swift - SpriteKit : how to vary skaction duration based on distance?

Question

好的，所以我有一个 Cgpoints 数组，当我遍历该数组时，我将 Sprite 节点移动到该数组。 Sprite 到下一个点的距离随每个点的不同而不同

func moveGuy() {
    let action = SKAction.move(to: points[i], duration: 2)
    action.timingMode = .easeInEaseOut
    guy.run(action)   
}

//UPDATE
override func update(_ currentTime: CFTimeInterval) {
    if(mouseIsDown)
    {
       moveGuy()
    }
}

我的问题是静态持续时间，这取决于 Sprite 在何处以较慢/较快的速度移动。无论 Sprite 必须移动多远，我都需要保持恒定的速度。

如何根据 Sprite 与终点的距离改变 SKAction 速度？

Answer 1

这需要使用距离公式。现在要保持恒定速度，您需要确定要移动的每秒点数 (pps)。

基本上公式变成距离/pps

假设我们想从 (0,0) 移动到 (0,300)(这是 300 点，所以需要 2 秒)

伪代码:

让持续时间 = sqrt((0 - 0) * (0 - 0) + (0 - 300) * (0 - 300))/(150)
持续时间 = sqrt(90000)/(150)
持续时间 = 300/150
持续时间 = 2

然后你会把它弹出到你的移动 Action 中:

let action = SKAction.move(to: points[i], duration: duration)

您的 Swift 代码应如下所示:

let pps = 150 //define points per second
func moveGuy() {
    var actions = [SKAction]()
    var previousPoint = guy.position // let's make sprite the starting point
    for point in points
    {
      //calculate the duration using distance / pps
      //pow seems to be slow and some people have created ** operator in response, but will not show that here
      let duration = sqrt((point.x - previousPoint.x) * (point.x - previousPoint.x) + 
                     (point.y - previousPoint.y) * (point.y - previousPoint.y)) / pps

      //assign the action to the duration
      let action = SKAction.move(to: point, duration: duration)
      action.timingMode = .easeInEaseOut
      actions.append(action)
      previousPoint = point
    }   
    guy.run(actions)
}

//Since the entire path is done in moveGuy now, we no longer want to be doing it on update, so instead we do it during the mouse click event
//I do not know OSX, so I do not know how mouse down really works, this may need to be fixed
//Also I am not sure what is suppose to happen if you click mouse twice,
//You will have to handle this because it will run 2 actions at once if not done
override func mouseDown(event:NSEvent)
{
    moveGuy()
}

现在您会注意到您的 sprite 在每次迭代时都在加速和减速，您可能不希望这样，因此对于您的计时模式，您可能想要这样做

//Use easeInEaseOut on our first move if we are only moving to 1 point
if points.count == 1
{
    action.timingMode = .easeInEaseOut
}
//Use easeIn on our first move unless we are only moving to 1 point
else if previousPoint == sprite.position
{
    action.timingMode = .easeIn
}
//Use easeOut on our last move unless we are only moving to 1 point
else if point == point.last
{
    action.timingMode = .easeOut
}
//Do nothing
else
{
    action.timingMode = .linear
}