iOS平台WebRTC视频通话集成AR功能及AR会话中使用WebRTC摄像头技术咨询

Great question! Combining WebRTC video calls with ARKit to share interactive AR content (like drawn lines) involves two key tasks: streaming your AR session feed over WebRTC and syncing AR content between peers so remote users see the same lines anchored to the real world. Here's a step-by-step breakdown:

1. Use ARSession as the Video Source for WebRTC #

Note: ARKit requires direct control of the camera to handle world tracking and scene analysis. You can't use WebRTC's default camera capture as input for your ARSession. Instead, we feed ARKit's processed frames (including your AR overlays) into WebRTC to share the AR experience remotely.

Step 1: Set Up Your ARSession & WebRTC #

First, configure a standard ARKit session with world tracking and set up a custom WebRTC video source:

import ARKit
import WebRTC

class ARWebRTCDemoViewController: UIViewController, ARSessionDelegate {
    var arscnView: ARSCNView!
    var webRTCPeerConnection: RTCPeerConnection!
    var customVideoSource: RTCVideoSource!
    var dataChannel: RTCDataChannel?
    
    override func viewDidLoad() {
        super.viewDidLoad()
        // Initialize ARSCNView
        arscnView = ARSCNView(frame: view.bounds)
        view.addSubview(arscnView)
        
        // Configure ARSession for world tracking
        let arConfig = ARWorldTrackingConfiguration()
        arConfig.planeDetection = .horizontal
        arscnView.session.delegate = self
        arscnView.session.run(arConfig)
        
        // Set up WebRTC custom video source
        let factory = RTCPeerConnectionFactory()
        customVideoSource = factory.videoSource()
        let videoTrack = factory.videoTrack(with: customVideoSource, trackId: "AR-video-track")
        webRTCPeerConnection.add(videoTrack)
        
        // Initialize data channel for AR content sync
        setupDataChannel()
    }
}

Step 2: Feed AR Frames to WebRTC #

Capture the ARSession's rendered frames (including your AR overlays) and send them to WebRTC. For better performance, use the ARSession delegate to get pixel buffers directly, or snapshot the ARSCNView:

func session(_ session: ARSession, didUpdateFrame frame: ARFrame) {
    // Option: Use ARSCNView snapshot to include AR overlays like lines
    guard let image = arscnView.snapshot() else { return }
    guard let pixelBuffer = image.convertToCVPixelBuffer() else { return }
    
    // Send the pixel buffer to WebRTC
    customVideoSource.capture(pixelBuffer, timestamp: frame.timestamp)
}

// Helper extension to convert UIImage to CVPixelBuffer
extension UIImage {
    func convertToCVPixelBuffer() -> CVPixelBuffer? {
        let attributes = [
            kCVPixelBufferCGImageCompatibilityKey: kCFBooleanTrue,
            kCVPixelBufferCGBitmapContextCompatibilityKey: kCFBooleanTrue
        ] as CFDictionary
        
        var pixelBuffer: CVPixelBuffer?
        let status = CVPixelBufferCreate(kCFAllocatorDefault,
                                         Int(size.width),
                                         Int(size.height),
                                         kCVPixelFormatType_32BGRA,
                                         attributes,
                                         &pixelBuffer)
        
        guard status == kCVReturnSuccess, let buffer = pixelBuffer else { return nil }
        
        CVPixelBufferLockBaseAddress(buffer, [])
        let context = CGContext(data: CVPixelBufferGetBaseAddress(buffer),
                                width: Int(size.width),
                                height: Int(size.height),
                                bitsPerComponent: 8,
                                bytesPerRow: CVPixelBufferGetBytesPerRow(buffer),
                                space: CGColorSpaceCreateDeviceRGB(),
                                bitmapInfo: CGImageAlphaInfo.premultipliedFirst.rawValue)
        
        context?.draw(cgImage!, in: CGRect(x: 0, y: 0, width: size.width, height: size.height))
        CVPixelBufferUnlockBaseAddress(buffer, [])
        
        return buffer
    }
}

2. Sync AR Drawings Between Local and Remote Users #

Streaming the AR video feed will show the line to remote users, but if they move their device, the line won't stay anchored to the real world. To fix this, share the 3D world coordinates of your drawings via WebRTC's data channels, so remote users can render the same line in their own AR session.

Step 1: Set Up WebRTC Data Channel #

Create a data channel to send AR content data reliably:

func setupDataChannel() {
    let config = RTCDataChannelConfiguration()
    config.isOrdered = true // Ensure data arrives in sequence
    guard let channel = webRTCPeerConnection.createDataChannel(withLabel: "AR-data", configuration: config) else { return }
    channel.delegate = self
    dataChannel = channel
}

Step 2: Send Local Drawing Data to Remote #

When the local user draws a line (e.g., via touch), convert the screen touch to world coordinates, create the line in your AR scene, and send the coordinates to the remote peer:

override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent?) {
    guard let touch = touches.first else { return }
    let touchLocation = touch.location(in: arscnView)
    
    // Convert touch to world space using ARKit hit test
    let hitResults = arscnView.hitTest(touchLocation, types: .existingPlaneUsingExtent)
    guard let hitResult = hitResults.first else { return }
    
    // Example: Draw a line from a fixed start point to the touch location
    let startWorldPos = SCNVector3(0, 0, -1) // Adjust based on your use case
    let endWorldPos = SCNVector3(hitResult.worldTransform.columns.3.x,
                                 hitResult.worldTransform.columns.3.y,
                                 hitResult.worldTransform.columns.3.z)
    
    // Add line to local AR scene
    addLineToARScene(from: startWorldPos, to: endWorldPos)
    
    // Serialize line data to send over WebRTC
    let lineData: [String: Float] = [
        "startX": startWorldPos.x, "startY": startWorldPos.y, "startZ": startWorldPos.z,
        "endX": endWorldPos.x, "endY": endWorldPos.y, "endZ": endWorldPos.z
    ]
    
    do {
        let jsonData = try JSONSerialization.data(withJSONObject: lineData)
        dataChannel?.sendData(jsonData)
    } catch {
        print("Failed to serialize line data: \(error)")
    }
}

func addLineToARScene(from start: SCNVector3, to end: SCNVector3) {
    let lineGeometry = SCNGeometry.line(from: start, to: end)
    let lineNode = SCNNode(geometry: lineGeometry)
    lineNode.geometry?.firstMaterial?.diffuse.contents = UIColor.red
    arscnView.scene.rootNode.addChildNode(lineNode)
}

// Helper extension to create a line geometry
extension SCNGeometry {
    static func line(from start: SCNVector3, to end: SCNVector3) -> SCNGeometry {
        let indices: [Int32] = [0, 1]
        let source = SCNGeometrySource(vertices: [start, end])
        let element = SCNGeometryElement(indices: indices, primitiveType: .line)
        return SCNGeometry(sources: [source], elements: [element])
    }
}

Step 3: Receive and Render Remote Drawings #

On the remote side, listen for incoming data from the WebRTC data channel, deserialize the coordinates, and add the line to your AR scene:

extension ARWebRTCDemoViewController: RTCDataChannelDelegate {
    func dataChannel(_ dataChannel: RTCDataChannel, didReceiveMessageWith buffer: RTCDataBuffer) {
        DispatchQueue.main.async { [weak self] in
            guard let self = self else { return }
            do {
                guard let lineData = try JSONSerialization.jsonObject(with: buffer.data, options: []) as? [String: Float] else { return }
                
                let start = SCNVector3(
                    x: lineData["startX"]!,
                    y: lineData["startY"]!,
                    z: lineData["startZ"]!
                )
                
                let end = SCNVector3(
                    x: lineData["endX"]!,
                    y: lineData["endY"]!,
                    z: lineData["endZ"]!
                )
                
                self.addLineToARScene(from: start, to: end)
            } catch {
                print("Failed to deserialize line data: \(error)")
            }
        }
    }
}

3. Critical: Align World Coordinates Between Peers #

By default, each ARSession has its own coordinate system. To ensure the remote user sees the line in the correct real-world position, sync the AR world map between peers:

• Local: Periodically capture the ARWorldMap, serialize it, and send it via WebRTC:

  func sendWorldMap() {
      arscnView.session.getCurrentWorldMap { [weak self] map, error in
          guard let self = self, let map = map else { return }
          do {
              let mapData = try NSKeyedArchiver.archivedData(withRootObject: map, requiringSecureCoding: true)
              self.dataChannel?.sendData(mapData)
          } catch {
              print("Failed to serialize world map: \(error)")
          }
      }
  }
  

• Remote: Deserialize the ARWorldMap and update your ARSession:

  func applyReceivedWorldMap(_ mapData: Data) {
      do {
          let worldMap = try NSKeyedUnarchiver.unarchivedObject(ofClass: ARWorldMap.self, from: mapData)
          let config = ARWorldTrackingConfiguration()
          config.initialWorldMap = worldMap
          arscnView.session.run(config, options: .resetTrackingAndRemoveExistingAnchors)
      } catch {
          print("Failed to apply world map: \(error)")
      }
  }
  

Key Tips #

• Performance: Using ARSCNView.snapshot() can be slow for high frame rates. For better performance, use Metal to render the AR scene directly into a texture and convert it to a CVPixelBuffer.
• Bandwidth: Compress the ARWorldMap before sending it (e.g., using NSKeyedArchiver with compression).
• Error Handling: Add retries for data channel messages and handle cases where the world map fails to sync.

内容的提问来源于stack exchange，提问作者user2499809