Glass and Light issues - UE connector

Omniverse General Discussion
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1

Hello everyone,

I’ve created my first test with Omniverse. Very exciting! I used one of my previous UE scenes from a Aston Martin DB5 piece I created last year. The connection worked great but I am noticing a couple of issues with translucency and lights:
_Glass on Realtime mode seems to be completely see through. No Reflections
_Even on Ray-Casting mode the UE shader seems dull.
_Translucency with opacity level in real time seems off. Looks fine in Path Tracer.
_Issue with light attenuation radius in path tracer. No gradient, just cuts off.
_Light’s radius shows as a black sphere when seen through glass. Both Path-tracer and Realtime
_Rectangular Light’s shape visible through translucent objects

I am sure there are some settings that I am not applying and many more I will need to tweak in order to get a better final image. So far this is very promising. More to come.

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2

For the glass issues, I have noticed this as well if the glass is part of the same mesh as the body.

Or , you can just try selecting the glass and applying OmniGlass from the Create\Materials menu

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3

All materials: Note that MDL doesn’t support all of the UE4 material nodes. Things like camera vector and object position are notable and can really change the look of an exported material. If you are using Material Instances (with a well-parameterized parent Material), you can edit those material parameters in Create, so maybe tweaking them will give you a better look.

  • Glass
    • Glass is hard to export. When you export, did you end up with a lot of warning messages about unsupported MDL functions? If so, maybe your glass material a great export target to MDL, or we have somethings to fix. I took MI_Glass from Epic’s Automotive Materials pack and I think I see some of the same issues that you have. Very little if no reflection, where OmniGlass looks amazing. If you’d like to provide your glass material to us we could take a look at it.
  • UE Shader seems dull
    • I assume you’re referring to your silver paint? Again, I get a nice paint from Epic’s materials pack, so we’d love to look at your material if you’d like to get it to us.
  • Translucency with opacity level in real time is wrong, good in path tracer
    • This is tricky, we are always working on aligning translucency between RT and PT.
  • Light attenuation radius in path tracer. No gradient, just cuts off.
    • I’d like to understand this better. I’m seeing a sphere light that diffuses nicely as I move it away from a plane
  • Light’s radius shows as black sphere with seen through glass
    • Allowing a sphere light’s radius to overlap with any geometry causes lots of issues in Create, I think you’ll also see boiling if you do this in other situations as the intensity rises. I would avoid it if possible.
  • Rectangular Light’s shape visible through translucent objects
    • I too see this, I will ask around about it
4

Thank you Frank,

I will give the OmniGlass a try. All of the glass is separate meshes.

5

Thank you Lou for taking the time. This is all great info.

  • I did not notice many error messages but I was not paying much attention to that. I was pretty stoke to see the model transfer successfully. The glass is from the automotive collection although it was initially done in UE 4.25
  • The car paint came through beautifully. I was referring to the glass material.
  • The light source is a small black sphere and what is getting cut in the Path tracer is just the attenuation radius. (Added an image - I can only add one at a time for the moment)
  • The image from above will also illustrate this issue better. Now that I think about it is a similar issue to the area lights but in the point light it shows black instead of white.

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6

Carlos, we spent some time looking at glass refraction and reflection in Unreal and MDL and found two issues:

  • We had a bug where refraction was removed with using the Fresnel node and we were using a bad default IOR of 1.0 instead of 1.491.
  • We found that Unreal Engine has a newish way to do Translucency IOR for ray tracing. This means that the parameters for controlling IOR are in both the material and the post process volume (PPV).

Looking at your project, you are using this new mechanism for Translucency IOR in ray tracing with the PPV, so we are working on ways to export this information correctly as MDL.

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In the mean time, you can adjust your glass MDL: MI_Glass_RT_Clear.mdl

Change:

float2 Refraction_mdl = float2(float2(1.0,0.0).x,float2(1.0,0.0).x);

to

float2 Refraction_mdl = float2(float2(1.491,0.0).x,float2(1.0,0.0).x);

Unfortunately Create has a bug where it must be restarted to reload MDL materials, but that will get you much nicer glass. Also, I added a domelight to give us add more environment reflections.

Before:

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After:

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7

Carlos, our latest hotfix (100.6) JUST missed this fix, but I want you to know that we’ve added RayTracing Translucency support in the MDL material export path. Now your car glass comes out looking really nice!

In Create I adjusted these items to make the image slightly nicer:

  • The point light radii in the headlights were reduced from 50 to 5 so that they didn’t overlap geometry (this causes dark circles on geo in PT)
  • The point lights were moved out in front of the geometry so black circles don’t appear on the translucent headlights
  • I set the Specular Multiplier to 0.0 in the rect lights behind the glass so they didn’t appear as white boxes behind the glass in PT mode. This was just to improve this screen shot as it probably changes these lights inappropriately in other views.

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