Scene not rendering properly in SceneKit - ios

Question

I created a floor in a scene and loaded a collada file(.dae) into my scene and tried to create a plane below that model. But I have problems like below.
This problem generates only when custom camera is used. Scene renders properly when system camera is used i.e if no custom camera is added
My code is as below:
import UIKit import SceneKit
class TestVC: UIViewController, SCNSceneRendererDelegate {
var cameraNode: SCNNode!
var modelNode: SCNNode!
var scnView: SCNView!
var camNode: SCNNode!
var cameraPosition: SCNVector3!
override func viewDidLoad() {
super.viewDidLoad()
scnView = SCNView(frame: self.view.frame)
scnView.delegate = self
view.addSubview(scnView)
scnView.delegate = self
let scene = SCNScene()
scnView.scene = scene
//camera
let camera = SCNCamera()
cameraNode = SCNNode()
cameraNode.camera = camera
camera.zFar = 1000
cameraPosition = SCNVector3(0, 100, 150)
cameraNode.position = cameraPosition
scene.rootNode.addChildNode(cameraNode)
//floor
let floor = SCNFloor()
floor.reflectivity = 0
let floorNode = SCNNode(geometry: floor)
let firstmaterial = SCNMaterial()
firstmaterial.diffuse.contents = UIImage(named: "art.scnassets/grass.jpg")
firstmaterial.diffuse.wrapS = SCNWrapMode.Repeat
firstmaterial.diffuse.wrapT = SCNWrapMode.Repeat
floor.materials = [firstmaterial]
scene.rootNode.addChildNode(floorNode)
let light = SCNLight()
let lightNode = SCNNode()
lightNode.light = light
light.type = SCNLightTypeAmbient
light.color = UIColor.darkGrayColor()
scene.rootNode.addChildNode(lightNode)
let light1 = SCNLight()
let light1Node = SCNNode()
light1Node.light = light1
light1Node.position = SCNVector3(0, 200, -100)
light1.type = SCNLightTypeOmni
scene.rootNode.addChildNode(light1Node)
let modelScene = SCNScene(named: "Barcelona Chair.dae")
let solNode = modelScene?.rootNode
solNode?.eulerAngles = SCNVector3(GLKMathDegreesToRadians(-90), 0, 0)
scene.rootNode.addChildNode(solNode!)
scnView.allowsCameraControl = true
let plane = SCNPlane(width: 100, height: 100)
let planeNode = SCNNode(geometry: plane)
planeNode.pivot = SCNMatrix4MakeRotation(Float(M_PI_2), 1, 0, 0)//(CGFloat(M_PI_2), 1, 0, 0)
planeNode.position = SCNVector3(0, 1, 0)
plane.firstMaterial?.diffuse.contents = UIColor.redColor()
scene.rootNode.addChildNode(planeNode)
}

Answer 1

What you're probably seeing is known as "z-fighting". Basically, your floor and your plane are coexisting - they are coplanar - so the rendering of them is ambiguous. Try lifting the plane up a little by setting its position higher than the floor plane, and you should see this problem go away.

Answer 2

Don't know why the above problem exists but I got a different way of doing the thing. You can use SCNShape to draw an overlay over a floor. I drew a rectangular path using UIBezierPath and set the path property of the SCNShape class. :)