ARKit

import ARKit

class ViewController: UIViewController {
    var sceneView: ARSCNView!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        sceneView = ARSCNView(frame: view.bounds)
        view.addSubview(sceneView)
        
        let configuration = ARWorldTrackingConfiguration()
        configuration.planeDetection = [.horizontal, .vertical]
        
        sceneView.session.run(configuration)
    }
    
    override func viewWillDisappear(_ animated: Bool) {
        super.viewWillDisappear(animated)
        sceneView.session.pause()
    }
}

import ARKit
import SceneKit

func addBox(at position: SCNVector3) {
    let box = SCNBox(width: 0.1, height: 0.1, length: 0.1, chamferRadius: 0)
    
    let material = SCNMaterial()
    material.diffuse.contents = UIColor.blue
    box.materials = [material]
    
    let boxNode = SCNNode(geometry: box)
    boxNode.position = position
    
    sceneView.scene.rootNode.addChildNode(boxNode)
}

// Usage: Place box 1 meter in front of camera
let cameraPosition = sceneView.pointOfView?.position ?? SCNVector3(0, 0, 0)
let boxPosition = SCNVector3(cameraPosition.x, cameraPosition.y, cameraPosition.z - 1)
addBox(at: boxPosition)

import ARKit

extension ViewController: ARSCNViewDelegate {
    func renderer(_ renderer: SCNSceneRenderer, didAdd node: SCNNode, for anchor: ARAnchor) {
        guard let planeAnchor = anchor as? ARPlaneAnchor else { return }
        
        let width = CGFloat(planeAnchor.planeExtent.width)
        let height = CGFloat(planeAnchor.planeExtent.height)
        let plane = SCNPlane(width: width, height: height)
        
        plane.materials.first?.diffuse.contents = UIColor.blue.withAlphaComponent(0.3)
        
        let planeNode = SCNNode(geometry: plane)
        planeNode.eulerAngles.x = -.pi / 2
        planeNode.position = SCNVector3(planeAnchor.center.x, 0, planeAnchor.center.z)
        
        node.addChildNode(planeNode)
    }
}