VSM Page artifacts for directional shadows

Development Rendering
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1

Hello

We are experiencing an issue in UE 5.5.2 where certain pages in VSM shadows coming from a directional light are missing / showing no shadows.

A few things that I have tried already:

  • Disable VSM cache
  • Change clipmap settings to increase detail
  • Increase maximum physical pages
  • Change the DirectionalLODBias

This seems to only affect actors with WPO materials, such as the foliage you see in the screenshots. Local lights seem to be working as expected, it’s only affecting directional ones. We have no Engine modifications around the VSM area which would affect this.

I’m currently debugging it in a few captures that I have, but I thought I’d ask just in case this is already encountered and fixed.

Thank you

Pantelis Lekakis - Firesprite

2

Steps to Reproduce

  • Place an actor with WPO
  • Place a shadow casting directional light
  • Move far away from the actor so that lower detail clipmaps are selected
  • Notice artifacts
3

Hello,

Thank you for reaching out.

I’ve been assigned this issue, and we will be looking into these VSM artifacts for you.

Can you please send us a minimal test project that demonstrates this, and include screenshots of the issue from the test project?

The guide for test projects: [Content removed]

4

If it helps, the issue occurs with local lights as well.

5

Hello,

The issue you are seeing is a known interaction between VSM caches and dynamic primitives, including WPO, mask changes, and similar.

For more information on this issue, including several different methods of addressing it, please see these tickets:

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When using WPO to increase the size of an object, you might want to set a Max World Position Offset Displacement distance in the Material, to correctly scale the object’s bounds. This affects both VSM cache invalidations and visibility culling.

Note that the dark square in the center is coming from Distance Field Shadowing, not VSMs.

Please let us know if this helps.

6

Hi Stephen,

Please find attached a test project where WPO is scaled - notice the VSM shadows.

7

And a video of the issue.

8

Thank you Stephen,

This is indeed fixing our issues, however due to the sheer amount of foliage in our level it’s not practical to do it on the material itself, as it causes significant performance hit, even for a small increase in value.

We’re internally looking into potentially moving this to the actor itself (and the GPU scene), so we can set this up on a per-actor basis.

Best regards

Pantelis Lekakis