration removes the generated copies, updates project references, and adds the generated links to .gitignore. Review those changes before committing.

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.