static void copyBWImage(BWImage src, int srcX, int srcY, BWImage dst, int dstX, int dstY) {
  copyBWImage(src, srcX, srcY, dst, dstX, dstY, src.getWidth()-srcX, src.getHeight()-srcY);
}

static void copyBWImage(BWImage src, int srcX, int srcY, BWImage dst, int dstX, int dstY, int w, int h) {
  w = min(w, dst.getWidth()-dstX);
  h = min(h, dst.getHeight()-dstY);
  w = min(w, src.getWidth()-srcX);
  h = min(h, src.getHeight()-srcY);
  for (int y = 0; y < h; y++)
    for (int x = 0; x < w; x++)
      dst.setByte(dstX+x, dstY+y, src.getByte(srcX+x, srcY+y));
}