anchor.diff:  
       if (_body == null)
         return;
  -    for(box2d.Fixture f = _body.getFixtureList(); f != null; f = f.getNext()) {
  +    for (box2d.Fixture f = _body.getFixtureList(); f != null; f = f.getNext()) {
         f.setDensity(density);
       }
     }
  
positive.code: 
      if (_body == null)
        return;
      for(box2d.Fixture f = _body.getFixtureList(); f != null; f = f.getNext()) {
        f.setSensor(isSensor);
      }
    }
  
    Offset linearVelocity;
    double angularVelocity;
  
    double linearDampening;
  
    double angularDampening;
  
    bool allowSleep;
  
  
negative.code:     this.friction = friction;
      this.restitution = restitution;
      this.isSensor = isSensor;
  
      this.linearVelocity = linearVelocity;
      this.angularVelocity = angularVelocity;
      this.angularDampening = angularDampening;
    }
  
    Object tag;
  
    final PhysicsShape shape;
  
    PhysicsBodyType type;
  
  