/** Returns the client window under the specified root subwindow. */ private static long findClientWindow(long window) { if (XlibUtil.isTrueToplevelWindow(window)) { return window; } Set<Long> children = XlibUtil.getChildWindows(window); for (Long child : children) { long win = findClientWindow(child); if (win != 0) { return win; } } return 0; }