Placing an object in front of camera at Touch Location - swift

Question

The following code places the node in front of the camera but always at the center 10cm away from the camera position. I want to place the node 10cm away in z-direction but at the x and y co-ordinates of where I touch the screen. So touching on different parts of the screen should result in a node being placed 10cm away in front of the camera but at the x and y location of the touch and not always at the center.
var cameraRelativePosition = SCNVector3(0,0,-0.1)
let sphere = SCNNode()
sphere.geometry = SCNSphere(radius: 0.0025)
sphere.geometry?.firstMaterial?.diffuse.contents = UIColor.white
Service.addChildNode(sphere, toNode: self.sceneView.scene.rootNode,
inView: self.sceneView, cameraRelativePosition:
cameraRelativePosition)
Service.swift
class Service: NSObject {
static func addChildNode(_ node: SCNNode, toNode: SCNNode, inView:
ARSCNView, cameraRelativePosition: SCNVector3) {
guard let currentFrame = inView.session.currentFrame else { return }
let camera = currentFrame.camera
let transform = camera.transform
var translationMatrix = matrix_identity_float4x4
translationMatrix.columns.3.x = cameraRelativePosition.x
translationMatrix.columns.3.y = cameraRelativePosition.y
translationMatrix.columns.3.z = cameraRelativePosition.z
let modifiedMatrix = simd_mul(transform, translationMatrix)
node.simdTransform = modifiedMatrix
toNode.addChildNode(node)
}
}
The result should look exactly like this : https://justaline.withgoogle.com

Answer 1

We can use the unprojectPoint(_:) method of SCNSceneRenderer (SCNView and ARSCNView both conform to this protocol) to convert a point on the screen to a 3D point.
When tapping the screen we can calculate a ray this way:
func getRay(for point: CGPoint, in view: SCNSceneRenderer) -> SCNVector3 {
let farPoint = view.unprojectPoint(SCNVector3(Float(point.x), Float(point.y), 1))
let nearPoint = view.unprojectPoint(SCNVector3(Float(point.x), Float(point.y), 0))
let ray = SCNVector3Make(farPoint.x - nearPoint.x, farPoint.y - nearPoint.y, farPoint.z - nearPoint.z)
// Normalize the ray
let length = sqrt(ray.x*ray.x + ray.y*ray.y + ray.z*ray.z)
return SCNVector3Make(ray.x/length, ray.y/length, ray.z/length)
}
The ray has a length of 1, so by multiplying it by 0.1 and adding the camera location we get the point you were searching for.