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How do I make transparent objects reflect light?

I've tried playing with the translucency mode, but even with the TLM_Surface (which apparently does nothing) transparent objects look incredibly artificial.

My game features a lot of semi-transparent objects, gelatinous blobs, glasses, water... right now I can see no way of making these materials.

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asked Mar 23 '14 at 12:58 PM in Rendering

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avatar image Pino of DFT Games Mar 23 '14 at 01:26 PM

I'd suggest to follow the Materials tutorial to understand how UE4 works: it's different from UDK and Unity: https://www.youtube.com/watch?v=lngF4VVNER4&list=PLZlv_N0_O1gbQjgY0nDwZNYe_N8IcYWS-

avatar image Ergobells Mar 23 '14 at 02:21 PM

I've seen the materials tutorial. I don't know, however, how to make semi-transparent objects behave like they're receiving light from the environment.

The closest I've seen is in the Material demo level, wherein some materials set with Volumetric materials reflect some of the light objects. But even there they have Z-sorting issues and seem to completely ignore the rest of the environment lighting.

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In order to get reflections from TLM_Surface you need to have a working scene already with at least one SphericalReflectionCapture actor. The nearest one will be used on the translucent surface. It's not a great reflection for many surfaces (flat water) and it's missing direct specular completely. This is an area we are working to improve.

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answered Jun 02 '14 at 11:52 PM

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One would expect that transparent surfaces will support specular lighting without any problems. Unfortunately I'm afraid that UE doesn't allow that right now. I tried to port my ocean shader from UE3, and had big problems getting specular highlights on water surface. I checked how Epic created water in the Cave example scene. Turns out they used two plane meshes one on top of the other. Lower plane simulated water color and specular reflections, while the top plane simulated water refraction. Guess we will need to wait until this gets improved.

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answered Mar 23 '14 at 04:25 PM

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avatar image Ergobells Mar 24 '14 at 03:09 PM

So there's just no way at all? That's... incredibly crippling.

Also, what cave scene are you talking about?

avatar image Jacky Mar 24 '14 at 03:15 PM

Use a high value of specular(1 or higher) if you want to boost the reflections.

avatar image Ergobells Mar 24 '14 at 03:31 PM

You've completely missed the point. There's no proper surface shading in transparent objects, even with TLM_Surface.

avatar image Jacky Mar 24 '14 at 03:37 PM

Transparent materials(set to TLM_Surface) do have reflections even though not so great, but it may look weak by default. However specular value helps in this occasion.

avatar image devel.bmad May 31 '14 at 10:07 PM

Are you using mac or win? I don't seem to see reflections of any kind on mac

avatar image Ben Halliday STAFF Mar 24 '14 at 03:24 PM

The Effects Cave is a project that will be available in the Marketplace soon. It includes a great deal of particle effects, lights, and reflections examples.

avatar image Ergobells Mar 24 '14 at 03:32 PM

Ah, alright. There's been a preview somewhere, I take it?

avatar image EF Mar 24 '14 at 03:45 PM

Oops, sorry. The scene is available for licensees and I assumed it's there for public users as well, without checking that first.

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If it's a flat plane, one solution is to add a cubemap texture to the emissive channel. I haven't had any luck with TLM_Surface myself. Even in the content examples it doesn't show any reflection, even though the label says it should.

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answered May 07 '14 at 02:26 AM

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