用 CGPath 做半圆路径，用 SKAction 跟随路径

Question

我不知道如何使用 CGPath 制作半圆路径。我有代码：

  let path = CGPathCreateMutable()
  let Width: CGFloat = 38.0
  let radius: CGFloat = (Width / 2.0) + (Treshold / 2.0)
  CGPathAddArc(pathOne, nil, x, 0.0, radius, firstPoint.position.x, secondPoint.position.x, true)
  let waitAction = SKAction.waitForDuration(1.0)
  let moveAction = SKAction.followPath(pathOne, duration: 3.0)
  capOne.runAction(SKAction.sequence([waitAction, moveAction]))

Answer 1

import SpriteKit

class GameScene: SKScene, SKPhysicsContactDelegate {

    override init(size: CGSize) {
        super.init(size: size)
        let square = SKSpriteNode(color: SKColor.redColor(), size: CGSizeMake(20, 20))
        square.position = CGPointMake(self.size.width/2, self.size.height/2)
        addChild(square)

        let bezierPath = UIBezierPath(arcCenter: CGPointMake(0, 0), radius: 100, startAngle: CGFloat(M_PI_2), endAngle: CGFloat(-M_PI_2), clockwise: false)

        let pathNode = SKShapeNode(path: bezierPath.CGPath)
        pathNode.strokeColor = SKColor.blueColor()
        pathNode.lineWidth = 3
        pathNode.position = square.position
        addChild(pathNode)

        square.runAction(SKAction.followPath(bezierPath.CGPath, asOffset: true, orientToPath: true, duration: 2))
    }

    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
}