UE 5.7.3 - Vulkan Parallel Rendering is broken on AMD gpus

Development Rendering
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1

Hey,

Parallel rendering seems to be broken for Amd gpus on Vulkan, when you change to Unlit and look at a translucent material like glass or at some niagara particles you get weird artifacts and sometimes it can crash.

Tested on:
rx 9060 xt, 9070 xt and rtx 5080.
Windows 11

Also tested on new projects. Everything used to work perfectly on UE 5.5.4.

image
image1170×818 115 KB

Fixed most issues with r.ParallelTranslucency=0, r.ParallelVelocity=0 and r.ParallelShadows=0

2

We are seeing the same issue on AMD in 5.7.3 having just upgraded from 5.4.4. Some specifics:

  • Lit view in packaged build
  • Only r.ParallelShadows=0 is required to fix it
  • Appears to be related to using cascaded shadow maps. The viewport or scissor region that is set to render the shadow map seems to be carried into later passes. I know this because the size of the corruption on screen changes when I change our CSM resolution by changing shadow quality setting in our pause menu.
  • Probably not relevant but we’re only using a single CSM cascade (due to mostly top down camera.)
  • Looks to me like it’s the deferred lighting pass that is broken as we get a lit area the size of the shadow map with everything outside it unlit.
3

Parallel shadows on our case didnt do much, it fixed some unlit bugs but no major issues nor crashes, biggest issue we had was glass (fixed with r.ParallelTranslucency=0) and some niagara particles that were causing most of the crashes (fixed with r.ParallelVelocity=0).

We are using Vulkan because dx12 and dx11 grooms using physics simulation are completely broken on AMD, a thing that has already been reported and the Grooms team confirmed they will be fixing it on another post. But UE 5.7 has been completely unstable for AMD on a lot of features.

A lot of Vulkan crashes are not happening on the new AMD drivers for some reason we dont know.
I would love if we got a response to this because its been a while, and no hotfix targeted this issue.