在ARKit面部追踪和后置摄像头之间进行Unity切换？

Question

I am making an application in Unity for iOS using ARKit. I would like to have a calibration scene first, which uses the ARKit face tracking tools to measure the distance from the phone to the face. This information is fed to the next scene which then uses the rear camera for an AR game.

I have successfully created both scenes separately, and added a GUI button which should switch them in a phone app. However, when I built the app to test it, pressing the button causes the app to crash.

Does anyone know whether this type of camera switching on iOS is even supported? If so, any suggestions on how to make it work? Do I need to change any configurations in the scenes?

Thank a lot!

EDIT: I think the problem is that the ARSession object (which has a different configuration for face tracking and back-camera AR) is not destroyed when the scene is changed. I'm not sure how to wrangle Unity into destroying this session and starting a new one.

STACK TRACE (last part)]

enter code here
=================================================================
Main Thread Checker: UI API called on a background thread: -[UIWindow rootViewController]
PID: 433, TID: 61976, Thread name: UnityGfxDeviceWorker, Queue name: com.apple.root.default-qos.overcommit, QoS: 21
Backtrace:
4   FaceRCalibration                    0x00000001080ed07c _ZN7Vuforia4initEv + 356020
5   FaceRCalibration                    0x00000001080ed49c _ZN7Vuforia4initEv + 357076
6   FaceRCalibration                    0x0000000108239de0 _ZN7Vuforia4initEv + 1719320
7   FaceRCalibration                    0x0000000108222c34 _ZN7Vuforia4initEv + 1624684
8   FaceRCalibration                    0x000000010804f9d0 onSurfaceCreated + 32
9   FaceRCalibration                    0x000000010784221c _ZN9GfxDevice26InsertCustomMarkerCallbackEPFviEi + 48
10  FaceRCalibration                    0x0000000107c4252c _ZN15GfxDeviceWorker10RunCommandER20ThreadedStreamBuffer + 11056
11  FaceRCalibration                    0x00000001073591c8 GfxDeviceWorkerAutoreleasePoolProxy + 68
12  FaceRCalibration                    0x0000000107c47fe0 _ZN15GfxDeviceWorker6RunExtER20ThreadedStreamBuffer + 84
13  FaceRCalibration                    0x0000000107c47f80 _ZN15GfxDeviceWorker3RunEv + 140
14  FaceRCalibration                    0x0000000107c3f86c _ZN15GfxDeviceWorker18RunGfxDeviceWorkerEPv + 12
15  FaceRCalibration                    0x0000000107707e5c _ZN6Thread16RunThreadWrapperEPv + 64
16  libsystem_pthread.dylib             0x0000000182d85220 <redacted> + 272
17  libsystem_pthread.dylib             0x0000000182d85110 <redacted> + 0
18  libsystem_pthread.dylib             0x0000000182d83b10 thread_start + 4
2018-08-13 15:02:44.496950+0100 FaceRCalibration[433:61976] [reports] Main Thread Checker: UI API called on a background thread: -[UIWindow rootViewController]
PID: 433, TID: 61976, Thread name: UnityGfxDeviceWorker, Queue name: com.apple.root.default-qos.overcommit, QoS: 21
Backtrace:
4   FaceRCalibration                    0x00000001080ed07c _ZN7Vuforia4initEv + 356020
5   FaceRCalibration                    0x00000001080ed49c _ZN7Vuforia4initEv + 357076
6   FaceRCalibration                    0x0000000108239de0 _ZN7Vuforia4initEv + 1719320
7   FaceRCalibration                    0x0000000108222c34 _ZN7Vuforia4initEv + 1624684
8   FaceRCalibration                    0x000000010804f9d0 onSurfaceCreated + 32
9   FaceRCalibration                    0x000000010784221c _ZN9GfxDevice26InsertCustomMarkerCallbackEPFviEi + 48
10  FaceRCalibration                    0x0000000107c4252c _ZN15GfxDeviceWorker10RunCommandER20ThreadedStreamBuffer + 11056
11  FaceRCalibration                    0x00000001073591c8 GfxDeviceWorkerAutoreleasePoolProxy + 68
12  FaceRCalibration                    0x0000000107c47fe0 _ZN15GfxDeviceWorker6RunExtER20ThreadedStreamBuffer + 84
13  FaceRCalibration                    0x0000000107c47f80 _ZN15GfxDeviceWorker3RunEv + 140
14  FaceRCalibration                    0x0000000107c3f86c _ZN15GfxDeviceWorker18RunGfxDeviceWorkerEPv + 12
15  FaceRCalibration                    0x0000000107707e5c _ZN6Thread16RunThreadWrapperEPv + 64
16  libsystem_pthread.dylib             0x0000000182d85220 <redacted> + 272
17  libsystem_pthread.dylib             0x0000000182d85110 <redacted> + 0
18  libsystem_pthread.dylib             0x0000000182d83b10 thread_start + 4
2018-08-13 15:02:44.632260+0100 FaceRCalibration[433:61976] DEBUG/AR(433) UIView has CAMetalLayer layer class
2018-08-13 15:02:44.632402+0100 FaceRCalibration[433:61976] DEBUG/AR(433) UIView does not respond to selector renderFrameVuforia
2018-08-13 15:02:44.632479+0100 FaceRCalibration[433:61976] DEBUG/AR(433) Could not find a UIView with CAEAGLLayer or CAMetalLayer layer class that responds to selector renderFrameVuforia
2018-08-13 15:02:44.864480+0100 FaceRCalibration[433:61734] [Common] _BSMachError: port da03; (os/kern) invalid capability (0x14) "Unable to insert COPY_SEND"
2018-08-13 15:02:44.887877+0100 FaceRCalibration[433:61734] [Common] _BSMachError: port da03; (os/kern) invalid capability (0x14) "Unable to insert COPY_SEND"
-> applicationWillResignActive()
ar_session_interrupted
UnityEngine.DebugLogHandler:Internal_Log(LogType, String, Object)
UnityEngine.DebugLogHandler:LogFormat(LogType, Object, String, Object[])
UnityEngine.Logger:Log(LogType, Object)
UnityEngine.Debug:Log(Object)
UnityEngine.XR.iOS.UnityARSessionNativeInterface:_ar_session_interrupted()

(Filename: /Users/builduser/buildslave/unity/build/Runtime/Export/Debug.bindings.h Line: 43)

-> applicationDidEnterBackground()
2018-08-13 15:03:00.267669+0100 FaceRCalibration[433:62230] TIC Read Status [6:0x0]: 1:57
2018-08-13 15:03:00.267723+0100 FaceRCalibration[433:62230] TIC Read Status [6:0x0]: 1:57
2018-08-13 15:03:04.129255+0100 FaceRCalibration[433:62583] dnssd_clientstub read_all(33) DEFUNCT
-> applicationWillEnterForeground()
-> applicationDidBecomeActive()
ar_session_interruption_ended
UnityEngine.DebugLogHandler:Internal_Log(LogType, String, Object)
UnityEngine.DebugLogHandler:LogFormat(LogType, Object, String, Object[])
UnityEngine.Logger:Log(LogType, Object)
UnityEngine.Debug:Log(Object)
UnityEngine.XR.iOS.UnityARSessionNativeInterface:_ar_session_interruption_ended()

(Filename: /Users/builduser/buildslave/unity/build/Runtime/Export/Debug.bindings.h Line: 43)

Unloading 6 Unused Serialized files (Serialized files now loaded: 0)
UnloadTime: 4.989750 ms
System memory in use before: 26.3 MB.
System memory in use after: 26.4 MB.

Unloading 9 unused Assets to reduce memory usage. Loaded Objects now: 2123.
Total: 3.255875 ms (FindLiveObjects: 0.764083 ms CreateObjectMapping: 0.056708 ms MarkObjects: 2.368958 ms  DeleteObjects: 0.065208 ms)

Setting up 1 worker threads for Enlighten.
  Thread -> id: 16c77f000 -> priority: 1 
libc++abi.dylib: terminating with uncaught exception of type Il2CppExceptionWrapper
(lldb) 

Answer 1

I have managed to fix this problem. You have to check null for anchorPrefab in 3 functions: FaceAdded, FaceUpdated, FaceRemoved and on the OnDestroy function, just release the event delegation from beginning and hide the anchorPrefab too. Full source code is below.

[SerializeField]
private GameObject anchorPrefab;

private UnityARSessionNativeInterface m_session;

// Use this for initialization
void Start()
{
    m_session = new UnityARSessionNativeInterface();

    Application.targetFrameRate = 60;
    ARKitFaceTrackingConfiguration config = new ARKitFaceTrackingConfiguration();
    config.alignment = UnityARAlignment.UnityARAlignmentGravity;
    config.enableLightEstimation = true;

    if (config.IsSupported)
    {

        m_session.RunWithConfig(config);

        UnityARSessionNativeInterface.ARFaceAnchorAddedEvent += FaceAdded;
        UnityARSessionNativeInterface.ARFaceAnchorUpdatedEvent += FaceUpdated;
        UnityARSessionNativeInterface.ARFaceAnchorRemovedEvent += FaceRemoved;

    }

}

void FaceAdded(ARFaceAnchor anchorData)
{
    if (anchorPrefab != null)
    {
        anchorPrefab.transform.position = UnityARMatrixOps.GetPosition(anchorData.transform);
        anchorPrefab.transform.rotation = UnityARMatrixOps.GetRotation(anchorData.transform);
        anchorPrefab.SetActive(true);
    }
}

void FaceUpdated(ARFaceAnchor anchorData)
{
    if (anchorPrefab != null)
    {
        anchorPrefab.transform.position = UnityARMatrixOps.GetPosition(anchorData.transform);
        anchorPrefab.transform.rotation = UnityARMatrixOps.GetRotation(anchorData.transform);
    }
}

void FaceRemoved(ARFaceAnchor anchorData)
{
    if (anchorPrefab != null)
    {
        anchorPrefab.SetActive(false);
    }
}



// Update is called once per frame
void Update()
{

}

void OnDestroy()
{
    if (anchorPrefab != null)
    {
        anchorPrefab.SetActive(false);
    }
    UnityARSessionNativeInterface.ARFaceAnchorAddedEvent -= FaceAdded;
    UnityARSessionNativeInterface.ARFaceAnchorUpdatedEvent -= FaceUpdated;
    UnityARSessionNativeInterface.ARFaceAnchorRemovedEvent -= FaceRemoved;
}