int gW, gH;
node[] ns;
int N = 8;  //MUST be even!!
void setup()
{
  gW = 400;
  gH = 400;
  size(gW,gH);
  ns = new node[N];
  for(int i=0; i<N; i++)
  {
    ns[i] = new node();
  }
  ellipseMode(CENTER_DIAMETER); 
}

void loop()
{
  background(235,242,245);
  for(int i=0; i<N-1; i=i+2)
  {
    ns[i].go();
    ns[i+1].go();
    for(int j=0; j<N; j++)
    {
      if(i!=j)  ns[i].target(ns[j]);
    }
  }
}

class node
{
  float x,y;
  float vx, vy;
  float s = 10;
  float maxv = 2.5;
  node(float xin, float yin, float vxin, float vyin)
  {
    x = xin; y = yin;
    vx = vxin; vy = vyin;
  }
  node()
  {
    x = random(gW); y = random(gH);
    vx = random(-5,5); vy = random(-5,5);
  }
  void go()
  {
    if(vx > maxv) vx = maxv;
    else if (vx < -maxv) vx = -maxv;
    if(vy > maxv) vy = maxv;
    else if (vy < -maxv) vy = -maxv;
    x = (x + vx) % gW;
    y = (y + vy) % gH;
    if (x < 0) x += gW;
    if (y < 0) y += gH;
    stroke(0);
    fill(78,97,108);
    ellipse(x,y,s,s);
  }
  void target(node n)
  {
    float dx = n.x - x;
    float dy = n.y - y;
    float sp = 20000;
    vx = vx + dx/sp;
    vy = vy + dy/sp;
    n.vx = n.vx - dx/sp;
    n.vy = n.vy - dy/sp;
    float d = abs(dx)+abs(dy);
    if(d < 120)
    {
      int a = (int)((230-78)*d/120);
      int b = (int)((230-97)*d/120);
      int c = (int)((230-108)*d/120);
      stroke(78+a,97+b,108+c);
      line(x,y,n.x,n.y);
    }
  }
}