SceneKit Fully Stop Simulation from Running at Instant? - ios

Question

Trying to get this simple rolling ball simulation running. I cannot seem to find a way to make the ball stop rolling at a said instant, then reset it to the start position with the isResting flag updating just as fast. when running, if the reset button is pressed the ball goes back to the start position but if it is not done rolling it will continue to roll. That is not desired.
import Cocoa
import SceneKit
class AppController : NSObject {
#IBOutlet weak var _sceneView: SCNView!
#IBOutlet weak var _pushButton: NSButton!
#IBOutlet weak var _resetButton: NSButton!
private let _radius = 25.0
private let _mySphereNode = SCNNode()
override func awakeFromNib() {
// assign empty scene
_sceneView.scene = SCNScene()
// setup the sphere
let mySphere = SCNSphere(radius: CGFloat(_radius))
mySphere.geodesic = true
mySphere.segmentCount = 50
mySphere.firstMaterial!.diffuse.contents = NSColor.purpleColor().CGColor
mySphere.firstMaterial!.specular.contents = NSColor.whiteColor().CGColor
// create node for adding sphere
_mySphereNode.position = SCNVector3(0.0, CGFloat(_radius), 0.0)
_mySphereNode.geometry = mySphere
// add physics
let spherePhysicsBody = SCNPhysicsBody.dynamicBody()
spherePhysicsBody.mass = 0.67 // Kg
spherePhysicsBody.friction = 0.3765
spherePhysicsBody.rollingFriction = 0.2734
spherePhysicsBody.damping = 0.5
_mySphereNode.physicsBody = spherePhysicsBody
// attach the sphere node to the scene's root node
_sceneView.scene!.rootNode.addChildNode(_mySphereNode)
// setup ambient light source
let ambientLightNode = SCNNode()
ambientLightNode.light = SCNLight()
ambientLightNode.light!.type = SCNLightTypeAmbient
ambientLightNode.light!.color = NSColor(white: 0.35, alpha: 1.0).CGColor
// add ambient light the scene
_sceneView.scene!.rootNode.addChildNode(ambientLightNode)
// setup onmidirectional light
let omniLightNode = SCNNode()
omniLightNode.light = SCNLight()
omniLightNode.light!.type = SCNLightTypeOmni
omniLightNode.light!.color = NSColor(white: 0.56, alpha: 1.0).CGColor
omniLightNode.position = SCNVector3Make(0.0, 200.0, 0.0)
_sceneView.scene!.rootNode.addChildNode(omniLightNode)
// add plane
let myPlane = SCNPlane(width: 125.0, height: 2000.0)
myPlane.widthSegmentCount = 10
myPlane.heightSegmentCount = 10
myPlane.firstMaterial!.diffuse.contents = NSColor.orangeColor().CGColor
myPlane.firstMaterial!.specular.contents = NSColor.whiteColor().CGColor
let planeNode = SCNNode()
planeNode.geometry = myPlane
// rotote -90.0 degrees about the y-axis, then rot
var rotMat = SCNMatrix4MakeRotation(-3.14/2.0, 0.0, 1.0, 0.0)
rotMat = SCNMatrix4Rotate(rotMat, -3.14/2.0, 1.0, 0.0, 0.0)
planeNode.transform = rotMat
planeNode.position = SCNVector3Make(0.0, 0.0, 0.0)
// add physcis to plane
planeNode.physicsBody = SCNPhysicsBody.staticBody()
// add plane to scene
_sceneView.scene!.rootNode.addChildNode(planeNode)
}
#IBAction func moveBall(sender: AnyObject) {
if _mySphereNode.physicsBody!.isResting == true {
let forceApplied = SCNVector3Make(40.0, 0.0, 0.0)
_mySphereNode.physicsBody!.applyForce(forceApplied, impulse: true)
}
else {
print("Ball not at rest!")
}
}
#IBAction func resetBall(sender: AnyObject) {
_mySphereNode.physicsBody!.resetTransform()
}
}
Is there a way to stop the SceneKit simulation dead stop and reset to a start position in a way that would force the isResting flag to update to true as well?

Answer 1

I found that invalidating the node's geometry and physics body, then reattaching them worked out. Here is the code:
import Cocoa
import SceneKit
class AppController : NSObject {
#IBOutlet weak var _sceneView: SCNView!
#IBOutlet weak var _pushButton: NSButton!
#IBOutlet weak var _resetButton: NSButton!
private let _mySphereNode = SCNNode()
private func setupScene() {
// setup ambient light source
let ambientLightNode = SCNNode()
ambientLightNode.light = SCNLight()
ambientLightNode.light!.type = SCNLightTypeAmbient
ambientLightNode.light!.color = NSColor(white: 0.35, alpha: 1.0).CGColor
// add ambient light the scene
_sceneView.scene!.rootNode.addChildNode(ambientLightNode)
// setup onmidirectional light
let omniLightNode = SCNNode()
omniLightNode.light = SCNLight()
omniLightNode.light!.type = SCNLightTypeOmni
omniLightNode.light!.color = NSColor(white: 0.56, alpha: 1.0).CGColor
omniLightNode.position = SCNVector3Make(0.0, 200.0, 0.0)
_sceneView.scene!.rootNode.addChildNode(omniLightNode)
// add plane
let myPlane = SCNPlane(width: 125.0, height: 2000.0)
myPlane.widthSegmentCount = 10
myPlane.heightSegmentCount = 10
myPlane.firstMaterial!.diffuse.contents = NSColor.orangeColor().CGColor
myPlane.firstMaterial!.specular.contents = NSColor.whiteColor().CGColor
let planeNode = SCNNode()
planeNode.geometry = myPlane
// rotote -90.0 degrees about the y-axis, then rot
var rotMat = SCNMatrix4MakeRotation(-3.14/2.0, 0.0, 1.0, 0.0)
rotMat = SCNMatrix4Rotate(rotMat, -3.14/2.0, 1.0, 0.0, 0.0)
planeNode.transform = rotMat
planeNode.position = SCNVector3Make(0.0, 0.0, 0.0)
// add physcis to plane
planeNode.physicsBody = SCNPhysicsBody.staticBody()
// add plane to scene
_sceneView.scene!.rootNode.addChildNode(planeNode)
}
private func setupBall() {
let _radius = 25.0
// setup the sphere
let mySphere = SCNSphere(radius: CGFloat(_radius))
mySphere.geodesic = true
mySphere.segmentCount = 50
mySphere.firstMaterial!.diffuse.contents = NSColor.purpleColor().CGColor
mySphere.firstMaterial!.specular.contents = NSColor.whiteColor().CGColor
_mySphereNode.position = SCNVector3(0.0, CGFloat(_radius), 0.0)
_mySphereNode.geometry = mySphere
// add physics
let spherePhysicsBody = SCNPhysicsBody.dynamicBody()
spherePhysicsBody.mass = 0.67 // Kg
spherePhysicsBody.friction = 0.3765
spherePhysicsBody.rollingFriction = 0.2734
spherePhysicsBody.damping = 0.5
_mySphereNode.physicsBody = spherePhysicsBody
}
private func stopBall() {
_mySphereNode.geometry = nil
_mySphereNode.physicsBody = nil
}
override func awakeFromNib() {
// assign empty scene
_sceneView.scene = SCNScene()
// attach the sphere node to the scene's root node
_sceneView.scene!.rootNode.addChildNode(_mySphereNode)
setupScene()
setupBall()
}
#IBAction func moveBall(sender: AnyObject) {
let forceApplied = SCNVector3Make(40.0, 0.0, 0.0)
if _mySphereNode.physicsBody?.isResting == true {
_mySphereNode.physicsBody!.applyForce(forceApplied, impulse: true)
}
}
#IBAction func resetBall(sender: AnyObject) {
// remove the ball from the sphere node
stopBall()
// reset the ball
setupBall()
}
}