ca.py

# Cellular automata
# https://natureofcode.com/book/chapter-7-cellular-automata/

def ca(rule, ncells):
    def _next_cell(a, b, c):
        a <<= 1
        a |= b
        a <<= 1
        a |= c
        return (rule & (1 << a)) >> a

    # seed row
    ra = [0] * ncells
    ra[ncells // 2] = 1
    rb = ra[:]

    while True:
        yield ra
        for i in range(ncells - 2):
            rb[i+1] = _next_cell(*ra[i:i+3])
        ra, rb = rb, ra


if __name__ == '__main__':
    from argparse import ArgumentParser
    from PIL import Image

    parser = ArgumentParser()
    parser.add_argument('rule', type=int)
    parser.add_argument('cells', type=int, default=512)
    parser.add_argument('generations', type=int, default=256)
    parser.add_argument('--ppc', help='pixels per cell', type=int, default=2)
    parser.add_argument('--out')
    args = parser.parse_args()

    ppc = args.ppc
    image = Image.new('1', (args.cells * ppc, args.generations * ppc))
    a = ca(args.rule, args.cells)
    for y in range(args.generations):
        for x, p in enumerate(next(a)):
            # draw cell
            oy, ox = y * ppc, x * ppc
            for py in range(ppc):
                for px in range(ppc):
                    image.putpixel((ox + px, oy + py), p)
    if args.out:
        image.save(args.out)
    else:
        image.show()