svoid bwCopy(BufferedImage src, BWImage dst, int dstX, int dstY) {
  bwCopy(new BWImage(src), dst, dstX, dstY);
}
  
svoid bwCopy(BWImage src, BWImage dst, int dstX, int dstY) {
  int w = dst.getWidth()-dstX;
  int h = dst.getHeight()-dstY;
  w = min(w, src.getWidth());
  h = min(h, src.getHeight());
  for (int y = 0; y < h; y++)
    for (int x = 0; x < w; x++)
      dst.setInt(dstX+x, dstY+y, src.getInt(x, y));
}