rough_ocean_coords.py

from __future__ import annotations
from PIL import Image, ImageDraw


def neighbours(x, y):
    return [(x - 1, y), (x + 1, y), (x, y - 1), (x, y + 1), (x - 1, y - 1), (x + 1, y - 1), (x - 1, y + 1),
            (x + 1, y + 1)]


def find_ocean_coords(filename, testsize=(128, 128)):
    im = Image.open(filename)
    mapim = im.resize(testsize)

    # take top left corner... if it's land, you might need to test other corners.
    # but I'm lazy, so I'm just going to assume it's always water.
    water_color = mapim.getpixel((0, 0))

    orig_w, orig_h = im.size
    w, h = mapim.size
    ratio_w = orig_w / w
    ratio_h = orig_h / h

    # find all connected water pixels of the same color
    seen = set()
    valid_coords = set()
    x, y = 0, 0
    stack = [(x, y)]

    # add all edges with same water color
    for x in range(w):
        if mapim.getpixel((x, 0)) == water_color:
            valid_coords.add((x, 0))
            stack.append((x, 0))
        if mapim.getpixel((x, h - 1)) == water_color:
            valid_coords.add((x, h - 1))
            stack.append((x, h - 1))
    for y in range(h):
        if mapim.getpixel((0, y)) == water_color:
            valid_coords.add((0, y))
            stack.append((0, y))
        if mapim.getpixel((w - 1, y)) == water_color:
            valid_coords.add((w - 1, y))
            stack.append((w - 1, y))

    # flood fill
    while stack:
        x, y = stack.pop()
        if (x, y) in seen or x < 0 or x >= w or y < 0 or y >= h:
            continue
        seen.add((x, y))
        if mapim.getpixel((x, y)) == water_color:
            valid_coords.add((x, y))
            stack.extend(neighbours(x, y))

    # convert to original image coordinates
    return {(int(x * ratio_w), int(y * ratio_h)) for x, y in valid_coords}


def main():
    ocean_coords = find_ocean_coords('maps/border_image.png')

    im = Image.open('maps/image.png')
    draw = ImageDraw.Draw(im)
    for x, y in ocean_coords:
        draw.ellipse((x - 2, y - 2, x + 2, y + 2), fill=(255, 0, 0))

    im.show()


if __name__ == '__main__':
    main()