# \[5.8.3\] Instanced Stereo: Volume-domain materials are only voxelized into Volumetric Fog for the left eye (regression from 5.5) **URL:** \ **Category:** Issues and Bug Reporting (Unreal Engine)\ **Tags:** stereo-rendering, unreal-engine\ **Created:** [October 19, 2026, 5:02am UTC](https://forums.unrealengine.com/t/5-8-3-instanced-stereo-volume-domain-materials-are-only-voxelized-into-volumetric-fog-for-the-left-eye-regression-from-5-5/2842316 "2026-10-19T05:02:13Z")\ **Posts on this page:** 2\ **Page:** 1
**Author:** ![adjnor](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@adjnor](https://forums.unrealengine.com/u/adjnor)\ **Post date:** [October 19, 2026, 5:02am UTC](https://forums.unrealengine.com/t/5-8-3-instanced-stereo-volume-domain-materials-are-only-voxelized-into-volumetric-fog-for-the-left-eye-regression-from-5-5/2842316/1 "2026-10-19T05:02:13Z")
### Summary With Instanced Stereo enabled, primitives using a **Volume** material domain (meshes injected into Volumetric Fog, e.g. the Ultra Volumetrics marketplace pack) only appear in the **left eye**. The right eye shows the Exponential Height Fog’s own volumetric fog, but none of the volume-material primitives. The same project/content renders correctly in both eyes in **UE 5.5**. ### What Type of Bug are you experiencing? Rendering (Graphics / Niagara) ### Steps to Reproduce 1. New map. Add an **Exponential Height Fog** , enable **Volumetric Fog**. 2. Add a mesh (e.g. a cube) with a material whose **Material Domain = Volume** (any non-zero Extinction/Albedo), placed in front of the player start (inside the Volumetric Fog distance). - Confirmed with Ultra Volumetrics’ `BP_UltraVolumetrics` (its `Fog` cube uses a Volume-domain material). 3. Project Settings: Instanced Stereo ON. 4. Play in **VR Preview** (or package and run with `-emulatestereo`). ### Expected Result The volume-material fog is visible in both eyes (as in 5.5). ### Observed Result - The Exponential Height Fog’s volumetric fog renders in **both** eyes. - The **Volume-domain primitives render only in the left eye**. The right eye has no contribution from them. - Disabling volumetric fog (`r.VolumetricFog 0`) removes the effect from both eyes (so it is the voxelization input, not the fog composite). `r.Fog.SeparateComposition 0` and `r.MegaLights.Volume 0` make no difference. ### Affects Versions 5.8 ### Platform(s) OpenXR ### Upload an image ![FogTest_UE5.8_emulatestereo.png](https://d3kjluh73b9h9o.cloudfront.net/original/4X/3/2/f/32f5cb76feb9bb87bc6b0262e729e89321a3530b.png) ![FogTest_UE5.5_emulatestereo.png](https://d3kjluh73b9h9o.cloudfront.net/original/4X/7/2/3/723093d3e65bfb3d9107379c0f7a632ba8baf084.png) ### Additional Notes Screenshots (same project and map, Ultra Volumetrics fog volume, `-emulatestereo`, left half = left eye) - `FogTest_UE5.5_emulatestereo.png` - UE 5.5: fog in **both** eyes. On-screen stereo info: _“Stereo rendering method: Multi-viewport”_. - `FogTest_UE5.8_emulatestereo.png` - UE 5.8: fog in the **left eye only**. On-screen stereo info: _“Stereo rendering method: Instanced-Stereo”_ (the stereo path itself changed between versions). - Both builds use the SAME project config (`vr.InstancedStereo=True`). The label differs only because 5.8’s `SceneRendering.cpp` stats text prints “Instanced-Stereo” for single-pass stereo, while 5.5 printed the implementation (“Multi-viewport” = 5.5’s instanced stereo on D3D12). It reflects the bIsMultiViewportEnabled → bIsSinglePassStereo refactor, not a different setting. ## Root cause (from reading the 5.8 source) In 5.8 the secondary (right-eye) view no longer computes its own relevance under single-pass/instanced stereo: - `Engine/Source/Runtime/Renderer/Private/SceneVisibility.cpp`, `FVisibilityTaskData::LaunchVisibilityTasks` (~line 4477): secondary views are skipped (`if (bIsSinglePassStereo && StereoPass == eSSP_SECONDARY) continue;`). - Same file, ~line 2367-2400 (`if (View.bIsSinglePassStereo)` block, comment _“Secondary views should not calculate relevance”_): the primary view copies its results to `View.GetInstancedView()` - `PrimitiveVisibilityMap`, `PrimitiveViewRelevanceMap`, `StaticMeshVisibilityMap`, translucency / custom depth / Substrate flags, etc. **`VolumetricMeshBatches` is not copied** (neither are `HeterogeneousVolumesMeshBatches` and `SkyMeshBatches`), so the secondary view’s list stays empty. - `VolumetricFogVoxelization.cpp`, `VoxelizeFogVolumePrimitives` (~line 706) runs per view and early-outs on `View.VolumetricMeshBatches.Num() > 0`, with instanced stereo forced off for that pass (`bForceInstanceStereoOff = true`), so the right eye’s fog volume never receives the volume primitives. In **5.5** the secondary view still ran its own relevance (`SceneVisibility.cpp` ~line 3554-3561: the secondary relevance command pipe forwards to the primary AND calls `Relevance.Context->AddPrimitives(...)` for itself), so both views had their `VolumetricMeshBatches`. ### Suggested fix In the 5.8 `bIsSinglePassStereo` copy block, also give the instanced view the volume mesh lists, e.g. `SecondaryView->VolumetricMeshBatches = View.VolumetricMeshBatches;` (and likewise `HeterogeneousVolumesMeshBatches`, probably `SkyMeshBatches`), after relevance has been finalized for the primary view. (The dynamic-mesh path - `ComputeDynamicMeshRelevance` / `GatherDynamicMeshElements`, which marks secondary-visible dynamic primitives on the primary only - likely needs the same treatment.) ---
**Author:** ![adjnor](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@adjnor](https://forums.unrealengine.com/u/adjnor)\ **Post date:** [October 19, 2026, 7:32am UTC](https://forums.unrealengine.com/t/5-8-3-instanced-stereo-volume-domain-materials-are-only-voxelized-into-volumetric-fog-for-the-left-eye-regression-from-5-5/2842316/2 "2026-10-19T07:32:04Z")
Here is a plugin made by claude to fix this issue. [UE5.8\_StereoFogFix.zip](https://forums.unrealengine.com/uploads/short-url/qUTgYqohyBxPMSI12SfA6Vjcs9Y.zip) (3.7 KB)