anchor.diff:      this.bullet: false,
       this.active: true,
       this.gravityScale: 1.0
  -  });
  +  }) {
  +    this.density = density;
  +    this.friction = friction;
  +    this.restitution = restitution;
  +    this.isSensor = isSensor;
  +  }
   
     Object tag;
   
  
positive.code: 
    PhysicsBodyType type;
  
    double density;
    double friction;
    double restitution;
    bool isSensor;
  
    Offset linearVelocity;
    double angularVelocity;
  
negative.code:   PhysicsBody(this.shape, {
      this.tag: null,
      this.type: PhysicsBodyType.dynamic,
      double density: 1.0,
      double friction: 0.0,
      double restitution: 0.0,
      bool isSensor: false,
      this.linearVelocity: Offset.zero,
      this.angularVelocity: 0.0,
      this.linearDampening: 0.0,
  