沿着一個軸旋轉一個精靈

Question

在SpriteKit中，我需要沿一個軸（例如穿過精靈中心的那個）旋轉一個精靈，就像用戶旋轉的一個輪子一樣。

我試着用applyTorque函數（施加一個只有角度而非線性的力），但我無法處理由屏幕上不同運動引起的不同力（屏幕上的觸摸時間越長，應用）。

有人可以幫我理解如何處理這個問題嗎？

Answer 1

下面是根據你向左/向右滑動的速度旋轉球的答案：

class GameScene: SKScene { 

    let speedLabel = SKLabelNode(text: "Speed: 0") 
    let wheel  = SKShapeNode(circleOfRadius: 25) 

    var recognizer: UIPanGestureRecognizer! 

    func pan(recognizer: UIPanGestureRecognizer) { 
    let velocity = recognizer.velocity(in: view!).x 

    // Play with this value until if feels right to you. 
    let adjustor = CGFloat(60) 

    let speed = velocity/adjustor 
    wheel.physicsBody!.angularVelocity = -speed 
    } 

    // Scene setup: 
    override func didMove(to view: SKView) { 
    removeAllChildren() 

    physicsBody = SKPhysicsBody(edgeLoopFrom: frame) 

    wheel.fillColor = .blue 
    wheel.physicsBody = SKPhysicsBody(circleOfRadius: 25) 
    wheel.physicsBody!.affectedByGravity = false 
    let wheelDot = SKSpriteNode(color: .gray, size: CGSize(width: 5, height:5)) 
    wheel.addChild(wheelDot) 
    wheelDot.position.y += 20 
    wheel.setScale(3) 

    speedLabel.setScale(3) 
    speedLabel.position.y = (frame.maxY - speedLabel.frame.size.height/2) - 45 

    recognizer = UIPanGestureRecognizer(target: self, action: #selector(pan)) 
    view.addGestureRecognizer(recognizer) 

    addChild(wheel) 
    addChild(speedLabel) 
    } 

    override func didSimulatePhysics() { 
    speedLabel.text = "Speed: \(abs(Int(wheel.physicsBody!.angularVelocity)))" 
    } 
} 

Answer 2

這裏是一個基本的順時針或逆時針旋轉輪子的例子，具體取決於您按下屏幕的左側還是右側。堅持提高速度：

class GameScene : SKScene { 

    enum Direction { case left, right } 

    var directionToMove: Direction? 

    let wheel = SKShapeNode(circleOfRadius: 25) 
    let speedLabel = SKLabelNode(text: "Speed: 0") 

    override func didMove(to view: SKView) { 
    // Scene setup: 
    anchorPoint = CGPoint(x: 0.5, y: 0.5) 
    removeAllChildren() 

    physicsBody = SKPhysicsBody(edgeLoopFrom: frame) 

    wheel.fillColor = .blue 
    wheel.physicsBody = SKPhysicsBody(circleOfRadius: 25) 
    wheel.physicsBody!.affectedByGravity = false 
    let wheelDot = SKSpriteNode(color: .gray, size: CGSize(width: 5, height:5)) 
    wheel.addChild(wheelDot) 
    wheelDot.position.y += 20 
    wheel.setScale(3) 


    speedLabel.setScale(3) 
    speedLabel.position.y = (frame.maxY - speedLabel.frame.size.height/2) - 45 

    addChild(wheel) 
    addChild(speedLabel) 
    } 

    // Change this to touchesBegan for iOS: 
    override func mouseDown(with event: NSEvent) { 
    // Change this to touches.first!.location(in: self) for iOS. 
    let location = event.location(in: self) 

    // Determine if touch left or right side: 
    if location.x > 0 { 
    directionToMove = .right 
    } 
    else if location.x < 0 { 
     directionToMove = .left 
    } 
    } 

    override func mouseUp(with event: NSEvent) { 
    // Stop applying gas: 
    directionToMove = nil 
    print("lol") 
    } 

    override func update(_ currentTime: TimeInterval) { 
    // This is how much speed we gain each frame: 
    let torque = CGFloat(0.01) 

    guard let direction = directionToMove else { return } 

    // Apply torque in the proper direction 
    switch direction { 
    case .left: 
     wheel.physicsBody!.applyTorque(torque) 
    case .right: 
     wheel.physicsBody!.applyTorque(-torque) 
    } 
    } 

    override func didSimulatePhysics() { 
    // Speedometer: 
    speedLabel.text = "Speed: \(abs(Int(wheel.physicsBody!.angularVelocity)))" 
    } 
}