Real time reflections in SceneKit using Metal

README.md

Using the ReflectionSession Class for Real Time Reflections in SceneKit

First, create a new ReflectionSession implementation with your SCNView object. Note: You only need one ReflectionSession object at a time.

let reflectionSession = ReflectionSession(inView: scnView)

Then, add the nodes that you want to be reflective to the ReflectionSession using the addNode(_:roughness:) method. Because .physicallyBased materials won't work, the roughness value will determine how much to blur the cubemap images, simulating a roughness effect.

reflectionSession.addNode(node1)
reflectionSession.addNode(node2, roughness: 0.2)

Now, all you need to do is call the update() method within the render loop of your scene.

override func viewDidLoad() {
  
  super.viewDidLoad()
  
  scnView.delegate = self
  
  // Other setup
  
}

func renderer(_ renderer: SCNSceneRenderer, willRenderScene scene: SCNScene, atTime time: TimeInterval) {
  
  reflectionSession.update()
  
}

Optional: You can use reflectionUpdateSpeed to set the frame rate of the reflections.

reflectionSession.reflectionUpdateSpeed = .slow      // Update reflection every six frames
reflectionSession.reflectionUpdateSpeed = .normal    // Default, update reflection every three frames
reflectionSession.reflectionUpdateSpeed = .fast      // Update reflection every two frames
reflectionSession.reflectionUpdateSpeed = .superFast // Update reflection every frame

Note: The framerate of the reflections will be lower if there are a lot of reflective objects on the screen at one time. Higher values for reflectionUpdateSpeed can slow down the actual frame rate of your game.

ReflectionSession.swift

//
//  ReflectionSession.swift
//

import Foundation
import SceneKit
import MetalPerformanceShaders

public class ReflectionSession {
    
    let reflectionMapSize = 200
    private let renderer: SCNRenderer
    private let scene: SCNScene?
    private let view: SCNView
    private let device: MTLDevice
    
    private var nodes: [SCNNode] = []
    
    private var commandQueue: MTLCommandQueue
    private var blurHandlers: [MPSImageBox?] = []
    
    // private var renderTimer: Timer
    
    public enum UpdateSpeed {
        case slow
        case normal
        case fast
        case reallyFast
    }
    
    public var reflectionUpdateSpeed: UpdateSpeed = .normal
    
    public init(inView view: SCNView) {
        
        device = MTLCreateSystemDefaultDevice()!
        renderer = SCNRenderer(device: device, options: nil)
        scene = view.scene
        self.view = view
        // renderTimer = Timer()
        commandQueue = device.makeCommandQueue()!
        
        let cubemapDescriptor = MTLTextureDescriptor.textureCubeDescriptor(pixelFormat: .rgba8Unorm, size: reflectionMapSize, mipmapped: false)
        cubemapDescriptor.usage = MTLTextureUsage(rawValue: MTLTextureUsage.renderTarget.rawValue | MTLTextureUsage.shaderRead.rawValue)
        pendingTexture = device.makeTexture(descriptor: cubemapDescriptor)!
        
        renderer.scene = scene
        scene?.rootNode.addChildNode(camera360Node)
        
        // renderTimer = Timer.scheduledTimer(timeInterval: 1.0 / 60.0, target: self, selector: #selector(update), userInfo: nil, repeats: true)
        // renderTimer.tolerance = (1.0 / 80.0)
        
    }
    
    public func addNode(_ node: SCNNode, roughness: Float = 0) {
        
        nodes.append(node)
        
        var kernelSize = Int(roughness * 95)
        if kernelSize > 0 {
            
            if Double(kernelSize) / 2 == Double(kernelSize / 2) { kernelSize -= 1 }
            if kernelSize > 95 { kernelSize = 95 }
            
            let blurHandler = MPSImageBox(device: device, kernelWidth: kernelSize, kernelHeight: kernelSize)
            blurHandler.edgeMode = .clamp
            
            blurHandlers.append(blurHandler)
            
        } else {
            
            blurHandlers.append(nil)
            
        }
        
        node.categoryBitMask = 2 << nodes.count
        
    }
    
    private var angles = ["x+", "x-", "y+", "y-", "z+", "z-"]
    private var currentAngle = 0
    private var currentNode = 0
    
    private let camera360Node = { () -> SCNNode in
        
        let rootNode = SCNNode()
        
        let xPlusCam = SCNNode()
        xPlusCam.name = "camera_x+"
        xPlusCam.camera = SCNCamera()
        xPlusCam.camera?.fieldOfView = 90
        xPlusCam.eulerAngles.y = GLKMathDegreesToRadians(90)
        rootNode.addChildNode(xPlusCam)
        
        let xMinusCam = SCNNode()
        xMinusCam.name = "camera_x-"
        xMinusCam.camera = SCNCamera()
        xMinusCam.camera?.fieldOfView = 90
        xMinusCam.eulerAngles.y = GLKMathDegreesToRadians(-90)
        rootNode.addChildNode(xMinusCam)
        
        let yPlusCam = SCNNode()
        yPlusCam.name = "camera_y+"
        yPlusCam.camera = SCNCamera()
        yPlusCam.camera?.fieldOfView = 90
        yPlusCam.eulerAngles.x = GLKMathDegreesToRadians(90)
        rootNode.addChildNode(yPlusCam)
        
        let yMinusCam = SCNNode()
        yMinusCam.name = "camera_y-"
        yMinusCam.camera = SCNCamera()
        yMinusCam.camera?.fieldOfView = 90
        yMinusCam.eulerAngles.x = GLKMathDegreesToRadians(-90)
        rootNode.addChildNode(yMinusCam)
        
        let zPlusCam = SCNNode()
        zPlusCam.name = "camera_z+"
        zPlusCam.camera = SCNCamera()
        zPlusCam.camera?.fieldOfView = 90
        zPlusCam.eulerAngles.y = GLKMathDegreesToRadians(180)
        rootNode.addChildNode(zPlusCam)
        
        let zMinusCam = SCNNode()
        zMinusCam.name = "camera_z-"
        zMinusCam.camera = SCNCamera()
        zMinusCam.camera?.fieldOfView = 90
        rootNode.addChildNode(zMinusCam)
        
        return rootNode
        
    }()
    //SCNScene(named: "art.scnassets/360Camera.scn")!.rootNode.childNode(withName: "360_cam", recursively: false)!
    
    private var pendingTexture: MTLTexture
    
    private func updateReflections() {
        
        let node = nodes[currentNode]
        
        let camera = camera360Node.childNode(withName: "camera_" + angles[currentAngle], recursively: false)!
        
        camera.camera?.categoryBitMask = ~node.categoryBitMask
        
        renderer.pointOfView = camera
        texturePending = true
        
        let renderPassDescriptor = MTLRenderPassDescriptor()
        renderPassDescriptor.colorAttachments[0].texture = pendingTexture
        renderPassDescriptor.colorAttachments[0].slice = currentAngle
        renderPassDescriptor.colorAttachments[0].loadAction = .clear
        renderPassDescriptor.colorAttachments[0].clearColor = MTLClearColorMake(0, 0, 0, 1.0)
        renderPassDescriptor.colorAttachments[0].storeAction = .store
        
        let commandBuffer = commandQueue.makeCommandBuffer()!
        renderer.render(withViewport: CGRect(x: 0, y: 0, width: 200, height: 200), commandBuffer: commandBuffer, passDescriptor: renderPassDescriptor)
        commandBuffer.commit()
        
        commandBuffer.waitUntilCompleted()
        
        currentAngle = (currentAngle + 1) % angles.count
        if currentAngle == 0 {
            
            if let blurHandler = blurHandlers[currentNode] {
                
                for slice in 0..<6 {
                    
                    let blurBuffer = commandQueue.makeCommandBuffer()!
                    let copyToEditable = blurBuffer.makeBlitCommandEncoder()!
                    
                    let copyDescriptor = MTLTextureDescriptor.texture2DDescriptor(pixelFormat: .rgba8Unorm, width: reflectionMapSize, height: reflectionMapSize, mipmapped: false)
                    let copyTexture = device.makeTexture(descriptor: copyDescriptor)!
                    
                    let blurDescriptor = MTLTextureDescriptor.texture2DDescriptor(pixelFormat: .rgba8Unorm, width: reflectionMapSize, height: reflectionMapSize, mipmapped: false)
                    blurDescriptor.usage = .shaderWrite
                    let blurTexture = device.makeTexture(descriptor: blurDescriptor)!
                    
                    copyToEditable.copy(from: pendingTexture, sourceSlice: slice, sourceLevel: 0, sourceOrigin: MTLOrigin(x: 0, y: 0, z: 0), sourceSize: MTLSize(width: reflectionMapSize, height: reflectionMapSize, depth: 1), to: copyTexture, destinationSlice: 0, destinationLevel: 0, destinationOrigin: MTLOrigin(x: 0, y: 0, z: 0))
                    copyToEditable.endEncoding()
                    
                    blurHandler.encode(commandBuffer: blurBuffer, sourceTexture: copyTexture, destinationTexture: blurTexture)
                    
                    let copyBackToCube = blurBuffer.makeBlitCommandEncoder()!
                    
                    copyBackToCube.copy(from: blurTexture, sourceSlice: 0, sourceLevel: 0, sourceOrigin: MTLOrigin(x: 0, y: 0, z: 0), sourceSize: MTLSize(width: reflectionMapSize, height: reflectionMapSize, depth: 1), to: pendingTexture, destinationSlice: slice, destinationLevel: 0, destinationOrigin: MTLOrigin(x: 0, y: 0, z: 0))
                    copyBackToCube.endEncoding()
                    
                    blurBuffer.commit()
                    blurBuffer.waitUntilCompleted()
                    
                }
                
            }
            
            node.geometry?.firstMaterial?.reflective.contents = pendingTexture
            
            currentNode = (currentNode + 1) % nodes.count
            camera360Node.worldPosition = nodes[currentNode].worldPosition
            
            let cubemapDescriptor = MTLTextureDescriptor.textureCubeDescriptor(pixelFormat: .rgba8Unorm, size: reflectionMapSize, mipmapped: false)
            cubemapDescriptor.usage = MTLTextureUsage(rawValue: MTLTextureUsage.renderTarget.rawValue | MTLTextureUsage.shaderRead.rawValue)
            pendingTexture = device.makeTexture(descriptor: cubemapDescriptor)!
            texturePending = false
            
        }
        
    }
    
    private var texturePending = false
    
    @objc public func update() {
        
        if nodes.isEmpty { return }
        
        if !texturePending {
            
            for _ in 0..<nodes.count {
                
                let node = nodes[currentNode]
                
                if let pointOfView = view.pointOfView {
                    
                    if view.isNode(node, insideFrustumOf: pointOfView) {
                        
                        break
                        
                    }
                    
                    currentNode = (currentNode + 1) % nodes.count
                    
                }
                
            }
            
        }
        
        switch reflectionUpdateSpeed {
            
        case .slow:
            updateReflections()
        case .normal:
            for _ in 1...2 { updateReflections() }
        case .fast:
            for _ in 1...3 { updateReflections() }
        case .reallyFast:
            for _ in 1...6 { updateReflections() }
            
        }
        
    }
    
}

It seems to be working for me even with that error.

Yes, I already found that with disabled SSAO problem disappear.