将 SCNRenderer 与 ARKit 一起使用会产生奇怪的结果

问题描述

我正在尝试导出在 ARSCNView 渲染过程中创建的深度纹理。为了做到这一点，我编写了一个代码，使用自定义 MTLRenderPassDescriptor 在后台呈现 SCNScene。当我使用“GPU 捕获工具”跟踪绑定到 GPU 的资源时，我发现 SCNRenderer.render 方法中忽略了自定义 MTLRenderPassDescriptor。

我使用此代码将 SCNScene 渲染到屏幕外。

// Render Pass - render sceneView
renderer.scene = sceneView.scene
renderer.pointOfView = sceneView.pointOfView
renderer.render(atTime: 0,viewport: viewport,commandBuffer: commandBuffer,passDescriptor: renderPassDescriptor)

当我检查 GPU 捕获中的资源时，渲染器会生成自己的帧纹理和深度纹理，而不是 renderPassDescriptor 中描述的。根据{{​​3}}，这很奇怪。我还在没有 ARKit 会话的情况下测试了它，它按我的预期工作（渲染器使用 renderPassDescriptor 中描述的纹理资源）。 我怎样才能解决这个问题？这是 SceneKit 的错误吗？

the document

Image 1. I found in GPU capture that the depth texture is not linked to blit pass.

Image 2. The color attachment texture address is 0x144a4f310

Image 3. The depth attachment texture address is 0x144a50050

这是最低限度的工作示例。

import UIKit
import SceneKit
import ARKit

class ViewController: UIViewController,ARSCNViewDelegate,ARSessionDelegate {

  @IBOutlet var sceneView: ARSCNView!
  var ship: SCNNode!
  var device: MTLDevice!
  var renderer: SCNRenderer!
  var commandQueue: MTLCommandQueue!
  let textureSizeX = 2732
  let textureSizeY = 2048
  lazy var viewport = CGRect(x: 0,y: 0,width: CGFloat(textureSizeX),height: CGFloat(textureSizeY))
   
   
  override func viewDidLoad() {
    super.viewDidLoad()
     
    // Set the view's delegate
    sceneView.delegate = self
    sceneView.session.delegate = self
    sceneView.showsStatistics = true
    sceneView.scene = SCNScene()
     
    ship = SCNScene(named: "art.scnassets/ship.scn")?.rootNode.childNode(withName: "shipMesh",recursively: true)!
    sceneView.scene.rootNode.addChildNode(ship)
     
     
    // background renderer
    device = MTLCreateSystemDefaultDevice()!
    renderer = SCNRenderer(device: device,options: nil)
    commandQueue = device.makeCommandQueue()!
  }
   
  override func viewWillAppear(_ animated: Bool) {
    super.viewWillAppear(animated)
     
    guard let referenceImages = ARReferenceImage.referenceImages(inGroupNamed: "AR Resources",bundle: nil) else {
      fatalError("Missing expected asset catalog resources.")
    }

    // Create a session configuration
    let configuration = ARWorldTrackingConfiguration()
    configuration.detectionImages = referenceImages

    // Run the view's session
    sceneView.session.run(configuration,options: [.resetTracking,.removeExistingAnchors])
  }
   
  override func viewWillDisappear(_ animated: Bool) {
    super.viewWillDisappear(animated)
     
    // Pause the view's session
    sceneView.session.pause()
  }

  // MARK: - ARSCNViewDelegate
   
  // Override to create and configure nodes for anchors added to the view's session.
  func renderer(_ renderer: SCNSceneRenderer,willRenderScene scene: SCNScene,atTime time: TimeInterval) {
    doRender()
  }
   
  func doRender() {
    let renderPassDescriptor = makeRenderPassDescriptor()
    let commandBuffer = commandQueue.makeCommandBuffer()!
     
    // Render Pass - render sceneView
    renderer.scene = sceneView.scene
    renderer.pointOfView = sceneView.pointOfView
    renderer.render(atTime: 0,passDescriptor: renderPassDescriptor)
     
    // Blit Pass - copy depth texture to buffer
    let imageWidth = Int(textureSizeX)
    let imageHeight = Int(textureSizeY)
    let pixelCount = imageWidth * imageHeight
    let depthImageBuffer = device.makeBuffer(length: 4 * pixelCount,options: .storageModeShared)!
    let blitEncoder = commandBuffer.makeBlitCommandEncoder()!
    blitEncoder.copy(from: renderPassDescriptor.depthAttachment.texture!,             sourceSlice: 0,             sourceLevel: 0,             sourceOrigin: MTLOriginMake(0,0),             sourceSize: MTLSizeMake(imageWidth,imageHeight,1),             to: depthImageBuffer,             destinationOffset: 0,             destinationBytesPerRow: 4 * imageWidth,             destinationBytesPerImage: 4 * pixelCount,             options: .depthFromDepthStencil)

    blitEncoder.endEncoding()
     
     
    commandBuffer.commit()
    // Wait until depth buffer copying is done.
    commandBuffer.waitUntilCompleted()
  }
   
  func makeRenderPassDescriptor() -> MTLRenderPassDescriptor {
    let renderPassDescriptor = MTLRenderPassDescriptor()

    let frameBufferDescriptor = MTLTextureDescriptor.texture2DDescriptor(pixelFormat: .rgba8Unorm_srgb,width: textureSizeX,height: textureSizeY,mipmapped: false)
    frameBufferDescriptor.usage = [.renderTarget,.shaderRead]
    renderPassDescriptor.colorAttachments[0].texture = device.makeTexture(descriptor: frameBufferDescriptor)!
    renderPassDescriptor.colorAttachments[0].loadAction = .clear
    renderPassDescriptor.colorAttachments[0].storeAction = .store
    renderPassDescriptor.colorAttachments[0].clearColor = MTLClearColorMake(1,1,1.0)

    let depthBufferDescriptor: MTLTextureDescriptor = MTLTextureDescriptor.texture2DDescriptor(pixelFormat: .depth32Float,mipmapped: false)
    depthBufferDescriptor.usage = .renderTarget
    renderPassDescriptor.depthAttachment.texture = device.makeTexture(descriptor: depthBufferDescriptor)
    renderPassDescriptor.depthAttachment.loadAction = .clear
    renderPassDescriptor.depthAttachment.storeAction = .store
     
    return renderPassDescriptor
  }
   
  func session(_ session: ARSession,didFailWithError error: Error) {
    // Present an error message to the user
     
  }
   
  func session(_ session: ARSession,didUpdate frame: ARFrame) {

  }
   
  func sessionWasInterrupted(_ session: ARSession) {
    // Inform the user that the session has been interrupted,for example,by presenting an overlay
     
  }
   
  func sessionInterruptionEnded(_ session: ARSession) {
    // Reset tracking and/or remove existing anchors if consistent tracking is required
     
  }
}

解决方法

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