如何基于pan手势速度对雪碧套件节点施加角脉冲？

Question

我在这里要做的是旋转一个SKSpriteNode围绕它的锚点，并有它的速度和方向匹配的潘手势。因此，如果我的盘手势顺时针围绕雪碧，那么精灵会顺时针旋转。

我的代码存在的问题是，它对雪碧下面的平底锅(从左到右/从右到左)很好，但当我尝试垂直平移时就一点都不起作用了，如果我把雪碧移到雪碧上面，它会使它以错误的方式旋转。

到目前为止我得到的是-

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)
    }
}

我知道它没有用垂直平底锅旋转的原因，因为我只得到x值，所以我想我需要以某种方式组合它们。

我也尝试过使用applyImpulse:atPoint:，但是这会导致整个精灵被冲走。

Answer 1

以下步骤将根据pan手势旋转节点：

1. 将矢量从节点中心存储到pan手势的起始位置。
2. 形成从节点中心到pan手势结束位置的向量。
3. 确定两个向量的交叉乘积的符号
4. 计算pan手势的速度
5. 使用速度和方向对节点施加角脉冲。

这里有一个如何在Swift中实现这一点的例子..。

// 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)
    }
}