class Circle 
{

  
  float xPos;                            
  float yPos;
  
  int diam = 30;                             // circle diameter
  float G = 30;                              // gravitational constant
  
  color theColor;
  
  Vector3D a ;
  Vector3D v ;
  Vector3D l ;
  
  Circle[] otherCircles;
  int myIndex;
  
  Circle(Circle[] theOthers, int _myIndex)
  {
    
    xPos = random(width);                // random starting position
    yPos = random(height);
    
    l = new Vector3D(xPos,yPos);
    v = new Vector3D(0.0,0.0);
    a = new Vector3D(0.0,0.0);
   
    theColor = color(255,128); 
    otherCircles = theOthers;
    myIndex = _myIndex;
  }
  
  void drawCircle()
  {
    moveCircle();
    fill(theColor);
    ellipse(l.x, l.y, diam, diam);

  }
  void moveCircle()
  {
    Vector3D sum = new Vector3D();
    for (int i = 0; i < otherCircles.length; i++)
    {     
      float d = Vector3D.distance(l,otherCircles[i].l);                    // distance between circles
      if (myIndex != i)
      //if (myIndex != i && (abs(dist(otherCircles[i].l.x,otherCircles[i].l.y,l.x,l.y)) > 10))
      //if (myIndex != i && (abs(dist(otherCircles[i].xPos,otherCircles[i].yPos,xPos,yPos)) > 10))
      {
        //     -------------------------------------------------------------------------    gravity functions
        
        //println("go");
        Vector3D dir = Vector3D.sub(otherCircles[i].l,l);       // get the direction 
        dir.normalize();                          
        d = constrain(d,20,1000);                  // if too close, drop to threshold value
        d = sq(d);
        dir.mult(1/d);
        dir.mult(G);                               
        sum.add(dir);                             // summate forces
        //a = (a + (Vector3D.sub(otherCircles[i].l,l)).normalize()/(sq(Vector3D.distance(l, otherCircles[i].l))))/otherCircles.length; 
        //x_gravity = (x_gravity + (otherCircles[i].xPos - xPos)/(sq(dist(otherCircles[i].xPos,otherCircles[i].yPos,xPos,yPos))))/otherCircles.length;  
        //y_gravity = (y_gravity + (otherCircles[i].yPos - yPos)/(sq(dist(otherCircles[i].xPos,otherCircles[i].yPos,xPos,yPos))))/otherCircles.length;
        } 
    } 
    //sum.div(otherCircles.length);
    
   //      -----------------------------------------------------------------------------    bounce  
   if (l.x >= width)
   {
     v.x = -abs(v.x*damp) ;
   }
   if (l.x <= 0)
   {
     v.x = abs(v.x*damp) ;
   }
    
   if (l.y >= height)
   {
     v.y = -abs(v.y*damp);
   }
   if (l.y <= 0)
   {
     v.y = abs(v.y*damp);
   } 
  
  
    a = sum;                                // acceleration is sum of 
    
    a.mult(attracted);                      // attract or repulse
    
    v.add(a);
    //v.limit(1.0);
    //println(v.magnitude());
    l.add(v);
    
    /*
    xVel = xVel + 20*x_gravity*attracted;                    // change velocities
    yVel = yVel + 20*y_gravity*attracted; 
    
    xPos = xPos + xVel;                         // change positions
    yPos = yPos + yVel;
    */
    
  }   
}