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Why do SubSurface Material unable to receive shadow?

alt text

As shown in this image. I put an opaque block behind the SSS wall to block the light, but it doesn't do anything. I don't recall this is the behavior of SSS in UE4, is this a known issue in 4.4.1 or I'm just hallucinating? The light being used is Move-able Spotlight that cast shadows. Any ideas? Thanks in advance.

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asked Sep 10 '14 at 06:48 AM in Rendering

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avatar image Lovecraft_K ♦♦ STAFF Sep 11 '14 at 08:45 PM

Hey RinDreamX -

I have been looking into this and haven't been able to reproduce the issue you are having. Could you post a screenshot of your material setup including a look at your material attributes settings and a look at the spotlight's details panel as well?

I would also begin by looking at your opaque block and light radius and make sure that the cone of your spotlight and its attenuation radius encompass both block and subsurface plane. It looks like it does in the screenshot above, but its worth mentioning as an easy and often overlooked solution.

Thank You

Eric Ketchum

avatar image RinDreamX Sep 12 '14 at 05:57 AM

![alt text][1] ![alt text][2] ![alt text][3] ![alt text][4] [1]: /storage/temp/15173-sss_material_01.jpg [2]: /storage/temp/15174-sss_solidmaterial_01.jpg [3]: /storage/temp/15176-sss_spotlightproperty_01.jpg [4]: /storage/temp/15177-sss_problem_2.jpg

Hope this screen clarify a bit more. Essentially it's very basic 0 Opacity SSS material and Opaque material as a shadow caster. The Spot light is movable and cast shadow. In the shot no: 4 I disable inverse square, but it shouldn't matter and both did exhibit the same problem.

Thanks for looking into this issue.

avatar image RinDreamX Sep 12 '14 at 06:03 AM

Forgot to add, setting the light to Cast Translucent Shadow also didn't solve the problem :(

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Hey RinDreamX -

Remove the 0 opacity and your SSS will work as you wish it to. Having a zero in opacity is telling the material that it will hold no shadows (its functionally translucent in relation to the shadows cast - nothing to cast on).

Thank You

Eric Ketchum

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answered Sep 12 '14 at 06:14 PM

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Lovecraft_K ♦♦ STAFF
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avatar image RinDreamX Sep 13 '14 at 02:46 AM

That's it! Man felt dumb heheheh. Thank you so much for pointing this out. I believe I made the mistake on skipping this while using stationary light before (which is known to not work on SSS static object), that's why I didn't think the opacity 0 was the issue. alt text

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