How to set up game loop in Swift

Question

To set up a game loop in Objective-C I learnt that I should set up a CADisplayLink

updater = [CADisplayLink displayLinkWithTarget:self selector:@selector(gameLoop) ];
[updater setFrameInterval: 1];
[updater addToRunLoop: [NSRunLoop currentRunLoop] forMode: NSRunLoopCommonModes];

How do I do this in Swift?

I have tried to Google this but I cannot find any examples of this.

Answer 1

Pretty much just a direct translation from Objective-C to Swift with a few tweaks.

import QuartzCore
var updater = CADisplayLink(target: self, selector: Selector("gameLoop"))
updater.frameInterval = 1
updater.addToRunLoop(NSRunLoop.currentRunLoop(), forMode: NSRunLoopCommonModes)

Answer 2

Swift 3.x version of Brian Tracy's answer:

let updater = CADisplayLink(target: self, selector: #selector(self.gameLoop))
updater.preferredFramesPerSecond = 60
updater.add(to: RunLoop.current, forMode: RunLoopMode.commonModes)

Apart from the syntax changes of Swift 3, also note the iOS 10 API change from frameInterval (which still works, but produces a deprecated warning) to preferredFramesPerSecond.

Answer 3

Here's my GameLoop class (Swift 3)

import UIKit

class GameLoop : NSObject {

    var doSomething: () -> ()!
    var displayLink : CADisplayLink!

    init(doSomething: @escaping () -> ()) {
        self.doSomething = doSomething
        super.init()
        start()
    }

    // you could overwrite this too
    func handleTimer() {
        doSomething()
    }

    func start() {
        displayLink = CADisplayLink(target: self, selector: #selector(handleTimer))
        /*
        * If set to zero, the
        * display link will fire at the native cadence of the display hardware.
        * The display link will make a best-effort attempt at issuing callbacks
        * at the requested rate.
        */
        displayLink.preferredFramesPerSecond = 0
        displayLink.add(to: .main, forMode: .commonModes)
    }

    func stop() {
        displayLink.invalidate()
        displayLink.remove(from: .main, forMode: .commonModes)
        displayLink = nil
    }
}

If you're updating something on a background GCD queue and want to pull those changes to the Main queue (and runloop), you should use Dispatch Source for Data.