anchor.diff:    PhysicsJointRevolute(
       PhysicsBody bodyA,
       PhysicsBody bodyB,
  -    this.worldAnchor, {
  +    this._worldAnchor, {
         this.lowerAngle: 0.0,
         this.upperAngle: 0.0,
         this.enableLimit: false,
  
positive.code:   box2d.Joint _createB2Joint(PhysicsNode physicsNode) {
      // Create Joint Definition
      Vector2 vecAnchor = new Vector2(
        worldAnchor.x / physicsNode.b2WorldToNodeConversionFactor,
        worldAnchor.y / physicsNode.b2WorldToNodeConversionFactor
      );
  
      box2d.RevoluteJointDef b2Def = new box2d.RevoluteJointDef();
  
negative.code:     _completeCreation();
    }
  
    final Point _worldAnchor;
    final double lowerAngle;
    final double upperAngle;
    final bool enableLimit;
  