swift - 如何限制两条锚定线的运动，使它们像钟摆一样不断摆动

Question

我创建了两条锚定到 Sprite 的线，它们相隔 30˚。我希望两条线像钟摆一样左右摆动，始终从头到尾摆动(这样它们就可以从初始位置左右摆动 45°)。请查看下图，了解我要实现的目标:

下面是我能够实现的代码:

extension Int {
  var degreesToRadians: Double { return Double(self) * .pi / 180 }
}
extension FloatingPoint {
  var degreesToRadians: Self { return self * .pi / 180 }
  var radiansToDegrees: Self { return self * 180 / .pi }
}

class GameScene: SKScene, SKPhysicsContactDelegate {

var anchorSprite = SKSpriteNode(imageNamed: "swingPin")
var armLeft = SKSpriteNode(imageNamed: "swingArm")
var armRight = SKSpriteNode(imageNamed: "swingArm")

override func didMove(to view: SKView) {


    self.physicsWorld.gravity = CGVector(dx: 0, dy: -1.8)
    self.physicsWorld.contactDelegate = self

    var tealBg = SKSpriteNode(imageNamed: "tealBg")
    tealBg.position = CGPoint(x: frame.midX, y: frame.midY)
    tealBg.zPosition = 10
    addChild(tealBg)

    anchorSprite.position = CGPoint(x: frame.midX, y: frame.midY + frame.midY/2)
    anchorSprite.zPosition = 20

    anchorSprite.physicsBody = SKPhysicsBody(rectangleOf: anchorSprite.frame.size)
    anchorSprite.physicsBody?.categoryBitMask = pinCategory
    anchorSprite.physicsBody?.isDynamic = false
    addChild(anchorSprite)

    armRight.anchorPoint = CGPoint(x: 0.5, y: 1)
    armRight.position = anchorSprite.position
    armRight.zPosition = 20
    armRight.physicsBody = SKPhysicsBody(rectangleOf: armRight.frame.size)
    armRight.zRotation = CGFloat(Double(15).degreesToRadians)//CGFloat(Double.pi/6)
    armRight.physicsBody!.isDynamic = true

    addChild(armRight)

    armLeft.anchorPoint = CGPoint(x: 0.5, y: 1)
    armLeft.position = anchorSprite.position
    armLeft.zPosition = 20
    armLeft.physicsBody = SKPhysicsBody(rectangleOf: armRight.frame.size)
    armLeft.zRotation = CGFloat(Double(-15).degreesToRadians)//CGFloat(-Double.pi/6)
    armLeft.physicsBody!.isDynamic = true
    addChild(armLeft)

    // Create joint between two objects
    //Pin joint
    var pinAndRightArmJoint = SKPhysicsJointPin.joint(withBodyA: anchorSprite.physicsBody!, bodyB: armRight.physicsBody!, anchor: CGPoint(x: anchorSprite.position.x, y: self.armRight.frame.maxY))
    self.physicsWorld.add(pinAndRightArmJoint)

    var pinAndLeftArmJoint = SKPhysicsJointPin.joint(withBodyA: anchorSprite.physicsBody!, bodyB: armLeft.physicsBody!, anchor: CGPoint(x: anchorSprite.position.x, y: self.armLeft.frame.maxY))
    self.physicsWorld.add(pinAndLeftArmJoint)

    var fixArms = SKPhysicsJointFixed.joint(withBodyA: armLeft.physicsBody!, bodyB: armRight.physicsBody!, anchor: CGPoint.zero)
    self.physicsWorld.add(fixArms)

    pinAndRightArmJoint.shouldEnableLimits = true
    pinAndRightArmJoint.lowerAngleLimit = CGFloat(Double(-60).degreesToRadians)
    pinAndRightArmJoint.upperAngleLimit = CGFloat(Double(60).degreesToRadians)

 }


override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
    //armRight.physicsBody?.angularVelocity = -100.0

     let seq = SKAction.sequence([
        SKAction.rotate(byAngle: CGFloat(Double(45).degreesToRadians), duration: 0.5),
        SKAction.rotate(byAngle: CGFloat(Double(-45).degreesToRadians), duration: 1.0),
        SKAction.rotate(byAngle: CGFloat(Double(45).degreesToRadians), duration: 1.0),
        SKAction.rotate(byAngle: CGFloat(Double(-45).degreesToRadians), duration: 1.0),
        SKAction.rotate(byAngle: CGFloat(Double(45).degreesToRadians), duration: 1.0),
        SKAction.rotate(byAngle: CGFloat(Double(-45).degreesToRadians), duration: 1.0)
])
    armRight.run(seq)
}

根据上面的代码，我设置了下限和上限角度限制并尝试运行一个 Action ，但这只会让线条以一种非常不切实际的方式向侧面倾斜一点。我还尝试在物理体上应用角速度，但这只会使其以不一致的速度短暂摆动(我需要它从一端到另一端始终如一地摆动)。

注意

由于我每次都需要它从头到尾摆动，所以我需要摆动周期每次都一致，不一定是恒定的。当线向中心移动时，一个周期通常会摆动得更快，而当从一个方向改变到另一个方向时，周期会稍微慢一些。这就是我想要的运动感觉。

Answer 1

这是实际的答案:

将 addChild(armRight) 替换为 anchorSprite.addChild(armRight)。将 addChild(armLeft) 替换为 anchorSprite.addChild(armLeft)。删除armRight.position = anchorSprite.position 和删除armLeft.position = anchorSprite.position。此外，除非您在代码中将物理关节用于其他运动，否则请将其全部删除，因为我的解决方案不需要关节。

现在您的 ARM 是 anchorSprite 的子项并服从于它的坐标系。如果你想同时向同一个方向旋转双臂，你可以在 anchorSprite 上运行一个旋转 Action 。如果你想让 ARM 向不同的方向旋转，你必须分别在每只 ARM 上运行旋转 Action 。对于任何一种情况，您都可以使用我为这个问题制作的这个方便的功能:-P

func runPendulumRotationOnNode(_ node:SKNode, withAngle angle:CGFloat, period:TimeInterval, key:String) {
    let initialRotate = SKAction.rotate(byAngle: angle/2, duration: period/2)
    initialRotate.timingMode = .easeOut
    let rotate = SKAction.rotate(byAngle: angle, duration: period)
    rotate.timingMode = .easeInEaseOut
    let rotateForever = SKAction.repeatForever(SKAction.sequence([rotate.reversed(), rotate]))
    let rotateSequence = SKAction.sequence([initialRotate, rotateForever])
    node.run(rotateSequence, withKey:key)
}

我已经测试过了，效果很好!你可以这样调用它来一起旋转双臂:

runPendulumRotationOnNode(anchorSprite, withAngle:CGFloat.pi/2, period:0.5, key:"")

或者让 ARM 向相反的方向旋转，你可以这样使用:

runPendulumRotationOnNode(armRight, withAngle:CGFloat.pi/2, period:0.5, key:"")
runPendulumRotationOnNode(armLeft, withAngle:-CGFloat.pi/2, period:0.5, key:"")

一些小的注意事项，请注意我如何使用 CGFloat.pi，这是 π 的一个简单常数。此函数还假定钟摆从其旋转的中点开始，因此 π/2(90 度)将使摆臂在任一方向上旋转 π/4(45 度)。