将可移动控制点创建为四边形曲线

Question

我正在使用下面的代码绘制从触摸到触摸释放的四边形曲线，并在这些触摸点之间添加一个球作为曲线的控制点。如何让用户拖动此球并依次调整四边形曲线的尺寸？

下面的代码描绘了从触摸点到触摸释放的一条线，我尝试将它与允许拖动对象的代码相结合，但我需要将拖动连接到实际移动控制点，然后修改原始曲线。

导入SpriteKit    导入GameKit

class GameScene: SKScene, SKPhysicsContactDelegate {

var movableNode : SKNode?
let controlBall = SKShapeNode(circleOfRadius: 10)
let myPath = CGMutablePath()

struct PhysicsCategory {

    static let lineCategory : UInt32 = 4

}

var startPoint : CGPoint = CGPoint.zero
var endPoint : CGPoint = CGPoint.zero
var controlPoint : CGPoint = CGPoint.zero

override func didMove(to view: SKView) {

    self.physicsBody = SKPhysicsBody(edgeLoopFrom: self.frame)
    self.physicsBody?.categoryBitMask = PhysicsCategory.lineCategory

    controlBall.zPosition = +1

}

override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {

    for touch in touches {

        let location = touch.location(in: self)

        if controlBall.contains(location) {

            movableNode = controlBall

            movableNode?.position = location

        } else {

            startPoint = touch.location(in: self)
            myPath.move(to: touch.location(in: self))


        }
    }
}

override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) {

    if let touch = touches.first, movableNode != nil {

        movableNode?.position = touch.location(in: self)

    }
}

override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent?) {

    for touch in touches {

        let location = touch.location(in: self)

        if let touch = touches.first, movableNode != nil {
            movableNode?.position = touch.location(in: self)
            movableNode = nil
        }

        endPoint = touch.location(in: self)

        var controlPoint = CGPoint(x:(startPoint.x-(startPoint.x - endPoint.x)/2), y: startPoint.y - ((startPoint.y - endPoint.y)/2))

        myPath.addQuadCurve(to: endPoint, control: controlPoint)
        let controlBall = SKShapeNode(circleOfRadius: 10)
        controlBall.fillColor = SKColor.red
        controlBall.strokeColor = SKColor.black
        controlBall.position = CGPoint(x:controlPoint.x, y: controlPoint.y)
        self.addChild(controlBall)

        let line = SKShapeNode(path: myPath)
        line.lineWidth = 5.0
        line.strokeColor = SKColor.blue
        line.physicsBody = SKPhysicsBody(edgeLoopFrom: myPath)
        line.physicsBody?.categoryBitMask = PhysicsCategory.lineCategory
        self.addChild(line)

        line.physicsBody = SKPhysicsBody(edgeFrom: startPoint, to:  endPoint)

    }
}

override func touchesCancelled(_ touches: Set<UITouch>, with event: UIEvent?) {
    if let touch = touches.first {
        movableNode = nil
    }
}

}