halkyon/tool/app_icons.py

#!/usr/bin/env python3
"""Makes the apps' icons, one family (ADR 0031): each app's Lucide glyph on a dark
square (TILE, the apps' dark background; D8), fading from cobalt through the colours
APPS names, each lifted towards white (LIFT) so the glyph stands out on the dark tile,
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, Todo's apps/todo/snap/gui/halkyon-todo.png; 512 x 512 pixels, the
  Snap Store's size), the icon with rounded corners, as other apps' 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"
ENZIAN = "#5252CC"
PURPLE = "#8080FF"

# ADR 0031, D8: the tile is halkyon_ui's dark surface, and every stop is mixed this
# share towards white, so the gradient's darkest part (cobalt) keeps above 4.5 : 1
# against it.
TILE = "#131520"
LIFT = 0.3


@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, D5: each from cobalt into its app's backdrop.
APPS = {
    "learn": AppIcon(
        "apps/learn",
        "halkyon_learn_flutter",
        "halkyon_learn_icon.png",
        "graduation-cap",
        (COBALT, ENZIAN, PURPLE),
        snap="snap/gui/halkyon-learn.png",
    ),
    "todo": AppIcon(
        "apps/todo",
        "halkyon_todo_flutter",
        "halkyon_todo_icon.png",
        "list-todo",
        (COBALT, VIOLET, STRAWBERRY),
        snap="apps/todo/snap/gui/halkyon-todo.png",
    ),
    "train": AppIcon(
        "apps/train",
        "halkyon_train_flutter",
        "halkyon_train_icon.png",
        "dumbbell",
        (COBALT, VIOLET, STRAWBERRY, CARROT),
        snap="apps/train/snap/gui/halkyon-train.png",
    ),
    "meditate": AppIcon(
        "apps/meditate",
        "halkyon_meditate_flutter",
        "halkyon_meditate_icon.png",
        "sprout",
        (COBALT, PACIFIC, FERN),
    ),
}

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 lifted(colour: str) -> tuple[float, float, float]:
    """[colour] mixed LIFT towards white."""
    return tuple(c + (1 - c) * LIFT for c in rgb(colour))


def icon(glyph: str, stops: tuple[str, ...], svg: str) -> Image.Image:
    """[glyph] on TILE in the lifted 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(*rgb(TILE))
    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), *lifted(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()