Summary
On UE 5.8, enabling “Extended GBuffer” (Project Settings → Engine → Rendering → Mobile) completely disables the Subsurface Profile shading model’s SSS effect on Mobile Deferred Shading. Disabling this option immediately restores correct SSS rendering.
Engine Version:
5.8 (release)
Platform:
Mobile: Android, Vulkan (Deferred Shading)
Desktop: Windows, PC preview (SM6) — used as comparison baseline, unaffected
Steps to Reproduce:
- Create a new UE 5.8 project, set Mobile Shading = Deferred Shading.
- In Project Settings → Engine → Rendering → Mobile, enable “Extended GBuffer”.
- Create a Material with Shading Model = Subsurface Profile, Opacity = 1, BaseColor = skin tone constant, assign a new Subsurface Profile asset.
- Apply to a Sphere with a Directional Light + Sky Light.
- View in Mobile Preview (Android Vulkan) — observe no SSS effect.
- Disable “Extended GBuffer”, reload, view the same sphere again — SSS effect is restored.
Expected Result:
Subsurface Profile SSS should render correctly on Mobile Deferred Shading regardless of the “Extended GBuffer” setting.
Observed Result:
With Extended GBuffer = True, the SSS effect is completely absent on Mobile (surface looks flat/opaque, indistinguishable from Default Lit). “stat gpu” shows the “SubsurfaceScattering” pass registered but with no timing data (not executed), and “viewmode ShadingModel” renders the material as black (no shading model written to GBuffer).
With Extended GBuffer = False, SSS renders correctly and matches Desktop behavior. SSAO, SSR, and TAA all continue to work normally with Extended GBuffer disabled.
This strongly suggests the Subsurface Profile shading model’s GBuffer data (ShadingModelID and/or related SSS data) is not being correctly written or read when the Extended GBuffer layout is active in 5.8’s Mobile Deferred path.
Additional Notes:
This is a clean, 100% reproducible regression isolated to a single project setting. Confirmed unrelated to Substrate (reproduces with Substrate on/off), TSR (using TAA only), and r.AllowStaticLighting (already False). Happy to provide a minimal repro project if needed.
What Type of Bug are you experiencing?
Rendering (Graphics / Niagara)
Steps to Reproduce
- Create a new UE 5.8 project, set Mobile Shading = Deferred Shading.
- In Project Settings → Engine → Rendering → Mobile, enable “Extended GBuffer”.
- Create a Material with Shading Model = Subsurface Profile, Opacity = 1, BaseColor = skin tone constant, assign a new Subsurface Profile asset.
- Apply the material to a Sphere in a new level, lit with a Directional Light + Sky Light.
- View the sphere in Mobile Preview (Android Vulkan) — observe no SSS effect (flat/opaque, indistinguishable from Default Lit).
- Disable “Extended GBuffer”, reload the project, and view the same sphere again — SSS effect is restored correctly.
Expected Result
Subsurface Profile SSS should render correctly on Mobile Deferred Shading regardless of whether “Extended GBuffer” is enabled or disabled, consistent with its behavior on Desktop.
Observed Result
With Extended GBuffer = True, the SSS effect is completely absent on Mobile — the surface appears flat/opaque, indistinguishable from Default Lit. “stat gpu” shows the “SubsurfaceScattering” pass registered in the Graphics Queue but with no Avg/Max/Min timing data (not executed), and “viewmode ShadingModel” renders the material as completely black (no shading model classification written to GBuffer).
With Extended GBuffer = False, SSS renders correctly and matches Desktop behavior. SSAO, SSR, and TAA all continue to work normally with Extended GBuffer disabled, so this appears isolated to the Subsurface Profile shading model’s GBuffer data specifically.
This is a clean, 100% reproducible regression confirmed unrelated to Substrate (reproduces with Substrate on/off), TSR (using TAA only), and r.AllowStaticLighting (already False).
Affects Versions
5.8
Platform(s)
Android
iOS