App icons (day icon build)

day icon build renders every platform’s icon set from one master and keeps the copies in sync. It renders the master into build/day/host/, the derived tree every host project references and no repository build consumes; day icon check verifies nothing drifted (exit 5; it is a CI gate beside the duty-matrix check).

The master

Discovery order: an explicit path argument, then resource/icons/icon.svg, resource/icons/day-icon.svg, resource/icons/icon.png.

An SVG master may 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>           <!-- reserved: themed/tinted modes (not yet consumed) -->
<g id="day:dark">…</g>                 <!-- reserved: dark-mode variants (not yet consumed) -->

The composite (background + foregrounds) feeds every full-bleed output; the split layers feed Android’s adaptive icon (foreground centered on its content box and scaled so the farthest point it draws sits on the 66 dp safe circle; background full-bleed). The fit is to the circle, not the square around it, because launchers mask to shapes as small as a 72 dp circle: a motif that reaches into its box’s corners (a heart, a square) is drawn just small enough to keep them, while a round one fills the circle. The monochrome layer gets the same fit. An unlayered SVG or a PNG master still produces the complete legacy set; the adaptive foreground is then the whole art in the safe zone over a derived background color (the composite’s corner pixel; white when transparent).

Text must be outlined: text shaping is not compiled into day, which keeps resvg’s font stack out of the build (<text> is a hard error naming the fix).

A reserved layer (day:monochrome, day:dark) may carry display="none" so plain SVG viewers show the master as it ships; the layer-only documents re-enable it. Generated masters do this.

Generate

day icon new writes a seeded pseudo-random layered master (background gradient + foreground motif + hidden monochrome silhouette) to resource/icons/icon.svg and renders every output from it. It refuses to replace an existing master unless --overwrite.

• --seed <int|string> — reproduce a specific icon (a non-integer seed is hashed; the app-id convention below). Without it a fresh random seed is drawn and printed, so a liked icon can be regenerated.
• --out <file.svg> — preview mode: write the master (plus a 512 px PNG beside it) to a path instead of the project, touching nothing else. It works outside any project, so use it to browse seeds.

day new app uses the same generator for every fresh scaffold, seeded by the app id (scaffolding the same id twice yields the same icon); --icon-seed overrides the seed.

The generator composes from a limited palette drawn from the classic color-harmony schemes (analogous / complementary / split-complementary / triadic), with figure-ground contrast held by construction, one or two focal points in simple geometry within the masks’ safe zone, a subtle vertical background gradient, and symmetric / rotational / golden-section-balanced arrangements (day-vector/src/icongen.rs documents the sources). Generated monochrome layers stay inside the VectorDrawable subset, so Android’s themed icon ships as a true vector.

Outputs

Everything derived lives under build/day/host/<family>/, written by day prepare and never checked in. The host projects reach it by path: the Xcode projects reference ../../build/day/host/{ios,macos}/Assets.xcassets, the Gradle module adds build/day/host/android/res to its res source set, day pack reads the Linux and Windows icons there, and hvigor — whose resource roots are fixed — gets gitignored symlinks from both resources/base/media directories to build/day/host/harmony/media.

-p <target> limits a run to that target’s family. Everything renders in memory first, so day icon check compares bytes without touching the tree. Unchanged outputs are not rewritten, so actool and aapt2 see no new mtimes.

Overrides

A file in git is a source; a derived file is under build/. So customizing one platform’s icon means adding a source, never editing an output:

• resource/icons/<family>.svg (ios.svg, macos.svg, android.svg, linux.svg, windows.svg, harmony.svg, png.svg) replaces the master for that family alone.
• A checked-in resource/icons/ios/AppIcon.icon/ bundle, tuned in Icon Composer, is copied through as-is instead of generated.

Both are digested into the lock, so editing one invalidates it like editing the master does.

Modern formats

Beyond the legacy set, a layered SVG master also produces:

• Android themed icon (Android 13): a monochrome drawable the system tints (day:monochrome as a VectorDrawable when it fits the subset, else the adaptive foreground’s alpha as a bitmap mask), wired into the generated mipmap-anydpi-v26/ic_launcher.xml.
• HarmonyOS layered icon: layered_image.json + foreground.png/background.png (216 px) in the linked media set, with app.json5/module.json5 icon slots rewired to $media:layered_image (startWindowIcon keeps the flat startIcon.png). That rewrite of a source file is the one edit prepare makes under platform/, and it is idempotent.
• Icon Composer package (Xcode 26 Liquid Glass): AppIcon.icon/ — icon.json + SVG layer assets split from the master’s day: layers (day:monochrome ships as an asset for the Tinted appearance). Open it in Icon Composer to tune materials; the tuned bundle goes under resource/icons/ios/ as an override.

The lock and the build

build/day/host/host.lock.json records the generator (day-cli + engine version), a digest per source (the master and every override), and a digest per output. Every day build, launch, and pack calls ensure first: a no-op while the lock vouches for the sources and the generator and every listed output exists, a full prepare otherwise. The Xcode target’s “Build Rust (day)” phase does the same, so a build started from the Xcode GUI never compiles a stale or missing catalog. day prepare --check is the CI gate and what the VS Code extension asks before “Open in Xcode” or “Open in Android Studio”; day open -p <target> prepares and opens the project in one step.

Migrating an app

day prepare --migrate moves a project that committed its derived files to this layout. It deletes each legacy output the old resource/icons/icons.lock.json proves was generated (a hand-edited file stays, and is named, since it has become an override or a mistake), repoints the Xcode projects’ catalog references and the Gradle source set, gitignores the HarmonyOS links, and runs prepare. It touches nothing in git; review git status and commit the deletions.

Engine

day-vector is resvg/usvg/tiny-skia with text shaping off, plus hand-rolled .ico/.icns writers. The same crate powers resource/vectors/ staging (docs/vectors.md).