ios - 如何根据平移手势速度将角脉冲应用于 Sprite Kit 节点

Question

我在这里要做的是围绕其 anchor 旋转 SKSpriteNode 并使其速度和方向与平移手势相匹配。因此，如果我的平移手势是围绕 Sprite 顺时针旋转，那么 Sprite 会顺时针旋转。

我的代码存在的问题是，它非常适合在 Sprite 下方从左到右/从右到左平移，但当我尝试垂直平移时根本行不通，如果我这样做会使 Sprite 以错误的方式旋转在 Sprite 上方平移。

这是我到目前为止所得到的 -

let windmill = SKSpriteNode(imageNamed: "Windmill")

override func didMoveToView(view: SKView) {
    /* Setup gesture recognizers */
    let panGestureRecognizer = UIPanGestureRecognizer(target: self, action: "handlePanGesture:")
    self.view?.addGestureRecognizer(panGestureRecognizer)

    windmill.physicsBody = SKPhysicsBody(circleOfRadius: windmill.size.width)
    windmill.physicsBody?.affectedByGravity = false
    windmill.name = "Windmill"
    windmill.position = CGPoint(x: self.frame.size.width / 2, y: self.frame.size.height / 2)
    self.addChild(windmill)
}

func handlePanGesture(recognizer: UIPanGestureRecognizer) {
    if (recognizer.state == UIGestureRecognizerState.Changed)
    {
        pinwheel.physicsBody?.applyAngularImpulse(recognizer.velocityInView(self.view).x)
    }
}

我知道它不随垂直平移旋转的原因是我只得到 x 值，所以我想我需要以某种方式组合这些值。

我也尝试过使用 applyImpulse:atPoint:，但这会导致整个 Sprite 被扫除。

Answer 1

以下步骤将根据平移手势旋转节点:

1. 存储一个从节点中心到平移手势起始位置的向量
2. 从节点中心到平移手势结束位置形成一个向量
3. 确定两个向量叉积的符号
4. 计算平移手势的速度
5. 使用速度和方向向节点施加角脉冲

这是一个如何在 Swift 中执行此操作的示例...

// Declare a variable to store touch location
var startingPoint = CGPointZero

// Pin the pinwheel to its parent
pinwheel.physicsBody?.pinned = true
// Optionally set the damping property to slow the wheel over time
pinwheel.physicsBody?.angularDamping = 0.25

声明 pan 处理程序方法

func handlePanGesture(recognizer: UIPanGestureRecognizer) {
    if (recognizer.state == UIGestureRecognizerState.Began) {
        var location = recognizer.locationInView(self.view)
        location = self.convertPointFromView(location)
        let dx = location.x - pinwheel.position.x;
        let dy = location.y - pinwheel.position.y;
        // Save vector from node to touch location
        startingPoint = CGPointMake(dx, dy)
    }
    else if (recognizer.state == UIGestureRecognizerState.Ended)
    {
        var location = recognizer.locationInView(self.view)
        location = self.convertPointFromView(location)

        var dx = location.x - pinwheel.position.x;
        var dy = location.y - pinwheel.position.y;

        // Determine the direction to spin the node
        let direction = sign(startingPoint.x * dy - startingPoint.y * dx);

        dx = recognizer.velocityInView(self.view).x
        dy = recognizer.velocityInView(self.view).y

        // Determine how fast to spin the node. Optionally, scale the speed
        let speed = sqrt(dx*dx + dy*dy) * 0.25

        // Apply angular impulse
        pinwheel.physicsBody?.applyAngularImpulse(speed * direction)
    }
}