Rotate a sprite along an axis - sprite-kit

Question

In SpriteKit I need to rotate a sprite along an axis (e.g. the one that passes through the center of the sprite) just like a wheel to be spinned by the user.
I tried to use applyTorque function (to apply a force that is only angular and not linear), but I cannot handle the different forces caused by different movements on the screen (longer the touch on the screen, stronger the force to apply).
Can someone help me to understand how to deal with this problem?

Answer 1

Here is an answer that spins a ball according to how fast you swipe left / right:
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

Here is a basic example of spinning a wheel clockwise or counterclockwise depending on if you press on left / right side of screen. Hold to increase speed:
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)))"
}
}