site/tools/icons.py

"""The app icons: the asterisk, white with square ends, on the ground colour. Same geometry as icons/icon.svg.

    python3 tools/icons.py            -> icons/icon-512.png, icons/icon-192.png, icons/apple-touch-icon.png

Standard library only: three rotated rectangles, 3x3 supersampled, written as RGB PNG.
"""
import math
import struct
import zlib
from pathlib import Path

ROOT = Path(__file__).resolve().parent.parent
GROUND, INK = (11, 11, 14), (237, 240, 240)
SS = 3


def arms(size):
    """The three arms as (centre, unit direction, half-length, half-width) in pixel units."""
    c = size / 2
    half, hw = 150 / 512 * size, 29 / 512 * size
    return [((c, c), (math.cos(math.radians(90 + 60 * k)), math.sin(math.radians(90 + 60 * k))), half, hw) for k in range(3)]


def inside(x, y, shapes):
    for (cx, cy), (dx, dy), half, hw in shapes:
        px, py = x - cx, y - cy
        along, across = px * dx + py * dy, -px * dy + py * dx
        if abs(along) <= half and abs(across) <= hw:
            return True
    return False


def asterisk(size):
    shapes = arms(size)
    rows = []
    n = SS * SS
    for y in range(size):
        row = bytearray([0])  # PNG filter type 0
        for x in range(size):
            hit = 0
            for sy in range(SS):
                for sx in range(SS):
                    if inside(x + (sx + 0.5) / SS, y + (sy + 0.5) / SS, shapes):
                        hit += 1
            t = hit / n
            row.extend(int(round(g + (i - g) * t)) for g, i in zip(GROUND, INK))
        rows.append(bytes(row))
    return b"".join(rows)


def png(size, raw):
    def chunk(kind, data):
        return struct.pack(">I", len(data)) + kind + data + struct.pack(">I", zlib.crc32(kind + data) & 0xFFFFFFFF)
    ihdr = struct.pack(">IIBBBBB", size, size, 8, 2, 0, 0, 0)
    return b"\x89PNG\r\n\x1a\n" + chunk(b"IHDR", ihdr) + chunk(b"IDAT", zlib.compress(raw, 9)) + chunk(b"IEND", b"")


if __name__ == "__main__":
    out = ROOT / "icons"
    out.mkdir(exist_ok=True)
    for name, size in (("icon-512.png", 512), ("icon-192.png", 192), ("apple-touch-icon.png", 180)):
        (out / name).write_bytes(png(size, asterisk(size)))
        print("built: icons/" + name)