SceneKit - Adding drift to a sphere rotated via a pan gesture - ios

Question

I am using SceneKit and allowing users to rotate what they're seeing inside a sphere by using a pan gesture. This is working fine - except, I'd like to have the sphere keep rotating slightly in the direction of the pan gesture, to feel a bit more reactive.
Here's my setup for the scene:
// Create scene
let scene = SCNScene()
sceneView.scene = scene
let panRecognizer = UIPanGestureRecognizer(target: self,
action: #selector(ViewController.handlePanGesture(_:)))
sceneView.addGestureRecognizer(panRecognizer)
//Create sphere
let sphere = SCNSphere(radius: 50.0)
// sphere setup
sphereNode = SCNNode(geometry: sphere)
sphereNode!.position = SCNVector3Make(0,0,0)
scene.rootNode.addChildNode(sphereNode!)
// Create camera
let camera = SCNCamera()
// camera setup
cameraNode = SCNNode()
cameraNode!.camera = camera
cameraNode!.position = SCNVector3Make(0, 0, 0)
cameraOrbit = SCNNode()
cameraOrbit!.addChildNode(cameraNode!)
scene.rootNode.addChildNode(cameraOrbit!)
let lookAtConstraint = SCNLookAtConstraint(target: sphereNode!)
lookAtConstraint.gimbalLockEnabled = true
cameraNode!.constraints = [lookAtConstraint]
sceneView.pointOfView = cameraNode
And here is how the pan gesture is currently handled (courtesy of SCNCamera limit arcball rotation):
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
if (sender.state == .Ended) {
lastWidthRatio = widthRatio
lastHeightRatio = heightRatio
}
I'm not sure where to begin in adding in a slight continued rotation motion. Maybe adding a physicsBody and applying force? Maybe animating the change in eulerAngles?

Answer 1

The way I've handled things like this before is to split the gesture handler into sections for the gesture state beginning, changing and ending. If the rotation is working for you all you need to do is add code to the bottom of your if (sender.state == .Ended) statement.
After lastHeightRatio = heightRatio you can find the velocity of the pan in the view using sender.velocityInView(sender.view!) and then find the horizontal component as before, then add an SCNAction to rotate the node with an EaseOut timing mode.
You'll likely need a multiplier to translate the velocity in the view (measured in points) to the angle you wish to rotate through (measured in radians). A velocity of 10 points, which is relatively small, would result in a very fast rotation.
Also you'll need to remove all actions from the node when the gesture begins again if you want a touch to stop the residual rotation.
Some sampel code would be:
if (sender.state == .Ended) {
lastWidthRatio = widthRatio
lastHeightRatio = heightRatio
// Find velocity
let velocity = sender.velocityInView(sender.view!)
// Create Action for whichever axis is the correct one to rotate about.
// The 0.00001 is just a factor to provide the rotation speed to pan
// speed ratio you'd like. Play with this number and the duration to get the result you want
let rotate = SCNAction.rotateByX(velocity.x * 0.00001, y: 0, z: 0, duration: 2.0)
// Run the action on the camera orbit node (if I understand your setup correctly)
cameraOrbit.runAction(rotate)
}
This should be enough to get you started.