ARKit – Drag a node along a specific axis (not on a plane) - ios

Question

I am trying to drag a node exactly where my finger is on the screen on the Y-axis. But I don't find any way to do it, here is my current code. Do you have any idea?
var movedObject:SCNNode?
#objc func handlePan(_ recognizer: UIPanGestureRecognizer) {
if recognizer.state == .began {
let tapPoint: CGPoint = recognizer.location(in: sceneView)
let result = sceneView.hitTest(tapPoint, options: nil)
if result.count == 0 {
return
}
let hitResult: SCNHitTestResult? = result.first
movedObject = hitResult?.node //.parent?.parent
} else if recognizer.state == .changed {
if (movedObject != nil) {
let tapPoint: CGPoint = recognizer.location(in: sceneView)
let hitResults = sceneView.hitTest(tapPoint, types: .featurePoint)
let result: ARHitTestResult? = hitResults.last
if result?.worldTransform != nil{
let matrix: SCNMatrix4 = SCNMatrix4.init((result?.worldTransform)!)
let vector: SCNVector3 = SCNVector3Make(matrix.m41, matrix.m42, matrix.m43)
movedObject?.position = vector
}
}
} else if recognizer.state == .ended {
movedObject = nil
}
}

Answer 1

Found the solution ! I added some explanations in comments.
if (movedObject != nil) {
//Normalized-depth coordinate matching the plane I want
let projectedOrigin = sceneView.projectPoint((movedObject?.position)!)
//Location of the finger in the view on a 2D plane
let location2D = recognizer.location(in: sceneView)
//Location of the finger in a 3D vector
let location3D = SCNVector3Make(Float(location2D.x), Float(location2D.y), projectedOrigin.z)
//Unprojects a point from the 2D pixel coordinate system of the renderer to the 3D world coordinate system of the scene
let realLocation3D = sceneView.unprojectPoint(location3D)
if movedObject?.position != nil {
//Only updating Y axis position
movedObject?.position = SCNVector3Make((movedObject?.position.x)!, realLocation3D.y, (movedObject?.position.z)!)
}
}
Posts that help understand:
unProjectPoint & projectedOrigin
translation & unProjectPoint