Underlay passthrough is not function.

Pass-through Layer and Overlay pass-through is working and I can see my room. However, when I changed the Ovarlay to Underlay, the pass-through no longer works and I can only see the black environment.
Do you know why the Underlay passthrough does not work?
My environment is Meta quest pro and UE4.72 (Oculus-VR-v49), windows 11. I tried the pass-through template and it works for Overlay but not for Underlay pass-through.

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I just bumped into the exact same issue while playing around with the meta quest 3 and UE 5.2 and finally found a solution! Maybe it helps someone:

When the layer placement inside the OculusXRPassthroughLayer was set to Overlay, passthrough was working perfectly, but I didn’t see any 3d objects. When I set it to Underlay, I could see my 3d objects, but the passthrough was gone entirely. Setting it to overlay and reducing the alpha, I was able to see both, semi transparent passthrough and 3d objects. Still not what we want…

Now, all this was with an unreal project that I created from scratch, using the settings recommended here:
https://developer.oculus.com/documentation/unreal/unreal-passthrough-overview-gs/
Testing was done with a packaged project, installed on the quest 3, not with in-editor testing.

I could however get fully opaque passthrough and 3d objects working, when I used the vr template by epic. So in the end, I compared the rendering settings one by one between the projects and what actually did the trick for me was changing the Mobile Antialiasing Method from “None” to "Multisample Anti-Aliasing (MSAA) in the new project. With that, “Underlay” works as expected.