Path Tracer Normals Issue

Development Cinematics & Media
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1

We have noticed an issue with rendering normals in the path tracer. They are quite broken and seem to have some kind of orientation to camera thing going on.

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Deferred (Lit)

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Path Tracer

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Deferred (Lit)

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Path Tracer

As you can see the issue is not consistent as we move the camera. If you move the camera you can see is directly influenced by the camera angle.

I appreciate that normal maps technically violate the physical correctness of a path tracer and if that is the issue here then it would be better IMO if the Path Tracer ignored normals rather then rendered them broken. As a workaround we can use a PathTracingQualitySwitchReplace node in the material to effectively disable the normals, but we would have to apply that to all our materials.

What do you intend to happen with normals in the UE Path Tracer?

We have observed this in 5.7p1 as well as 5.6. We haven’t checked it earlier than 5.6 so it’s possible it is affecting older versions too.

2

Steps to Reproduce

  • Add a cube and a sunlight to an empty scene.
  • Create a simple material that has a grey base color, 0 spec and a normal map that points to /Engine/EngineProduction/ReferenceNormalMap.
  • Assign this material to the cube
  • Spin around the cube in path tracer mode and observe the broken normal rendering. A/B with Lit mode.
3

Hello,

Thank you for reaching out.

I’ve been assigned this issue, and we will be looking into these normals in the path tracer for you.

4

Hello,

Thank you for reporting this.

I can confirm this issue can be reproduced as described in the latest CL, and have opened a bug report.

We will reply when a public tracker is available.

5

Hello,

Here is the public tracker:

The tracker will be visible after it is approved internally at Epic Games and is publicly accessible.

If you have any further questions, please let us know.