SwiftUI: HitTest on Scenekit - swiftui

Question

Goal: SceneKit hit test with SwiftUI (instead of UIKit)
Problem: When I embed the default ship scene on a SwiftUI "UIViewRepresentable", the example handleTap function doesn't work. and I get his error:
"Argument of '#selector' refers to instance method 'handleTap' that is not exposed to Objective-C"
How an I create a hit test, and pass data to another SwiftUI view?
import SwiftUI
import SceneKit
var handleTap: (() -> Void)
struct ScenekitView : UIViewRepresentable {
let scene = SCNScene(named: "ship.scn")!
func makeUIView(context: Context) -> SCNView {
// create and add a camera to the scene
let cameraNode = SCNNode()
cameraNode.camera = SCNCamera()
scene.rootNode.addChildNode(cameraNode)
// place the camera
cameraNode.position = SCNVector3(x: 0, y: 0, z: 15)
// retrieve the ship node
let ship = scene.rootNode.childNode(withName: "ship", recursively: true)!
// retrieve the SCNView
let scnView = SCNView()
return scnView
}
func updateUIView(_ scnView: SCNView, context: Context) {
scnView.scene = scene
// allows the user to manipulate the camera
scnView.allowsCameraControl = true
// show statistics such as fps and timing information
scnView.showsStatistics = true
// configure the view
scnView.backgroundColor = UIColor.black
// add a tap gesture recognizer
let tapGesture = UITapGestureRecognizer(target: self, action: #selector(handleTap(_:)))
scnView.addGestureRecognizer(tapGesture)
}
func handleTap(_ gestureRecognize: UIGestureRecognizer) {
// retrieve the SCNView
let scnView = SCNView()
// check what nodes are tapped
let p = gestureRecognize.location(in: scnView)
let hitResults = scnView.hitTest(p, options: [:])
// check that we clicked on at least one object
if hitResults.count > 0 {
// retrieved the first clicked object
let result = hitResults[0]
// get material for selected geometry element
let material = result.node.geometry!.firstMaterial
// highlight it
SCNTransaction.begin()
SCNTransaction.animationDuration = 0.5
// on completion - unhighlight
SCNTransaction.completionBlock = {
SCNTransaction.begin()
SCNTransaction.animationDuration = 0.5
material?.emission.contents = UIColor.black
SCNTransaction.commit()
}
material?.emission.contents = UIColor.green
SCNTransaction.commit()
}
}
}
#if DEBUG
struct ScenekitView_Previews : PreviewProvider {
static var previews: some View {
ScenekitView()
}
}
#endif

Answer 1

Just hit this issue myself and finally found a solution: make a dummy struct that pulls from a class that actually holds your SCNView.
This works for me:
struct ScenekitView : UIViewRepresentable {
let scenekitClass = ScenekitClass()
func makeUIView(context: Context) -> SCNView {
return scenekitClass.view
}
func updateUIView(_ scnView: SCNView, context: Context) {
// your update UI view contents look like they can all be done in the initial creation
}
}
class ScenekitClass {
let view = SCNView()
let scene = SCNScene(named: "ship.scn")!
init() {
// create and add a camera to the scene
let cameraNode = SCNNode()
cameraNode.camera = SCNCamera()
scene.rootNode.addChildNode(cameraNode)
// place the camera
cameraNode.position = SCNVector3(x: 0, y: 0, z: 15)
// attach the scene
view.scene = scene
// allows the user to manipulate the camera
view.allowsCameraControl = true
// show statistics such as fps and timing information
view.showsStatistics = true
// configure the view
view.backgroundColor = UIColor.black
// add a tap gesture recognizer
let tapGesture = UITapGestureRecognizer(target: self, action: #selector(handleTap(_:)))
view.addGestureRecognizer(tapGesture)
}
#objc func handleTap(_ gestureRecognize: UIGestureRecognizer) {
// check what nodes are tapped
let p = gestureRecognize.location(in: view)
let hitResults = view.hitTest(p, options: [:])
// check that we clicked on at least one object
if hitResults.count > 0 {
// retrieved the first clicked object
let result = hitResults[0]
// get material for selected geometry element
let material = result.node.geometry!.firstMaterial
// highlight it
SCNTransaction.begin()
SCNTransaction.animationDuration = 0.5
// on completion - unhighlight
SCNTransaction.completionBlock = {
SCNTransaction.begin()
SCNTransaction.animationDuration = 0.5
material?.emission.contents = UIColor.black
SCNTransaction.commit()
}
material?.emission.contents = UIColor.green
SCNTransaction.commit()
}
}
}
Based on this question.

Answer 2

For whatever reason, the SwiftUI SceneView does not conform to the SCNSceneRenderer protocol. If it did, then it would not be necessary to make use of a UIViewRepresentable (or NSViewRepresentable for macOS) view.
I have a complete example app, for macOS, here:
https://github.com/Thunor/HitTestApp

Answer 3

SceneView has a delegate argument. You can use a SCNSceneRenderDelegate to capture the SCNSceneRenderer and use it for hit testing. Here's an example:
import SwiftUI
import SceneKit
import Foundation
class RenderDelegate: NSObject, SCNSceneRendererDelegate {
// dummy render delegate to capture renderer
var lastRenderer: SCNSceneRenderer!
func renderer(_ renderer: SCNSceneRenderer, updateAtTime time: TimeInterval) {
// store the renderer for hit testing
lastRenderer = renderer
}
}
class Model: ObservableObject {
let scene = SCNScene(named: "scene.usdz")!
let renderDelegate = RenderDelegate()
}
struct ContentView: View {
#ObservedObject var model = Model()
var body: some View {
SceneView(scene: model.scene, options: [.allowsCameraControl, .autoenablesDefaultLighting], delegate: model.renderDelegate)
.gesture(
SpatialTapGesture(count: 1)
.onEnded(){ event in
// hit test
guard let renderer = model.renderDelegate.lastRenderer else { return }
let hits = renderer.hitTest(event.location, options: nil)
if let tappedNode = hits.first?.node {
// do something
}
}
)
}
}