class cell
{
  position p;
  vector velocity;  
  float velocityDamping=0.01;
//  float mass;
  connection c;
  gene g;
  neuron n;
  
  float resistance;
  
  boolean isNeuron=false;                //cells tagged with this marker is capable of giving output signals
  boolean isMuscle=false;                //cells tagged with this marker is capable of varying spring distances
  
  cell(position pt)
  {
    p=new position(pt); 
    velocity=new vector(p,0,0);   
    c=new connection();
  }
  void update()
  {     
    doDrag();
    doFriction();  
    if(useGravity)
      doGravity();  
    doVelocity();    
//    doBorders();      
  }    
  void doGravity()
  {
    velocity=velocity.add(GRAVITY_VECTOR);
  }
  void doDrag()
  {
    boolean neg=false;
    if(velocity.m<0)
      neg=true;
    resistance=sqrt(velocity.m);
    resistance*=FLUID_FORCE;
    if(resistance<0.1)
      resistance=0;
    resistance+=1;
    
//    if(neg)
//      resistance*=-1;
  }
  void doFriction()
  {
    velocity.m*=FRICTION_FORCE;
    velocity.m*=1-velocityDamping;
  }
  void doVelocity()
  {
    p=p.displace(velocity);  
  }
  void doBorders()
  {
    boolean collide=false;
    if(p.x<10)
    {
      p.x=10;
      collide=true;
    }  
      
    else
      if(p.x>width-10)
      {
        p.x=width-10;
        collide=true;
      } 
    if(p.y<120)
    {
      p.y=120;
      collide=true;
    }
    else
      if(p.y>height-50)
      {
        p.y=height-50;
        collide=true;
      }
    if(collide)
      velocity.m*=.7;
  }
  float x()
  {
    return p.x;  
  }
  float y()
  {
    return p.y;
  }
}