使用Swift在向下循环中移动SKSpriteNode

r = a + bθ

其中a是起始半径; b是螺旋每转增加的半径,θ是当前角.

螺旋基本上是一个美化圆(IMO),因此要以螺旋方式移动节点,您需要能够使用角度,半径和中心点计算圆上的点：

func pointOnCircle(#angle: CGFloat,#radius: CGFloat,#center: CGPoint) -> CGPoint {
    return CGPoint(x: center.x + radius * cos(anglE),y: center.y + radius * sin(anglE))
}

接下来,扩展SKAction,以便您可以轻松创建螺旋动作：

extension SKAction {
    static func spiral(#starTradius: CGFloat,endRadius: CGFloat,angle 
         @R_976_10586@lAngle: CGFloat,centerPoint: CGPoint,duration: NSTimeInterval) -> SKAction {

        // The distance the node will travel away from/toWARDs the 
        // center point,per revolution.
        let radiusPerRevolution = (endRadius - starTradius) / @R_976_10586@lAngle

        let action = SKAction.customActionWithDuration(duration) { node,time in
            // The current angle the node is at.
            let θ = @R_976_10586@lAngle * time / CGFloat(duration)

            // The equation,r = a + bθ
            let radius = starTradius + radiusPerRevolution * θ

            node.position = pointOnCircle(angle: θ,radius: radius,center: centerPoint)
        }

        return action
    }
}

最后,一个使用的例子.在didMoveToView中：

let node = SKSpriteNode(color: UIColor.redColor(),size: CGSize(width: 10,height: 10))
node.position = CGPoint(x: size.width / 2,y: size.height / 2)
addChild(nodE)

let spiral = SKAction.spiral(starTradius: size.width / 2,endRadius: 0,angle: CGFloat(M_PI) * 2,centerPoint: node.position,duration: 5.0)

node.runAction(spiral)