ARKit – Poster as a window to a virtual room - swift

Question

I am working on iOS app using ARKit.
In real world, there is a poster on the wall. The poster is a fixed thing, so any needed preprocessing may be applied.
The goal is to make this poster a window into a virtual room. So that when user approaches the poster, he can look "through" it at some virtual 3D environment (room). Of course, user cannot go through the "window" and then wander in that 3D environment. He only can observe a virtual room looking "through" the poster.
I know that it's possible to make this poster detectable by ARKit, and to play some visual effects around it, or even a movie on top of it.
But I did not find information how to turn it into a window into virtual 3D world.
Any ideas and links to sample projects are greatly appreciated.

Answer 1

Look at this video posted on Augmented Images webpage (use Chrome browser to watch this video).
It's easy to create that type of a virtual cube. All you need is a 3D model of simple cube primitive without a front polygon (in order to see its inner surface). Also you need a plane with a square hole. Assign an out-of-the-box RealityKit occlusion material or a hand-made SceneKit occlusion material for this plane and it will hide all the outer walls of cube behind it (look at a picture below).
In Autodesk Maya Occlusion material is a Hold-Out option in Render Stats (for Viewport 2.0 only):
When you'll be tracking your poster on a wall (with detectionImages option activated), your app must recognize a picture and "load" 3D cube and its masking plane with occlusion shader. So, if ARImageAnchor on a poster and a pivot point of 3D cube must meet, cube's pivot point has to be located on a front edge of cube (at the same level where a wall's surface is).
If you wish to download Apple's sample code containing Image Detection experience – just click a blue button on the same webpage with detectionImages.
Here is a short example of my code:
#IBOutlet var sceneView: ARSCNView!
override func viewDidLoad() {
super.viewDidLoad()
sceneView.delegate = self // for using renderer() methods of ARSCNViewDelegate
sceneView.scene = SCNScene()
}
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated)
resetTrackingConfiguration()
}
func resetTrackingConfiguration() {
guard let refImage = ARReferenceImage.referenceImages(inGroupNamed: "Poster",
bundle: nil)
else { return }
let config = ARWorldTrackingConfiguration()
config.detectionImages = refImage
config.maximumNumberOfTrackedImages = 1
let options = [ARSession.RunOptions.removeExistingAnchors,
ARSession.RunOptions.resetTracking]
sceneView.session.run(config, options: ARSession.RunOptions(options))
}
...and, of course, a SceneKit's renderer() instance method:
func renderer(_ renderer: SCNSceneRenderer,
didAdd node: SCNNode,
for anchor: ARAnchor) {
guard let imageAnchor = anchor as? ARImageAnchor,
let _ = imageAnchor.referenceImage.name
else { return }
anchorsArray.append(imageAnchor)
if anchorsArray.first != nil {
node.addChildNode(portalNode)
}
}