Stereo portal or mirror support with single pass rendering

I want to create a stereo portal system or a stereo mirror system with single pass rendering for performances.
However, I have some troubles stated below:

• XR camera won't directly render images to stereo render texture created by XRSettings.eyeTextureDesc.
• XR camera overwrite the position and the rotation by trackings, so It's hard to set the Camera to the mirror position.
• In Stereo Pass mode, it's unable to set custom eye projection matrices to XR Camera, so creating mirror texture needs one more pass to flip it.
• It's not easy to get correct eye separation by devices.
• and so on...

I have some workaround without single pass rendering but I think they aren't effective implements in XR.
I hope that freature supports to solve the problems are provided by Unity.

 

Now, I implement them like below:

• Set camera position by using SetStereoViewMatrix.

I use SetStereoViewMatrix to disable camera's overwrites by tracking.
However, in this case, I need to calculate correct eye separation in consideration of device settings updates.

• Get render results by command buffer.

Code (CSharp):

1. renderTexture = new RenderTexture(XRSettings.eyeTextureDesc);
2.  
3. CommandBuffer commandBuffer = new CommandBuffer();
4. // effectMaterial is to flip render texture.
5. commandBuffer.Blit(BuiltinRenderTextureType.CameraTarget, renderTargetId, effectMaterial);
6. camera.AddCommandBuffer(CameraEvent.AfterEverything, commandBuffer);

This implement doesn't prevent the camera from rendering to Screen. so it has a overhead.

• Exchange left and right textures by shader for mirroring.

unity_StereoEyeIndex = 1 - i.stereoTargetEyeIndex

Exchanging textures would have some trouble. For instance, results of left texture and right texture aren't aligned in Y axis.
When setting the same view matrix to left and right, you can see this.