Set texture for unscanned areas

[100YardDasher]

How can I cover the unscanned areas with an image using the renderer class?
I managed to make it work by running the ARView while scanning and set:

planeNode?.geometry?.firstMaterial?.diffuse.contents = UIImage(named: "background")
planeNode?.position.z = -70
arView.pointOfView?.addChildNode(planeNode!)

but that causes a lot of other issues. How to do it using your renderer class?