SCNCamera moving camera's pivot - ios

Question

I need to focus to certain node, for example a pyramid. Then apply distance to the camera, then move the camera based on user click. My approach is like this :
import SceneKit
class GameViewController: UIViewController {
let scene = SCNScene()
override func viewDidLoad() {
super.viewDidLoad()
let camera = SCNCamera()
camera.usesOrthographicProjection = true
camera.orthographicScale = 4
camera.zNear = 1
camera.zFar = 100
let cameraNode = SCNNode()
cameraNode.position = SCNVector3(x: 0, y: 0, z: 6)
cameraNode.camera = camera
let cameraOrbit = SCNNode()
cameraOrbit.name = "orbit"
cameraOrbit.addChildNode(cameraNode)
scene.rootNode.addChildNode(cameraOrbit)
let Py = SCNPyramid(width: 2, height: 3, length: 2)
Py.firstMaterial?.diffuse.contents = UIColor.purple()
let P = SCNNode(geometry: Py)
P.position = SCNVector3(x:0,y:0,z:2) //see the note
scene.rootNode.addChildNode(P)
/* N O T E :
the position of the pyramid must not be changed
as my intention is to rotate the camera
not the pyramid node
I repeat, I don't want to rotate the pyramid
*/
let scnView = self.view as! SCNView
scnView.scene = scene
scnView.allowsCameraControl = false
scnView.backgroundColor = UIColor.black()
// user rotates the camera by tapping
let tapGesture = UITapGestureRecognizer(target: self, action: #selector(handleTap(_:)))
scnView.addGestureRecognizer(tapGesture)
}
//the function which does camera rotation :
func handleTap(_ gestureRecognize: UIGestureRecognizer) {
//I guess the solution is around here
//like modify the cameraOrbit.position ?
//or cameraNode.position ?
//tried both but doesn't work
//or I used them wrong
let cameraOrbit = scene.rootNode.childNode(withName: "orbit", recursively: true)!
SCNTransaction.begin()
SCNTransaction.animationDuration = 2
cameraOrbit.eulerAngles.z += Float(M_PI_2) //see below
SCNTransaction.commit()
/*
I realise that by performing rotation on the camera
(the camera position is unchanged) works for z rotation,
but this is not what I want. What I want is a solution,
which also works for eulerAngles.x and eulerAngles.y.
I used eulerAngles.z as example since it's easier to observe.
I guess the true solution involves moving the camera
with specific trajectory, not only rotation of "anchored" camera.
*/
}
//...
}
The result is :
What I want to achieve is to make the rotation relative to its centre :
My question is, how to adjust the pivot so I can achieve the rotation relative to the pyramid's centre?
Note : I don't want to rotate the pyramid.

Answer 1

I found the solution, but I can't explain why. Please comment if you can explain.
The camera orbit position must be set to match the object's location (in this case, the pyramid). So
cameraOrbit.position = P.position
Then here comes the mystery solution, add cameraOrbit.position.y by half of pi :
cameraOrbit.position.y += Float(M_PI_2)
//therefore we have the final cameraOrbit.position as (0, pi/2, 2)
Tested and works perfectly for all cameraOrbit.eulerAngles.
But I don't have a clue why it works. If pi/2 is coming from some projection thingy, then why it's tucked on y only? I mean, when I do any of the cameraOrbit.eulerAngles, I don't need to assign this pi/2 to either x or z.
Here it is the complete code
import SceneKit
class GameViewController: UIViewController {
let scene = SCNScene()
override func viewDidLoad() {
super.viewDidLoad()
let camera = SCNCamera()
camera.usesOrthographicProjection = true
camera.orthographicScale = 4
camera.zNear = 1
camera.zFar = 100
let cameraNode = SCNNode()
cameraNode.position = SCNVector3(x: 0, y: 0, z: 6)
cameraNode.camera = camera
let cameraOrbit = SCNNode()
cameraOrbit.name = "orbit"
cameraOrbit.addChildNode(cameraNode)
scene.rootNode.addChildNode(cameraOrbit)
let Py = SCNPyramid(width: 2, height: 3, length: 2)
Py.firstMaterial?.diffuse.contents = UIColor.purple()
let P = SCNNode(geometry: Py)
P.position = SCNVector3(x:0,y:0,z:2)
scene.rootNode.addChildNode(P)
// S O L U T I O N :
cameraOrbit.position = P.position
cameraOrbit.position.y += Float(M_PI_2)
//therefore we have the final cameraOrbit.position as (0, pi/2, 2)
let scnView = self.view as! SCNView
scnView.scene = scene
scnView.allowsCameraControl = false
scnView.backgroundColor = UIColor.black()
// user rotates the camera by tapping
let tapGesture = UITapGestureRecognizer(target: self, action: #selector(handleTap(_:)))
scnView.addGestureRecognizer(tapGesture)
}
//the function which does camera rotation :
func handleTap(_ gestureRecognize: UIGestureRecognizer) {
//I was wrong, the solution is not here
let cameraOrbit = scene.rootNode.childNode(withName: "orbit", recursively: true)!
SCNTransaction.begin()
SCNTransaction.animationDuration = 2
cameraOrbit.eulerAngles.z += Float(M_PI_2) //works also for x and y
SCNTransaction.commit()
}
...
}