Question

使用Swift和SpriteKit，我想以螺旋模式移动SKSpritenode，但没有找到合适的资源让我开始。更确切地说，我想在向下循环中移动一个精灵节点。我已经检查了一系列SKActions，但由于它们不是平行执行的，因此与移动相结合的圆形运动将不起作用。我很高兴有任何提示，教程或片段让我走上正轨。

Thanx提前，马库斯

Answer 1

I've put together some sample code which you can adapt for your purposes. I've based the code off the equation for an Archimedean Spiral:

r = a + bθ

Where a is the starting radius; b is the radius the spiral will increase by per revolution and θ is the current angle.

A spiral is basically a glorified circle (IMO), so to move your node in a spiral you need to be able to calculate point on a circle using an angle, radius and center point:

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

Next, extend SKAction so you can easily create a spiral action:

extension SKAction {
    static func spiral(#startRadius: CGFloat, endRadius: CGFloat, angle 
         totalAngle: CGFloat, centerPoint: CGPoint, duration: NSTimeInterval) -> SKAction {

        // The distance the node will travel away from/towards the 
        // center point, per revolution.
        let radiusPerRevolution = (endRadius - startRadius) / totalAngle

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

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

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

        return action
    }
}

Finally, an example of use. In didMoveToView:

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)

Answer 2

虽然上面提到的解决方案很精彩，但有一种更简单的方法。

添加一个spinnerNode，并使用rotateBy
将您的精灵作为孩子添加到spinnerNode（默认情况下，您的精灵将使用spinnerNode旋转）
将您的spriteNode（使用moveTo）移动到wheelNode的中心（您的精灵将以螺旋形路径行进到中心）

使用Swift在向下循环中移动SKSpriteNode

2 个答案: