SceneKit: Hit test not work with billboarded quads - ios

Question

I made billboarded quads using SceneKit.
The cameraNode is synchronized with UIDeviceMotion, and the billboard nodes are appearing as I expected.
The thing is, I want these nodes to be called when I tap it.
For this, I used UITapGestureRecognizer with hitTest.
Here is some of my code.
// ==== in viewDidLoad
// initialize tap gesture
let tapGesture = UITapGestureRecognizer(target: self, action: #selector(onNodeTapped))
sceneView.addGestureRecognizer(tapGesture)
// initialize scenekit.scene
let scene = SCNScene()
scene.rootNode.addChildNode(cameraNode)
scene.rootNode.addChildNode(worldNode)
sceneView.scene = scene
sceneView.autoenablesDefaultLighting = true
sceneView.pointOfView = cameraNode
And this is the tap handler
func onNodeTapped(_ gestureRecognize: UIGestureRecognizer) {
let location = gestureRecognize.location(in: sceneView) // <---- updated
let hitResults = sceneView.hitTest(location, options: nil)
for result in hitResults {
// FOR_TEST: hit test visualization
if let material = result.node.geometry?.materials.first {
SCNTransaction.begin()
SCNTransaction.animationDuration = 0.5
SCNTransaction.completionBlock = {
SCNTransaction.begin()
SCNTransaction.animationDuration = 0.5
material.emission.contents = UIColor.black
SCNTransaction.commit()
}
material.emission.contents = UIColor.red
SCNTransaction.commit()
}
// target tap event handling
if let target = (result.node as? TargetNode)?.target {
if onTargetTapped(target) {
return
}
}
}
}
This code works very rarly. What I mean is the visualization part respond only 1 out of 20 times, and the onTargetTapped is called only 1 out of 100...
The weired thing is the targeting is fine, which means this is not the coordinate problem.
I found something related to SCNHitTestOption.categoryBitMask, but it didn't help at all.
Also, when I open this Scenview, this error message appears on the console.
"[SceneKit] Error: error in _C3DUnProjectPoints"
Maybe this message is related to the hitTest malfunctioning?
Updated
This code is for building billboard SCNGeometry and SCNNode
override func initializeGeometry() -> SCNGeometry {
let geometry = SCNPlane(width: width, height: height)
let material = geometry.materials.first
material?.diffuse.contents = initializeTexture()
material?.writesToDepthBuffer = false
material?.readsFromDepthBuffer = false
return geometry
}
// ==== building node
node = SCNNode()
node.geometry = initializeGeometry()
node.categoryBitMask = MyConstraints.targetNodeHitTestCategoryBitMask
node.constraints = [SCNBillboardConstraint()]

Answer 1

You're retrieving the tap coordinates in annotationsDisplayView, but then passing those coordinates to sceneView for the hit test lookup. Unless those views are precisely on top of each other, you'll get a mismatch.
I think you want
let location = gestureRecognize.location(in: sceneView)
instead.
I was curious whether the hit test would use the rotated version of the billboard. I confirmed that it does. Here's a working (Mac) sample.
In the SCNView subclass:
override func mouseDown(with theEvent: NSEvent) {
/* Called when a mouse click occurs */
// check what nodes are clicked
let p = self.convert(theEvent.locationInWindow, from: nil)
let hitResults = self.hitTest(p, options: [:])
// check that we clicked on at least one object
if hitResults.count > 0 {
Swift.print("hit me")
}
for result in hitResults {
Swift.print(result.node.name)
// get its material
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 = NSColor.black
SCNTransaction.commit()
}
material.emission.contents = NSColor.yellow
SCNTransaction.commit()
}
super.mouseDown(with: theEvent)
}
And in the view controller:
override func awakeFromNib(){
super.awakeFromNib()
// create a new scene
let scene = SCNScene()
let side = CGFloat(2.0)
let quad1 = SCNNode.init(geometry: SCNPlane(width: side, height: side))
quad1.name = "green"
quad1.geometry?.firstMaterial?.diffuse.contents = NSColor.green
let quad2 = SCNNode.init(geometry: SCNPlane(width: side, height: side))
quad2.name = "red"
quad2.geometry?.firstMaterial?.diffuse.contents = NSColor.red
let quad3 = SCNNode.init(geometry: SCNPlane(width: side, height: side))
quad3.name = "blue"
quad3.geometry?.firstMaterial?.diffuse.contents = NSColor.blue
scene.rootNode.addChildNode(quad1)
scene.rootNode.addChildNode(quad2)
scene.rootNode.addChildNode(quad3)
let rotation = CGFloat(M_PI_2) * 0.9
quad1.position.y = side/2
quad1.eulerAngles.y = rotation
quad2.position.x = side/2
quad2.eulerAngles.x = rotation
// comment out these constraints to verify that they matter
quad1.constraints = [SCNBillboardConstraint()]
quad2.constraints = [SCNBillboardConstraint()]
// 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)
// create and add a light to the scene
let lightNode = SCNNode()
lightNode.light = SCNLight()
lightNode.light!.type = .omni
lightNode.position = SCNVector3(x: 0, y: 10, z: 10)
scene.rootNode.addChildNode(lightNode)
// create and add an ambient light to the scene
let ambientLightNode = SCNNode()
ambientLightNode.light = SCNLight()
ambientLightNode.light!.type = .ambient
ambientLightNode.light!.color = NSColor.darkGray
scene.rootNode.addChildNode(ambientLightNode)
// set the scene to the view
self.gameView!.scene = scene
// allows the user to manipulate the camera
self.gameView!.allowsCameraControl = true
// show statistics such as fps and timing information
self.gameView!.showsStatistics = true
// configure the view
self.gameView!.backgroundColor = NSColor.black
}

Answer 2

Hit testing should work whether your node is billboard constrained or not. It does for me.
override func viewDidLoad() {
self.sceneView.addGestureRecognizer(UITapGestureRecognizer(target: self, action: #selector(tap(_:))))
...
}
#objc func tap(_ recognizer: UITapGestureRecognizer) {
let loc = recognizer.location(in: self.sceneView)
if let hit = self.sceneView.hitTest(loc) {
...
}
}