SCNCamera limit arcball rotation - swift

Question

I have a scene setup with SCNCamera that rotates around an object.
What would be the best way to limit the extents of rotation the camera can achieve around the object?
Example: instead of being able to rotate around a whole sphere, how would I limit rotation to a single hemisphere?
My first attempt was to see if there was any clamps for .allowsCameraControl. Could not find anything.
I then tried adapting c# Unity : mouse orbit script, no luck.
Some pointers on how to approach or solve this would great.
Boilerplate Arcball thanks to this answer.
var lastWidthRatio: Float = 0
var lastHeightRatio: Float = 0
let camera = SCNCamera()
let cameraNode = SCNNode()
let cameraOrbit = SCNNode()
override func viewDidLoad() {
super.viewDidLoad()
// create a new scene
let scene = SCNScene(named: "art.scnassets/ship.scn")!
// create and add a camera to the scene
camera.usesOrthographicProjection = true
camera.orthographicScale = 9
camera.zNear = 0
camera.zFar = 100
cameraNode.position = SCNVector3(x: 0, y: 0, z: 50)
cameraNode.camera = camera
cameraOrbit.addChildNode(cameraNode)
scene.rootNode.addChildNode(cameraOrbit)
// retrieve the ship node
let ship = scene.rootNode.childNodeWithName("ship", recursively: true)!
// retrieve the SCNView
let scnView = self.view as! SCNView
// set the scene to the view
scnView.scene = scene
// add a tap gesture recognizer
let gesture = UIPanGestureRecognizer(target: self, action: "panDetected:");
scnView.addGestureRecognizer(gesture);
}
func panDetected(sender: UIPanGestureRecognizer) {
let translation = sender.translationInView(sender.view!)
let widthRatio = Float(translation.x) / Float(sender.view!.frame.size.width) + lastWidthRatio
let heightRatio = Float(translation.y) / Float(sender.view!.frame.size.height) + lastHeightRatio
self.cameraOrbit.eulerAngles.y = Float(-2 * M_PI) * widthRatio
self.cameraOrbit.eulerAngles.x = Float(-M_PI) * heightRatio
print(Float(-2 * M_PI) * widthRatio)
if (sender.state == .Ended) {
lastWidthRatio = widthRatio % 1
lastHeightRatio = heightRatio % 1
}
}

Answer 1

Maybe this could be useful for readers.
class GameViewController: UIViewController {
var cameraOrbit = SCNNode()
let cameraNode = SCNNode()
let camera = SCNCamera()
//HANDLE PAN CAMERA
var lastWidthRatio: Float = 0
var lastHeightRatio: Float = 0.2
var WidthRatio: Float = 0
var HeightRatio: Float = 0.2
var fingersNeededToPan = 1
var maxWidthRatioRight: Float = 0.2
var maxWidthRatioLeft: Float = -0.2
var maxHeightRatioXDown: Float = 0.02
var maxHeightRatioXUp: Float = 0.4
//HANDLE PINCH CAMERA
var pinchAttenuation = 20.0 //1.0: very fast ---- 100.0 very slow
var lastFingersNumber = 0
override func viewDidLoad() {
super.viewDidLoad()
// create a new scene
let scene = SCNScene(named: "art.scnassets/ship.scn")!
// create and add a light to the scene
let lightNode = SCNNode()
lightNode.light = SCNLight()
lightNode.light!.type = SCNLightTypeOmni
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 = SCNLightTypeAmbient
ambientLightNode.light!.color = UIColor.darkGrayColor()
scene.rootNode.addChildNode(ambientLightNode)
//Create a camera like Rickster said
camera.usesOrthographicProjection = true
camera.orthographicScale = 9
camera.zNear = 1
camera.zFar = 100
cameraNode.position = SCNVector3(x: 0, y: 0, z: 50)
cameraNode.camera = camera
cameraOrbit = SCNNode()
cameraOrbit.addChildNode(cameraNode)
scene.rootNode.addChildNode(cameraOrbit)
//initial camera setup
self.cameraOrbit.eulerAngles.y = Float(-2 * M_PI) * lastWidthRatio
self.cameraOrbit.eulerAngles.x = Float(-M_PI) * lastHeightRatio
// retrieve the SCNView
let scnView = self.view as! SCNView
// set the scene to the view
scnView.scene = scene
//allows the user to manipulate the camera
scnView.allowsCameraControl = false //not needed
// add a tap gesture recognizer
let panGesture = UIPanGestureRecognizer(target: self, action: "handlePan:")
scnView.addGestureRecognizer(panGesture)
// add a pinch gesture recognizer
let pinchGesture = UIPinchGestureRecognizer(target: self, action: "handlePinch:")
scnView.addGestureRecognizer(pinchGesture)
}
func handlePan(gestureRecognize: UIPanGestureRecognizer) {
let numberOfTouches = gestureRecognize.numberOfTouches()
let translation = gestureRecognize.translationInView(gestureRecognize.view!)
if (numberOfTouches==fingersNeededToPan) {
widthRatio = Float(translation.x) / Float(gestureRecognize.view!.frame.size.width) + lastWidthRatio
heightRatio = Float(translation.y) / Float(gestureRecognize.view!.frame.size.height) + lastHeightRatio
// HEIGHT constraints
if (heightRatio >= maxHeightRatioXUp ) {
heightRatio = maxHeightRatioXUp
}
if (heightRatio <= maxHeightRatioXDown ) {
heightRatio = maxHeightRatioXDown
}
// WIDTH constraints
if(widthRatio >= maxWidthRatioRight) {
widthRatio = maxWidthRatioRight
}
if(widthRatio <= maxWidthRatioLeft) {
widthRatio = maxWidthRatioLeft
}
self.cameraOrbit.eulerAngles.y = Float(-2 * M_PI) * widthRatio
self.cameraOrbit.eulerAngles.x = Float(-M_PI) * heightRatio
print("Height: \(round(heightRatio*100))")
print("Width: \(round(widthRatio*100))")
//for final check on fingers number
lastFingersNumber = fingersNeededToPan
}
lastFingersNumber = (numberOfTouches>0 ? numberOfTouches : lastFingersNumber)
if (gestureRecognize.state == .Ended && lastFingersNumber==fingersNeededToPan) {
lastWidthRatio = widthRatio
lastHeightRatio = heightRatio
print("Pan with \(lastFingersNumber) finger\(lastFingersNumber>1 ? "s" : "")")
}
}
func handlePinch(gestureRecognize: UIPinchGestureRecognizer) {
let pinchVelocity = Double.init(gestureRecognize.velocity)
//print("PinchVelocity \(pinchVelocity)")
camera.orthographicScale -= (pinchVelocity/pinchAttenuation)
if camera.orthographicScale <= 0.5 {
camera.orthographicScale = 0.5
}
if camera.orthographicScale >= 10.0 {
camera.orthographicScale = 10.0
}
}

Answer 2

It looks like you're almost there, using just the #Rickster code from
the answer you cited.
The change you could make would be in these lines:
self.cameraOrbit.eulerAngles.y = Float(-2 * M_PI) * widthRatio
self.cameraOrbit.eulerAngles.x = Float(-M_PI) * heightRatio
which implicitly allow pitch and yaw to cover the entire
sphere. That's where you can do your limiting. For instance,
instead of allowing the pitch (eulerAngles.x) to vary from 0
to -π, you could do
self.cameraOrbit.eulerAngles.x = Float(-M_PI_2) + Float(-M_PI_2) * heightRatio
to vary smoothly between -π/2 and -π, using full screen
vertical scrolling to cover that range. Or you could put
hard min/max limits/checks in those two lines to constrain
to a particular area of the globe.
(Edit to address the inertia comment)
For rotational damping, or inertia, I'd approach it by using the built in SceneKit Physics, and perhaps put the camera on an invisible (no geometry) SCNNode. That camera node becomes a gimbal, similar to the approach taken in this project: An interactive seven-foot globe created entirely in RubyMotion and SceneKit.
The virtual gimbal then gets an SCNPhysicsBody (you add that, it doesn't come with one by default) with some damping. Or perhaps you put the physics on your central object, and give that object some angularDamping.