拖动绕固定点旋转节点

Question

我试图在这个问题中创建一个类似于“奖杯轮”的可旋转节点。到目前为止，我具有甩尾功能，可以使用效果很好的UIPanGestureRecognizer在物理物体上添加角度脉冲。我也可以通过触摸停止旋转。

现在，我试图通过拖动或滑动手势来微调方向盘，这样，如果玩家对最终的效果不满意，就可以手动旋转/拖动/旋转它所喜欢的旋转方式。

目前，我将触摸的位置保存在touchesBegan中，并尝试在更新循环中增加节点的zRotation。

旋转不跟随我的手指，而且很生涩。我不确定我的手指运动是否获得足够准确的读数，或者手指的变化位置是否没有准确地转换为弧度。我怀疑先检测触摸然后在更新中处理它不是一个很好的解决方案。

这是我的代码。

    override func touchesBegan(touches: Set<NSObject>, withEvent event: UIEvent?) {
    if let touch = touches.first as? UITouch {
        var location = touch.locationInView(self.view)
        location = self.convertPointFromView(location)

        mostRecentTouchLocation = location

        let node = nodeAtPoint(location)
        if node.name == Optional("left") && node.physicsBody?.angularVelocity != 0
        {
            node.physicsBody = SKPhysicsBody(circleOfRadius:150)
            node.physicsBody?.applyAngularImpulse(0)
            node.physicsBody?.pinned = true
        }
    }
}

    override func update(currentTime: CFTimeInterval) {
        /* Called before each frame is rendered */
        if mostRecentTouchLocation != CGPointZero{
        let node = nodeAtPoint(mostRecentTouchLocation)
        if node.name == Optional("left")
        {
            var positionInScene:CGPoint = mostRecentTouchLocation
            let deltaX:Float = Float(positionInScene.x) - Float(node.position.x)
            let deltaY:Float = Float(positionInScene.y) - Float(node.position.y)
            let angle:CGFloat = CGFloat(atan2f(deltaY, deltaX))
            let maths:CGFloat = angle - (CGFloat(90) * (CGFloat(M_PI) / 180.0))
            node.zRotation += maths
            mostRecentTouchLocation = CGPointZero
        }
    }
}

我在更新中将一些数学计算分散在多行中，以使调试更加容易。

如果需要，我可以添加PanGestureRecognizer代码，但现在我将尽量使其简短。

编辑
这是基于GilderMan推荐的最新代码。我认为它的效果更好，但是旋转远非平稳。它以较大的幅度跳跃并且没有很好地跟随手指。这是否意味着我的角度计算有问题？

    override func didSimulatePhysics() {
    if mostRecentTouchLocation != CGPointZero {
        let node = nodeAtPoint(mostRecentTouchLocation)
        if node.name == Optional("left")
        {
            var positionInScene:CGPoint = mostRecentTouchLocation
            let deltaX:Float = Float(positionInScene.x) - Float(node.position.x)
            let deltaY:Float = Float(positionInScene.y) - Float(node.position.y)
            let angle:CGFloat = CGFloat(atan2f(deltaY, deltaX))
            node.zRotation += angle
            println(angle)
            mostRecentTouchLocation = CGPointZero
        }
    }
}

Answer 1

以下代码模拟了根据触摸旋转的奖轮。当用户的手指移动时，轮子会与手指的速度成比例地旋转。当用户在方向盘上滑动时，方向盘将与滑动速度成比例地旋转。您可以更改angularDamping物理物体的属性以减慢或增加砂轮停止的速度。

class GameScene: SKScene {
    var startingAngle:CGFloat?
    var startingTime:TimeInterval?

    override func didMove(to view: SKView) {
        let wheel = SKSpriteNode(imageNamed: "Spaceship")
        wheel.name = "wheel"
        wheel.setScale(0.5)
        wheel.physicsBody = SKPhysicsBody(circleOfRadius: wheel.size.width/2)
        // Change this property as needed (increase it to slow faster)
        wheel.physicsBody!.angularDamping = 0.25
        wheel.physicsBody?.pinned = true
        wheel.physicsBody?.affectedByGravity = false
        addChild(wheel)
    }

    override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
        for touch in touches {
            let location = touch.location(in:self)
            let node = atPoint(location)
            if node.name == "wheel" {
                let dx = location.x - node.position.x
                let dy = location.y - node.position.y
                // Store angle and current time
                startingAngle = atan2(dy, dx)
                startingTime = touch.timestamp
                node.physicsBody?.angularVelocity = 0
            }
        }
    }

    override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) {
        for touch in touches{
            let location = touch.location(in:self)
            let node = atPoint(location)
            if node.name == "wheel" {
                let dx = location.x - node.position.x
                let dy = location.y - node.position.y

                let angle = atan2(dy, dx)
                // Calculate angular velocity; handle wrap at pi/-pi
                var deltaAngle = angle - startingAngle!
                if abs(deltaAngle) > CGFloat.pi {
                    if (deltaAngle > 0) {
                        deltaAngle = deltaAngle - CGFloat.pi * 2
                    }
                    else {
                        deltaAngle = deltaAngle + CGFloat.pi * 2
                    }
                }
                let dt = CGFloat(touch.timestamp - startingTime!)
                let velocity = deltaAngle / dt

                node.physicsBody?.angularVelocity = velocity

                // Update angle and time
                startingAngle = angle
                startingTime = touch.timestamp
            }
        }
    }

    override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent?) {
        startingAngle = nil
        startingTime = nil
    }
}