anchor.diff:    final PhysicsShape shapeB;
     final isTouching;
     bool isEnabled;
  +  final List<Point> touchingPoints;
  +  final Offset touchingNormal;
   }
   
   class _ContactCallbackInfo {
  
positive.code: 
        if (match) {
          // We have contact and a matched callback, setup contact info
          PhysicsContact contact = new PhysicsContact(
            bodyA._node,
            bodyB._node,
            fixtureA.userData,
            fixtureB.userData,
            b2Contact.isTouching(),
            b2Contact.isEnabled()
          );
  
          if (type == PhysicsContactType.postSolve) {
  
          }
  
          // Make callback
          info.callback(type, contact);
  
negative.code:     this.shapeA,
      this.shapeB,
      this.isTouching,
      this.isEnabled,
      this.touchingPoints,
      this.touchingNormal
    );
  
    final Node nodeA;
  