Code for tweet https://twitter.com/chunkyguy/status/1130088721364213760

cornell_box_scenekit.swift

import Foundation
import SceneKit
import GLKit

class World {
    let scene = SCNScene()
    
    func setUp() {
        let worldNode = scene.rootNode
        addLights(to: worldNode)
        addCamera(to: worldNode)
        addScene(to: worldNode)
    }
}

private extension World {
    private func addCamera(to parent: SCNNode) {
        let cameraNode = SCNNode()
        cameraNode.camera = SCNCamera()
        cameraNode.position = SCNVector3(0, 0, 1)
        cameraNode.look(at: SCNVector3(0, 0, 0))
        parent.addChildNode(cameraNode)
    }
}

private extension World {
    private func addLights(to parent: SCNNode) {
        addRoomLight(to: parent)
        addSpotLight(to: parent)
    }
    
    private func addRoomLight(to parent: SCNNode) {
        let light = SCNLight()
        light.type = .omni
        light.color = UIColor(white: 0.5, alpha: 1).cgColor
        let node = SCNNode()
        node.light = light
        node.position = SCNVector3(0, 0, 1)
        parent.addChildNode(node)
    }
    
    private func addSpotLight(to parent: SCNNode) {
        let light = SCNLight()
        light.type = .spot
        light.color = UIColor.white.cgColor
        light.castsShadow = true
        let node = SCNNode()
        node.light = light
        node.position = SCNVector3(0, 1, 0)
        node.look(at: SCNVector3(0, 0, 0))
        parent.addChildNode(node)
    }
}

private extension World {
    private func addScene(to parent: SCNNode) {
        addWalls(to: parent)
        addCubes(to: parent)
        addLightSource(to: parent)
    }
}

private extension World {
    private func addWalls(to parent: SCNNode) {
        let wallColor = UIColor(white: 0.8, alpha: 1)
        addWall(
            to: parent,
            color: wallColor,
            position: simd_float3(0, 0, -0.5)
        )
        addWall(
            to: parent,
            color: .green,
            position: simd_float3(-0.5, 0, 0),
            rotation: simd_float4(0, 1, 0, GLKMathDegreesToRadians(90))
        )
        addWall(
            to: parent,
            color: .red,
            position: simd_float3(0.5, 0, 0),
            rotation: simd_float4(0, 1, 0, GLKMathDegreesToRadians(270))
        )
        addWall(
            to: parent,
            color: wallColor,
            position: simd_float3(0, 0.5, 0),
            rotation: simd_float4(1, 0, 0,GLKMathDegreesToRadians(270))
        )
        addWall(
            to: parent,
            color: wallColor,
            position: simd_float3(0, -0.5, 0),
            rotation: simd_float4(1, 0, 0, GLKMathDegreesToRadians(90))
        )
    }
    
    private func addWall(to parent: SCNNode, color: UIColor, position: simd_float3, rotation: simd_float4 = simd_float4.zero) {
        let geometry = SCNPlane(width: 1, height: 1)
        let material = SCNMaterial()
        material.isDoubleSided = true
        material.diffuse.contents = color.cgColor
        geometry.materials = [material]
        let wall = SCNNode(geometry: geometry)
        wall.simdPosition = position
        wall.simdRotation = rotation
        parent.addChildNode(wall)
    }
}

private extension World {
    private func addCubes(to parent: SCNNode) {
        addCube(
            to: parent,
            height: 0.6,
            positionX: -0.2,
            positionZ: -0.5,
            rotation: 20
        )
        addCube(
            to: parent,
            height: 0.3,
            positionX: 0.1,
            positionZ: -0.25,
            rotation: -25
        )
    }
    
    private func addCube(to parent: SCNNode, height: CGFloat, positionX: CGFloat, positionZ: CGFloat, rotation: CGFloat) {
        let cubeGeo = SCNBox(width: 0.3, height: height, length: 0.3, chamferRadius: 0)
        let cubeMat = SCNMaterial()
        cubeMat.diffuse.contents = UIColor.lightGray.cgColor
        cubeGeo.materials = [cubeMat]
        let cube = SCNNode(geometry: cubeGeo)
        cube.position = SCNVector3(positionX, -0.5 + height/2.0, positionZ)
        cube.rotation = SCNVector4(0, 1, 0, GLKMathDegreesToRadians(Float(rotation)))
        parent.addChildNode(cube)
    }
}

private extension World {
    private func addLightSource(to parent: SCNNode) {
        let geometry = SCNPlane(width: 0.05, height: 0.05)
        let material = SCNMaterial()
        material.isDoubleSided = true
        material.emission.contents = UIColor.white.cgColor
        geometry.materials = [material]
        let node = SCNNode(geometry: geometry)
        node.position = SCNVector3(0, 0.49, 0)
        node.rotation = SCNVector4(1, 0, 0, GLKMathDegreesToRadians(270))
        parent.addChildNode(node)
    }
}