SceneKit - Replace material to an array of nodes

Question

Goal: add default material to all child node on a Scenekit scene.

What I did:

// get child noses from scene
let allNodes = scene.rootNode.childNodes

//create a defaul material
let defaultMaterial = SCNMaterial()  
defaultMaterial.diffuse.contents = NSColor.red
         
//add defaul material to all child nodes
allChildNodes.replaceMaterial(at: 0, with: defaultMaterial)

Problem:

Looks like "replaceMaterial" doesn't work with an array of nodes.

Question:

How I add a material to an array of nodes?

Answer 1

Applying a material to an array of nodes

Try this code to achieve your goal:

import SceneKit

class ViewController : NSViewController {
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        let sceneView = self.view as! SCNView
        let scene = SCNScene(named: "art.scnassets/scene.scn")!
        sceneView.scene = scene
        
        let material = SCNMaterial()
        material.diffuse.contents = NSColor.systemYellow
        
        let allNodes = scene.rootNode.childNodes[0].childNodes
                
        for i in 0...(allNodes.count-1) {
            allNodes[i].geometry?.firstMaterial = material
        }
    }
}

---

Applying a material to an array of nodes

Also, you can apply any random color to any model with one click.

import SwiftUI
import SceneKit

struct ContentView : View { 
    let scene = SCNScene()
    let opts: SceneView.Options =  [.allowsCameraControl, .autoenablesDefaultLighting]
    var body: some View {
        ZStack {
            SceneView(scene: scene, options: opts).ignoresSafeArea()
            self.createModel()                
            VStack {
                Spacer()
                Button("Update Material Color") {
                    let material = scene.rootNode.childNodes[0].geometry?.materials[0]
                    material?.diffuse.contents = randomColor()
                }
            }
        }
    }
    func createModel() -> EmptyView {
        let node = SCNNode(geometry: SCNSphere(radius: 0.25))
        node.geometry?.materials[0].diffuse.contents = randomColor()
        node.geometry?.materials[0].lightingModel = .physicallyBased
        scene.rootNode.addChildNode(node)
        scene.background.contents = NSColor.black
        return EmptyView()
    }
    func randomColor() -> NSColor {
        return NSColor(red: .random(in: 0...1), green: .random(in: 0...1),
                      blue: .random(in: 0...1), alpha: 1.0)
    }
}