a better approach to handling the pan gesture in scenekit. For use in part 3 of medium post

scenekit-better-pan-gesture-recognizer.swift

@objc func handlePan(panGesture: UIPanGestureRecognizer) {
  guard let view = view as? SCNView else { return }
  switch panGesture.state {
  case .began:
    let location = panGesture.location(in: self.view)
    guard let hitNodeResult = view.hitTest(location, options: nil).first else { return }
    panStartZ = CGFloat(view.projectPoint(lastPanLocation!).z)
    lastPanLocation = hitNodeResult.worldCoordinates
    draggingNode = hitNodeResult.node
  case .changed:
    let location = panGesture.location(in: view)
    let worldTouchPosition = view.unprojectPoint(SCNVector3(location.x, location.y, panStartZ!))
    let movementVector = SCNVector3(
      worldTouchPosition.x - lastPanLocation!.x,
      worldTouchPosition.y - lastPanLocation!.y,
      worldTouchPosition.z - lastPanLocation!.z)
    geometryNode.localTranslate(by: movementVector)
    self.lastPanLocation = worldTouchPosition
  default:
    break
  }
}