Background Blur Crash with 5.7 and Instanced Stereo

Development Platform & Builds XR Development
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1

Hi,

This is a 100% reproducible crash with the following steps in Unreal 5.7.1:

  1. Create a new project (even an empty template)
  2. Enable Instanced Stereo
  3. Create a User Widget
  4. Add a Background Blur
  5. Set the Blur intensity greater than zero (e.g. to 10)

You will get a crash
Fatal error: [File:D:\build++UE5\Sync\Engine\Source\Runtime\RHI\Private\PipelineStateCache.cpp] [Line: 584]
Shader compilation failures are Fatal.

Since we are developing a game that can run both with and without VR, we would need background blur when the game is launched not in VR.

(Our project comes from 5.4, which doesn’t have this problem. didn’t test it in 5.5 or 5.6)

Also, not sure, but could it be related to these? (however, in the blank project I didn’t touch any Virtual Textures and/or PCG)

Is there any plan to fix this?

2

Hello!
I ran into this as well: Kawase Dual filter post by ROJO (@ayoROJO) / X

This is due to the DualKawaseFilter for slate blur added in 5.7.
The implementor was a contractor and can’t fix it, but says he could report the issue.

Try setting UI.SlatePostBlurUseDualKawaseFilter=0 to disable this new shader and it should fix your crash.

3

Hi Ronald, thank you so much for this solution. I just tested it, and the problem seems solved on my side. I really appreciate the help!

Also, using UI.SlatePostBlurUseDualKawaseFilter=0 didn’t introduce any visual side effects for me. I hope ROJO can find the solution as well.