GameLoop.swift

import UIKit

// Copyright 2017 Dan Rosenstark dr2050.com
// See http://stackoverflow.com/a/28570282/8047, too
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
    }
}