Bug in VR Since 5.6 (and 5.7 preview) with Instanced Stereo + Baked Reflection Capture + Deferred Rendering + Post Process Volume

Development Rendering
1

Since version 5.6, I’m experiencing a VR bug whenever these features are enabled at the same time (and unfortunately, I need all of them):

  • Instanced Stereo

  • Baked Reflection Capture

  • Deferred Rendering

  • Post Process Volume

I’ve submitted a bug report twice, but it still hasn’t appeared in the issue tracker.

I need Instanced Stereo for performance reasons, but also because Niagara Fluids shows other bugs in the left eye when Instanced Stereo is disabled.

Is anyone else experiencing the same problem? Does anyone have an idea for a possible fix or workaround to prevent this?

Capture d'écran 2025-08-07 105029
Capture d'écran 2025-08-07 1050291265×633 38.4 KB

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2

Am I the only one experiencing this bug?

I noticed it right after reopening my project in 5.6, and it’s still there in 5.7. It feels like a major regression, and it’s keeping me stuck on 5.5.

3

We’re experiencing the same issue, except we are using forward rendering

4

Try turning off r.forward.lightgridhzbcull, it corrupts the lightgrid in vr and that looks like what your issue is but I can’t remember if I only saw with instanced stereo or also without it. It says r.forward but applies to deferred too, I think light frustum style grid was just originally created for desktop forward but it’s used on deferred for a while.

Side effect is turning it off will make volumetric fog more expensive (will draw occluded lights into the fog).

I think it’s fixed on the 5.7 branch in git but not in the preview. (sorry misremembered this)

5

It seem to work !! Great :grinning_face:

I will make more test but many thanks :+1:

UPDATE : it works in my test scene for reporting the bug, but not in my project.
Seem it’s another rendering issue wich occur only to reflection. When I disable my reflection capture sphere/box i have the rendering in left and right eyes.

6

@Asterion_VR1

Did you hear back from Epic about this?
Does it still occur in 5.7 release?

7

It’s most likely a general issue with all features that depend on HZB in VR. 5.6 broke something about the HZB in VR, so a lot of features have issues since then (culling, reflection captures, and other features as well). The easiest way to reproduce is this:

  1. Create a VR template project

  2. Launch VR preview and enable “r.HZBOcclusion 1”

  3. Move your hand in front of the left eye and see objects incorrectly become invisible on the right eye (the right eye incorrectly uses HZB occlusion info from the left eye). If you test the same in 5.5 or even all the way back to 4.27, you won’t see an issue.

Unfortunately it was not fixed in 5.7 yet, 5.7 seems to be identical like 5.6 regarding this regression.

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