Glitchy transparency on materials with opacity (UsdPreviewSurfaceTranslucentTwoSided)

[Im_Ninooo]

Hello. I’m having weird transparency issues with assets imported from Blender with the Alpha channel plugged in. Please help.

This is what it looks like in Blender:

And just for reference, in USD Composer:

[Im_Ninooo]

And as usual I find a workaround right after creating the thread 🤣

1. Find the UsdPreviewSurface material.
   

2. Double-click to edit it and connect the Opacity Mask input to the same node as the Opacity input.
   

   

3. Override the Blend Mode on all affected materials to ‘Masked’
   

Fixed.

Alternatively, you can also override the blend mode on UsdPreviewSurfaceTranslucentTwoSided so that it fixes all materials that inherit it.

[JulianCao]

Thanks, Im_Ninooo. If I understood correctly, is this a bug of using a preview surface material for transparency? It’s not mdl material, right?

[Im_Ninooo]

Correct, and to be honest, I haven’t figured out how to use MDL materials in UE5 yet.

If I uncheck the “Convert to USD Preview Surface” option while exporting from Blender then I get blank materials and no textures in Unreal.

If I change the render context to mdl during import, I get Failed to create MDL material for prim ... errors.

If you could please explain to me what the correct way of doing this is, I’d appreciate it!

[JulianCao]

@Im_Ninooo

Failed to create MDL material for prim

Unfortunately, this error message isn’t from Unreal Connect. I believe you used Unreal official USD plugin to do the importing.
The import function of Unreal Connect is always under Omniverse Catalog, please try that.

[JulianCao]

Then I reviewed your issue again. I think it’s the same problem that you used the wrong plugin to import preview surface material.

This is the Unreal Connect Preview surface material

[Im_Ninooo]

oh, that explains a lot, but unfortunately importing it via the plugin breaks the materials 😅

I think it might be time for me to ditch Omniverse. I’ve put a lot of effort into trying to use it and it’s only let me down. A friend of mine has been playing with GLTF and it’s been working pretty well with Unreal.

Thanks for all the support you and the others have provided!

[JulianCao]

I’m sorry to hear that. It looks like a normal display issue in Unreal Connect, but it should be caused by other 2 things:

1. Blender did the wrong preview surface exporting for normal.
   I guess it doesn’t set a correct scale and bias for Normal texture. This’s a right normal exporting example

def Shader “Pants_InstanceNormalTex”
{
uniform token info:id = “UsdUVTexture”
float4 inputs:bias = (-1, 1, -1, -1)
asset inputs:file = @omniverse://localhost/Library/Preview/Materials/PreviewSurfaceTextures/Pants_Instance_Normal.png@
float4 inputs:scale = (2, -2, 2, 2)
token inputs:sourceColorSpace = “raw”
float2 inputs:st.connect = </Root/Astronaut_posed1Z/Looks/Pants_Instance/PrimST.outputs:result>
token inputs:wrapS = “repeat”
token inputs:wrapT = “repeat”
float3 outputs:rgb
}

I will confirm the issue from Blender side.

2. Unreal USD plugin did the wrong importing for the normal property of preview surface, but with a wrong blender exporting data, make it look right.
   
   
   
   We can see the normal texture is directly set to normal property. It looks right in Unreal, because Unreal will do normal sampling internally, but it’s not right in USD preview surface style for other platforms.

Anyway, thanks for helping us with a better Omniverse

[JulianCao]

Blender did have a bug with exporting the normal.

def Shader “preview_Image_Texture_001”
{
uniform token info:id = “UsdUVTexture”
asset inputs:file = @./textures/woodTex_normal_512x512.png@
token inputs:sourceColorSpace = “sRGB”
float2 inputs:st.connect = </root/materials/TexNormalMat/preview_uvmap.outputs:result>
token inputs:wrapS = “repeat”
token inputs:wrapT = “repeat”
float3 outputs:rgb
}

[Im_Ninooo]

@JulianCao

Blender did have a bug with exporting the normal.

Interesting.

Well, I ended up having some weird armature offset issues with GLTF that aren’t present with USD so for now I’ll have to continue using Omniverse’s Blender plugin for exporting and UE5’s native USD importer (which also has it’s issues!).

I should be a beta tester… the bugs just keep finding me! 😅

[JulianCao]

Blender has fixed the normal map issue on the preview surface material. It will go out in next release.

[Im_Ninooo]

PreviewSurface or MDL? Because unless I did something wrong that material with broken normals was imported as MDL.

[JulianCao]

It’s the issue of Preview surface.

[Im_Ninooo]

ah, so the issue I’m still having with MDL Normals is likely the one from this thread that’s already fixed.

[Im_Ninooo]

Fixed in the latest UE5 Connector plugin. thanks!