Poor quality shadows at an angle

Development Rendering
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Hi!

I’ve been struggling with managing the shadows on a building with a single-slope roof. It seems whenever the light catches the roof at an angle close to the roof’s angle itself - so any moment that isn’t early dawn, dusk, or midday - the shadows show some horrible stepping in them.

I’ve tried fiddling with every shadow-linked attribute I could find, both on my directional light and on the mesh, but I can’t seem to find the solution.

Optimisation isn’t really an issue in this situation so I don’t mind if the solution is heavy to compute, but using the path tracer isn’t really an option.

Does anyone have an idea of what’s going on?
Thanks!

GrossShadows
GrossShadows1479×802 395 KB

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seems like shadowmap depth precision issue typical of shadowmaps. aka “shadow acne” LearnOpenGL - Shadow Mapping

unfortunately i’m not sure how to fix on ue. tbh is the first time i see that issue in ue.

it might have to do with the size and depth of the cache itself. or maybe the shadow uv for your meshes. or how your uvs are specified.

maybe someone else can help you or this can give you a hint.

good luck.

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look for slope bias. this can help on shallow shadow angles. but also introduce ring artefacts.

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Thank you both for your help. I dug a bit more, and apparently what I’m dealing with is called projective aliasing, which seems to be a known weakness of virtual shadow maps. Changing the slope bias unfortunately doesn’t help in that situation.

I’m starting to wonder if it would be possible to use lightmaps instead of dynamic shadows on that one specific actor, and if it would look any better…

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good work researching.

you can change some settings regarding shadows on the material and the mesh component. might be worth experimenting.