4.14 (VR, Forward Rendering, Instanced Stereo) Staionary Light Causing Shadow sorting error in Left Eye.

Hey Tim Hobson!

Happy New year to you, sir! As promised, I’ve added another issue here, which I’m struggling to figure out. My scene is running Forward Rendering, and requires a lot of instances. For some reason, many of my meshes are creating rendering errors in the left eye of my Oculus CV1. We are using forward rendering, as well as Instanced Stereo. The error, however occurs on horizontal, top facing surfaces which leads me to suspect that it is the the Stationary Directional light which is the culprit, and that the highlights it creates are being sorted after shadows. We are using Cascaded shadow maps, as described in the VR Best Practices page.

I’ve added several images here to show this occuring…

Here is a shot of the issue as it occurs. Initially, I supposed this to be affecting instances only…

You can see here how the geometry is arranged. I took the selected chunks and returned them to standard static mesh placements and relit the scene…

We can now see a return of the light map failure to reassign on the rear chunk which is still an instance (Presumably this is now at LOD1) but the replacement of a non-instanced mesh in the foreground has done nothing to alleviate the issue with shadow sorting. This behaviour doesn’t seem to occur all the time or on all meshes, so I’m unsure what the common thread is. I daresay there’s a running cause, but I have been unable to figure it out. In the case of this offending mesh, I applied a different material instance, built from the same master, and this object subsequently failed to render!

Alas, we are now out of my element, and I’m not sure how to proceed. For now, I have switched back to a dynamic scenario while I continue to build out the level and under these circumstances the issue is not present.

Would appreciated any advice/insight.

Best,

Hi Jack,

I got a few minutes to try and see if I could come up with something to get this issue, but wasn’t able to reproduce. I imagine that my simple scene just doesn’t have the complexity, even with a lot of instances, to get the issue.

There was an issue I recall that will be fixed in 4.15 that you could try and see if you see any results. In your BP under the instance enable the option for “Use As Occluder” and see if the issue persists. If it doesn’t then that will be fixed in 4.15 so you don’t need that enabled.

Also, I see that the lighting has been built for the scene. If you build it, does the issue persist? Can you also try forcing LODs to stay at LOD0 and see if this still happens? (Use r.ForceLOD 0. Use -1 to put it back to default and use LOD transitions.)

We have the 4.15 Previews starting next week or the week after and there have been a number of improvements for Forward Rendering that may resolve the issue as well.

Thanks!

Tim

Heya Tim,

Apologies for the delay in my response. Alas a personal trauma rather derailed me for the last couple of weeks. I’ll get the latest preview in and try the suggestions you’ve made here and report back as soon as I know anything. Many thanks again for your help!

Understandable. Just post back when you can to re-open and I’ll take a look. Thanks!

Hello, how did you find this issue ?

I am having the same problem, i had configured my project using instance stereo and forward rendering and the error still occurs

It seems similar to the issue I have here (unreal 5.3) Shadow issue for one eye in VR Template using stationary lighting