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2 Sided material - back face display issue?

So I'm trying to set up a grass clump model and I'm experiencing an issue I've never seen before. For some reason the back faces of the 2 sided material are completely black both inside the model viewier and the scene. Its not a lightmass issue as the mesh has proper lighting coords. I tried changing the lighting model to the new 2 sided foliage and this just made the black parts go bright grey.

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Product Version: UE 4.7
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asked Jun 04 '15 at 08:45 PM in Rendering

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avatar image TorQueMoD Jun 05 '15 at 05:08 AM

Yeah its most definitely the lighting model. I tried changing to every one available and none of them work properly. They all either make the back faces too bright or too dark. Also switching to an Unlit lighting model now makes the entire material go completely black instead of full bright like it used to.

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Hi TorQueMoD -

A few things to check. Make sure that you have a color plugged into the Subsurface Color input, otherwise the engine will default to black. Make sure that you are using a Opacity and/or Opacity Mask if you have any alpha values (which the image looks like you are but it doesn't hurt to check). In addition, make sure that you are using the Masked Shader Model or Translucent.

Finally are you rendering on a mobile device or in Mobile Preview mode? If so, remember the Two Sided Foliage Lighting Model is a Subsurface lighting model and is currently not available on Mobile devices.

I have included a Test Project here which is rendering correctly please look at it and see if there is anything I might be missing.

Thank You

Eric Ketchum

Sample Project

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answered Jun 05 '15 at 03:08 PM

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Lovecraft_K ♦♦ STAFF
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avatar image TorQueMoD Jun 05 '15 at 06:56 PM

Thank you Eric. I'm rather embarrassed now that I didn't notice the subsurface color input. That fixed the issue. I'm curious if you have to use this now with unlit materials as those are showing up black as well.

avatar image Lovecraft_K ♦♦ STAFF Jun 08 '15 at 02:45 PM

For unlit materials you should only have to plug in an emissive color and check Two-Sided in the Material Attributes. You can also setup a Lerp between the front and back color using TwoSided Sign node as the Alpha and plug into Emissive Color.

Thank You

Eric Ketchum

avatar image PC-hris Feb 28 '19 at 06:50 AM

Following the advice from your response Eric, I accidentally fixed my unrelated problem. I had no idea that subsurface color was important lol.

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