feat: the apps' icons as one family, drawn by one tool (ADR 0031)

tool/app_icons.py at the root replaces Learn's and Todo's scripts: each
app's Lucide glyph (lucide-static 1.50.0) drawn by librsvg, fading from
cobalt through the colours ADR 0031 names, then every platform's
launcher icon through flutter_launcher_icons, Windows' .ico with every
size, and Learn's snap icon.

Learn's icon becomes the graduation cap, its window's on Linux too, with
Lucide's notice in its licence list; the kingfisher stays the emblem on
the rail and the launch screen. Todo's becomes list-todo, Train's bike.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

tool/app_icons.py

@@ -0,0 +1,214 @@
+#!/usr/bin/env python3
+"""Makes the apps' icons, one family (ADR 0031): each app's Lucide glyph on a white
+square, fading from cobalt through the colours APPS names, top left to bottom right
+across Lucide's 24-unit box, the stops evenly spaced, at Lucide's stroke width (2),
+1024 x 1024 pixels (<app>/<flutter package>/assets/icon/<icon>); the launchers and
+the launch screens round its corners themselves. Then, for each app:
+
+- Lucide's licence (ISC) beside the icon (assets/icon/LICENSE-lucide.txt), which the
+  app registers in its licence list;
+- the snap's icon where the app has a snap (Learn's snap/gui/halkyon-learn.png at the
+  repository's root, 512 x 512 pixels, the Snap Store's size), the icon with rounded
+  corners, as other apps' white tiles have (radius 142.222 of 512, about 28 %);
+- through flutter_launcher_icons, configured in the app's pubspec: Android's adaptive
+  icon and its older square one, iOS's, macOS's (the rounded tile on Apple's grid,
+  824 of 1024 pixels) and Windows' (the rounded tile), from the images derived in
+  the app's build/icons/, which git ignores;
+- Windows' .ico once more, with every size Windows shows (16 to 256 pixels): the tool
+  writes only the 256 one and leaves Windows to scale it down for its small views;
+- the iOS project file as it was: the tool sets every build setting with
+  ASSETCATALOG in its name to the icon set's name, Xcode's yes-or-no
+  ASSETCATALOG_COMPILER_GENERATE_SWIFT_ASSET_SYMBOL_EXTENSIONS too, which breaks the
+  project (flutter_launcher_icons issue 634); the project names its icon set already.
+
+The glyphs come from lucide-static at a pinned release (LUCIDE below), fetched from
+jsDelivr, and are drawn by librsvg, as they have arcs and curves (bike's wheels).
+
+Run from the repository's root with Python 3, Pillow, PyGObject with librsvg and
+pycairo (Ubuntu's python3-pil, python3-gi, gir1.2-rsvg-2.0, python3-cairo), the apps'
+dependencies fetched, naming the apps to draw, or none for all of them:
+
+    python3 -I tool/app_icons.py train
+"""
+
+import subprocess
+import sys
+import urllib.request
+from dataclasses import dataclass
+from io import BytesIO
+from pathlib import Path
+
+import cairo
+import gi
+
+gi.require_version("Rsvg", "2.0")
+from gi.repository import GLib, Rsvg  # noqa: E402 (after the version is required)
+from PIL import Image, ImageDraw  # noqa: E402
+
+LUCIDE = "1.50.0"
+CDN = f"https://cdn.jsdelivr.net/npm/lucide-static@{LUCIDE}"
+
+COBALT = "#3C57E5"
+VIOLET = "#8E4FD6"
+STRAWBERRY = "#EC3E7C"
+CARROT = "#F78400"
+PACIFIC = "#179FD9"
+FERN = "#3CBB3A"
+REEF = "#1DA583"
+
+
+@dataclass(frozen=True)
+class AppIcon:
+    """An app's icon: where it goes, its glyph and its gradient's colours."""
+
+    folder: str
+    package: str
+    icon: str
+    glyph: str
+    stops: tuple[str, ...]
+    snap: str | None = None
+
+
+# ADR 0031, D2. Meditate's (circle-dot, cobalt, pacific, reef) comes with Meditate.
+APPS = {
+    "learn": AppIcon(
+        "apps/learn",
+        "halkyon_learn_flutter",
+        "halkyon_learn_icon.png",
+        "graduation-cap",
+        (COBALT, VIOLET, STRAWBERRY),
+        snap="snap/gui/halkyon-learn.png",
+    ),
+    "todo": AppIcon(
+        "apps/todo",
+        "halkyon_todo_flutter",
+        "halkyon_todo_icon.png",
+        "list-todo",
+        (COBALT, PACIFIC, FERN),
+    ),
+    "train": AppIcon(
+        "apps/train",
+        "halkyon_train_flutter",
+        "halkyon_train_icon.png",
+        "bike",
+        (COBALT, VIOLET, STRAWBERRY, CARROT),
+    ),
+}
+
+SIZE = 1024
+# The 24-unit box Lucide draws in takes this share of the square, centred: well
+# inside the circle Android's adaptive icons keep (66 %).
+GLYPH = 0.6
+# The corners the launch screen and launchers round to.
+RADIUS = 142.222 / 512
+SUPERSAMPLING = 4
+SNAP_SIZE = 512
+# Apple's grid: the tile is 824 of the icon's 1024 pixels, centred.
+MACOS_CANVAS = 1024
+MACOS_TILE = 824
+WINDOWS_SIZES = [16, 20, 24, 32, 40, 48, 64, 128, 256]
+
+
+def fetch(name: str) -> str:
+    with urllib.request.urlopen(f"{CDN}/{name}", timeout=30) as response:
+        return response.read().decode("utf-8")
+
+
+def rgb(colour: str) -> tuple[float, float, float]:
+    return tuple(int(colour[i : i + 2], 16) / 255 for i in (1, 3, 5))
+
+
+def icon(glyph: str, stops: tuple[str, ...], svg: str) -> Image.Image:
+    """[glyph] on white in the gradient of [stops], SIZE pixels square."""
+    if f"lucide-static v{LUCIDE}" not in svg:
+        raise SystemExit(f"Not lucide-static {LUCIDE}'s {glyph}.")
+    if 'viewBox="0 0 24 24"' not in svg or 'stroke-width="2"' not in svg:
+        raise SystemExit(f"{glyph} isn't drawn in Lucide's 24 units at width 2.")
+    # The strokes alone, as a mask the gradient shows through.
+    handle = Rsvg.Handle.new_from_data(svg.replace("currentColor", "#000").encode())
+    box = SIZE * GLYPH
+    offset = (SIZE - box) / 2
+    mask = cairo.ImageSurface(cairo.FORMAT_ARGB32, SIZE, SIZE)
+    viewport = Rsvg.Rectangle()
+    viewport.x, viewport.y, viewport.width, viewport.height = offset, offset, box, box
+    try:
+        handle.render_document(cairo.Context(mask), viewport)
+    except GLib.Error as error:
+        raise SystemExit(f"librsvg couldn't draw {glyph}: {error.message}")
+
+    tile = cairo.ImageSurface(cairo.FORMAT_RGB24, SIZE, SIZE)
+    context = cairo.Context(tile)
+    context.set_source_rgb(1, 1, 1)
+    context.paint()
+    gradient = cairo.LinearGradient(offset, offset, offset + box, offset + box)
+    for i, colour in enumerate(stops):
+        gradient.add_color_stop_rgb(i / (len(stops) - 1), *rgb(colour))
+    context.set_source(gradient)
+    context.mask_surface(mask)
+
+    png = BytesIO()
+    tile.write_to_png(png)
+    png.seek(0)
+    return Image.open(png).convert("RGB")
+
+
+def rounded(source: Image.Image, size: int) -> Image.Image:
+    """[source] at [size] pixels, its corners rounded off to transparency."""
+    picture = source.convert("RGBA").resize((size, size), Image.LANCZOS)
+    large = size * SUPERSAMPLING
+    mask = Image.new("L", (large, large), 0)
+    ImageDraw.Draw(mask).rounded_rectangle(
+        (0, 0, large - 1, large - 1), radius=RADIUS * large, fill=255
+    )
+    picture.putalpha(mask.resize((size, size), Image.LANCZOS))
+    return picture
+
+
+def make(app: AppIcon, license_text: str) -> None:
+    package = Path(app.folder) / app.package
+    source = icon(app.glyph, app.stops, fetch(f"icons/{app.glyph}.svg"))
+    path = package / "assets/icon" / app.icon
+    path.parent.mkdir(parents=True, exist_ok=True)
+    source.save(path, optimize=True)
+    print(f"Wrote {path}.")
+    license_path = package / "assets/icon/LICENSE-lucide.txt"
+    license_path.write_text(license_text, encoding="utf-8")
+    print(f"Wrote {license_path}.")
+    if app.snap:
+        rounded(source, SNAP_SIZE).save(app.snap, optimize=True)
+        print(f"Wrote {app.snap}.")
+
+    derived = package / "build/icons"
+    derived.mkdir(parents=True, exist_ok=True)
+    rounded(source, 1024).save(derived / "rounded.png")
+    macos = Image.new("RGBA", (MACOS_CANVAS, MACOS_CANVAS), (0, 0, 0, 0))
+    margin = (MACOS_CANVAS - MACOS_TILE) // 2
+    macos.alpha_composite(rounded(source, MACOS_TILE), (margin, margin))
+    macos.save(derived / "macos.png")
+
+    ios_project = package / "ios/Runner.xcodeproj/project.pbxproj"
+    kept = ios_project.read_bytes()
+    subprocess.run(["dart", "run", "flutter_launcher_icons"], cwd=package, check=True)
+    ios_project.write_bytes(kept)
+
+    windows_icon = package / "windows/runner/resources/app_icon.ico"
+    rounded(source, 256).save(
+        windows_icon, format="ICO", sizes=[(size, size) for size in WINDOWS_SIZES]
+    )
+    print(f"Wrote {windows_icon} with {len(WINDOWS_SIZES)} sizes.")
+
+
+def main() -> None:
+    names = sys.argv[1:] or list(APPS)
+    unknown = [name for name in names if name not in APPS]
+    if unknown:
+        raise SystemExit(f"No icon for {', '.join(unknown)}: {', '.join(APPS)}.")
+    if not Path("tool/app_icons.py").is_file():
+        raise SystemExit("Run this from the repository's root.")
+    license_text = fetch("LICENSE")
+    for name in names:
+        make(APPS[name], license_text)
+
+
+if __name__ == "__main__":
+    main()