vector getSpringForce(position from,position to,float desiredLength,float constant)
{
  vector force=new vector(from,to);
  
  if(dist(from,to)>.5)
  {
    vector deltaLength=new vector(force);
    position targetPos=new position(to.displace(getHeading(to,from),desiredLength));
    deltaLength=new vector(from,targetPos);
//    fill(255,0,0);
//    ellipse(targetPos.x,targetPos.y,5,5);
    force=new vector(deltaLength);
    force.m*=constant;
//    force.m=float(int(force.m*100))/100;
//    force.m=constrain(force.m,-10,10);
//    if(force.m<.01)
//      force.m=0;
  }
  return force;
}

vector getSpringForceVerlet(position from,position to,float desiredLength,float constant)
{

  float dx=to.x-from.x;
  float dy=to.y-from.y;
  float d1=sqrt(dx*dx+dy*dy);
  float d2=constant*(d1-desiredLength)/d1;
  dx=dx*d2;
  dy=dy*d2;
  
  position newFrom=new position(from.x+dx,from.y+dy);
//  from.y+=dy;
//  to.x-=dx;
//  to.y-=dy;
  
  vector force=new vector(from,newFrom);
  
  return force;
}

float getSpringForceScalar(float from,float to,float desiredLength,float constant)
{
  float force=to;
  force-=from;
  if(force!=0)
  {
    float deltaLength=force;
    float targetLength=desiredLength;
    deltaLength=deltaLength-targetLength;
    force=deltaLength;
    force*=constant;
  }

  return force;
}