Flickering SCNTube with transparency - swift

Question

UPDATED
I create some SCNTubes with following materials:
let radius: CGFloat = 0.3
let height: CGFloat = 0.5
let color: UIColor = UIColor(red:0.17, green:0.62, blue:0.76, alpha:1.0)
let geometryTube = SCNTube(innerRadius: (radius - 0.1), outerRadius: radius, height: height)
let matOuter = SCNMaterial()
matOuter.diffuse.contents = color
matOuter.transparency = 0.1
let matInner = SCNMaterial()
matInner.diffuse.contents = color
matInner.transparency = 0.6
let matTop = SCNMaterial()
matTop.diffuse.contents = color
geometryTube.materials = [matOuter, matInner, matTop]
for index in 0...20 {
let node = SCNNode(geometry: geometryTube)
node.position = SCNVector3(1.0 + Double(index), -1.0, 0.0);
sceneView.scene.rootNode.addChildNode(node)
}
Depending on the angle the tubes are flickering.

Answer 1

The materials property is designed to have one material for each geometry - whereas you are assigning three materials to a single geometry.
These are all overlapping and scenekit is having to decide what to render at each point.
EDIT: My answer (above) was wrong - rather than delete it I'll add this to highlight why I was wrong:
If a geometry has the same number of materials as it has geometry
elements, the material index corresponds to the element index. For
geometries with fewer materials than elements, SceneKit determines the
material index for each element by calculating the index of that
element modulo the number of materials. For example, in a geometry
with six elements and three materials, SceneKit renders the element at
index 5 using the material at index 5 % 3 = 2.
Apologies to OP for not being helpful with your question.

Answer 2

You might want to look at how your geometry is lit.
For example there are many different types of lightingModel properties you can use e.g.
Try for example to set each materials .lightingModel property to .constant e.g:
matOuter.lightingModel = .constant
Another option you may also want to explore SCNTransparencyMode as well...