Bug Unable to use Camera.SetStereoViewMatrix in instanced mode.

I've been trying to implement a VR mirror and I'm not exactly seeing a way to get it to work, because calling
SetStereoViewMatrix breaks rendering.

Basically, consider following script:

Code (csharp):

1.  
2. using UnityEngine;
3.  
4. public class StereoCamDebug: MonoBehaviour{
5.     Camera cam;
6.  
7.     void Awake(){
8.         cam = GetComponent<Camera>();
9.     }
10.  
11.     void LateUpdate(){
12.         if (cam.stereoEnabled){
13.             setupStereoMatrices();
14.         }
15.     }
16.  
17.     void setupStereoMatrices(){
18.         cam.ResetStereoProjectionMatrices();
19.         cam.ResetStereoViewMatrices();
20.  
21.         var leftView = cam.GetStereoViewMatrix(Camera.StereoscopicEye.Left);
22.         var rightView = cam.GetStereoViewMatrix(Camera.StereoscopicEye.Right);
23.  
24.         var leftProj = cam.GetStereoProjectionMatrix(Camera.StereoscopicEye.Left);
25.         var rightProj = cam.GetStereoProjectionMatrix(Camera.StereoscopicEye.Right);
26.  
27.         Debug.Log($"leftView: {leftView}; rightView: {rightView}");
28.         Debug.Log($"leftProj: {leftProj}; rightProj: {rightProj}");
29.  
30.         //cam.SetStereoViewMatrix(Camera.StereoscopicEye.Left, leftView);
31.         //cam.SetStereoViewMatrix(Camera.StereoscopicEye.Right, rightView);
32.     }
33. }
34.  
35.  

The moment I uncomment "cam.SetStereoViewMatrix", I get this:

Spoiler

Or

Spoiler

Code (csharp):

1.  
2. leftView: -1.00000    0.00000    0.00000    0.03504
3. 0.00000    1.00000    0.00001    -0.00001
4. 0.00000    -0.00001    1.00000    -3.54000
5. 0.00000    0.00000    0.00000    1.00000
6. ; rightView: -1.00000    0.00000    0.00000    -0.03504
7. 0.00000    1.00000    0.00001    -0.00001
8. 0.00000    -0.00001    1.00000    -3.54000
9. 0.00000    0.00000    0.00000    1.00000
10.  
11. UnityEngine.Debug:Log (object)
12. StereoCamDebug:setupStereoMatrices () (at Assets/Scripts/StereoCamDebug.cs:26)
13. StereoCamDebug:LateUpdate () (at Assets/Scripts/StereoCamDebug.cs:12)
14.  
15. leftProj: 0.78129    0.00000    0.00000    0.00000
16. 0.00000    0.75355    0.00000    0.00000
17. 0.00000    0.00000    -1.00006    -0.06000
18. 0.00000    0.00000    -1.00000    0.00000
19. ; rightProj: 0.78129    0.00000    0.00000    0.00000
20. 0.00000    0.75355    0.00000    0.00000
21. 0.00000    0.00000    -1.00006    -0.06000
22. 0.00000    0.00000    -1.00000    0.00000
23.  
24. UnityEngine.Debug:Log (object)
25. StereoCamDebug:setupStereoMatrices () (at Assets/Scripts/StereoCamDebug.cs:27)
26. StereoCamDebug:LateUpdate () (at Assets/Scripts/StereoCamDebug.cs:12)
27.  
28. Can't calculate the eye texture aspect ratio. Culling/Shadows are likely to break.
29. UnityEngine.GUIUtility:processEvent (int,intptr,bool&)
30.  
31. Screen position out of view frustum (screen pos 0.000000, 0.000000, 1000.000000) (Camera rect 0 0 0 0)
32. UnityEngine.GUIUtility:processEvent (int,intptr,bool&)
33.  
34. Screen position out of view frustum (screen pos 0.000000, 0.000000, 1000.000000) (Camera rect 0 0 0 0)
35. UnityEngine.GUIUtility:processEvent (int,intptr,bool&)
36.  
37. Assertion failed on expression: 'std::abs(det) > FLT_MIN'
38. UnityEngine.GUIUtility:processEvent (int,intptr,bool&)
39.  
40. Assertion failed on expression: 'std::abs(det) > FLT_MIN'
41. UnityEngine.GUIUtility:processEvent (int,intptr,bool&)
42.  
43. Assertion failed on expression: 'std::abs(det) > FLT_MIN'
44. UnityEngine.GUIUtility:processEvent (int,intptr,bool&)
45.  
46. Assertion failed on expression: 'std::abs(det) > FLT_MIN'
47. UnityEngine.GUIUtility:processEvent (int,intptr,bool&)
48.  
49. Assertion failed on expression: 'std::abs(det) > FLT_MIN'
50. UnityEngine.GUIUtility:processEvent (int,intptr,bool&)
51.  
52. Assertion failed on expression: 'std::abs(det) > FLT_MIN'
53. UnityEngine.GUIUtility:processEvent (int,intptr,bool&)
54.  
55. Assertion failed on expression: 'std::abs(det) > FLT_MIN'
56. UnityEngine.GUIUtility:processEvent (int,intptr,bool&)
57.  
58. Assertion failed on expression: 'std::abs(det) > FLT_MIN'
59. UnityEngine.GUIUtility:processEvent (int,intptr,bool&)
60.  
61. Screen position out of view frustum (screen pos 0.000000, 0.000000, 1000.000000) (Camera rect 0 0 0 0)
62. UnityEngine.GUIUtility:processEvent (int,intptr,bool&)
63.  

Meaning I can't set any matrices, so that effectively kills my attempt to setup mirror camera.

This is on unity 2021.2.5f1 .

How can I deal with this? I'd expect matrices to be compatible since they're taken from the camera itself.

By the way, the unity example from here also doens't function:
https://docs.unity3d.com/ScriptReference/Camera.SetStereoViewMatrix.html

So, how can I deal with this? @bgolus , @mabulous , maybe one of you would know?

There's also this thread:
https://forum.unity.com/threads/some-weird-issues-w-setstereoviewmatrix.754664/

But with no solution.

 

I've received no advice regarding this issue, and I've found no way to work around it. I'm marking this as a bug.