class Agent {
  color c;
  Edge e;
  float x, y, speed;
  int steps;

  Agent(Edge e) {
    this.e = e;
    this.x = e.n0.x;
    this.y = e.n0.y;
    speed = .5 + random(.5); // in pixels
    speed = speed/e.len();   // in fraction of length
    steps = 0;
    c = randomBrightColor();
  }
  void step(){
    steps += 1;
    float delta = steps*speed;
    if(abs(delta) >= 1.0) {
      Node toNode = (speed > 0)?e.n1:e.n0;
      e = (Edge)randomOtherOneOf(toNode.edges, e);
      steps = 0;
      delta = 0;
      speed = (toNode==e.n0)?abs(speed):-abs(speed);
    }
    Node p = (speed > 0)?e.n0:e.n1;
    x = p.x + e.dx()*delta;
    y = p.y + e.dy()*delta;
    paint();
  }
  void paint(){
    noStroke();
    fill(c);
    rect(x-2,y-2,5,5);
  }
}