ARKIT - How to stick two objects - swift

Question

I have two objects (two cubes). First, I add to the scene the first cube. Then I want to add the second one and I want it to be stuck to the first one, on one side of the first one - I will select which side by clicking on it (like in the image below). Is it possible to just click a face of the first cube and the second one to automatically appear into the scene and stick to the first cube? I cannot figure how to do this.
Photo

Answer 1

When you create an SCNBoxGeometry:
The SCNBox class automatically creates SCNGeometryElement objects as
needed to handle the number of materials.
As such in order to access these elements you would need to create an SCNMaterial for each face of the Box. Then you can perform an SCNHitTest to detect which face has been detected:
When you perform a hit-test search, SceneKit looks for SCNGeometry
objects along the ray you specify. For each intersection between the
ray and and a geometry, SceneKit creates a hit-test result to provide
information about both the SCNNode object containing the geometry and
the location of the intersection on the geometry’s surface.
So how would we approach this?
Lets assume you have created to SCNNodes called:
var cubeOne = SCNNode()
var cubeTwo = SCNNode()
These are both assigned 6 different SCNMaterials (one for each face) like so:
override func viewDidLoad() {
super.viewDidLoad()
cubeOne.geometry = cubeGeometry()
cubeOne.position = SCNVector3(0, -0.5, -1.5)
cubeOne.name = "Cube One"
cubeTwo.geometry = cubeGeometry2()
cubeTwo.position = SCNVector3(30, 0, -1.5)
cubeTwo.name = "Cube Two"
self.augmentedRealityView.scene.rootNode.addChildNode(cubeOne)
self.augmentedRealityView.scene.rootNode.addChildNode(cubeTwo)
}
/// Returns The 6 Faces Of An SCNBox
///
/// - Returns: SCNGeometry
func cubeGeometry() -> SCNGeometry{
var colours: [UIColor] = [.red, .green, .cyan, .yellow, .purple, .blue]
var faces = [SCNMaterial] ()
let cubeGeometry = SCNBox(width: 0.2, height: 0.2, length: 0.2, chamferRadius: 0)
for faceIndex in 0..<5{
let material = SCNMaterial()
material.diffuse.contents = colours[faceIndex]
faces.append(material)
}
cubeGeometry.materials = faces
return cubeGeometry
}
Now you have assigned 6 materials to the faces, you will have six geometry elements which correspond to each side of your SCNBox.
Now having done this lets quickly create an enum which corresponds to the order of the faces:
enum BoxFaces: Int{
case Front, Right, Back, Left, Top, Botton
}
Now when we perform a hitTest we can log the location of the hit e.g:
/// Detects Which Cube Was Detected & Logs The Geometry Index
///
/// - Parameter gesture: UITapGestureRecognizer
#IBAction func cubeTapped(_ gesture: UITapGestureRecognizer){
//1. Get The Current Touch Location
let currentTouchLocation = gesture.location(in: self.augmentedRealityView)
//2. Perform An SCNHitTest
guard let hitTest = self.augmentedRealityView.hitTest(currentTouchLocation, options: nil).first else { return }
//3. If The Node In Cube One Then Get The Index Of The Touched Material
if let namedNode = hitTest.node.name{
if namedNode == "Cube One"{
//4. Get The Geometry Index
if let faceIndex = BoxFaces(rawValue: hitTest.geometryIndex){
print("User Has Hit \(faceIndex)")
//5. Position The Second Cube
positionStickyNode(faceIndex)
}
}
}
}
In part 5 you will notice the call to the function positionStickyNode which places the secondCube at the corresponding location of the 1st Cube:
/// Position The Second Cube Based On The Face Tapped
///
/// - Parameter index: BoxFaces
func positionStickyNode(_ index: BoxFaces){
let (min, max) = cubeTwo.boundingBox
let cubeTwoWidth = max.x - min.x
let cubeTwoHeight = max.y - min.y
switch index {
case .Front:
cubeTwo.simdPosition = float3(cubeOne.position.x, cubeOne.position.y, cubeOne.position.z + cubeTwoWidth)
case .Right:
cubeTwo.simdPosition = float3(cubeOne.position.x + cubeTwoWidth, cubeOne.position.y, cubeOne.position.z)
case .Back:
cubeTwo.simdPosition = float3(cubeOne.position.x, cubeOne.position.y, cubeOne.position.z - cubeTwoWidth)
case .Left:
cubeTwo.simdPosition = float3(cubeOne.position.x - cubeTwoWidth, cubeOne.position.y, cubeOne.position.z)
case .Top:
cubeTwo.simdPosition = float3(cubeOne.position.x, cubeOne.position.y + cubeTwoHeight, cubeOne.position.z)
case .Botton:
cubeTwo.simdPosition = float3(cubeOne.position.x, cubeOne.position.y - cubeTwoHeight, cubeOne.position.z)
}
This is a very crude example and will work when your cubes are the same size... You have more than enough however, to now figure out how this would work for different sizes etc.
Hope it helps...