SceneKit SCNSceneRendererDelegate - renderer function not called

Question

I recently asked a question which had a pretty obvious answer. I'm still working on the same project and running into another problem. I need to implement per frame logic and the SCNSceneRendererDelegate protocol worked perfectly fine on iOS, but on OSX, the renderer function is not firing. I have created a little example project to illustrate my problem. It consists of a Scene Kit View in storyboard and following code in the ViewController class:

import Cocoa
import SceneKit

class ViewController: NSViewController, SCNSceneRendererDelegate {

    @IBOutlet weak var sceneView: SCNView!

    let cubeNode = SCNNode()

    override func viewDidLoad() {

        super.viewDidLoad()

        let scene = SCNScene()

        let sphere = SCNSphere(radius: 0.1)
        sphere.firstMaterial!.diffuse.contents = NSColor.yellowColor()
        let sphereNode = SCNNode(geometry: sphere)
        scene.rootNode.addChildNode(sphereNode)

        let cube = SCNBox(width: 0.2, height: 0.2, length: 0.2, chamferRadius: 0)
        cube.firstMaterial!.diffuse.contents = NSColor.greenColor()
        cubeNode.geometry = cube
        cubeNode.position = SCNVector3(1,0,0)
        scene.rootNode.addChildNode(cubeNode)

        let cameraNode = SCNNode()
        cameraNode.camera = SCNCamera()
        cameraNode.position = SCNVector3(2, 1, 2)
        let constraint = SCNLookAtConstraint(target: cubeNode)
        cameraNode.constraints = [constraint]
        scene.rootNode.addChildNode(cameraNode)

        sceneView.scene = scene
        sceneView.backgroundColor = NSColor(red: 0.5, green: 0, blue: 0.3, alpha: 1)
        sceneView.allowsCameraControl = true

        sceneView.delegate = self
        sceneView.playing = true

    }

    func renderer(renderer: SCNSceneRenderer, updateAtTime time: NSTimeInterval) {
        cubeNode.position.x += 0.1
    }
}

All I want is to basically move the cube with every frame. But nothing happens. What is weird is that when I set sceneView.allowsCameraControl to true, the renderer function is called whenever I click or drag on the screen (which makes sense because it needs to update the view based on camera angles). But I would want it to be called every frame.

Is there an error I don't see or is this a bug in my Xcode?

Edit: I have tried following the instructions in the answer below and now have the following code for the ViewController:

import Cocoa
import SceneKit

class ViewController: NSViewController {

    @IBOutlet weak var sceneView: SCNView!
    let scene = MyScene(create: true)

    override func viewDidLoad() {

        super.viewDidLoad()

        sceneView.scene = scene
        sceneView.backgroundColor = NSColor(red: 0.5, green: 0, blue: 0.3, alpha: 1)
        sceneView.allowsCameraControl = true

        sceneView.delegate = scene
        sceneView.playing = true

    }

}

And a MyScene class:

import Foundation
import SceneKit

final class MyScene: SCNScene, SCNSceneRendererDelegate {

    let cubeNode = SCNNode()

    convenience init(create: Bool) {
        self.init()

        let sphere = SCNSphere(radius: 0.1)
        sphere.firstMaterial!.diffuse.contents = NSColor.yellowColor()
        let sphereNode = SCNNode(geometry: sphere)
        rootNode.addChildNode(sphereNode)

        let cube = SCNBox(width: 0.2, height: 0.2, length: 0.2, chamferRadius: 0)
        cube.firstMaterial!.diffuse.contents = NSColor.greenColor()
        cubeNode.geometry = cube
        cubeNode.position = SCNVector3(1,0,0)
        rootNode.addChildNode(cubeNode)

        let cameraNode = SCNNode()
        cameraNode.camera = SCNCamera()
        cameraNode.position = SCNVector3(2, 1, 2)
        let constraint = SCNLookAtConstraint(target: cubeNode)
        cameraNode.constraints = [constraint]

        rootNode.addChildNode(cameraNode)
    }

    @objc func renderer(aRenderer: SCNSceneRenderer, updateAtTime time: NSTimeInterval) {
        cubeNode.position.x += 0.01
    }
}

However, it is still not working. What am I doing wrong?

Edit: setting sceneView.loops = true fixes the described problem

Answer 1

In addition to several helpful hints in this chain, the final one for me to get delegate called was the following: If you use the pre Swift 4 methods for the SCNSceneRendererDelegate class, it compiles fine with no errors or warnings, but the delegate is never called.

Thus the obsolete pre-Swift 4 definition:

func renderer(aRenderer:SCNSceneRenderer, updateAtTime time:TimeInterval) {...}

(which I got from a snippet on the web) compiled just fine and was never called, while the correct definition

func renderer(_ renderer:SCNSceneRenderer, updateAtTimet time:TimeInterval) {...}

compiles and gets called!

Since SCNSceneRendererDelegate is a protocol, the normal Swift protections afforded by override are not appropriate. Since SCNSceneRendererDelegate defines its methods as optional (which I like), it is not caught that way either.

Answer 2

I don't understand what's causing the problem, but I was able to replicate it. I got it to work, though, by adding a meaningless SCNAction:

let dummyAction = SCNAction.scaleBy(1.0, duration: 1.0)
let repeatAction = SCNAction.repeatActionForever(dummyAction)
cubeNode.runAction(repeatAction)

The render loop fires only if the scene is "playing" (see SKScene becomes unresponsive while being idle). I expect that setting

    sceneView.isPlaying = true

(as you're already doing) would be enough to trigger the render callbacks.

The code I have above is not a solution. It's a nasty hack to work around your problem and allow you to get on with life.