Elementary Cellular Automata PNG images generator. Based on Nicolas Seriot's gist (https://goo.gl/fh4d5Y).

eca.py

#!/usr/bin/env python3

__author__ = "Ahmad Alhour"
__date__ = "2017-10-29"
__website__ = "https://gist.github.com/aalhour/533b8ea1a1d71bbfb026c16d956aa6d2"

"""
eca.py

Elementary Cellular Automata PNG images generator. Based on Nicolas Seriot's gist (https://goo.gl/fh4d5Y).

How to use:
    python3 eca.py -h

Resources:
    - http://mathworld.wolfram.com/CellularAutomaton.html
    - http://mathworld.wolfram.com/ElementaryCellularAutomaton.html
    - https://en.wikipedia.org/wiki/Elementary_cellular_automaton
    - https://en.wikipedia.org/wiki/Rule_110
"""


import os
import argparse
from typing import List
import png


SUPPORTED_ECA_RULES = [
    30,  # 0b00011110
    54,  # 0b00110110
    60,  # 0b00111100
    62,  # 0b00111110
    90,  # 0b01011010
    94,  # 0b01011110
    102, # 0b01100110
    110, # 0b01101110
    122, # 0b01111010
    126, # 0b01111110
    150, # 0b10010110
    158, # 0b10011110
    182, # 0b10110110
    188, # 0b10111100
    190, # 0b10111110
    220, # 0b11011100
    222, # 0b11011110
    250  # 0b11111010
]


def create_argument_parser() -> argparse.ArgumentParser:
    """
    Creates an argument parser for the command line.
    """
    arg_parser = argparse.ArgumentParser(prog="eca")
    
    arg_parser.add_argument(
        "--width", 
        type=int, default=1000, help="Image width in pixels, i.e.: 1000.")
    arg_parser.add_argument(
        "--height",
        type=int, default=1000, help="Image height in pixels, i.e.: 1000.")
    arg_parser.add_argument(
        "--rule", 
        type=int, default=110, choices=SUPPORTED_ECA_RULES, help="Elementary Cellular Automaton Rule.")
    arg_parser.add_argument(
        "--name", 
        type=str, action="store", default=None, 
        help="Desired name of the image. If not specified a random name will be generated.")
    
    return arg_parser


def generate_random_str() -> str:
    """
    Generates a pseudo-random hexadecimal string.
    """
    return os.urandom(6).hex()


def write_data_to_png_file(matrix: List[List[int]], filename: str) -> None:
    """
    Writes a given PNG matrix (2D array) to a file with the specified filename string. 
    """
    ll = [[255 - b * 255 for b in row] for row in matrix]
    png.from_array(ll, 'L').save(filename)


def compute_eca_matrix(width: int=1000, height: int=1000, rule: int=110) -> List[List[int]]:
    """
    Given an 2D image size, in addition to an ECA rule in integer representation,
     generate an ECA matrix to be written to an image file.
    """
    ###
    # Helper functions
    #
    def next_row(row: List[int], rule_bits: List[int]) -> List[int]:
        """
        Generates the next row in the PNG matrix given the current row vector and
        the bytearray of the ECA rule.
        """
        r = row[-1:] + row + row[:1]
        return [rule_bits[r[i]*4 + b*2 + r[i+2]] for (i, b) in enumerate(row)]
    
    # Get the rule's bits from its decimal representation.
    rule_bits = [int(x) for x in '{0:08b}'.format(rule)[::-1]]

    # Setup the first row in the matrix.
    row = [0] * width
    row[width//2] = 1
    
    eca_matrix = [row]
    
    for i in range(height-1):
        row = next_row(row, rule_bits)
        eca_matrix.append(row)

    return eca_matrix

def main():
    """
    Entry point. Parses the command line for parameters and generates the PNG image accordingly.
    """
    # Create a new argument parser.
    arg_parser = create_argument_parser()

    # Parse teh command line arguments.
    args = arg_parser.parse_args()

    # Compute the ECA Matrix.
    eca_matrix = compute_eca_matrix(args.width, args.height, args.rule)

    # Construct the image and file names.
    image_name = args.name if args.name else generate_random_str()
    file_name = "{name}__r{rule}_w{width}_h{height}.png".format(
        name=image_name, rule=args.rule, width=args.width, height=args.height)
    
    # Write the matrix to a new PNG file.
    write_data_to_png_file(eca_matrix, file_name)

    # Print the file path back to the user.
    print("Image was saved at: {}".format(os.path.abspath(file_name)))


if __name__ == "__main__":
    main()