halkyon/tool/app_icons.py

#!/usr/bin/env python3
"""Makes the app's icons for every platform from its own, the kingfisher on white
(halkyon_learn_flutter/assets/icon/halkyon_icon.png).

- The snap's, snap/gui/halkyon-learn.png (512 x 512 pixels, the Snap Store's size),
  which the Store and the desktop file show as they are: the picture 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).
- 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 derived images it hands to the tool go to halkyon_learn_flutter/build/icons/,
which git ignores. The rounded corners' mask is drawn at four times the size and
scaled down, so their edges are smooth.

Run from the repository root with Python 3 and Pillow (python3-pil on Ubuntu), the
app's dependencies fetched:

    python3 tool/app_icons.py
"""

import subprocess
from pathlib import Path

from PIL import Image, ImageDraw

APP = Path("halkyon_learn_flutter")
SOURCE = APP / "assets/icon/halkyon_icon.png"
DERIVED = APP / "build/icons"
SNAP_ICON = Path("snap/gui/halkyon-learn.png")
WINDOWS_ICON = APP / "windows/runner/resources/app_icon.ico"
IOS_PROJECT = APP / "ios/Runner.xcodeproj/project.pbxproj"
RADIUS = 142.222 / 512
SUPERSAMPLING = 4
# 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 rounded(size: int) -> Image.Image:
    """The icon at [size] pixels, its corners rounded off to transparency."""
    icon = Image.open(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
    )
    mask = mask.resize((size, size), Image.LANCZOS)
    # Keeps what the icon itself makes transparent, and takes the corners away.
    transparent = Image.new("L", (size, size), 0)
    icon.putalpha(Image.composite(icon.getchannel("A"), transparent, mask))
    return icon


def main() -> None:
    rounded(512).save(SNAP_ICON, optimize=True)
    print(f"Wrote {SNAP_ICON}.")

    DERIVED.mkdir(parents=True, exist_ok=True)
    rounded(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(MACOS_TILE), (margin, margin))
    macos.save(DERIVED / "macos.png")

    ios_project = IOS_PROJECT.read_bytes()
    subprocess.run(["dart", "run", "flutter_launcher_icons"], cwd=APP, check=True)
    IOS_PROJECT.write_bytes(ios_project)

    rounded(256).save(
        WINDOWS_ICON, format="ICO", sizes=[(size, size) for size in WINDOWS_SIZES]
    )
    print(f"Wrote {WINDOWS_ICON} with {len(WINDOWS_SIZES)} sizes.")


if __name__ == "__main__":
    main()