// use x for black and _ for white
static BWImage bwImageFromString(S s) {
  LS lines = tlft(s);
  if (empty(lines)) null;
  int h = l(lines), w = l(first(lines));
  BWImage out = new(w, h);
  for y to h: {
    S line = lines.get(y);
    print ifdef bwImageFromString(+line);
    for x to w:
      if (charAt(line, x) != 'x')
        out.setInt(x, y, 255);
  }
  ret out;
}