如何使用UIPinchGestureRecognizer速度

Question

当用户停止捏住时，我尝试使用UIPinchGestureRecognizer的属性velocity在SceneKit节点中播放动画，但是我不了解velocity的属性如何计算/应该使用。

这是我的代码：

var initialScale = simd_float3(1)
@objc private func handlePinch(sender: UIPinchGestureRecognizer) {
let scale = simd_float3(Float(sender.scale))
let state = sender.state
let vel = Float(sender.velocity)

if state == .began {
  updateQ.async(group: updateGrp) {
    log.debug("Begin scale: \(scale)")
    log.debug("Begin vel: \(vel)")

    if let node = self.activeNode {
      self.initialScale = node.simdScale
    }
    else {
      self.initialScale = self.layeredImgNode.simdScale
    }
  }
}
else if state == .changed {
  updateQ.async(group: updateGrp) {
    log.debug("Changed scale: \(scale)")
    log.debug("Changed vel: \(vel)")

    let scale = self.initialScale * scale

    if let node = self.activeNode {
      node.simdScale = scale
    }
    else {
      self.layeredImgNode.simdScale = scale
    }
  }
}
else if state == .ended {
  updateQ.async(group: updateGrp) {
    log.debug("End scale: \(scale)")
    log.debug("End vel: \(vel)")


    // Calculate for how long to run the animation
    let time = Double(vel / Float(10))
    let target = self.initialScale * (scale + simd_float3(vel))
    log.debug("End target: \(target) and time: \(time)")

    self.initialScale = simd_float3(1)

    SCNTransaction.begin()
    SCNTransaction.animationDuration = time
    if let node = self.activeNode {
      node.simdScale = target
    }
    else {
      self.layeredImgNode.simdScale = target
    }
    SCNTransaction.commit()
  }
}

文档指出velocity为“捏合速度每秒的比例因子”。但是，我仍然不知道如何使用它。有人可以帮我吗？

谢谢。