void TimeKeeper::idleSleep(float seconds)
{
  float dtime= idleTime - TimeKeeper::getCurrent();
  if ((dtime < -1)||(dtime > 1)) {
    idleTime= TimeKeeper::getCurrent();
    idleTime.seconds -= 0.5;
    // allow for some extra frames to catch up
    return;
  }
  if (dtime > 0) {
    TimeKeeper::sleep(dtime);
  }
  idleTime.seconds += seconds;
}