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:           }
          }
        }
  
        canvas.restore();
  
        // Draw contacts
        for (box2d.ContactEdge edge = body.getContactList(); edge != null; edge = edge.next) {
          box2d.Contact contact = edge.contact;
          Vector2 cA = new Vector2.zero();
          Vector2 cB = new Vector2.zero();
  
          box2d.Fixture fixtureA = contact.fixtureA;
          box2d.Fixture fixtureB = contact.fixtureB;
  
          fixtureA.getAABB(contact.getChildIndexA()).getCenterToOut(cA);
          fixtureB.getAABB(contact.getChildIndexB()).getCenterToOut(cB);
  
          Point p1 = new Point(
            cA.x * b2WorldToNodeConversionFactor,
            cA.y * b2WorldToNodeConversionFactor
          );
  
          Point p2 = new Point(
            cB.x * b2WorldToNodeConversionFactor,
            cB.y * b2WorldToNodeConversionFactor
          );
  
          shapePaint.color = new Color(0x33ffffff);
          canvas.drawLine(p1, p2, shapePaint);
  
          box2d.WorldManifold worldManifold = new box2d.WorldManifold();
          contact.getWorldManifold(worldManifold);
  
          shapePaint.color = new Color(0xffffffff);
  
          for (Vector2 pt in worldManifold.points) {
            Point pCenter = new Point(
              pt.x * b2WorldToNodeConversionFactor,
              pt.y * b2WorldToNodeConversionFactor
            );
            Offset offset = new Offset(
              worldManifold.normal.x * 5.0,
              worldManifold.normal.y * 5.0
            );
  
            Point p2 = pCenter + offset;
            Point p1 = new Point(pCenter.x - offset.dx, pCenter.y - offset.dy);
            canvas.drawLine(p1, p2, shapePaint);
            canvas.drawCircle(pCenter, 5.0, shapePaint);
          }
        }
  
  
      }
    }
  }
  