class Leader {
  float x, y;
  float lastx, lasty;
  Leader() {
    setPosition(width/2, height/2);
  }
  Leader (float _x, float _y) {
    setPosition(_x, _y);
  }
  void setPosition(float _x, float _y) {
    x = _x;
    y = _y;
  }  
  // move is expected to be overridden
  // (the default is purely random movement, ignoring timeslice)
  void move(float dt) {
    lastx = x;
    lasty = y;
    x = random(width);
    y = random(height);
  }
  // drawing a leader would be mainly for debugging purposes
  // (normally would draw those objects that follow the leader)
  // (stroke is expected to be set elsewhere)
  void draw() {
    point(x,y);
  }
}