How to connect two SCNSpheres in 3D space using Bezier path in Swift? - swift

Question

I have the following code:
func createScene(){
count += 1
let sphereGeom = SCNSphere(radius: 1.5)
sphereGeom.firstMaterial?.diffuse.contents = UIColor.redColor()
let path = UIBezierPath()
path.moveToPoint(CGPoint(x: 0, y: 0))
let radius = 3.0
var radians = Double(0)
var yPosition = Float(5.4)
while count <= 20 {
if radians >= 2{
radians -= 2
}
let sphereNode = SCNNode(geometry: sphereGeom)
let angle = Double(radians * M_PI)
let xPosition = Float(radius * cos(angle))
let zPosition = Float(radius * sin(angle))
sphereNode.position = SCNVector3(xPosition, yPosition, zPosition)
let cgX = CGFloat(xPosition)
let cgY = CGFloat(yPosition)
path.addQuadCurveToPoint(CGPoint(x: cgX, y: cgY), controlPoint: CGPoint(x: (cgX / 2), y: (cgY / 2)))
path.addLineToPoint(CGPoint(x: (cgX - (cgX * 0.01)), y: cgY))
path.addQuadCurveToPoint(CGPoint(x: 1, y: 0), controlPoint: CGPoint(x: (cgX / 2), y: ((cgY / 2) - (cgY * 0.01))))
let shape = SCNShape(path: path, extrusionDepth: 3.0)
shape.firstMaterial?.diffuse.contents = UIColor.blueColor()
let shapeNode = SCNNode(geometry: shape)
shapeNode.eulerAngles.y = Float(-M_PI_4)
self.rootNode.addChildNode(shapeNode)
count += 1
radians += 0.5556
yPosition -= 1.35
self.rootNode.addChildNode(sphereNode)
}
I want to add a Bezier path connecting each sphere to the next one, creating a spiral going down the helix. For some reason, when I add this code, the shape doesn't even appear. But when I use larger x and y values, I see the path fine, but it is no way oriented to the size of the spheres. I don't understand why it disappears when I try to make it smaller.

Answer 1

Your SCNShape doesn't ever get extruded. Per Apple doc,
An extrusion depth of zero creates a flat, one-sided shape.
With larger X/Y values your flat shape happens to become visible. You can't build a 3D helix with SCNShape, though: the start and end planes of the extrusion are parallel.
You'll have to use custom geometry, or approximate your helix with a series of elongated SCNBox nodes. And I bet someone out there knows how to do this with a shader.