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Reflections/specularity on Translucent materials

I was trying to give my glass material reflectivity and it didn't work. Then I found in the docs that "At this time, Unreal Engine 4 has no means to handle specularity (i.e. reflection) on translucent materials. This means that any reflections on objects such as water or glass will need to be faked via reflection mapping."

Does that mean specularity will eventually work on translucent materials?

When faking the reflection via reflection mapping, is there a way how to access "Reflection capture spheres" so that reflections are at least somewhat dynamic in sense of reflecting correct static environment from capture spheres compared to some statically set cube map?

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asked Mar 11 '14 at 04:57 AM in Rendering

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ue4-archive ♦♦ STAFF
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Check and see if your build has a TranslucencyLightingMode (material property) of TLM_Surface. That mode applies the cubemap from the nearest reflection capture to the translucency. It has some issues - no parallax, and moving objects will pop as they switch between cubemaps.

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answered Mar 11 '14 at 04:57 AM

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Hello, thanks for the reply.

Seems like my build (1808360 - latest beta for external testers) doesn't have TLM_Surface, only PerPixel and PerPixelNonDirectional. So I guess this feature comes with some later beta build. Once we have access to it, are those reflections controlled by Roughness and Metallic as in Opaque material?

Is the poping of moving objects planned to be "fixed" or is that a technical limitation which won't be easy to change?

Are SSR planned to work with translucent materials in future?

Thanks

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answered Mar 11 '14 at 04:57 AM

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avatar image ue4-archive ♦♦ STAFF Mar 11 '14 at 04:57 AM

Once we have access to it, are those reflections controlled by Roughness and Metallic as in Opaque material?

Yes

Is the poping of moving objects planned to be "fixed" or is that a technical limitation which won't be easy to change?

There are two approaches we can take - fade the reflections out when switching and then fade in again, or apply two reflections all the time. Neither of those are very appealing. But we definitely need to do something. We can also add an option to always keep using the first reflection capture cubemap assigned even after moving, under the assumption that not popping is more important than using the right cubemap. I don't know when we'll be able to get to this.

Are SSR planned to work with translucent materials in future?

Not at this point. SSR requires deferred shading, and translucency is incompatible with deferred shading unfortunately.

avatar image ue4-archive ♦♦ STAFF Mar 11 '14 at 04:57 AM

I have two additional questions:

  1. Will translucent materials have spec highlights any time soon?

  2. Will there be an alternative solution for real-time reflections on translucent materials for water etc. in the future?

avatar image ue4-archive ♦♦ STAFF Mar 11 '14 at 04:57 AM

Will translucent materials have spec highlights any time soon?

Unfortunately no. We want to implement that but it is a big task (requires Forward+ shading) and it's a ways down our task list.

Will there be an alternative solution for real-time reflections on translucent materials for water etc. in the future?

It's not in the plan at the moment, but I think we really need that for good water. Reflection environment cubemaps don't provide accurate parallax and SSR is inconsistent in its coverage. We need something that renders a simplified version of the scene to a planar reflection, like GTA5.

avatar image JamesSF69 Mar 19 '15 at 03:59 AM

Wow! Really, no spec for Translucent/transparent materials??? That's one of the main things that makes glass, glass. I thought it was just something I was doing wrong, but been doing some research and found out that indeed there is NO specular for a glass material? that's insane. Hope you decide to push this UP the list. As a graphic artist and designer, this is almost a deal breaker to develop on U4 James

avatar image ue4-archive ♦♦ STAFF Mar 11 '14 at 04:57 AM

Ok, thanks.

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