private void movePoly(int x, int y) {
		int dx = x - (poly.xpoints[0] - x0);
		int dy = y - (poly.ypoints[0] - y0);
		for (int i = 0; i < poly.npoints; i++) {
			poly.xpoints[i] += dx;
			poly.ypoints[i] += dy;
		}
	}