svoid orBitMatrixWithItselfShifted(int dx, int dy, BitMatrix m) {
  if (dx == 0 && dy == 0);
  int w = m.getWidth(), h = m.getHeight();
  if (dx <= 0 && dy <= 0) {
    for (int y = -dy; y < h; y++)
      for (int x = -dx; x < h; x++)
        if (m.get(x, y))
          m.set(x+dx, y+dy, true);
  } else if (dx <= 0 && dy > 0) {
    for (int y = 0; y < h-y; y++)
      for (int x = -dx; x < h; x++)
        if (m.get(x, y))
          m.set(x+dx, y+dy, true);
  } else if (dx > 0 && dy <= 0) {
    for (int y = -dy; y < h; y++)
      for (int x = 0; x < h-dx; x++)
        if (m.get(x, y))
          m.set(x+dx, y+dy, true);
  } else if (dx > 0 && dy > 0) {
    for (int y = 0; y < h-dy; y++)
      for (int x = 0; x < h-dx; x++)
        if (m.get(x, y))
          m.set(x+dx, y+dy, true);
  }
}