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.setFriction(friction);
       }
     }
  
positive.code: 
      if (_body == null)
        return;
      for(box2d.Fixture f = _body.getFixtureList(); f != null; f = f.getNext()) {
        f.setRestitution(restitution);
      }
    }
  
negative.code: 
      if (_body == null)
        return;
      for (box2d.Fixture f = _body.getFixtureList(); f != null; f = f.getNext()) {
        f.setSensor(isSensor);
      }
    }
  
    Offset _linearVelocity;
  
    Offset get linearVelocity {
      if (_body == null)
        return _linearVelocity;
      else {
        double dx = _body.linearVelocity.x * _physicsNode.b2WorldToNodeConversionFactor;
        double dy = _body.linearVelocity.y * _physicsNode.b2WorldToNodeConversionFactor;
        return new Offset(dx, dy);
      }
    }
  
    set linearVelocity(Offset linearVelocity) {
      _linearVelocity = linearVelocity;
  
      if (_body != null) {
        Vector2 vec = new Vector2(
          linearVelocity.dx / _physicsNode.b2WorldToNodeConversionFactor,
          linearVelocity.dy / _physicsNode.b2WorldToNodeConversionFactor
        );
        _body.linearVelocity = vec;
      }
    }
  
    double _angularVelocity;
  
    double get angularVelocity {
      if (_body == null)
        return _angularVelocity;
      else
        return _body.angularVelocity;
    }
  
    set angularVelocity(double angularVelocity) {
      _angularVelocity = angularVelocity;
  
      if (_body != null) {
        _body.angularVelocity = angularVelocity;
      }
    }
  
    // TODO: Should this be editable in box2d.Body ?
    final double linearDampening;
  
    double _angularDampening;
  
    double get angularDampening => _angularDampening;
  
    set angularDampening(double angularDampening) {
      _angularDampening = angularDampening;
  
      if (_body != null)
        _body.angularDamping = angularDampening;
    }
  
    bool allowSleep;
  
  