static Boolean isHeadless_cache;

static bool isHeadless() {
  if (isHeadless_cache != null) ret isHeadless_cache;
  if (isAndroid()) ret isHeadless_cache = true;
  if (GraphicsEnvironment.isHeadless()) ret isHeadless_cache = true;
  
  // Also check if AWT actually works.
  // If DISPLAY variable is set but no X server up, this will notice.
  
  try {
    SwingUtilities.isEventDispatchThread();
    ret isHeadless_cache = false;
  } catch (Throwable e) { ret isHeadless_cache = true; }
}